docs(search): point the field-table comments at field_descriptors()

Both comments still described the pre-fingerprint layout: _fields.py said
the internal-only fields "stay hardcoded in build_schema()", and the
fast-flag test said build_schema() honors the flag only in its U64 and
DATE branches. Both now live in field_descriptors(), and _fields.py's
header is the one thing a future editor reads before touching the field
table, so a stale pointer there is the expensive kind.

Comments only; no executable line is touched.

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

src/documents/search/_fields.py

@@ -6,8 +6,8 @@ from whoosh_compat import SubpathSpec
 
 # Internal-only schema fields with no query-syntax meaning of their own
 # (sort shadow fields, bigram CJK fields, simple_title/simple_content,
-# autocomplete_word, notes_text) are NOT represented here — they stay
-# hardcoded in _schema.py's build_schema().
+# autocomplete_word, notes_text) are NOT represented here — they are
+# declared in _schema.py's field_descriptors().
 #
 # analyzer/pattern_normalizer are deliberately left at FieldSpec's default
 # (None): they're language-specific and only meaningful to whoosh-compat's

src/documents/tests/search/test_schema.py

@@ -140,8 +140,8 @@ class TestFastFlagAgreement:
         # whoosh-compat's registry trusts PUBLIC_FIELDS' fast flag when resolving
         # field:* existence checks (its FAST_FIELD strategy); a fast=True
         # entry whose actual tantivy column is not fast would make those
-        # searches silently match nothing at search time. build_schema()
-        # only honors the flag in its U64 and DATE branches today, so this
+        # searches silently match nothing at search time. Only the U64 and
+        # DATE descriptors can carry the flag today, so this
         # pins the agreement for EVERY kind: a future fast=True
         # TEXT/KEYWORD/JSON entry the builder silently ignores fails here
         # instead of at a user's query.