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>

src/documents/management/commands/document_importer.py

@@ -459,11 +459,14 @@ class Command(CryptMixin, PaperlessCommand):
                         if not compress_type_readable(info.compress_type)
                     }
                     if unsupported:
-                        names = ", ".join(sorted(unreadable_method_names(unsupported)))
-                        raise CommandError(
+                        names = sorted(unreadable_method_names(unsupported))
+                        message = (
                             f"This archive uses compression this Python cannot "
-                            f"read ({names}). zstd archives require Python 3.14+.",
+                            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/test_management_exporter.py

@@ -1143,6 +1143,47 @@ class TestExportImport(
                 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: