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/routes/knowledge.py

@@ -1,4 +1,4 @@
-"""Unified Knowledge endpoint — notes, tasks, plans, and processes in one queryable feed."""
+"""Unified Knowledge endpoint — every record kind in one queryable feed."""
 import logging
 
 from quart import Blueprint, jsonify, request
@@ -6,12 +6,18 @@ from quart import Blueprint, jsonify, request
 from scribe.auth import get_current_user_id, login_required
 from scribe.routes.utils import parse_pagination
 from scribe.services.access import label_shared_items
+from scribe.services.knowledge import FACET_TYPES
 
 logger = logging.getLogger(__name__)
 
 knowledge_bp = Blueprint("knowledge", __name__, url_prefix="/api/knowledge")
 
-_VALID_TYPES = {"note", "task", "plan", "process"}
+# Derived from the service's facet table, never re-listed here. This set was a
+# hand-kept copy and had drifted three kinds behind it: it admitted `plan`
+# (retired in 0066) and rejected `issue` (shipped in 0065, 435 rows) and
+# `snippet` — so the browse surface could not filter to the kinds it was
+# already rendering badges for (#3128).
+_VALID_TYPES = FACET_TYPES
 _VALID_SORTS = {"modified", "created", "alpha", "type"}
 
 
@@ -21,7 +27,9 @@ async def list_knowledge():
     """Return paginated knowledge objects with optional filtering.
 
     Query params:
-      type        — one of note|task|plan|process (omit for all)
+      type        — a facet from services.knowledge._FACETS: a record type
+                    (note|process|snippet) or a task kind (task for any,
+                    else work|issue|spike|plan). Omit for all.
       tags        — comma-separated tag filter (AND logic)
       sort        — modified|created|alpha|type (default: modified)
       q           — search query (semantic when provided, keyword fallback)
@@ -127,7 +135,7 @@ async def get_knowledge_batch():
 @knowledge_bp.route("/tags", methods=["GET"])
 @login_required
 async def list_knowledge_tags():
-    """Return all tags used across knowledge objects (excludes tasks)."""
+    """Return all tags used across knowledge objects, narrowed to one facet."""
     uid = get_current_user_id()
     note_type = request.args.get("type", "").strip().lower() or None