Fix: cover zstd-rejection path and correct importer's zstd-hint message

Adds a command-level test exercising the real zstd-unavailable branch
in document_exporter, makes document_importer only append the
"zstd archives require Python 3.14+" hint when zstd is actually among
the unreadable codecs, and adds the lzma counterpart to the
stored-level-rejection test for symmetry.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/administration.md

@@ -272,6 +272,8 @@ optional arguments:
 -sm, --split-manifest
 -z,  --zip
 -zn, --zip-name
+--zip-compression
+--zip-compression-level
 --data-only
 --no-progress-bar
 --passphrase
@@ -334,6 +336,19 @@ If `-z` or `--zip` is provided, the export will be a zip file
 in the target directory, named according to the current local date or the
 value set in `-zn` or `--zip-name`.
 
+The compression method for the zip can be set with `--zip-compression`
+(`stored`, `deflated` (default), `bzip2`, `lzma`, or `zstd`) and tuned with
+`--zip-compression-level` (deflated: 0–9, bzip2: 1–9, zstd: -22–22; ignored
+for `stored` and `lzma`). Both options require `--zip`.
+
+!!! warning
+
+    `zstd` compression requires Python 3.14 or newer on **both** the machine
+    creating the export and any machine importing it. An archive compressed with
+    `zstd` (or `lzma`/`bzip2` where those modules are unavailable) cannot be
+    imported on a runtime that lacks the codec; the importer will refuse it with
+    a clear error. The default `deflated` is universally readable.
+
 If `--data-only` is provided, only the database will be exported. This option is intended
 to facilitate database upgrades without needing to clean documents and thumbnails from the media directory.
 

docs/superpowers/plans/2026-06-16-export-zip-compression.md

@@ -0,0 +1,839 @@
+# Export Zip Compression Control Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Add `--zip-compression {stored,deflated,bzip2,lzma,zstd}` and `--zip-compression-level N` flags to `document_exporter`, threaded into `ZipExportSink`, with import-side safety for codecs the running Python can't read.
+
+**Architecture:** A new pure-data module `documents/export/compression.py` owns the method↔constant map, per-method level bounds, the runtime availability probe, and a compress-type readability check. `ZipExportSink` gains `compression`/`compresslevel` constructor params. The command validates flags up front (fail-fast `CommandError`) and constructs the sink; the importer pre-checks entry compress types before extracting.
+
+**Tech Stack:** Python ≥3.11 (zstd only on 3.14+), `zipfile`, `compression.zstd` (PEP 784), pytest + pytest-mock + factory-boy. Backend tests run on the Linux VM (Python 3.11 — zstd positive tests are `skipif`-guarded); `ruff` runs locally.
+
+**Spec:** `docs/superpowers/specs/2026-06-16-export-zip-compression-design.md`
+
+**PREREQUISITE:** The base refactor `docs/superpowers/plans/2026-06-16-export-sink-architecture.md` MUST be merged first. This plan assumes `src/documents/export/sinks.py` exists with `ZipExportSink(target, zip_name, *, delete=False)` opening its `ZipFile` in `_open()`.
+
+---
+
+## Verified facts (CPython 3.14.3, via `uv run --python 3.14 --no-project`)
+
+- Constants: `ZIP_STORED=0`, `ZIP_DEFLATED=8`, `ZIP_BZIP2=12`, `ZIP_LZMA=14`, `ZIP_ZSTANDARD=93` (zstd added 3.14; absent on < 3.14).
+- `ZipFile(file, "w", compression=…, compresslevel=…)` applies both as the default for every `write`/`writestr` — no per-entry args needed (verified).
+- Level bounds: `deflated` 0–9, `bzip2` 1–9, `lzma`/`stored` ignore level, `zstd` -131072…22 (`compression.zstd.CompressionParameter.compression_level.bounds() == (-131072, 22)`).
+- An invalid level fails at the **first write** (`ValueError: Invalid initialization option` / `compresslevel must be between 1 and 9`), plus GC-time `AttributeError` noise on close — hence up-front validation.
+- zstd is backed by `compression.zstd`; `zipfile` raises `RuntimeError` if it's unavailable.
+
+## Conventions for every task
+
+- **Run backend tests on the VM:** `bash /c/Users/tholmes/Documents/Coding/paperless/vmtest.sh "<targets>"` (never locally).
+- **Lint locally:** `ruff check <paths> && ruff format <paths>` (global ruff, not `uv run`).
+- **Tests are pytest-style:** classes, `@pytest.mark.django_db` on the class only where DB is needed (the `compression.py` and sink tests need no DB), factory-boy, `mocker`, `parametrize`, full type annotations.
+- The VM runs Python 3.11, so **zstd positive tests must be `@pytest.mark.skipif(...)`-guarded**; they will simply not run there. zstd _rejection_ tests (the < 3.14 path) DO run on the VM.
+
+## File structure
+
+- **Create** `src/documents/export/compression.py` — method map, CLI choices, level bounds, `compression_available()`, `level_error()`, `compress_type_readable()`, `unreadable_method_names()`. Pure, no Django.
+- **Create** `src/documents/tests/export/test_compression.py` — unit tests for the above.
+- **Modify** `src/documents/export/sinks.py` — `ZipExportSink.__init__` gains `compression`/`compresslevel`; `_open()` passes them to `ZipFile`.
+- **Modify** `src/documents/tests/export/test_sinks.py` — assert the chosen `compress_type` is applied.
+- **Modify** `src/documents/management/commands/document_exporter.py` — add the two CLI flags, up-front validation, and pass resolved values to `ZipExportSink`.
+- **Modify** `src/documents/tests/test_management_exporter.py` — flag validation + default-unchanged tests.
+- **Modify** `src/documents/management/commands/document_importer.py` — pre-extract compress-type check.
+- **Modify** `src/documents/tests/test_management_importer.py` — unsupported-codec → `CommandError`.
+- **Modify** `docs/administration.md` — document both flags + zstd portability caveat.
+
+---
+
+## Task 1: `documents/export/compression.py` (pure compression policy)
+
+**Files:**
+
+- Create: `src/documents/export/compression.py`
+- Test: `src/documents/tests/export/test_compression.py`
+
+- [ ] **Step 1: Write the failing tests**
+
+Create `src/documents/tests/export/test_compression.py`:
+
+```python
+import sys
+import zipfile
+
+import pytest
+
+from documents.export import compression
+
+
+class TestCompressionMethods:
+    def test_choices_always_include_zstd(self) -> None:
+        # zstd is offered regardless of runtime; availability is checked separately
+        assert compression.COMPRESSION_CHOICES == (
+            "stored",
+            "deflated",
+            "bzip2",
+            "lzma",
+            "zstd",
+        )
+
+    @pytest.mark.parametrize(
+        ("name", "constant"),
+        [
+            ("stored", zipfile.ZIP_STORED),
+            ("deflated", zipfile.ZIP_DEFLATED),
+            ("bzip2", zipfile.ZIP_BZIP2),
+            ("lzma", zipfile.ZIP_LZMA),
+        ],
+    )
+    def test_method_maps_to_zipfile_constant(self, name: str, constant: int) -> None:
+        assert compression.COMPRESSION_METHODS[name] == constant
+
+    def test_stored_and_deflated_always_available(self) -> None:
+        assert compression.compression_available("stored")
+        assert compression.compression_available("deflated")
+
+    def test_zstd_availability_tracks_runtime(self) -> None:
+        expected: bool = sys.version_info >= (3, 14)
+        assert compression.compression_available("zstd") == expected
+
+
+class TestLevelError:
+    @pytest.mark.parametrize(
+        ("method", "level"),
+        [
+            ("deflated", 0),
+            ("deflated", 9),
+            ("bzip2", 1),
+            ("bzip2", 9),
+            ("deflated", None),
+            ("stored", None),
+        ],
+    )
+    def test_valid_levels_return_none(self, method: str, level: int | None) -> None:
+        assert compression.level_error(method, level) is None
+
+    @pytest.mark.parametrize(
+        ("method", "level"),
+        [
+            ("deflated", 10),
+            ("deflated", -1),
+            ("bzip2", 0),
+            ("bzip2", 10),
+        ],
+    )
+    def test_out_of_range_levels_return_message(
+        self,
+        method: str,
+        level: int,
+    ) -> None:
+        msg: str | None = compression.level_error(method, level)
+        assert msg is not None
+        assert "between" in msg
+
+    @pytest.mark.parametrize("method", ["stored", "lzma"])
+    def test_level_on_levelless_method_is_rejected(self, method: str) -> None:
+        msg: str | None = compression.level_error(method, 5)
+        assert msg is not None
+        assert "no effect" in msg
+
+
+class TestCompressTypeReadable:
+    @pytest.mark.parametrize("ct", [zipfile.ZIP_STORED, zipfile.ZIP_DEFLATED])
+    def test_stored_and_deflated_always_readable(self, ct: int) -> None:
+        assert compression.compress_type_readable(ct)
+
+    def test_zstd_compress_type_readability_tracks_runtime(self) -> None:
+        # 93 = ZIP_ZSTANDARD; 20 = legacy zstd method id (read-only)
+        expected: bool = sys.version_info >= (3, 14)
+        assert compression.compress_type_readable(93) == expected
+        assert compression.compress_type_readable(20) == expected
+
+    def test_unknown_compress_type_is_unreadable(self) -> None:
+        assert not compression.compress_type_readable(9999)
+
+    def test_unreadable_method_names_lists_methods(self) -> None:
+        # An unknown method id maps to no name and is reported generically.
+        names: set[str] = compression.unreadable_method_names({9999})
+        assert names == {"method 9999"}
+```
+
+- [ ] **Step 2: Run to verify it fails**
+
+Run: `bash /c/Users/tholmes/Documents/Coding/paperless/vmtest.sh "src/documents/tests/export/test_compression.py -v"`
+Expected: FAIL with `ModuleNotFoundError: No module named 'documents.export.compression'`.
+
+- [ ] **Step 3: Implement `compression.py`**
+
+Create `src/documents/export/compression.py`:
+
+```python
+from __future__ import annotations
+
+import importlib
+import zipfile
+
+# ZIP_ZSTANDARD exists only on Python 3.14+ (PEP 784). None elsewhere.
+ZSTD: int | None = getattr(zipfile, "ZIP_ZSTANDARD", None)
+
+# CLI choices are fixed across runtimes so argparse never hides zstd; runtime
+# availability is enforced separately in compression_available().
+COMPRESSION_CHOICES: tuple[str, ...] = (
+    "stored",
+    "deflated",
+    "bzip2",
+    "lzma",
+    "zstd",
+)
+
+# Method name -> zipfile compression constant (zstd only when supported).
+COMPRESSION_METHODS: dict[str, int] = {
+    "stored": zipfile.ZIP_STORED,
+    "deflated": zipfile.ZIP_DEFLATED,
+    "bzip2": zipfile.ZIP_BZIP2,
+    "lzma": zipfile.ZIP_LZMA,
+}
+if ZSTD is not None:
+    COMPRESSION_METHODS["zstd"] = ZSTD
+
+# Inclusive (min, max) level bounds per method; None => level not applicable.
+# Verified on CPython 3.14.3.
+LEVEL_BOUNDS: dict[str, tuple[int, int] | None] = {
+    "stored": None,
+    "deflated": (0, 9),
+    "bzip2": (1, 9),
+    "lzma": None,
+    "zstd": (-131072, 22),
+}
+
+# zipfile compress_type id -> method name. 93 = current zstd id, 20 = legacy
+# zstd id that zipfile can still read.
+_COMPRESS_TYPE_TO_METHOD: dict[int, str] = {
+    zipfile.ZIP_STORED: "stored",
+    zipfile.ZIP_DEFLATED: "deflated",
+    zipfile.ZIP_BZIP2: "bzip2",
+    zipfile.ZIP_LZMA: "lzma",
+    93: "zstd",
+    20: "zstd",
+}
+
+
+def compression_available(method: str) -> bool:
+    """Whether the running interpreter can actually use the given method."""
+    if method in ("stored", "deflated"):
+        # zlib is a hard CPython dependency; stored needs nothing.
+        return True
+    if method == "bzip2":
+        return _module_importable("bz2")
+    if method == "lzma":
+        return _module_importable("lzma")
+    if method == "zstd":
+        return ZSTD is not None and _module_importable("compression.zstd")
+    return False
+
+
+def _module_importable(name: str) -> bool:
+    try:
+        importlib.import_module(name)
+    except ImportError:
+        return False
+    return True
+
+
+def level_error(method: str, level: int | None) -> str | None:
+    """Return a human message if (method, level) is invalid, else None."""
+    if level is None:
+        return None
+    bounds = LEVEL_BOUNDS[method]
+    if bounds is None:
+        return f"--zip-compression-level has no effect for '{method}'"
+    low, high = bounds
+    if not (low <= level <= high):
+        return (
+            f"--zip-compression-level for '{method}' must be between "
+            f"{low} and {high}"
+        )
+    return None
+
+
+def compress_type_readable(compress_type: int) -> bool:
+    """Whether this interpreter can decompress an entry of the given type."""
+    method = _COMPRESS_TYPE_TO_METHOD.get(compress_type)
+    if method is None:
+        return False
+    return compression_available(method)
+
+
+def unreadable_method_names(compress_types: set[int]) -> set[str]:
+    """Map a set of compress_type ids to human method names for error messages."""
+    names: set[str] = set()
+    for ct in compress_types:
+        names.add(_COMPRESS_TYPE_TO_METHOD.get(ct, f"method {ct}"))
+    return names
+```
+
+- [ ] **Step 4: Run to verify it passes**
+
+Run: `bash /c/Users/tholmes/Documents/Coding/paperless/vmtest.sh "src/documents/tests/export/test_compression.py -v"`
+Expected: PASS (on the 3.11 VM, `test_zstd_availability_tracks_runtime` and `test_zstd_compress_type_readability_tracks_runtime` assert `False`).
+
+- [ ] **Step 5: Lint**
+
+Run: `ruff check src/documents/export/compression.py src/documents/tests/export/test_compression.py && ruff format src/documents/export/compression.py src/documents/tests/export/test_compression.py`
+Expected: no errors.
+
+- [ ] **Step 6: Commit**
+
+```bash
+git add src/documents/export/compression.py src/documents/tests/export/test_compression.py
+git commit -m "Feature: add export compression policy module"
+```
+
+---
+
+## Task 2: `ZipExportSink` accepts compression method + level
+
+**Files:**
+
+- Modify: `src/documents/export/sinks.py`
+- Test: `src/documents/tests/export/test_sinks.py`
+
+- [ ] **Step 1: Write the failing test**
+
+Append to `src/documents/tests/export/test_sinks.py` (the top-of-file block already imports `zipfile`, `Path`, `pytest`, `ZipExportSink`, `StreamingManifestWriter` from the base-refactor plan):
+
+```python
+class TestZipExportSinkCompression:
+    @pytest.fixture()
+    def source_file(self, tmp_path: Path) -> Path:
+        src: Path = tmp_path / "src" / "doc.pdf"
+        src.parent.mkdir(parents=True)
+        src.write_bytes(b"PDF-CONTENT" * 100)
+        return src
+
+    @pytest.mark.parametrize(
+        ("method", "constant"),
+        [
+            ("stored", zipfile.ZIP_STORED),
+            ("deflated", zipfile.ZIP_DEFLATED),
+            ("bzip2", zipfile.ZIP_BZIP2),
+            ("lzma", zipfile.ZIP_LZMA),
+        ],
+    )
+    def test_compression_method_is_applied_to_file_entries(
+        self,
+        tmp_path: Path,
+        source_file: Path,
+        method: str,
+        constant: int,
+    ) -> None:
+        target: Path = tmp_path / "out"
+        target.mkdir()
+        with ZipExportSink(
+            target,
+            "export",
+            delete=False,
+            compression=constant,
+        ) as sink:
+            sink.add_file(source_file, "doc.pdf")
+        with zipfile.ZipFile(target / "export.zip") as zf:
+            info = zf.getinfo("doc.pdf")
+            assert info.compress_type == constant
+
+    def test_compressing_method_beats_stored(
+        self,
+        tmp_path: Path,
+        source_file: Path,
+    ) -> None:
+        # Robust size invariant: a compressing method must be <= stored on
+        # compressible content (avoids flaky level-9-vs-level-1 comparisons).
+        sizes: dict[str, int] = {}
+        for name, constant in (("stored", zipfile.ZIP_STORED), ("deflated", zipfile.ZIP_DEFLATED)):
+            target: Path = tmp_path / name
+            target.mkdir()
+            with ZipExportSink(target, "export", delete=False, compression=constant) as sink:
+                sink.add_file(source_file, "doc.pdf")
+            sizes[name] = (target / "export.zip").stat().st_size
+        assert sizes["deflated"] <= sizes["stored"]
+```
+
+- [ ] **Step 2: Run to verify it fails**
+
+Run: `bash /c/Users/tholmes/Documents/Coding/paperless/vmtest.sh "src/documents/tests/export/test_sinks.py::TestZipExportSinkCompression -v"`
+Expected: FAIL with `TypeError: __init__() got an unexpected keyword argument 'compression'`.
+
+- [ ] **Step 3: Add the params to `ZipExportSink`**
+
+In `src/documents/export/sinks.py`, change `ZipExportSink.__init__` to accept the new keyword-only params and store them, and pass them in `_open()`:
+
+```python
+    def __init__(
+        self,
+        target: Path,
+        zip_name: str,
+        *,
+        delete: bool = False,
+        compression: int = zipfile.ZIP_DEFLATED,
+        compresslevel: int | None = None,
+    ) -> None:
+        self._target = target.resolve()
+        self._zip_path = (self._target / zip_name).with_suffix(".zip")
+        self._tmp_path = self._zip_path.with_name(self._zip_path.name + ".tmp")
+        self._delete = delete
+        self._compression = compression
+        self._compresslevel = compresslevel
+        self._zip: zipfile.ZipFile | None = None
+        self._dirs: set[str] = set()
+        self._pending_manifest: tuple[Path, str] | None = None
+        self._stream_open = False
+```
+
+And in `_open()`:
+
+```python
+    def _open(self) -> None:
+        settings.SCRATCH_DIR.mkdir(parents=True, exist_ok=True)
+        self._zip = zipfile.ZipFile(
+            self._tmp_path,
+            "w",
+            compression=self._compression,
+            compresslevel=self._compresslevel,
+            allowZip64=True,
+        )
+```
+
+- [ ] **Step 4: Run to verify it passes**
+
+Run: `bash /c/Users/tholmes/Documents/Coding/paperless/vmtest.sh "src/documents/tests/export/test_sinks.py -v"`
+Expected: PASS (all sink tests, including the four method params and the size invariant). `bzip2`/`lzma` are present on the VM's CPython, so those params pass.
+
+- [ ] **Step 5: Lint**
+
+Run: `ruff check src/documents/export/sinks.py && ruff format src/documents/export/sinks.py`
+Expected: no errors.
+
+- [ ] **Step 6: Commit**
+
+```bash
+git add src/documents/export/sinks.py src/documents/tests/export/test_sinks.py
+git commit -m "Feature: ZipExportSink accepts compression method and level"
+```
+
+---
+
+## Task 3: Wire CLI flags + validation into `document_exporter`
+
+**Files:**
+
+- Modify: `src/documents/management/commands/document_exporter.py`
+- Test: `src/documents/tests/test_management_exporter.py`
+
+- [ ] **Step 1: Add the argparse flags**
+
+In `document_exporter.py`, add the import near the other `documents.export` import:
+
+```python
+from documents.export.compression import COMPRESSION_CHOICES
+from documents.export.compression import COMPRESSION_METHODS
+from documents.export.compression import compression_available
+from documents.export.compression import level_error
+from documents.export.compression import ZSTD
+```
+
+In `add_arguments`, after the `--zip-name` argument, add:
+
+```python
+        parser.add_argument(
+            "--zip-compression",
+            choices=COMPRESSION_CHOICES,
+            default=None,
+            help=(
+                "Compression method for the export zip (requires --zip). "
+                "Default: deflated. 'zstd' requires Python 3.14+ on both the "
+                "exporting and importing machine."
+            ),
+        )
+
+        parser.add_argument(
+            "--zip-compression-level",
+            type=int,
+            default=None,
+            help=(
+                "Compression level for the export zip (requires --zip). "
+                "deflated: 0-9, bzip2: 1-9, zstd: -131072..22; ignored for "
+                "stored/lzma."
+            ),
+        )
+```
+
+- [ ] **Step 2: Read + validate the flags in `handle()`**
+
+In `handle()`, after the existing `--compare-*` + `--zip` guard, add the compression flag handling. Insert before the sink construction:
+
+```python
+        zip_compression: str | None = options["zip_compression"]
+        zip_compression_level: int | None = options["zip_compression_level"]
+
+        if not self.zip_export and (
+            zip_compression is not None or zip_compression_level is not None
+        ):
+            raise CommandError(
+                "--zip-compression and --zip-compression-level require --zip",
+            )
+
+        compression_method = zip_compression or "deflated"
+        if self.zip_export:
+            if not compression_available(compression_method):
+                if compression_method == "zstd" and ZSTD is None:
+                    raise CommandError(
+                        "zstd compression requires Python 3.14 or newer",
+                    )
+                raise CommandError(
+                    f"Compression method '{compression_method}' is not "
+                    f"available on this Python runtime",
+                )
+            level_msg = level_error(compression_method, zip_compression_level)
+            if level_msg is not None:
+                raise CommandError(level_msg)
+```
+
+- [ ] **Step 3: Pass the resolved values into `ZipExportSink`**
+
+Change the `ZipExportSink(...)` construction in `handle()` to:
+
+```python
+        if self.zip_export:
+            sink = ZipExportSink(
+                self.target,
+                options["zip_name"],
+                delete=self.delete,
+                compression=COMPRESSION_METHODS[compression_method],
+                compresslevel=zip_compression_level,
+            )
+        else:
+            sink = DirectoryExportSink(
+                self.target,
+                compare_checksums=self.compare_checksums,
+                compare_json=self.compare_json,
+                delete=self.delete,
+            )
+```
+
+- [ ] **Step 4: Write the command-level tests**
+
+Add to the `TestExportImport` class in `src/documents/tests/test_management_exporter.py` (imports `call_command`, `CommandError`, `ZipFile`, `timezone` already present):
+
+```python
+    def test_compression_flags_require_zip(self) -> None:
+        for args in (
+            ["--zip-compression", "lzma"],
+            ["--zip-compression-level", "5"],
+        ):
+            with self.assertRaises(CommandError):
+                call_command(
+                    "document_exporter",
+                    self.target,
+                    *args,
+                    skip_checks=True,
+                )
+
+    def test_zip_compression_level_out_of_range_raises(self) -> None:
+        with self.assertRaises(CommandError):
+            call_command(
+                "document_exporter",
+                self.target,
+                "--zip",
+                "--zip-compression",
+                "deflated",
+                "--zip-compression-level",
+                "99",
+                skip_checks=True,
+            )
+
+    def test_zip_compression_level_rejected_for_stored(self) -> None:
+        with self.assertRaises(CommandError):
+            call_command(
+                "document_exporter",
+                self.target,
+                "--zip",
+                "--zip-compression",
+                "stored",
+                "--zip-compression-level",
+                "5",
+                skip_checks=True,
+            )
+
+    def test_zip_lzma_compression_round_trips(self) -> None:
+        call_command(
+            "document_exporter",
+            self.target,
+            "--zip",
+            "--zip-compression",
+            "lzma",
+            skip_checks=True,
+        )
+        expected = str(
+            self.target / f"export-{timezone.localdate().isoformat()}.zip",
+        )
+        self.assertIsFile(expected)
+        with ZipFile(expected) as zip_file:
+            info = zip_file.getinfo("manifest.json")
+            # manifest.json carries the chosen method; deflated is the default
+            self.assertEqual(info.compress_type, 14)  # ZIP_LZMA
+
+    def test_default_zip_uses_deflate(self) -> None:
+        call_command(
+            "document_exporter",
+            self.target,
+            "--zip",
+            skip_checks=True,
+        )
+        expected = str(
+            self.target / f"export-{timezone.localdate().isoformat()}.zip",
+        )
+        with ZipFile(expected) as zip_file:
+            info = zip_file.getinfo("manifest.json")
+            self.assertEqual(info.compress_type, 8)  # ZIP_DEFLATED
+```
+
+- [ ] **Step 5: Run the tests**
+
+Run: `bash /c/Users/tholmes/Documents/Coding/paperless/vmtest.sh "src/documents/tests/test_management_exporter.py -v"`
+Expected: PASS — the new tests plus all existing exporter tests stay green.
+
+- [ ] **Step 6: Lint**
+
+Run: `ruff check src/documents/management/commands/document_exporter.py src/documents/tests/test_management_exporter.py && ruff format src/documents/management/commands/document_exporter.py src/documents/tests/test_management_exporter.py`
+Expected: no errors.
+
+- [ ] **Step 7: Commit**
+
+```bash
+git add src/documents/management/commands/document_exporter.py src/documents/tests/test_management_exporter.py
+git commit -m "Feature: add --zip-compression and --zip-compression-level flags"
+```
+
+---
+
+## Task 4: Importer pre-check for unreadable codecs
+
+**Files:**
+
+- Modify: `src/documents/management/commands/document_importer.py`
+- Test: `src/documents/tests/test_management_importer.py`
+
+- [ ] **Step 1: Write the failing test**
+
+The importer test file `src/documents/tests/test_management_importer.py` is
+`TestCase`-style (`class TestCommandImport(... TestCase)`, `self.assertRaises`,
+`DirectoriesMixin` gives `self.dirs.scratch_dir`). Match that style. Add this
+method to `TestCommandImport`. It builds a valid zip and patches the readability
+probe so the check fires deterministically on any runtime:
+
+```python
+    def test_import_rejects_unreadable_compression(self) -> None:
+        """
+        GIVEN:
+            - A zip archive with an entry whose compression this Python can't read
+        WHEN:
+            - Import is attempted
+        THEN:
+            - A CommandError naming the issue is raised, before extraction
+        """
+        import zipfile
+        from unittest import mock
+
+        archive = Path(self.dirs.scratch_dir) / "export.zip"
+        with zipfile.ZipFile(archive, "w") as zf:
+            zf.writestr("manifest.json", "[]")
+
+        with mock.patch(
+            "documents.management.commands.document_importer.compress_type_readable",
+            return_value=False,
+        ):
+            with self.assertRaises(CommandError) as e:
+                call_command(
+                    "document_importer",
+                    str(archive),
+                    "--no-progress-bar",
+                    skip_checks=True,
+                )
+        self.assertIn("compression", str(e.exception))
+```
+
+- [ ] **Step 2: Run to verify it fails**
+
+Run: `bash /c/Users/tholmes/Documents/Coding/paperless/vmtest.sh "src/documents/tests/test_management_importer.py -k unreadable_compression -v"`
+Expected: FAIL — no pre-check exists yet, so the import proceeds (or fails with a different error).
+
+- [ ] **Step 3: Implement the pre-check**
+
+In `document_importer.py`, add the import:
+
+```python
+from documents.export.compression import compress_type_readable
+from documents.export.compression import unreadable_method_names
+```
+
+Find the zip-handling block (around `document_importer.py:453`):
+
+```python
+                with ZipFile(self.source) as zf:
+                    zf.extractall(tmp_dir)
+```
+
+Replace it with a pre-check before extraction:
+
+```python
+                with ZipFile(self.source) as zf:
+                    unsupported = {
+                        info.compress_type
+                        for info in zf.infolist()
+                        if not compress_type_readable(info.compress_type)
+                    }
+                    if unsupported:
+                        names = ", ".join(sorted(unreadable_method_names(unsupported)))
+                        raise CommandError(
+                            f"This archive uses compression this Python cannot "
+                            f"read ({names}). zstd archives require Python 3.14+.",
+                        )
+                    zf.extractall(tmp_dir)
+```
+
+Confirm `CommandError` is imported in `document_importer.py` (it is used elsewhere; if not, add `from django.core.management.base import CommandError`).
+
+- [ ] **Step 4: Run to verify it passes**
+
+Run: `bash /c/Users/tholmes/Documents/Coding/paperless/vmtest.sh "src/documents/tests/test_management_importer.py -v"`
+Expected: PASS — the new test plus all existing importer tests (normal deflated/stored archives still import).
+
+- [ ] **Step 5: Lint**
+
+Run: `ruff check src/documents/management/commands/document_importer.py src/documents/tests/test_management_importer.py && ruff format src/documents/management/commands/document_importer.py src/documents/tests/test_management_importer.py`
+Expected: no errors.
+
+- [ ] **Step 6: Commit**
+
+```bash
+git add src/documents/management/commands/document_importer.py src/documents/tests/test_management_importer.py
+git commit -m "Feature: importer rejects archives with unreadable compression"
+```
+
+---
+
+## Task 5: Document the flags
+
+**Files:**
+
+- Modify: `docs/administration.md`
+
+- [ ] **Step 1: Add the flags to the option list**
+
+In `docs/administration.md`, update the usage block (around line 257) to include the new flags:
+
+```
+document_exporter target [-c] [-d] [-f] [-na] [-nt] [-p] [-sm] [-z]
+
+optional arguments:
+-c,  --compare-checksums
+-cj, --compare-json
+-d,  --delete
+-f,  --use-filename-format
+-na, --no-archive
+-nt, --no-thumbnail
+-p,  --use-folder-prefix
+-sm, --split-manifest
+-z,  --zip
+-zn, --zip-name
+--zip-compression
+--zip-compression-level
+--data-only
+--no-progress-bar
+--passphrase
+```
+
+- [ ] **Step 2: Add the prose**
+
+After the `-z`/`--zip` paragraph (around line 330), add:
+
+```markdown
+The compression method for the zip can be set with `--zip-compression`
+(`stored`, `deflated` (default), `bzip2`, `lzma`, or `zstd`) and tuned with
+`--zip-compression-level` (deflated: 0–9, bzip2: 1–9, zstd: -131072–22; ignored
+for `stored` and `lzma`). Both options require `--zip`.
+
+!!! warning
+
+    `zstd` compression requires Python 3.14 or newer on **both** the machine
+    creating the export and any machine importing it. An archive compressed with
+    `zstd` (or `lzma`/`bzip2` where those modules are unavailable) cannot be
+    imported on a runtime that lacks the codec; the importer will refuse it with
+    a clear error. The default `deflated` is universally readable.
+```
+
+- [ ] **Step 3: Verify the docs build is not broken (lint markdown)**
+
+Run: `ruff check docs/ 2>/dev/null; echo "docs are markdown; rely on prettier pre-commit"`
+(No code to test. The prettier pre-commit hook will reformat on commit.)
+
+- [ ] **Step 4: Commit**
+
+```bash
+git add docs/administration.md
+git commit -m "Docs: document --zip-compression and --zip-compression-level"
+```
+
+---
+
+## Task 6: Final verification
+
+**Files:** none (verification only).
+
+- [ ] **Step 1: Full backend suites on the VM**
+
+Run: `bash /c/Users/tholmes/Documents/Coding/paperless/vmtest.sh "src/documents/tests/export/ src/documents/tests/test_management_exporter.py src/documents/tests/test_management_importer.py -v"`
+Expected: PASS, no failures.
+
+- [ ] **Step 2: Spot-check the zstd happy path on Python 3.14 (cannot run under Django on the 3.11 VM)**
+
+The zstd positive round-trip can't run in the 3.11 test env. Confirm the policy module behaves on a real 3.14 interpreter with a standalone check (no Django needed):
+
+Run:
+
+```bash
+uv run --python 3.14 --no-project python -c "import sys; sys.path.insert(0,'src'); import django; print('skip')" 2>/dev/null || \
+uv run --python 3.14 --no-project python -c "
+import zipfile, io
+from compression.zstd import CompressionParameter as CP
+print('zstd const', zipfile.ZIP_ZSTANDARD, 'bounds', CP.compression_level.bounds())
+buf = io.BytesIO()
+with zipfile.ZipFile(buf,'w',compression=zipfile.ZIP_ZSTANDARD,compresslevel=19) as zf:
+    zf.writestr('a.txt','x'*1000)
+with zipfile.ZipFile(buf) as zf:
+    assert zf.getinfo('a.txt').compress_type == zipfile.ZIP_ZSTANDARD
+    assert zf.read('a.txt') == b'x'*1000
+print('zstd round-trip OK')
+"
+```
+
+Expected: prints `zstd const 93 bounds (-131072, 22)` and `zstd round-trip OK`. This validates the constant, bounds, and that a zstd archive round-trips — the parts the 3.11 CI cannot exercise.
+
+- [ ] **Step 3: Type-check on the VM (pyrefly)**
+
+```bash
+tar czf - src pyproject.toml uv.lock .pyrefly-baseline.json | ssh -o BatchMode=yes -p 2244 trenton@localhost 'tar xzf - -C ~/projects/paperless-ngx'
+ssh -o BatchMode=yes -p 2244 trenton@localhost 'bash -lc "cd ~/projects/paperless-ngx && uv run pyrefly check"'
+```
+
+Expected: no new type errors beyond the baseline. (Note: `import compression.zstd` is guarded behind `importlib.import_module`, so it is never statically resolved on the 3.11 baseline.)
+
+- [ ] **Step 4: Final lint**
+
+Run: `ruff check src/documents/export/ src/documents/management/commands/document_exporter.py src/documents/management/commands/document_importer.py && ruff format --check src/documents/export/ src/documents/management/commands/document_exporter.py src/documents/management/commands/document_importer.py`
+Expected: clean.
+
+---
+
+## Notes for the implementer
+
+- **Default behavior is unchanged:** with no flags, the sink is constructed with `compression=ZIP_DEFLATED, compresslevel=None` — byte-method-identical to today (`shutil.make_archive` used `ZIP_DEFLATED` with no level). `test_default_zip_uses_deflate` pins this.
+- **zstd availability is gated three ways and never imported statically:** the constant via `getattr`, the codec via `importlib.import_module("compression.zstd")`, and the CLI value rejected with a friendly message on < 3.14. The choices list always contains `zstd` so argparse doesn't hide it.
+- **The importer pre-check is the safety net** for portability foot-guns — without it an unreadable entry raises a bare `NotImplementedError` mid-`extractall`. The check runs on `infolist()` (metadata only) before any extraction.
+- **Why `--zip-compression` defaults to `None`, not `"deflated"`:** so `handle()` can detect "user passed it without `--zip`" and fail fast. The effective default is resolved as `zip_compression or "deflated"`.

docs/superpowers/specs/2026-06-16-export-zip-compression-design.md

@@ -0,0 +1,236 @@
+# Export Zip Compression Control — Design
+
+**Date:** 2026-06-16
+**Branch base:** `dev`
+**Status:** Design complete (zstd facts verified on CPython 3.14.3) — **depends on**
+`2026-06-16-export-sink-architecture-design.md` being implemented first.
+
+## Prerequisite
+
+This builds directly on the export sink refactor. It assumes `ZipExportSink`
+already exists and is the single place that owns `zipfile.ZipFile` creation and
+entry writes. Do not start this until that refactor has landed; without it, the
+change would have to touch the command's zip branches again.
+
+## Problem
+
+Zip export is hardwired to `ZIP_DEFLATED` at the library default level. Users
+have no way to trade speed against archive size — a fast `ZIP_STORED` pass for a
+quick local copy, or a maximal `ZIP_LZMA` pass for the smallest off-site backup.
+The sink refactor turns "which compression" into a single constructor argument,
+so exposing it is now a small, isolated change.
+
+## Goal
+
+Let the operator choose the zip compression method and level from the CLI, with
+behavior identical to today when the flags are omitted. All knowledge of
+compression stays inside `ZipExportSink`; the command only parses flags and maps
+them to sink arguments.
+
+## Scope
+
+In scope:
+
+- `ZipExportSink` gains `compression: int` and `compresslevel: int | None`
+  constructor parameters (default `ZIP_DEFLATED`, `None` → library default),
+  passed straight to `zipfile.ZipFile(...)`.
+- New `document_exporter` flags: `--zip-compression` and
+  `--zip-compression-level`, valid only with `--zip`.
+- Validation: method availability, level range per method, and the
+  requires-`--zip` guard.
+- Import-side: a pre-extract support check in `document_importer` that turns an
+  unsupported codec into a clear `CommandError` (the importer otherwise decompresses
+  transparently via `ZipFile.extractall`).
+- Docs: add both flags and the zstd-portability caveat to `docs/administration.md`
+  (the `document_exporter` option list, lines ~257-270 and the `-z`/`-zn` section,
+  lines ~328-330). New flags are long-form only (`--zip-compression`,
+  `--zip-compression-level`) — no short aliases, to avoid `-zc`/`-zl` collisions
+  with the existing `-z`/`-zn`.
+
+Out of scope:
+
+- Compression for any non-zip sink (folder has none; a future S3 sink would
+  handle its own object storage compression separately).
+- Changing the default. Omitting the flags must produce a byte-compatible-method
+  archive to today's (`ZIP_DEFLATED`, default level).
+
+## Design
+
+### `ZipExportSink` changes
+
+The base sink's signature is `ZipExportSink(target, zip_name, *, delete)`; this
+adds two keyword-only params after `delete`:
+
+```python
+def __init__(
+    self,
+    target: Path,
+    zip_name: str,
+    *,
+    delete: bool = False,
+    compression: int = zipfile.ZIP_DEFLATED,
+    compresslevel: int | None = None,
+) -> None:
+    ...
+    # opened in __enter__:
+    self._zip = zipfile.ZipFile(
+        self._tmp_path,
+        "w",
+        compression=compression,
+        compresslevel=compresslevel,
+        allowZip64=True,
+    )
+```
+
+`ZipFile` applies `compression`/`compresslevel` as the default for every
+`write`/`writestr` (verified: a `ZipFile(..., compression=ZIP_BZIP2)` yields
+entries with `compress_type == ZIP_BZIP2` without per-call args), so `add_file` /
+`add_json` / the manifest entry need no changes. Directory marker entries are
+empty so their compressed payload is zero, but they are still _tagged_ with the
+chosen `compress_type` — harmless, but tests that read `infolist()` should filter
+or account for marker entries (see Testing).
+
+### CLI flags (`document_exporter`)
+
+- `--zip-compression {stored,deflated,bzip2,lzma}` — and `zstd` **when the
+  runtime supports it** (see below). Maps to the matching `zipfile.ZIP_*`
+  constant. Default `deflated`.
+- `--zip-compression-level N` — integer. Per-method accepted ranges (verified
+  against the [3.14 `zipfile` docs](https://docs.python.org/3.14/library/zipfile.html#zipfile.ZipFile)):
+  - `deflated`: **0–9** (`zlib` also accepts `-1` = "default", identical to
+    omitting the flag / `compresslevel=None`).
+  - `bzip2`: **1–9** (`0` is invalid for bzip2).
+  - `lzma`, `stored`: level has **no effect** — passing `--zip-compression-level`
+    with either is a `CommandError`, not a silent accept (consistent with the
+    base refactor's fail-fast posture).
+  - `zstd`: **-131072 … 22** (the documented commonly-accepted range; the
+    authoritative bounds are
+    `compression.zstd.CompressionParameter.compression_level.bounds()`).
+
+  Default: unset → library default (`compresslevel=None`).
+
+Both flags require `--zip`; passing either without `--zip` raises a
+`CommandError`, matching the incremental-flag rule from the base refactor.
+
+**Why validate up front (not let `zipfile` raise) — verified on 3.14.3:** an
+invalid level does _not_ fail at `ZipFile(...)` construction — it fails at the
+**first `write`/`writestr` call**, with an opaque message
+(`ValueError: Invalid initialization option` for deflated > 9, or
+`ValueError: compresslevel must be between 1 and 9` for bzip2). Worse, on context
+exit the half-initialized write handle emits a secondary
+`AttributeError: '_ZipWriteFile' object has no attribute '_compressor'` during GC
+finalization, so the user sees stack-trace noise unrelated to the real cause.
+Up-front validation turns all of that into a single clean `CommandError`.
+
+### Validation (in `handle()`, before constructing the sink)
+
+1. **Requires `--zip`.** Either flag without `--zip` → `CommandError`.
+2. **Method availability — via a named, patchable seam.** Expose a module-level
+   helper `compression_available(method: str) -> bool` that does
+   `try: import bz2 / import lzma / from compression import zstd except ImportError:
+return False` — **not** `importlib.util.find_spec`, which can report a stdlib
+   C-extension as present when importing it actually fails. `stored`/`deflated`
+   are always available (`zlib` is a hard CPython dependency). For `zstd` the probe
+   must import `compression.zstd` (3.14+), not merely check that
+   `zipfile.ZIP_ZSTANDARD` exists. Making this a named function is also what lets
+   the test patch "method unavailable" with `mocker`. If the chosen method is
+   unavailable, raise a `CommandError` naming the missing capability — `zipfile`
+   itself would otherwise raise a bare `RuntimeError`
+   ("Compression requires the (missing) … module").
+3. **Level range.** Reject an out-of-range `--zip-compression-level` for the
+   chosen method with a clear `CommandError`; reject the flag entirely for
+   `stored`/`lzma` (see above).
+
+### zstd (Python 3.14+)
+
+**Verified empirically on CPython 3.14.3** (via `uv run --python 3.14 --no-project`)
+and against [PEP 784](https://peps.python.org/pep-0784/) +
+[the 3.14 `zipfile` docs](https://docs.python.org/3.14/library/zipfile.html):
+
+- The compression-method constant is **`zipfile.ZIP_ZSTANDARD`** (added 3.14; its
+  numeric value is `93`). It does **not** exist on < 3.14.
+- It is backed by the new **`compression.zstd`** stdlib module (PEP 784 added a
+  `compression` namespace package; legacy `bz2`/`lzma`/`zlib` imports are
+  unchanged). `zipfile` raises `RuntimeError` if `compression.zstd` is
+  unavailable when zstd is requested.
+- Accepted `compresslevel` is **`-131072 … 22`**, confirmed at runtime via
+  `compression.zstd.CompressionParameter.compression_level.bounds() == (-131072, 22)`.
+
+Gate everything zstd-related at runtime so nothing is imported or referenced on
+< 3.14 (the project targets Python ≥ 3.11):
+
+```python
+_ZSTD: int | None = getattr(zipfile, "ZIP_ZSTANDARD", None)  # None before 3.14
+```
+
+Presence of the _constant_ does not guarantee the _codec_ is usable, so the
+availability probe (validation step 2) imports `compression.zstd`, not merely
+checks the constant.
+
+Keep `zstd` in the `--zip-compression` `choices` **always** (even on < 3.14), and
+reject it in validation with a friendly "zstd requires Python 3.14+" message. If
+it were dropped from `choices` on older runtimes, argparse would emit a generic
+"invalid choice" that reads as though the option never existed — worse UX.
+
+### Import-side compatibility
+
+`document_importer` reads zips with `ZipFile(self.source).extractall(...)`
+(`document_importer.py:453`), which decompresses each entry transparently using
+whatever method it was stored with — **provided the matching module exists on the
+importing machine.**
+
+The failure mode when it doesn't is unfriendly and must be handled: a zstd (or
+otherwise unsupported) entry raises a bare `NotImplementedError` **per-entry,
+during `extractall`** — _not_ at `ZipFile(self.source)` open, and `is_zipfile()`
+still returns true (a zstd archive is a valid zip container). So the importer
+enters the zip branch, creates its temp dir, may partially extract other entries,
+then blows up mid-extract with no context. **Mitigation (in scope here):** before
+extracting, inspect `ZipFile(self.source).infolist()` compress types and, if any
+is unsupported on this runtime, raise a `CommandError` naming the method and the
+requirement (e.g. "this archive uses zstd, which needs Python 3.14+") instead of
+letting `NotImplementedError` escape.
+
+Per-method summary (document in help text + `administration.md`):
+
+- `deflated`/`stored`: universally importable.
+- `bzip2`/`lzma`: importable wherever the `bz2`/`lzma` modules are present
+  (essentially always).
+- `zstd`: importable only on Python 3.14+. An archive compressed with `zstd` is
+  **not** importable on older runtimes.
+
+## Testing
+
+New cases in the sink tests and an export→import round-trip
+(pytest classes, factory-boy, `mocker`, `parametrize`, typed; run on the VM):
+
+- **Round-trip per method.** Parametrize over the available methods (skip `zstd`
+  below 3.14, skip `bzip2`/`lzma` if the module is somehow absent): export a
+  small library, import it back, assert documents/manifest match.
+- **Method is applied.** Assert each written _file_ entry's `compress_type`
+  equals the requested method (read back via `ZipFile.infolist()`), filtering out
+  directory marker entries (which are tagged but empty).
+- **Level affects size — robustly.** Do **not** compare deflate level 9 vs 1
+  (on small or incompressible fixtures level 9 can equal or slightly exceed level
+  1, causing flaky CI). Instead assert that a compressing method on a
+  moderately-compressible fixture yields a total smaller than `stored`
+  (`ZIP_STORED`), which is a stable invariant.
+- **Validation.** Each flag without `--zip` → `CommandError`; out-of-range level
+  (`--zip-compression-level 99`) → a clean `CommandError` from validation
+  (asserting we never reach the `writestr` that would raise the masked
+  `ValueError`); `--zip-compression-level` with `stored`/`lzma` → `CommandError`;
+  unavailable method (patch the named availability seam with `mocker`) →
+  `CommandError`; on < 3.14, `--zip-compression zstd` → the friendly
+  "requires 3.14+" `CommandError`.
+- **Import pre-check.** An archive containing an unsupported compress type
+  produces a `CommandError` from the importer naming the method, not a raw
+  `NotImplementedError` (simulate by patching the importer's support probe).
+- **Default unchanged.** Omitting both flags yields file entries with
+  `compress_type == ZIP_DEFLATED`, identical to pre-feature behavior.
+
+## Risks
+
+- **Foot-gun archives.** A user could produce a `zstd`/`lzma` archive their
+  import target can't read. Mitigation: explicit help text and the import-side
+  notes above; the default stays the universally-readable `deflated`.
+- **Optional-module assumptions.** Don't assume `bz2`/`lzma` are always compiled
+  in; probe and error clearly. Mitigation: the availability validation step.

src/documents/export/compression.py

@@ -0,0 +1,108 @@
+from __future__ import annotations
+
+import importlib
+import zipfile
+
+# ZIP_ZSTANDARD exists only on Python 3.14+ (PEP 784). None elsewhere.
+ZSTD: int | None = getattr(zipfile, "ZIP_ZSTANDARD", None)
+
+# CLI choices are fixed across runtimes so argparse never hides zstd; runtime
+# availability is enforced separately in compression_available().
+COMPRESSION_CHOICES: tuple[str, ...] = (
+    "stored",
+    "deflated",
+    "bzip2",
+    "lzma",
+    "zstd",
+)
+
+# Method name -> zipfile compression constant (zstd only when supported).
+COMPRESSION_METHODS: dict[str, int] = {
+    "stored": zipfile.ZIP_STORED,
+    "deflated": zipfile.ZIP_DEFLATED,
+    "bzip2": zipfile.ZIP_BZIP2,
+    "lzma": zipfile.ZIP_LZMA,
+}
+if ZSTD is not None:
+    COMPRESSION_METHODS["zstd"] = ZSTD
+
+# Inclusive (min, max) level bounds per method; None => level not applicable.
+# Verified on CPython 3.14.3.
+#
+# zstd's raw library bounds are (-131072, 22)
+# (compression.zstd.CompressionParameter.compression_level.bounds()) — the
+# minimum is an internal implementation constant (-ZSTD_TARGETLENGTH_MAX),
+# not a meaningful distinct "level"; deeper negative values than -22 buy
+# nothing over -22 in practice. We expose the conventional zstd CLI range
+# instead of the raw library bounds.
+LEVEL_BOUNDS: dict[str, tuple[int, int] | None] = {
+    "stored": None,
+    "deflated": (0, 9),
+    "bzip2": (1, 9),
+    "lzma": None,
+    "zstd": (-22, 22),
+}
+
+# zipfile compress_type id -> method name. 93 = current zstd id, 20 = legacy
+# zstd id that zipfile can still read.
+_COMPRESS_TYPE_TO_METHOD: dict[int, str] = {
+    zipfile.ZIP_STORED: "stored",
+    zipfile.ZIP_DEFLATED: "deflated",
+    zipfile.ZIP_BZIP2: "bzip2",
+    zipfile.ZIP_LZMA: "lzma",
+    93: "zstd",
+    20: "zstd",
+}
+
+
+def compression_available(method: str) -> bool:
+    """Whether the running interpreter can actually use the given method."""
+    if method in ("stored", "deflated"):
+        # zlib is a hard CPython dependency; stored needs nothing.
+        return True
+    if method == "bzip2":
+        return _module_importable("bz2")
+    if method == "lzma":
+        return _module_importable("lzma")
+    if method == "zstd":
+        return ZSTD is not None and _module_importable("compression.zstd")
+    return False
+
+
+def _module_importable(name: str) -> bool:
+    try:
+        importlib.import_module(name)
+    except ImportError:
+        return False
+    return True
+
+
+def level_error(method: str, level: int | None) -> str | None:
+    """Return a human message if (method, level) is invalid, else None."""
+    if level is None:
+        return None
+    bounds = LEVEL_BOUNDS[method]
+    if bounds is None:
+        return f"--zip-compression-level has no effect for '{method}'"
+    low, high = bounds
+    if not (low <= level <= high):
+        return (
+            f"--zip-compression-level for '{method}' must be between {low} and {high}"
+        )
+    return None
+
+
+def compress_type_readable(compress_type: int) -> bool:
+    """Whether this interpreter can decompress an entry of the given type."""
+    method = _COMPRESS_TYPE_TO_METHOD.get(compress_type)
+    if method is None:
+        return False
+    return compression_available(method)
+
+
+def unreadable_method_names(compress_types: set[int]) -> set[str]:
+    """Map a set of compress_type ids to human method names for error messages."""
+    names: set[str] = set()
+    for ct in compress_types:
+        names.add(_COMPRESS_TYPE_TO_METHOD.get(ct, f"method {ct}"))
+    return names

src/documents/export/sinks.py

@@ -0,0 +1,353 @@
+from __future__ import annotations
+
+import abc
+import hashlib
+import json
+import os
+import shutil
+import tempfile
+import zipfile
+from contextlib import AbstractContextManager
+from contextlib import contextmanager
+from pathlib import Path
+from pathlib import PurePosixPath
+from typing import TYPE_CHECKING
+
+from django.conf import settings
+from django.core.serializers.json import DjangoJSONEncoder
+
+from documents.file_handling import delete_empty_directories
+from documents.utils import compute_checksum
+from documents.utils import copy_file_with_basic_stats
+
+if TYPE_CHECKING:
+    from collections.abc import Iterator
+    from typing import TextIO
+
+
+def _dumps(content: list | dict) -> str:
+    """Serialize export JSON consistently across all sinks."""
+    return json.dumps(content, cls=DjangoJSONEncoder, indent=2, ensure_ascii=False)
+
+
+class StreamingManifestWriter:
+    """Incrementally writes a JSON array to a text handle, one record at a time.
+
+    Knows nothing about folders or zips: it writes the array framing and records
+    to whatever handle the sink's ``stream()`` yields. The sink owns the handle's
+    lifecycle (atomic rename, compare, spooling).
+    """
+
+    def __init__(self, handle: TextIO) -> None:
+        self._file = handle
+        self._first = True
+        self._file.write("[")
+
+    def write_record(self, record: dict) -> None:
+        if not self._first:
+            self._file.write(",\n")
+        else:
+            self._first = False
+        self._file.write(_dumps(record))
+
+    def write_batch(self, records: list[dict]) -> None:
+        for record in records:
+            self.write_record(record)
+
+    def close(self) -> None:
+        """Write the closing bracket. Does NOT close the handle (the sink owns it)."""
+        self._file.write("\n]")
+
+
+class ExportSink(AbstractContextManager, abc.ABC):
+    """Destination for a document export.
+
+    The command declares export contents via three verbs; the sink decides how to
+    persist each. ``arcname`` is always a relative POSIX path
+    (e.g. ``"manifest.json"``, ``"originals/foo.pdf"``).
+
+    Contract:
+      * At most one ``stream()`` open at a time (it is the manifest);
+        ``add_file``/``add_json`` may be called while it is open.
+      * Context-manager: normal exit finalizes, an exception aborts. No partial or
+        failed run leaves a complete-looking artifact.
+    """
+
+    @abc.abstractmethod
+    def add_file(
+        self,
+        source: Path,
+        arcname: str,
+        *,
+        checksum: str | None = None,
+    ) -> None: ...
+
+    @abc.abstractmethod
+    def add_json(self, content: list | dict, arcname: str) -> None: ...
+
+    @abc.abstractmethod
+    def stream(self, arcname: str) -> AbstractContextManager[TextIO]: ...
+
+    def _open(self) -> None:
+        """Hook called on context entry. Override as needed."""
+
+    @abc.abstractmethod
+    def _finalize(self) -> None:
+        """Commit on clean exit."""
+
+    @abc.abstractmethod
+    def _abort(self) -> None:
+        """Roll back on exception."""
+
+    def __enter__(self) -> ExportSink:
+        self._open()
+        return self
+
+    def __exit__(self, exc_type, exc_val, exc_tb) -> None:
+        if exc_type is not None:
+            self._abort()
+        else:
+            self._finalize()
+
+
+class DirectoryExportSink(ExportSink):
+    """Writes loose files into a target directory, with incremental sync.
+
+    Owns the snapshot/skip/compare/prune machinery that used to live in the
+    command (``files_in_export_dir``, ``check_and_copy``, ``check_and_write_json``,
+    and the ``--delete`` pass).
+    """
+
+    def __init__(
+        self,
+        target: Path,
+        *,
+        compare_checksums: bool,
+        compare_json: bool,
+        delete: bool,
+    ) -> None:
+        self._target = target.resolve()
+        self._compare_checksums = compare_checksums
+        self._compare_json = compare_json
+        self._delete = delete
+        self._snapshot: set[Path] = set()
+        self._stream_open = False
+
+    def _open(self) -> None:
+        for x in self._target.glob("**/*"):
+            if x.is_file():
+                self._snapshot.add(x.resolve())
+
+    def add_file(
+        self,
+        source: Path,
+        arcname: str,
+        *,
+        checksum: str | None = None,
+    ) -> None:
+        target = (self._target / arcname).resolve()
+        self._snapshot.discard(target)
+        perform_copy = False
+        if target.exists():
+            source_stat = source.stat()
+            target_stat = target.stat()
+            if self._compare_checksums and checksum:
+                perform_copy = compute_checksum(target) != checksum
+            elif (
+                source_stat.st_mtime != target_stat.st_mtime
+                or source_stat.st_size != target_stat.st_size
+            ):
+                perform_copy = True
+        else:
+            perform_copy = True
+        if perform_copy:
+            target.parent.mkdir(parents=True, exist_ok=True)
+            copy_file_with_basic_stats(source, target)
+
+    @staticmethod
+    def _content_unchanged(target: Path, new_bytes: bytes) -> bool:
+        """True if ``target`` already holds byte-identical content (BLAKE2b)."""
+        return (
+            hashlib.blake2b(target.read_bytes()).hexdigest()
+            == hashlib.blake2b(new_bytes).hexdigest()
+        )
+
+    def add_json(self, content: list | dict, arcname: str) -> None:
+        target = (self._target / arcname).resolve()
+        json_str = _dumps(content)
+        perform_write = True
+        if target in self._snapshot:
+            self._snapshot.discard(target)
+            if self._compare_json and self._content_unchanged(
+                target,
+                json_str.encode("utf-8"),
+            ):
+                perform_write = False
+        if perform_write:
+            target.parent.mkdir(parents=True, exist_ok=True)
+            target.write_text(json_str, encoding="utf-8")
+
+    @contextmanager
+    def stream(self, arcname: str) -> Iterator[TextIO]:
+        if self._stream_open:
+            raise RuntimeError("A stream is already open on this sink")
+        target = (self._target / arcname).resolve()
+        tmp = target.with_suffix(target.suffix + ".tmp")
+        target.parent.mkdir(parents=True, exist_ok=True)
+        handle = tmp.open("w", encoding="utf-8")
+        self._stream_open = True
+        try:
+            yield handle
+        except BaseException:
+            handle.close()
+            tmp.unlink(missing_ok=True)
+            raise
+        else:
+            handle.close()
+            self._commit_streamed_file(target, tmp)
+        finally:
+            self._stream_open = False
+
+    def _commit_streamed_file(self, target: Path, tmp: Path) -> None:
+        if target in self._snapshot:
+            self._snapshot.discard(target)
+            if self._compare_json and self._content_unchanged(
+                target,
+                tmp.read_bytes(),
+            ):
+                tmp.unlink()
+                return
+        tmp.rename(target)
+
+    def _finalize(self) -> None:
+        if self._delete:
+            for f in self._snapshot:
+                f.unlink()
+                delete_empty_directories(f.parent, self._target)
+
+    def _abort(self) -> None:
+        # Folder mode is in-place/incremental: streamed .tmp files are already
+        # cleaned in stream(); leave everything else intact and skip the prune.
+        return None
+
+
+class ZipExportSink(ExportSink):
+    """Writes a single zip archive, produced atomically only on success.
+
+    Builds into ``<target>/<zip_name>.zip.tmp`` and renames to ``.zip`` on clean
+    finalize. The manifest stream is spooled to a temp file in SCRATCH_DIR and
+    added as an entry at finalize (a zip entry cannot be interleaved with others).
+    """
+
+    def __init__(
+        self,
+        target: Path,
+        zip_name: str,
+        *,
+        delete: bool = False,
+        compression: int = zipfile.ZIP_DEFLATED,
+        compresslevel: int | None = None,
+    ) -> None:
+        self._target = target.resolve()
+        self._zip_path = (self._target / zip_name).with_suffix(".zip")
+        self._tmp_path = self._zip_path.with_name(self._zip_path.name + ".tmp")
+        self._delete = delete
+        self._compression = compression
+        self._compresslevel = compresslevel
+        self._zip: zipfile.ZipFile | None = None
+        self._dirs: set[str] = set()
+        self._pending_manifest: tuple[Path, str] | None = None
+        self._stream_open = False
+
+    def _open(self) -> None:
+        settings.SCRATCH_DIR.mkdir(parents=True, exist_ok=True)
+        self._zip = zipfile.ZipFile(
+            self._tmp_path,
+            "w",
+            compression=self._compression,
+            compresslevel=self._compresslevel,
+            allowZip64=True,
+        )
+
+    def _ensure_dirs(self, arcname: str) -> None:
+        assert self._zip is not None
+        dir_arc = ""
+        for part in PurePosixPath(arcname).parts[:-1]:
+            dir_arc += f"{part}/"
+            if dir_arc not in self._dirs:
+                self._dirs.add(dir_arc)
+                self._zip.mkdir(dir_arc)
+
+    def add_file(
+        self,
+        source: Path,
+        arcname: str,
+        *,
+        checksum: str | None = None,
+    ) -> None:
+        assert self._zip is not None
+        self._ensure_dirs(arcname)
+        self._zip.write(source, arcname=arcname)
+
+    def add_json(self, content: list | dict, arcname: str) -> None:
+        assert self._zip is not None
+        self._ensure_dirs(arcname)
+        self._zip.writestr(arcname, _dumps(content))
+
+    @contextmanager
+    def stream(self, arcname: str) -> Iterator[TextIO]:
+        if self._stream_open:
+            raise RuntimeError("A stream is already open on this sink")
+        settings.SCRATCH_DIR.mkdir(parents=True, exist_ok=True)
+        fd, tmp_name = tempfile.mkstemp(
+            dir=settings.SCRATCH_DIR,
+            prefix="export-manifest-",
+            suffix=".json",
+        )
+        tmp = Path(tmp_name)
+        handle = os.fdopen(fd, "w", encoding="utf-8")
+        self._stream_open = True
+        try:
+            yield handle
+        except BaseException:
+            handle.close()
+            tmp.unlink(missing_ok=True)
+            raise
+        else:
+            handle.close()
+            self._pending_manifest = (tmp, arcname)
+        finally:
+            self._stream_open = False
+
+    def _finalize(self) -> None:
+        assert self._zip is not None
+        if self._pending_manifest is not None:
+            tmp, arcname = self._pending_manifest
+            self._ensure_dirs(arcname)
+            self._zip.write(tmp, arcname=arcname)
+            tmp.unlink(missing_ok=True)
+            self._pending_manifest = None
+        self._zip.close()
+        self._zip = None
+        if self._delete:
+            self._wipe_destination()
+        self._tmp_path.replace(self._zip_path)
+
+    def _wipe_destination(self) -> None:
+        skip = {self._zip_path.resolve(), self._tmp_path.resolve()}
+        for item in self._target.glob("*"):
+            if item.resolve() in skip:
+                continue
+            if item.is_dir():
+                shutil.rmtree(item)
+            else:
+                item.unlink()
+
+    def _abort(self) -> None:
+        if self._zip is not None:
+            self._zip.close()
+            self._zip = None
+        self._tmp_path.unlink(missing_ok=True)
+        if self._pending_manifest is not None:
+            self._pending_manifest[0].unlink(missing_ok=True)
+            self._pending_manifest = None

src/documents/management/commands/document_exporter.py

@@ -1,8 +1,4 @@
-import hashlib
-import json
 import os
-import shutil
-import tempfile
 from itertools import islice
 from pathlib import Path
 from typing import TYPE_CHECKING
@@ -19,7 +15,6 @@ from django.contrib.auth.models import User
 from django.contrib.contenttypes.models import ContentType
 from django.core import serializers
 from django.core.management.base import CommandError
-from django.core.serializers.json import DjangoJSONEncoder
 from django.db import transaction
 from django.utils import timezone
 from filelock import FileLock
@@ -34,7 +29,15 @@ if TYPE_CHECKING:
 if settings.AUDIT_LOG_ENABLED:
     from auditlog.models import LogEntry
 
-from documents.file_handling import delete_empty_directories
+from documents.export.compression import COMPRESSION_CHOICES
+from documents.export.compression import COMPRESSION_METHODS
+from documents.export.compression import ZSTD
+from documents.export.compression import compression_available
+from documents.export.compression import level_error
+from documents.export.sinks import DirectoryExportSink
+from documents.export.sinks import ExportSink
+from documents.export.sinks import StreamingManifestWriter
+from documents.export.sinks import ZipExportSink
 from documents.file_handling import generate_filename
 from documents.management.commands.base import PaperlessCommand
 from documents.management.commands.mixins import CryptMixin
@@ -60,8 +63,6 @@ from documents.settings import EXPORTER_ARCHIVE_NAME
 from documents.settings import EXPORTER_FILE_NAME
 from documents.settings import EXPORTER_SHARE_LINK_BUNDLE_NAME
 from documents.settings import EXPORTER_THUMBNAIL_NAME
-from documents.utils import compute_checksum
-from documents.utils import copy_file_with_basic_stats
 from paperless import version
 from paperless.models import ApplicationConfiguration
 from paperless_mail.models import MailAccount
@@ -84,87 +85,6 @@ def serialize_queryset_batched(
         yield serializers.serialize("python", chunk)
 
 
-class StreamingManifestWriter:
-    """Incrementally writes a JSON array to a file, one record at a time.
-
-    Writes to <target>.tmp first; on close(), optionally BLAKE2b-compares
-    with the existing file (--compare-json) and renames or discards accordingly.
-    On exception, discard() deletes the tmp file and leaves the original intact.
-    """
-
-    def __init__(
-        self,
-        path: Path,
-        *,
-        compare_json: bool = False,
-        files_in_export_dir: "set[Path] | None" = None,
-    ) -> None:
-        self._path = path.resolve()
-        self._tmp_path = self._path.with_suffix(self._path.suffix + ".tmp")
-        self._compare_json = compare_json
-        self._files_in_export_dir: set[Path] = (
-            files_in_export_dir if files_in_export_dir is not None else set()
-        )
-        self._file = None
-        self._first = True
-
-    def open(self) -> None:
-        self._path.parent.mkdir(parents=True, exist_ok=True)
-        self._file = self._tmp_path.open("w", encoding="utf-8")
-        self._file.write("[")
-        self._first = True
-
-    def write_record(self, record: dict) -> None:
-        if not self._first:
-            self._file.write(",\n")
-        else:
-            self._first = False
-        self._file.write(
-            json.dumps(record, cls=DjangoJSONEncoder, indent=2, ensure_ascii=False),
-        )
-
-    def write_batch(self, records: list[dict]) -> None:
-        for record in records:
-            self.write_record(record)
-
-    def close(self) -> None:
-        if self._file is None:
-            return
-        self._file.write("\n]")
-        self._file.close()
-        self._file = None
-        self._finalize()
-
-    def discard(self) -> None:
-        if self._file is not None:
-            self._file.close()
-            self._file = None
-        if self._tmp_path.exists():
-            self._tmp_path.unlink()
-
-    def _finalize(self) -> None:
-        """Compare with existing file (if --compare-json) then rename or discard tmp."""
-        if self._path in self._files_in_export_dir:
-            self._files_in_export_dir.remove(self._path)
-            if self._compare_json:
-                existing_hash = hashlib.blake2b(self._path.read_bytes()).hexdigest()
-                new_hash = hashlib.blake2b(self._tmp_path.read_bytes()).hexdigest()
-                if existing_hash == new_hash:
-                    self._tmp_path.unlink()
-                    return
-        self._tmp_path.rename(self._path)
-
-    def __enter__(self) -> "StreamingManifestWriter":
-        self.open()
-        return self
-
-    def __exit__(self, exc_type, exc_val, exc_tb) -> None:
-        if exc_type is not None:
-            self.discard()
-        else:
-            self.close()
-
-
 class Command(CryptMixin, PaperlessCommand):
     help = (
         "Decrypt and rename all files in our collection into a given target "
@@ -276,6 +196,28 @@ class Command(CryptMixin, PaperlessCommand):
             help="Sets the export zip file name",
         )
 
+        parser.add_argument(
+            "--zip-compression",
+            choices=COMPRESSION_CHOICES,
+            default=None,
+            help=(
+                "Compression method for the export zip (requires --zip). "
+                "Default: deflated. 'zstd' requires Python 3.14+ on both the "
+                "exporting and importing machine."
+            ),
+        )
+
+        parser.add_argument(
+            "--zip-compression-level",
+            type=int,
+            default=None,
+            help=(
+                "Compression level for the export zip (requires --zip). "
+                "deflated: 0-9, bzip2: 1-9, zstd: -22..22; ignored for "
+                "stored/lzma."
+            ),
+        )
+
         parser.add_argument(
             "--data-only",
             default=False,
@@ -314,20 +256,13 @@ class Command(CryptMixin, PaperlessCommand):
         self.passphrase: str | None = options.get("passphrase")
         self.batch_size: int = options["batch_size"]
 
-        self.files_in_export_dir: set[Path] = set()
         self.exported_files: set[str] = set()
 
-        # If zipping, save the original target for later and
-        # get a temporary directory for the target instead
-        temp_dir = None
-        self.original_target = self.target
-        if self.zip_export:
-            settings.SCRATCH_DIR.mkdir(parents=True, exist_ok=True)
-            temp_dir = tempfile.TemporaryDirectory(
-                dir=settings.SCRATCH_DIR,
-                prefix="paperless-export",
+        if self.zip_export and (self.compare_checksums or self.compare_json):
+            raise CommandError(
+                "--compare-checksums and --compare-json have no effect when "
+                "used with --zip",
             )
-            self.target = Path(temp_dir.name).resolve()
 
         if not self.target.exists():
             raise CommandError("That path doesn't exist")
@@ -338,33 +273,55 @@ class Command(CryptMixin, PaperlessCommand):
         if not os.access(self.target, os.W_OK):
             raise CommandError("That path doesn't appear to be writable")
 
-        try:
-            # Prevent any ongoing changes in the documents
-            with FileLock(settings.MEDIA_LOCK):
-                self.dump()
+        zip_compression: str | None = options["zip_compression"]
+        zip_compression_level: int | None = options["zip_compression_level"]
 
-                # We've written everything to the temporary directory in this case,
-                # now make an archive in the original target, with all files stored
-                if self.zip_export and temp_dir is not None:
-                    shutil.make_archive(
-                        self.original_target / options["zip_name"],
-                        format="zip",
-                        root_dir=temp_dir.name,
+        if not self.zip_export and (
+            zip_compression is not None or zip_compression_level is not None
+        ):
+            raise CommandError(
+                "--zip-compression and --zip-compression-level require --zip",
+            )
+
+        compression_method = zip_compression or "deflated"
+        if self.zip_export:
+            if not compression_available(compression_method):
+                if compression_method == "zstd" and ZSTD is None:
+                    raise CommandError(
+                        "zstd compression requires Python 3.14 or newer",
                     )
+                raise CommandError(
+                    f"Compression method '{compression_method}' is not "
+                    f"available on this Python runtime",
+                )
+            level_msg = level_error(compression_method, zip_compression_level)
+            if level_msg is not None:
+                raise CommandError(level_msg)
 
-        finally:
-            # Always cleanup the temporary directory, if one was created
-            if self.zip_export and temp_dir is not None:
-                temp_dir.cleanup()
+        sink: ExportSink
+        if self.zip_export:
+            sink = ZipExportSink(
+                self.target,
+                options["zip_name"],
+                delete=self.delete,
+                compression=COMPRESSION_METHODS[compression_method],
+                compresslevel=zip_compression_level,
+            )
+        else:
+            sink = DirectoryExportSink(
+                self.target,
+                compare_checksums=self.compare_checksums,
+                compare_json=self.compare_json,
+                delete=self.delete,
+            )
 
-    def dump(self) -> None:
-        # 1. Take a snapshot of what files exist in the current export folder
-        for x in self.target.glob("**/*"):
-            if x.is_file():
-                self.files_in_export_dir.add(x.resolve())
+        # Prevent any ongoing changes in the documents while exporting
+        with FileLock(settings.MEDIA_LOCK), sink:
+            self.dump(sink)
 
-        # 2. Create manifest, containing all correspondents, types, tags, storage paths
-        # note, documents and ui_settings
+    def dump(self, sink: ExportSink) -> None:
+        # 1. Create manifest, containing all correspondents, types, tags, storage
+        #    paths, note, documents and ui_settings
         _excluded_usernames = ["consumer", "AnonymousUser"]
         manifest_key_to_object_query: dict[str, QuerySet[Any]] = {
             "correspondents": Correspondent.objects.all(),
@@ -427,13 +384,9 @@ class Command(CryptMixin, PaperlessCommand):
 
         document_manifest: list[dict] = []
         share_link_bundle_manifest: list[dict] = []
-        manifest_path = (self.target / "manifest.json").resolve()
 
-        with StreamingManifestWriter(
-            manifest_path,
-            compare_json=self.compare_json,
-            files_in_export_dir=self.files_in_export_dir,
-        ) as writer:
+        with sink.stream("manifest.json") as handle:
+            writer = StreamingManifestWriter(handle)
             with transaction.atomic():
                 for key, qs in manifest_key_to_object_query.items():
                     if key == "documents":
@@ -479,84 +432,55 @@ class Command(CryptMixin, PaperlessCommand):
                 )
             }
 
-            # 3. Export files from each document
-            for index, document_dict in enumerate(
-                self.track(
-                    document_manifest,
-                    description="Exporting documents...",
-                    total=len(document_manifest),
-                ),
+            # 2. Export files from each document
+            for document_dict in self.track(
+                document_manifest,
+                description="Exporting documents...",
+                total=len(document_manifest),
             ):
                 document = document_map[document_dict["pk"]]
 
-                # 3.1. generate a unique filename
+                # generate a unique filename, then the arcnames for its files
                 base_name = self.generate_base_name(document)
-
-                # 3.2. write filenames into manifest
-                original_target, thumbnail_target, archive_target = (
+                original_arc, thumbnail_arc, archive_arc = (
                     self.generate_document_targets(document, base_name, document_dict)
                 )
 
-                # 3.3. write files to target folder
                 if not self.data_only:
                     self.copy_document_files(
                         document,
-                        original_target,
-                        thumbnail_target,
-                        archive_target,
+                        sink,
+                        original_arc,
+                        thumbnail_arc,
+                        archive_arc,
                     )
 
                 if self.split_manifest:
-                    self._write_split_manifest(document_dict, document, base_name)
+                    self._write_split_manifest(sink, document_dict, document, base_name)
                 else:
                     writer.write_record(document_dict)
 
             for bundle_dict in share_link_bundle_manifest:
                 bundle = share_link_bundle_map[bundle_dict["pk"]]
-
-                bundle_target = self.generate_share_link_bundle_target(
+                bundle_arc = self.generate_share_link_bundle_target(
                     bundle,
                     bundle_dict,
                 )
-
-                if not self.data_only and bundle_target is not None:
-                    self.copy_share_link_bundle_file(bundle, bundle_target)
-
+                if not self.data_only and bundle_arc is not None:
+                    self.copy_share_link_bundle_file(bundle, sink, bundle_arc)
                 writer.write_record(bundle_dict)
 
-        # 4.2 write version information to target folder
-        extra_metadata_path = (self.target / "metadata.json").resolve()
+            writer.close()
+
+        # 3. Write version (and crypto params) to metadata.json
+        # Django stores most crypto values in the field itself; we store
+        # them once here for the whole export
         metadata: dict[str, str | int | dict[str, str | int]] = {
             "version": version.__full_version_str__,
         }
-
-        # 4.2.1 If needed, write the crypto values into the metadata
-        # Django stores most of these in the field itself, we store them once here
         if self.passphrase:
             metadata.update(self.get_crypt_params())
-
-        self.check_and_write_json(
-            metadata,
-            extra_metadata_path,
-        )
-
-        if self.delete:
-            # 5. Remove files which we did not explicitly export in this run
-            if not self.zip_export:
-                for f in self.files_in_export_dir:
-                    f.unlink()
-
-                    delete_empty_directories(
-                        f.parent,
-                        self.target,
-                    )
-            else:
-                # 5. Remove anything in the original location (before moving the zip)
-                for item in self.original_target.glob("*"):
-                    if item.is_dir():
-                        shutil.rmtree(item)
-                    else:
-                        item.unlink()
+        sink.add_json(metadata, "metadata.json")
 
     def generate_base_name(self, document: Document) -> Path:
         """
@@ -584,73 +508,69 @@ class Command(CryptMixin, PaperlessCommand):
         document: Document,
         base_name: Path,
         document_dict: dict,
-    ) -> tuple[Path, Path | None, Path | None]:
+    ) -> tuple[str, str | None, str | None]:
         """
-        Generates the targets for a given document, including the original file, archive file and thumbnail (depending on settings).
+        Generates the relative POSIX arcnames for a document's original, thumbnail
+        and archive files (depending on settings), and records them in the manifest.
         """
         original_name = base_name
         if self.use_folder_prefix:
             original_name = Path("originals") / original_name
-        original_target = (self.target / original_name).resolve()
-        document_dict[EXPORTER_FILE_NAME] = str(original_name)
+        original_arc = original_name.as_posix()
+        document_dict[EXPORTER_FILE_NAME] = original_arc
 
         if not self.no_thumbnail:
             thumbnail_name = base_name.parent / (base_name.stem + "-thumbnail.webp")
             if self.use_folder_prefix:
                 thumbnail_name = Path("thumbnails") / thumbnail_name
-            thumbnail_target = (self.target / thumbnail_name).resolve()
-            document_dict[EXPORTER_THUMBNAIL_NAME] = str(thumbnail_name)
+            thumbnail_arc = thumbnail_name.as_posix()
+            document_dict[EXPORTER_THUMBNAIL_NAME] = thumbnail_arc
         else:
-            thumbnail_target = None
+            thumbnail_arc = None
 
         if not self.no_archive and document.has_archive_version:
             archive_name = base_name.parent / (base_name.stem + "-archive.pdf")
             if self.use_folder_prefix:
                 archive_name = Path("archive") / archive_name
-            archive_target = (self.target / archive_name).resolve()
-            document_dict[EXPORTER_ARCHIVE_NAME] = str(archive_name)
+            archive_arc = archive_name.as_posix()
+            document_dict[EXPORTER_ARCHIVE_NAME] = archive_arc
         else:
-            archive_target = None
+            archive_arc = None
 
-        return original_target, thumbnail_target, archive_target
+        return original_arc, thumbnail_arc, archive_arc
 
     def copy_document_files(
         self,
         document: Document,
-        original_target: Path,
-        thumbnail_target: Path | None,
-        archive_target: Path | None,
+        sink: ExportSink,
+        original_arc: str,
+        thumbnail_arc: str | None,
+        archive_arc: str | None,
     ) -> None:
         """
-        Copies files from the document storage location to the specified target location.
-
-        If the document is encrypted, the files are decrypted before copying them to the target location.
+        Hands the document's files to the sink (original, thumbnail, archive).
         """
-        self.check_and_copy(
-            document.source_path,
-            document.checksum,
-            original_target,
-        )
+        sink.add_file(document.source_path, original_arc, checksum=document.checksum)
 
-        if thumbnail_target:
-            self.check_and_copy(document.thumbnail_path, None, thumbnail_target)
+        if thumbnail_arc:
+            sink.add_file(document.thumbnail_path, thumbnail_arc)
 
-        if archive_target:
+        if archive_arc:
             if TYPE_CHECKING:
                 assert isinstance(document.archive_path, Path)
-            self.check_and_copy(
+            sink.add_file(
                 document.archive_path,
-                document.archive_checksum,
-                archive_target,
+                archive_arc,
+                checksum=document.archive_checksum,
             )
 
     def generate_share_link_bundle_target(
         self,
         bundle: ShareLinkBundle,
         bundle_dict: dict,
-    ) -> Path | None:
+    ) -> str | None:
         """
-        Generates the export target for a share link bundle file, when present.
+        Generates the relative POSIX arcname for a share link bundle file, if any.
         """
         if not bundle.file_path:
             return None
@@ -666,25 +586,22 @@ class Command(CryptMixin, PaperlessCommand):
         bundle_dict["fields"]["file_path"] = portable_bundle_path.as_posix()
         bundle_dict[EXPORTER_SHARE_LINK_BUNDLE_NAME] = export_bundle_path.as_posix()
 
-        return (self.target / export_bundle_path).resolve()
+        return export_bundle_path.as_posix()
 
     def copy_share_link_bundle_file(
         self,
         bundle: ShareLinkBundle,
-        bundle_target: Path,
+        sink: ExportSink,
+        bundle_arc: str,
     ) -> None:
         """
-        Copies a share link bundle ZIP into the export directory.
+        Hands a share link bundle ZIP to the sink.
         """
         bundle_source_path = bundle.absolute_file_path
         if bundle_source_path is None:
             raise FileNotFoundError(f"Share link bundle {bundle.pk} has no file path")
 
-        self.check_and_copy(
-            bundle_source_path,
-            None,
-            bundle_target,
-        )
+        sink.add_file(bundle_source_path, bundle_arc)
 
     def _encrypt_record_inline(self, record: dict) -> None:
         """Encrypt sensitive fields in a single record, if passphrase is set."""
@@ -700,6 +617,7 @@ class Command(CryptMixin, PaperlessCommand):
 
     def _write_split_manifest(
         self,
+        sink: ExportSink,
         document_dict: dict,
         document: Document,
         base_name: Path,
@@ -721,81 +639,4 @@ class Command(CryptMixin, PaperlessCommand):
         manifest_name = base_name.with_name(f"{base_name.stem}-manifest.json")
         if self.use_folder_prefix:
             manifest_name = Path("json") / manifest_name
-        manifest_name = (self.target / manifest_name).resolve()
-        manifest_name.parent.mkdir(parents=True, exist_ok=True)
-        self.check_and_write_json(content, manifest_name)
-
-    def check_and_write_json(
-        self,
-        content: list[dict] | dict,
-        target: Path,
-    ) -> None:
-        """
-        Writes the source content to the target json file.
-        If --compare-json arg was used, don't write to target file if
-        the file exists and checksum is identical to content checksum.
-        This preserves the file timestamps when no changes are made.
-        """
-
-        target = target.resolve()
-        perform_write = True
-        if target in self.files_in_export_dir:
-            self.files_in_export_dir.remove(target)
-            if self.compare_json:
-                target_checksum = hashlib.blake2b(target.read_bytes()).hexdigest()
-                src_str = json.dumps(
-                    content,
-                    cls=DjangoJSONEncoder,
-                    indent=2,
-                    ensure_ascii=False,
-                )
-                src_checksum = hashlib.blake2b(src_str.encode("utf-8")).hexdigest()
-                if src_checksum == target_checksum:
-                    perform_write = False
-
-        if perform_write:
-            target.write_text(
-                json.dumps(
-                    content,
-                    cls=DjangoJSONEncoder,
-                    indent=2,
-                    ensure_ascii=False,
-                ),
-                encoding="utf-8",
-            )
-
-    def check_and_copy(
-        self,
-        source: Path,
-        source_checksum: str | None,
-        target: Path,
-    ) -> None:
-        """
-        Copies the source to the target, if target doesn't exist or the target doesn't seem to match
-        the source attributes
-        """
-
-        target = target.resolve()
-        if target in self.files_in_export_dir:
-            self.files_in_export_dir.remove(target)
-
-        perform_copy = False
-
-        if target.exists():
-            source_stat = source.stat()
-            target_stat = target.stat()
-            if self.compare_checksums and source_checksum:
-                target_checksum = compute_checksum(target)
-                perform_copy = target_checksum != source_checksum
-            elif (
-                source_stat.st_mtime != target_stat.st_mtime
-                or source_stat.st_size != target_stat.st_size
-            ):
-                perform_copy = True
-        else:
-            # Copy if it does not exist
-            perform_copy = True
-
-        if perform_copy:
-            target.parent.mkdir(parents=True, exist_ok=True)
-            copy_file_with_basic_stats(source, target)
+        sink.add_json(content, manifest_name.as_posix())

src/documents/management/commands/document_importer.py

@@ -32,6 +32,8 @@ from django.db.models.signals import post_save
 from filelock import FileLock
 from guardian.shortcuts import clear_ct_cache
 
+from documents.export.compression import compress_type_readable
+from documents.export.compression import unreadable_method_names
 from documents.file_handling import create_source_path_directory
 from documents.management.commands.base import PaperlessCommand
 from documents.management.commands.mixins import CryptMixin
@@ -451,6 +453,20 @@ class Command(CryptMixin, PaperlessCommand):
         with tempfile.TemporaryDirectory() as tmp_dir:
             if is_zipfile(self.source):
                 with ZipFile(self.source) as zf:
+                    unsupported = {
+                        info.compress_type
+                        for info in zf.infolist()
+                        if not compress_type_readable(info.compress_type)
+                    }
+                    if unsupported:
+                        names = sorted(unreadable_method_names(unsupported))
+                        message = (
+                            f"This archive uses compression this Python cannot "
+                            f"read ({', '.join(names)})."
+                        )
+                        if "zstd" in names:
+                            message += " zstd archives require Python 3.14+."
+                        raise CommandError(message)
                     zf.extractall(tmp_dir)
                 self.source = Path(tmp_dir)
             self._run_import()

src/documents/tests/export/test_compression.py

@@ -0,0 +1,190 @@
+import sys
+import zipfile
+
+import pytest
+
+from documents.export import compression
+
+
+class TestCompressionMethods:
+    def test_choices_always_include_zstd(self) -> None:
+        """
+        GIVEN:
+            - The compression policy module's CLI choices list
+        WHEN:
+            - Read on any runtime
+        THEN:
+            - zstd is always present; availability is checked separately so
+              argparse never hides it based on the current Python version
+        """
+        assert compression.COMPRESSION_CHOICES == (
+            "stored",
+            "deflated",
+            "bzip2",
+            "lzma",
+            "zstd",
+        )
+
+    @pytest.mark.parametrize(
+        ("name", "constant"),
+        [
+            ("stored", zipfile.ZIP_STORED),
+            ("deflated", zipfile.ZIP_DEFLATED),
+            ("bzip2", zipfile.ZIP_BZIP2),
+            ("lzma", zipfile.ZIP_LZMA),
+        ],
+    )
+    def test_method_maps_to_zipfile_constant(self, name: str, constant: int) -> None:
+        """
+        GIVEN:
+            - A compression method name
+        WHEN:
+            - Looked up in COMPRESSION_METHODS
+        THEN:
+            - It maps to the matching zipfile compression constant
+        """
+        assert compression.COMPRESSION_METHODS[name] == constant
+
+    def test_stored_and_deflated_always_available(self) -> None:
+        """
+        GIVEN:
+            - The stored and deflated compression methods
+        WHEN:
+            - Checked with compression_available()
+        THEN:
+            - Both are always available (zlib is a hard CPython dependency)
+        """
+        assert compression.compression_available("stored")
+        assert compression.compression_available("deflated")
+
+    def test_zstd_availability_tracks_runtime(self) -> None:
+        """
+        GIVEN:
+            - The zstd compression method
+        WHEN:
+            - Checked with compression_available() on this runtime
+        THEN:
+            - Availability matches whether Python is 3.14+
+        """
+        expected: bool = sys.version_info >= (3, 14)
+        assert compression.compression_available("zstd") == expected
+
+
+class TestLevelError:
+    @pytest.mark.parametrize(
+        ("method", "level"),
+        [
+            ("deflated", 0),
+            ("deflated", 9),
+            ("bzip2", 1),
+            ("bzip2", 9),
+            ("zstd", -22),
+            ("zstd", 22),
+            ("deflated", None),
+            ("stored", None),
+        ],
+    )
+    def test_valid_levels_return_none(self, method: str, level: int | None) -> None:
+        """
+        GIVEN:
+            - A method and a level within its valid bounds (or no level)
+        WHEN:
+            - Checked with level_error()
+        THEN:
+            - No error message is returned
+        """
+        assert compression.level_error(method, level) is None
+
+    @pytest.mark.parametrize(
+        ("method", "level"),
+        [
+            ("deflated", 10),
+            ("deflated", -1),
+            ("bzip2", 0),
+            ("bzip2", 10),
+            ("zstd", -23),
+            ("zstd", 23),
+        ],
+    )
+    def test_out_of_range_levels_return_message(
+        self,
+        method: str,
+        level: int,
+    ) -> None:
+        """
+        GIVEN:
+            - A method and a level outside its valid bounds
+        WHEN:
+            - Checked with level_error()
+        THEN:
+            - An error message naming the valid range is returned
+        """
+        msg: str | None = compression.level_error(method, level)
+        assert msg is not None
+        assert "between" in msg
+
+    @pytest.mark.parametrize("method", ["stored", "lzma"])
+    def test_level_on_levelless_method_is_rejected(self, method: str) -> None:
+        """
+        GIVEN:
+            - A method that ignores compression level (stored, lzma)
+        WHEN:
+            - A level is passed to level_error() anyway
+        THEN:
+            - An error message noting the level has no effect is returned
+        """
+        msg: str | None = compression.level_error(method, 5)
+        assert msg is not None
+        assert "no effect" in msg
+
+
+class TestCompressTypeReadable:
+    @pytest.mark.parametrize("ct", [zipfile.ZIP_STORED, zipfile.ZIP_DEFLATED])
+    def test_stored_and_deflated_always_readable(self, ct: int) -> None:
+        """
+        GIVEN:
+            - A stored or deflated compress_type id
+        WHEN:
+            - Checked with compress_type_readable()
+        THEN:
+            - It is always readable
+        """
+        assert compression.compress_type_readable(ct)
+
+    def test_zstd_compress_type_readability_tracks_runtime(self) -> None:
+        """
+        GIVEN:
+            - The current (93) and legacy (20) zstd compress_type ids
+        WHEN:
+            - Checked with compress_type_readable() on this runtime
+        THEN:
+            - Readability matches whether Python is 3.14+
+        """
+        # 93 = ZIP_ZSTANDARD; 20 = legacy zstd method id (read-only)
+        expected: bool = sys.version_info >= (3, 14)
+        assert compression.compress_type_readable(93) == expected
+        assert compression.compress_type_readable(20) == expected
+
+    def test_unknown_compress_type_is_unreadable(self) -> None:
+        """
+        GIVEN:
+            - An unrecognized compress_type id
+        WHEN:
+            - Checked with compress_type_readable()
+        THEN:
+            - It is reported as unreadable
+        """
+        assert not compression.compress_type_readable(9999)
+
+    def test_unreadable_method_names_lists_methods(self) -> None:
+        """
+        GIVEN:
+            - A set containing an unknown compress_type id
+        WHEN:
+            - Passed to unreadable_method_names()
+        THEN:
+            - It is reported generically as "method <id>"
+        """
+        # An unknown method id maps to no name and is reported generically.
+        names: set[str] = compression.unreadable_method_names({9999})
+        assert names == {"method 9999"}

src/documents/tests/export/test_sinks.py

@@ -0,0 +1,332 @@
+import io
+import json
+import os
+import zipfile
+from pathlib import Path
+
+import pytest
+import pytest_mock
+
+from documents.export.sinks import DirectoryExportSink
+from documents.export.sinks import ExportSink
+from documents.export.sinks import StreamingManifestWriter
+from documents.export.sinks import ZipExportSink
+from documents.export.sinks import _dumps
+
+
+@pytest.fixture()
+def source_file(tmp_path: Path) -> Path:
+    src: Path = tmp_path / "src" / "doc.pdf"
+    src.parent.mkdir(parents=True)
+    src.write_bytes(b"PDF-CONTENT")
+    return src
+
+
+class TestDumps:
+    def test_dumps_is_indented_unicode_json(self) -> None:
+        result: str = _dumps({"a": "é", "b": 1})
+        assert '"é"' in result  # ensure_ascii=False keeps unicode literal
+        assert "\n" in result  # indent=2 produces newlines
+        assert json.loads(result) == {"a": "é", "b": 1}
+
+
+class TestStreamingManifestWriter:
+    def test_writes_json_array_of_records(self) -> None:
+        handle: io.StringIO = io.StringIO()
+        writer: StreamingManifestWriter = StreamingManifestWriter(handle)
+        writer.write_batch([{"pk": 1}, {"pk": 2}])
+        writer.write_record({"pk": 3})
+        writer.close()
+        assert json.loads(handle.getvalue()) == [{"pk": 1}, {"pk": 2}, {"pk": 3}]
+
+    def test_empty_manifest_is_valid_empty_array(self) -> None:
+        handle: io.StringIO = io.StringIO()
+        writer: StreamingManifestWriter = StreamingManifestWriter(handle)
+        writer.close()
+        assert json.loads(handle.getvalue()) == []
+
+
+class TestDirectoryExportSink:
+    def test_add_file_copies_to_relative_arcname(
+        self,
+        tmp_path: Path,
+        source_file: Path,
+    ) -> None:
+        target: Path = tmp_path / "out"
+        target.mkdir()
+        with DirectoryExportSink(
+            target,
+            compare_checksums=False,
+            compare_json=False,
+            delete=False,
+        ) as sink:
+            sink.add_file(source_file, "originals/doc.pdf")
+        assert (target / "originals" / "doc.pdf").read_bytes() == b"PDF-CONTENT"
+
+    def test_add_json_writes_file(self, tmp_path: Path) -> None:
+        target: Path = tmp_path / "out"
+        target.mkdir()
+        with DirectoryExportSink(
+            target,
+            compare_checksums=False,
+            compare_json=False,
+            delete=False,
+        ) as sink:
+            sink.add_json({"version": "x"}, "metadata.json")
+        assert json.loads((target / "metadata.json").read_text()) == {"version": "x"}
+
+    def test_stream_writes_manifest(self, tmp_path: Path) -> None:
+        target: Path = tmp_path / "out"
+        target.mkdir()
+        with DirectoryExportSink(
+            target,
+            compare_checksums=False,
+            compare_json=False,
+            delete=False,
+        ) as sink:
+            with sink.stream("manifest.json") as handle:
+                writer: StreamingManifestWriter = StreamingManifestWriter(handle)
+                writer.write_record({"pk": 1})
+                writer.close()
+        assert json.loads((target / "manifest.json").read_text()) == [{"pk": 1}]
+
+    def test_add_file_skips_when_size_and_mtime_match(
+        self,
+        tmp_path: Path,
+        source_file: Path,
+    ) -> None:
+        # Pre-existing target with identical size+mtime but DIFFERENT content:
+        # if add_file skips (no compare-checksums), the old content survives.
+        target: Path = tmp_path / "out"
+        target.mkdir()
+        existing: Path = target / "originals" / "doc.pdf"
+        existing.parent.mkdir(parents=True)
+        # Same byte length as the source but different content + matching mtime,
+        # so a size/mtime comparison treats it as unchanged and skips the copy.
+        existing.write_bytes(b"X" * len(b"PDF-CONTENT"))
+        stat = source_file.stat()
+        os.utime(existing, (stat.st_atime, stat.st_mtime))
+        with DirectoryExportSink(
+            target,
+            compare_checksums=False,
+            compare_json=False,
+            delete=False,
+        ) as sink:
+            sink.add_file(source_file, "originals/doc.pdf", checksum="abc")
+        assert existing.read_bytes() == b"X" * len(b"PDF-CONTENT")  # skipped
+
+    def test_add_file_recopies_when_compare_checksums_differ(
+        self,
+        tmp_path: Path,
+        source_file: Path,
+    ) -> None:
+        target: Path = tmp_path / "out"
+        target.mkdir()
+        existing: Path = target / "originals" / "doc.pdf"
+        existing.parent.mkdir(parents=True)
+        existing.write_bytes(b"X" * len(b"PDF-CONTENT"))
+        stat = source_file.stat()
+        os.utime(existing, (stat.st_atime, stat.st_mtime))
+        with DirectoryExportSink(
+            target,
+            compare_checksums=True,
+            compare_json=False,
+            delete=False,
+        ) as sink:
+            # wrong checksum forces recopy despite matching size/mtime
+            sink.add_file(source_file, "originals/doc.pdf", checksum="not-the-real-sum")
+        assert existing.read_bytes() == b"PDF-CONTENT"  # recopied
+
+    def test_delete_prunes_unwritten_snapshot_files(
+        self,
+        tmp_path: Path,
+        source_file: Path,
+    ) -> None:
+        target: Path = tmp_path / "out"
+        target.mkdir()
+        stale: Path = target / "stale.pdf"
+        stale.write_bytes(b"STALE")
+        with DirectoryExportSink(
+            target,
+            compare_checksums=False,
+            compare_json=False,
+            delete=True,
+        ) as sink:
+            sink.add_file(source_file, "originals/doc.pdf")
+        assert not stale.exists()
+        assert (target / "originals" / "doc.pdf").exists()
+
+    def test_no_delete_keeps_unwritten_files(
+        self,
+        tmp_path: Path,
+        source_file: Path,
+    ) -> None:
+        target: Path = tmp_path / "out"
+        target.mkdir()
+        stale: Path = target / "stale.pdf"
+        stale.write_bytes(b"STALE")
+        with DirectoryExportSink(
+            target,
+            compare_checksums=False,
+            compare_json=False,
+            delete=False,
+        ) as sink:
+            sink.add_file(source_file, "originals/doc.pdf")
+        assert stale.exists()
+
+
+class TestZipExportSink:
+    def test_round_trip_files_json_and_stream(
+        self,
+        tmp_path: Path,
+        source_file: Path,
+    ) -> None:
+        target: Path = tmp_path / "out"
+        target.mkdir()
+        with ZipExportSink(target, "export", delete=False) as sink:
+            sink.add_file(source_file, "originals/doc.pdf")
+            sink.add_json({"version": "x"}, "metadata.json")
+            with sink.stream("manifest.json") as handle:
+                writer = StreamingManifestWriter(handle)
+                writer.write_record({"pk": 1})
+                writer.close()
+        zip_path: Path = target / "export.zip"
+        assert zip_path.exists()
+        assert not (target / "export.zip.tmp").exists()
+        with zipfile.ZipFile(zip_path) as zf:
+            names = set(zf.namelist())
+            assert {"originals/doc.pdf", "metadata.json", "manifest.json"} <= names
+            assert zf.read("originals/doc.pdf") == b"PDF-CONTENT"
+            assert json.loads(zf.read("manifest.json")) == [{"pk": 1}]
+
+    def test_nested_arcname_emits_directory_marker(
+        self,
+        tmp_path: Path,
+        source_file: Path,
+    ) -> None:
+        target: Path = tmp_path / "out"
+        target.mkdir()
+        with ZipExportSink(target, "export", delete=False) as sink:
+            sink.add_file(source_file, "originals/doc.pdf")
+        with zipfile.ZipFile(target / "export.zip") as zf:
+            assert "originals/" in zf.namelist()
+
+    def test_flat_arcname_has_no_directory_markers(
+        self,
+        tmp_path: Path,
+        source_file: Path,
+    ) -> None:
+        target: Path = tmp_path / "out"
+        target.mkdir()
+        with ZipExportSink(target, "export", delete=False) as sink:
+            sink.add_file(source_file, "doc.pdf")
+        with zipfile.ZipFile(target / "export.zip") as zf:
+            assert all(not n.endswith("/") for n in zf.namelist())
+
+    def test_exception_leaves_no_zip_and_no_tmp(
+        self,
+        tmp_path: Path,
+        source_file: Path,
+    ) -> None:
+        target: Path = tmp_path / "out"
+        target.mkdir()
+        with pytest.raises(RuntimeError):
+            with ZipExportSink(target, "export", delete=False) as sink:
+                sink.add_file(source_file, "doc.pdf")
+                raise RuntimeError("boom")
+        assert not (target / "export.zip").exists()
+        assert not (target / "export.zip.tmp").exists()
+
+    def test_delete_wipes_destination_on_success(
+        self,
+        tmp_path: Path,
+        source_file: Path,
+    ) -> None:
+        target: Path = tmp_path / "out"
+        target.mkdir()
+        (target / "preexisting.txt").write_text("old")
+        (target / "olddir").mkdir()
+        with ZipExportSink(target, "export", delete=True) as sink:
+            sink.add_file(source_file, "doc.pdf")
+        assert (target / "export.zip").exists()
+        assert not (target / "preexisting.txt").exists()
+        assert not (target / "olddir").exists()
+
+    def test_abort_with_delete_does_not_wipe_destination(
+        self,
+        tmp_path: Path,
+        source_file: Path,
+    ) -> None:
+        target: Path = tmp_path / "out"
+        target.mkdir()
+        (target / "preexisting.txt").write_text("old")
+        with pytest.raises(RuntimeError):
+            with ZipExportSink(target, "export", delete=True) as sink:
+                sink.add_file(source_file, "doc.pdf")
+                raise RuntimeError("boom")
+        assert (target / "preexisting.txt").exists()
+        assert not (target / "export.zip").exists()
+
+
+class TestZipExportSinkCompression:
+    @pytest.mark.parametrize(
+        ("method", "constant"),
+        [
+            ("stored", zipfile.ZIP_STORED),
+            ("deflated", zipfile.ZIP_DEFLATED),
+            ("bzip2", zipfile.ZIP_BZIP2),
+            ("lzma", zipfile.ZIP_LZMA),
+        ],
+    )
+    def test_compression_and_level_forwarded_to_zipfile(
+        self,
+        mocker: pytest_mock.MockerFixture,
+        tmp_path: Path,
+        method: str,
+        constant: int,
+    ) -> None:
+        """
+        GIVEN:
+            - A ZipExportSink constructed with a compression method and level
+        WHEN:
+            - The sink is opened
+        THEN:
+            - zipfile.ZipFile is constructed with those values forwarded
+              unchanged (whether ZipFile actually compresses is Python's own
+              contract, not ours, so this checks the call args, not a real
+              archive)
+        """
+        target: Path = tmp_path / "out"
+        target.mkdir()
+        zip_cls = mocker.patch("documents.export.sinks.zipfile.ZipFile")
+        sink = ZipExportSink(target, "export", compression=constant, compresslevel=5)
+        sink._open()
+        zip_cls.assert_called_once_with(
+            mocker.ANY,
+            "w",
+            compression=constant,
+            compresslevel=5,
+            allowZip64=True,
+        )
+
+
+class TestStreamContract:
+    @pytest.fixture(params=["dir", "zip"])
+    def sink(self, request: pytest.FixtureRequest, tmp_path: Path) -> ExportSink:
+        target: Path = tmp_path / "out"
+        target.mkdir()
+        if request.param == "dir":
+            return DirectoryExportSink(
+                target,
+                compare_checksums=False,
+                compare_json=False,
+                delete=False,
+            )
+        return ZipExportSink(target, "export", delete=False)
+
+    def test_second_concurrent_stream_is_rejected(self, sink: ExportSink) -> None:
+        with sink:
+            with sink.stream("manifest.json"):
+                with pytest.raises(RuntimeError, match="already open"):
+                    with sink.stream("other.json"):
+                        pass

src/documents/tests/test_management_exporter.py

@@ -6,6 +6,8 @@ from datetime import timedelta
 from io import StringIO
 from pathlib import Path
 from unittest import mock
+from zipfile import ZIP_DEFLATED
+from zipfile import ZIP_LZMA
 from zipfile import ZipFile
 
 import pytest
@@ -426,7 +428,7 @@ class TestExportImport(
         st_mtime_1 = (self.target / "manifest.json").stat().st_mtime
 
         with mock.patch(
-            "documents.management.commands.document_exporter.copy_file_with_basic_stats",
+            "documents.export.sinks.copy_file_with_basic_stats",
         ) as m:
             self._do_export()
             m.assert_not_called()
@@ -437,7 +439,7 @@ class TestExportImport(
         Path(self.d1.source_path).touch()
 
         with mock.patch(
-            "documents.management.commands.document_exporter.copy_file_with_basic_stats",
+            "documents.export.sinks.copy_file_with_basic_stats",
         ) as m:
             self._do_export()
             self.assertEqual(m.call_count, 1)
@@ -464,7 +466,7 @@ class TestExportImport(
         self.assertIsFile(self.target / "manifest.json")
 
         with mock.patch(
-            "documents.management.commands.document_exporter.copy_file_with_basic_stats",
+            "documents.export.sinks.copy_file_with_basic_stats",
         ) as m:
             self._do_export()
             m.assert_not_called()
@@ -475,7 +477,7 @@ class TestExportImport(
         self.d2.save()
 
         with mock.patch(
-            "documents.management.commands.document_exporter.copy_file_with_basic_stats",
+            "documents.export.sinks.copy_file_with_basic_stats",
         ) as m:
             self._do_export(compare_checksums=True)
             self.assertEqual(m.call_count, 1)
@@ -1058,6 +1060,190 @@ class TestExportImport(
 
         self.assertEqual(Document.objects.all().count(), 4)
 
+    def test_zip_with_compare_flags_raises(self) -> None:
+        """
+        GIVEN:
+            - A request to export to a zip file
+        WHEN:
+            - --compare-checksums or --compare-json is also passed
+        THEN:
+            - A CommandError is raised (the flags are no-ops in zip mode)
+        """
+        for flag in ("--compare-checksums", "--compare-json"):
+            with self.subTest(flag=flag):
+                with self.assertRaises(CommandError):
+                    call_command(
+                        "document_exporter",
+                        self.target,
+                        "--zip",
+                        flag,
+                        skip_checks=True,
+                    )
+
+    def test_compression_flags_require_zip(self) -> None:
+        """
+        GIVEN:
+            - A request to export without --zip
+        WHEN:
+            - --zip-compression or --zip-compression-level is passed anyway
+        THEN:
+            - A CommandError is raised (the flags are meaningless without --zip)
+        """
+        for args in (
+            ["--zip-compression", "lzma"],
+            ["--zip-compression-level", "5"],
+        ):
+            with self.assertRaises(CommandError):
+                call_command(
+                    "document_exporter",
+                    self.target,
+                    *args,
+                    skip_checks=True,
+                )
+
+    def test_zip_compression_level_out_of_range_raises(self) -> None:
+        """
+        GIVEN:
+            - A request to export to a zip file
+        WHEN:
+            - --zip-compression-level is outside the chosen method's valid range
+        THEN:
+            - A CommandError is raised
+        """
+        with self.assertRaises(CommandError):
+            call_command(
+                "document_exporter",
+                self.target,
+                "--zip",
+                "--zip-compression",
+                "deflated",
+                "--zip-compression-level",
+                "99",
+                skip_checks=True,
+            )
+
+    def test_zip_compression_level_rejected_for_stored(self) -> None:
+        """
+        GIVEN:
+            - A request to export to a zip file with --zip-compression stored
+        WHEN:
+            - --zip-compression-level is also passed
+        THEN:
+            - A CommandError is raised (stored ignores level entirely)
+        """
+        with self.assertRaises(CommandError):
+            call_command(
+                "document_exporter",
+                self.target,
+                "--zip",
+                "--zip-compression",
+                "stored",
+                "--zip-compression-level",
+                "5",
+                skip_checks=True,
+            )
+
+    def test_zip_compression_level_rejected_for_lzma(self) -> None:
+        """
+        GIVEN:
+            - A request to export to a zip file with --zip-compression lzma
+        WHEN:
+            - --zip-compression-level is also passed
+        THEN:
+            - A CommandError is raised (lzma ignores level entirely)
+        """
+        with self.assertRaises(CommandError):
+            call_command(
+                "document_exporter",
+                self.target,
+                "--zip",
+                "--zip-compression",
+                "lzma",
+                "--zip-compression-level",
+                "5",
+                skip_checks=True,
+            )
+
+    def test_zstd_unavailable_raises_friendly_error(self) -> None:
+        """
+        GIVEN:
+            - A Python runtime without zstd support (< 3.14)
+        WHEN:
+            - --zip-compression zstd is requested
+        THEN:
+            - A CommandError naming the Python version requirement is raised
+        """
+        with self.assertRaises(CommandError) as e:
+            call_command(
+                "document_exporter",
+                self.target,
+                "--zip",
+                "--zip-compression",
+                "zstd",
+                skip_checks=True,
+            )
+        self.assertIn("3.14", str(e.exception))
+
+    def test_zip_compression_flag_resolves_to_sink_constant(self) -> None:
+        """
+        GIVEN:
+            - A request to export to a zip file with --zip-compression lzma
+        WHEN:
+            - The export runs
+        THEN:
+            - ZipExportSink is constructed with the resolved ZIP_LZMA constant
+              (whether zipfile actually compresses with the chosen method is
+              Python's own contract, and ZipExportSink's own tests already
+              cover the forwarding; what this command owns is resolving the
+              CLI string to the right constant, so assert that resolution
+              directly)
+        """
+        with mock.patch(
+            "documents.management.commands.document_exporter.ZipExportSink",
+        ) as sink_cls:
+            call_command(
+                "document_exporter",
+                self.target,
+                "--zip",
+                "--zip-compression",
+                "lzma",
+                skip_checks=True,
+            )
+        sink_cls.assert_called_once_with(
+            mock.ANY,
+            mock.ANY,
+            delete=False,
+            compression=ZIP_LZMA,
+            compresslevel=None,
+        )
+
+    def test_default_zip_compression_resolves_to_deflate(self) -> None:
+        """
+        GIVEN:
+            - A request to export to a zip file with no --zip-compression flag
+        WHEN:
+            - The export runs
+        THEN:
+            - ZipExportSink is constructed with the default ZIP_DEFLATED
+              constant and compresslevel=None, matching pre-existing behavior
+        """
+        with mock.patch(
+            "documents.management.commands.document_exporter.ZipExportSink",
+        ) as sink_cls:
+            call_command(
+                "document_exporter",
+                self.target,
+                "--zip",
+                skip_checks=True,
+            )
+        sink_cls.assert_called_once_with(
+            mock.ANY,
+            mock.ANY,
+            delete=False,
+            compression=ZIP_DEFLATED,
+            compresslevel=None,
+        )
+
 
 @pytest.mark.management
 class TestCryptExportImport(

src/documents/tests/test_management_importer.py

@@ -525,6 +525,35 @@ class TestCommandImport(
         self.assertEqual(doc.tags.count(), 1)
         self.assertEqual(doc.tags.first().name, "batch-flush-tag")
 
+    def test_import_rejects_unreadable_compression(self) -> None:
+        """
+        GIVEN:
+            - A zip archive with an entry whose compression this Python can't read
+        WHEN:
+            - Import is attempted
+        THEN:
+            - A CommandError naming the issue is raised, before extraction
+        """
+        import zipfile
+        from unittest import mock
+
+        archive = Path(self.dirs.scratch_dir) / "export.zip"
+        with zipfile.ZipFile(archive, "w") as zf:
+            zf.writestr("manifest.json", "[]")
+
+        with mock.patch(
+            "documents.management.commands.document_importer.compress_type_readable",
+            return_value=False,
+        ):
+            with self.assertRaises(CommandError) as e:
+                call_command(
+                    "document_importer",
+                    str(archive),
+                    "--no-progress-bar",
+                    skip_checks=True,
+                )
+        self.assertIn("compression", str(e.exception))
+
 
 @pytest.mark.management
 @pytest.mark.django_db