fix(knowledge): the browse vocabulary catches up three kinds, and a snippet's mirror survives the generic door (#3128 recs 2-6)

Spike #3128 found the storage sound and the retrieval vocabulary frozen
before `issue` shipped (0065). Five things, in the order they had to land.

**The mirror (rec 5, the data-integrity one).** `notes.data` is DERIVED from
a snippet's body, but only `update_snippet` knew that. `update_note` is a
hasattr loop with no snippet awareness, and both doors reach it — so PATCH
/api/notes/<snippet_id> {body} rewrote the body and left the mirror behind.
`snippet_fields` PREFERS the mirror, so the row went on reporting its old
repo/path/symbol to the location reverse lookup and to prior-art recall while
displaying its new body: surfaced with full authority, and wrong.
`snippets.recompose_data` rebuilds it from the body, carrying `verification`
and `provenance` (neither is in the body to parse). An explicit `data` still
wins, so every snippet-service write is untouched.

**One facet table (rec 3), before adding any facet.** The type predicate was
written three times — SQL, Python over semantic candidates, and a ternary
computing the `is_task` pre-filter — and agreed only by luck. Adding `issue`
to the SQL arm alone would have set the pre-filter to is_task=False, handed
the Python arm a candidate set with no tasks in it, and returned an empty
semantic half for the Issues facet forever with nothing red. `_FACETS` now
generates all three. The Python arm also regains the `status IS NULL` half its
SQL twin always had.

**Issue and spike become facets (rec 2).** 435 issues — 17% of every task —
were filterable nowhere on the human surface, while retired `plan` (90 rows)
had a chip of its own. `_VALID_TYPES` was a hand-kept copy and is now derived.
`plan` stays a valid facet for its legacy rows; it loses its chip.

**Snippets stop being half-present in the feed (rec 4).** All 90 were in the
All list, in no count, wearing an empty badge, and opening in the note editor.
Counts now group by task_kind — every kind for the same two round-trips, which
is why `issue` had no number — and total includes snippets, so the All chip
matches the list it labels. Snippet cards route to /snippets/:id.

**The prose that excused it (rec 6).** `snippet_fields` and the `data` column
both still said pre-0070 rows were "never backfilled". True when 0070 landed,
false since `backfill_snippet_data` shipped, and it read as licence for a
stale mirror.

Tests: the pre-filter can never exclude a row its own facet accepts (the
regression, parameterised over every facet); both dialects select exactly
their own rows; an unknown facet matches nothing; the mirror follows a body or
title write, carries the verdict, and yields to an explicit `data`.
`compiled_sql` moves to tests/helpers rather than becoming a third copy.

Write-up: note #3161.

src/scribe/services/notes.py

@@ -9,6 +9,13 @@ from scribe.models.note import Note, TaskKind, TaskPriority, TaskStatus
 
 logger = logging.getLogger(__name__)
 
+# The fields `snippets.parse_snippet_fields` reads. Writing any of them can
+# change what a snippet's derived `data` mirror should say, so update_note
+# recomposes the mirror when one moves. Kept here as a set of NAMES rather
+# than imported, because it describes update_note's own `fields` dict, not the
+# parser's signature.
+_PARSED_FROM_BODY = frozenset({"title", "body", "tags"})
+
 
 def embed_note(note) -> None:
     """Refresh a note's embedding, fire-and-forget.
@@ -439,6 +446,23 @@ async def update_note(user_id: int, note_id: int, **fields: object) -> Note | No
             elif key == "tags" and isinstance(value, list):
                 value = _normalize_tags(value)
             setattr(note, key, value)
+        # A snippet's `data` is DERIVED from its body — so a write that moves
+        # the body through this generic door must move the mirror with it
+        # (#3128). Without this, PATCH /api/notes/<snippet_id> {body} left the
+        # mirror behind, and snippet_fields PREFERS the mirror: the row went on
+        # reporting its old repo/path/symbol to prior-art recall while showing
+        # its new body. `update_snippet` composes the mirror itself and passes
+        # it explicitly, so an explicit `data` always wins — the caller that
+        # knows the field set beats the one that can only re-read the body.
+        if "data" not in fields and not _PARSED_FROM_BODY.isdisjoint(fields):
+            # Imported here, not at module scope: services/snippets.py calls
+            # back into this module (update_snippet -> update_note), so a
+            # top-level import is a cycle.
+            from scribe.services.snippets import (
+                SNIPPET_NOTE_TYPE, recompose_data,
+            )
+            if note.note_type == SNIPPET_NOTE_TYPE:
+                note.data = recompose_data(note)
         # Auto-set lifecycle timestamps on status transitions
         if "status" in fields:
             _now = datetime.now(timezone.utc)