feat(search): the agent's search can ask for every kind the corpus has (#4250)

The engine took `note_type` and `task_kind` all along. What was missing was a
way to say them: the MCP tool's `content_type` knew `note`, `task` and `all`,
and `/api/search` knew the same two — so an agent could not ask "has this
snippet already been recorded" or "what lessons apply here" without searching
everything and reading past the rest. Browse offered nine kinds from the same
data.

The cause is that each door kept its own map. `_FACETS` in services/knowledge
is where a kind is declared, and #3161 made adding one a single edit by
generating the SQL filter, the Python predicate and the door's validation from
it — but the two search doors were written before that and never joined. So
this adds the third dialect, `search_filters_for`, and one composition over it,
`content_type_filters`, and both doors now derive instead of listing.

Two names keep a meaning of their own, and the docstrings say so: `all` is no
filter, and `note` is BROAD — any non-task, snippets and lessons included —
where the browse facet of the same name is narrow (`note_type == 'note'`).
They are left different deliberately; narrowing this one would stop returning
snippets to every caller that already asks this way.

An unrecognised kind is now refused rather than answered. Both doors used to
fall through: the MCP tool into a filter matching no row, the route into no
filter at all, so `?content_type=snippets` returned the whole corpus while
looking like a narrowed search. An empty result set is a claim — "the corpus
holds nothing like this" — and an agent acts on that claim by building the
thing it could not find, so a typo must not be able to make it.

The docstring is the agent-facing contract (#2846), and a test now holds it to
the table: every kind `_FACETS` declares has to appear in it, because a filter
an agent has not been told about is unreachable however well it is wired.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01821k5B3Ysecp9fNYs92Kuy

src/scribe/mcp/tools/search.py

@@ -11,6 +11,7 @@ import time
 
 from scribe.mcp._context import current_user_id
 from scribe.services.access import owner_names_for
+from scribe.services.knowledge import content_type_filters
 from scribe.services.text import MATCHED_PASSAGE, excerpt_fields
 from scribe.services.embeddings import (
     DEFAULT_SIMILARITY_THRESHOLD, semantic_search_milestones, semantic_search_notes,
@@ -28,6 +29,18 @@ from scribe.services.retrieval_telemetry import record_retrieval, retrieval_summ
 _EXCERPT_CHARS = 1000
 
 
+# The kinds `content_type` accepts are DERIVED from the facet table, not listed
+# again here — that table is where a kind is declared (#3161), and a second
+# hand-kept copy in this module is precisely how the agent's door came to offer
+# two kinds while browse offered nine (#4250). `content_type_filters` carries
+# the mapping, the 'all'/'note' special cases and the refusal.
+#
+# These two do not reach `semantic_search_notes` at all: they have their own
+# search and their own result shape, so they are dispatched before the mapping
+# and passed in only so the refusal message lists everything THIS door takes.
+_OWN_SEARCH = ("rule", "milestone")
+
+
 async def _search_rules(uid: int, q: str, limit: int, project_id: int) -> dict:
     """Rules by meaning — a separate result shape because a rule IS different.
 
@@ -170,8 +183,28 @@ async def search(
 
     Args:
         q: search query string.
-        content_type: 'all' (default), 'note' (notes only), 'task' (tasks
-            only), or 'rule' (RULES only — the operator's standing
+        content_type: which kind of record to search. 'all' (default) spans
+            every note and task.
+
+            THE BROAD TWO: 'note' is any non-task record — it still includes
+            snippets, lessons and processes, so it means "knowledge, not work
+            items". 'task' is any task whatever its kind.
+
+            THE SPECIFIC KINDS, each narrowing to one: 'snippet' (recorded
+            prior art — reach for this BEFORE writing a helper, rather than
+            searching 'all' and reading past the issues), 'lesson' (a
+            transferable insight, the kind that exists to be recalled by
+            situation), 'process' (a stored procedure the operator saved),
+            'issue' (corrective work — "has this already been reported?"),
+            'spike' (a time-boxed investigation, whose output is an answer),
+            'work', and 'plan' (retired; the ~90 legacy plan-tasks).
+
+            An unrecognised value is REFUSED with the list of valid ones
+            rather than quietly returning nothing: an empty result set is a
+            claim that the corpus holds nothing, and a typo must not be able
+            to make that claim.
+
+            Or 'rule' (RULES only — the operator's standing
             instructions, searchable by meaning since milestone 307).
             Reach for 'rule' when you want to know whether a standing
             instruction covers something: "is there a rule about release
@@ -225,11 +258,12 @@ async def search(
         return await _search_rules(uid, q, limit, project_id)
     if content_type == "milestone":
         return await _search_milestones(uid, q, limit, project_id)
-    is_task = {"note": False, "task": True}.get(content_type)  # None => any
+    filters = content_type_filters(content_type, extra=_OWN_SEARCH)
+    is_task = filters.get("is_task")
     t0 = time.perf_counter()
     report: dict = {}
     raw = await semantic_search_notes(
-        uid, q, limit=limit, is_task=is_task,
+        uid, q, limit=limit, **filters,
         project_id=project_id or None,
         system_id=system_id or None,
         # A LESSON is reachable from any project (milestone 385). The kind

src/scribe/routes/search.py

@@ -8,6 +8,7 @@ from scribe.services.embeddings import (
     INTERACTIVE_SEARCH_THRESHOLD as _REST_SEARCH_THRESHOLD,
 )
 from scribe.services.embeddings import semantic_search_notes
+from scribe.services.knowledge import content_type_filters
 from scribe.services.retrieval_telemetry import record_retrieval
 
 # The interactive floor lives in embeddings.py now, shared with Browse search
@@ -16,15 +17,6 @@ from scribe.services.retrieval_telemetry import record_retrieval
 search_bp = Blueprint("search", __name__, url_prefix="/api/search")
 
 
-def _content_type_to_is_task(content_type: str) -> bool | None:
-    """Map content_type query param to semantic_search_notes is_task arg."""
-    if content_type == "note":
-        return False
-    if content_type == "task":
-        return True
-    return None  # "all" or unknown → no filter
-
-
 @search_bp.route("", methods=["GET"])
 @login_required
 async def search_route():
@@ -33,9 +25,18 @@ async def search_route():
     if not q:
         return jsonify({"error": "q is required"}), 400
 
-    content_type = request.args.get("content_type", "all")
     limit = min(request.args.get("limit", 10, type=int), 50)
-    is_task = _content_type_to_is_task(content_type)
+    # Every kind the facet table declares, derived rather than mapped here —
+    # this route used to know exactly two and read anything else as "no
+    # filter", so `?content_type=snippets` silently returned the whole corpus
+    # (#4250). An unknown kind is now a 400 naming the ones that exist: a
+    # result set is an answer, and it should not be able to answer a question
+    # nobody asked.
+    try:
+        filters = content_type_filters(request.args.get("content_type", "all"))
+    except ValueError as exc:
+        return jsonify({"error": str(exc)}), 400
+    is_task = filters.get("is_task")
     # Same association filters the MCP tool takes (#33). Optional, default
     # global: this route has NO frontend consumer today (measured 2026-08-08 —
     # the web UI searches through /api/knowledge), so it serves API callers,
@@ -46,7 +47,7 @@ async def search_route():
     t0 = time.perf_counter()
     report: dict = {}
     results = await semantic_search_notes(
-        uid, q, limit=limit, is_task=is_task, threshold=_REST_SEARCH_THRESHOLD,
+        uid, q, limit=limit, **filters, threshold=_REST_SEARCH_THRESHOLD,
         project_id=project_id, system_id=system_id,
         # The user typed this, so it reaches everything they may read.
         scope="read",

src/scribe/services/knowledge.py

@@ -376,6 +376,69 @@ def matches_facet(note, note_type: str | None) -> bool:
     return not note.is_task and note.note_type == value
 
 
+def search_filters_for(facet: str) -> dict:
+    """The semantic-search kwargs one facet implies: is_task + note_type/task_kind.
+
+    A third dialect of the same table, for the arm that has no SQL statement to
+    narrow and no fetched row to test — it is passing filters INTO
+    `semantic_search_notes`. `_apply_type_filter` is the SQL dialect and
+    `matches_facet` the Python one; all three read `_FACETS`, which is what
+    keeps "adding a kind" a single edit (#3161).
+
+    Returns kwargs rather than a tuple so a caller splats it and cannot pair
+    `task_kind` with `is_task=False` by writing the positions out of order.
+    """
+    is_task, value = _facet(facet)
+    if is_task:
+        return {"is_task": True, "task_kind": value}
+    return {"is_task": False, "note_type": value}
+
+
+# The two names a `content_type` parameter carries that are not facets. Both
+# search doors that take one — the MCP tool and /api/search — have always
+# spelled them this way, so they are the contract rather than a convenience:
+#
+#   'all' (and empty) — no kind filter at all.
+#   'note'            — ANY non-task record, so snippets, lessons and processes
+#                       are all still in scope. The BROWSE facet of the same
+#                       name is narrower (`note_type == 'note'` exactly). The
+#                       two are deliberately different: narrowing this one
+#                       would stop returning snippets to every caller that
+#                       already asks this way, and the doors document the
+#                       containment instead.
+_CONTENT_TYPE_BROAD = {
+    "": {"is_task": None},
+    "all": {"is_task": None},
+    "note": {"is_task": False},
+}
+
+
+def content_type_filters(content_type: str, extra: tuple = ()) -> dict:
+    """The search kwargs a door's `content_type` parameter implies.
+
+    Lives here, beside `_FACETS`, because a door that keeps its own map is how
+    this went wrong: the agent's search offered two kinds and browse offered
+    nine, and a third copy in `/api/search` offered two more quietly still
+    (#4250). Derived, so adding a kind stays one edit (#3161).
+
+    Raises on anything unrecognised. `_facet` alone would fall back to reading
+    an unknown string as a note_type, which matches no row — so a typo comes
+    back as a confident empty result, and an empty result is a CLAIM that the
+    corpus holds nothing of the sort. A door has to be able to say "that is not
+    a kind" instead. `extra` names kinds the caller dispatches elsewhere (the
+    MCP tool's 'rule' and 'milestone'), so the refusal lists what that door
+    really accepts and not a vocabulary from some other door.
+    """
+    if content_type in _CONTENT_TYPE_BROAD:
+        return dict(_CONTENT_TYPE_BROAD[content_type])
+    if content_type in FACET_TYPES:
+        return search_filters_for(content_type)
+    raise ValueError(
+        f"unknown content_type {content_type!r}. Valid: "
+        + ", ".join(sorted({"all", *FACET_TYPES, *extra}))
+    )
+
+
 def _apply_type_filter(stmt, note_type: str | None):
     """Apply the type facet to a Note select. Trashed rows are always excluded."""
     stmt = stmt.where(Note.deleted_at.is_(None))