feat: query_policy semantic-layer-only restricts agents to predefined semantic-layer measures (#334)

* feat(sl): add predefined_measures_only guard to semantic query planning

SemanticQuery gains a predefined_measures_only flag; the planner rejects
any measure resolved with Provenance.COMPOSED (runtime aggregate
expressions and query-time derivations) while predefined measures,
predefined derived chains, dimensions, filters, and segments pass.

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

* feat(config): add per-connection query_policy to warehouse connections

query_policy: semantic-layer-only | read-only-sql (default) on the
warehouse connection schema, plus a policy module with the raw-SQL
guard, federated member restriction lookup, and the project-level
predicate used to gate sql_execution registration.

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

* feat(cli): enforce query_policy on raw SQL through one shared executor

ktx sql and the MCP sql_execution tool now share executeProjectRawSql
(resolve, policy check, read-only validation, execute), collapsing
their duplicated validate-then-execute paths. Restricted connections
are rejected before validation; federated raw SQL is rejected when any
member is restricted. sql_execution is not registered when every SQL
connection is restricted, and connection_list marks restricted
connections so agents route to sl_query. executeProjectReadOnlySql
stays generic for ktx-internal SQL (scan, ingest, SL-generated).

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

* feat(sl): compile queries with predefined_measures_only from query_policy

compileLocalSlQuery injects the flag from the connection's query_policy,
never from caller input, covering both ktx sl query and the MCP
sl_query tool through the daemon compile path.

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

* docs: document query_policy semantic-layer-only

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

* fix(sl): close semantic-layer-only bypasses via filters and federated hint

The predefined_measures_only guard only inspected query.measures, so a
composed aggregate written into `filters` slipped through _classify_filters
into a HAVING clause untouched — letting a restricted agent evaluate
arbitrary aggregates (e.g. threshold-probing `sum(x) BETWEEN a AND b`).
Reject filter clauses that compose an aggregate function; a HAVING that
compares a predefined measure by name (`orders.revenue > 100`) still works.

Also make the federated sl_query error policy-aware: when a member is
restricted, raw federated SQL is disabled too, so stop directing the agent
to `ktx sql -c _ktx_federated` / sql_execution (a guaranteed failure) and
point to per-connection semantic-layer queries instead.

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
Co-authored-by: Andrey Avtomonov <andreybavt@gmail.com>

python/ktx-sl/semantic_layer/planner.py

@@ -62,6 +62,10 @@ class QueryPlanner:
         # 2. Resolve measures (parse, look up pre-defined, classify)
         raw_measures = self._resolve_measures(query.measures)
 
+        if query.predefined_measures_only:
+            self._reject_composed_measures(raw_measures)
+            self._reject_composed_filter_aggregates(query.filters)
+
         # 3. Topological sort for derived measures
         measures = self._topological_sort_measures(raw_measures)
 
@@ -239,6 +243,42 @@ class QueryPlanner:
         measures = self._qualify_duplicate_names(measures)
         return measures
 
+    def _reject_composed_measures(self, measures: list[ResolvedMeasure]) -> None:
+        composed = [m for m in measures if m.provenance is Provenance.COMPOSED]
+        if not composed:
+            return
+        rejected = ", ".join(f"'{m.expr}'" for m in composed)
+        raise ValueError(
+            f"Only predefined semantic-layer measures can be queried on this "
+            f"connection (query_policy: semantic-layer-only); composed measure "
+            f"expressions are not allowed: {rejected}. Use measures declared "
+            f"on the semantic-layer sources, referenced as 'source.measure'."
+        )
+
+    def _reject_composed_filter_aggregates(self, filters: list[str]) -> None:
+        # Predefined measures are compared in HAVING by name (e.g.
+        # `orders.revenue > 100`), which parses as a plain column ref. Any
+        # aggregate function written into a filter is therefore a runtime-composed
+        # aggregate the policy forbids — without this guard it would slip through
+        # `_classify_filters` into HAVING and evaluate an arbitrary aggregate.
+        composed: list[str] = []
+        for f in filters:
+            if not f or not f.strip():
+                continue
+            for clause in self._split_top_level_and(f):
+                if self.parser.parse(clause).is_aggregate:
+                    composed.append(clause)
+        if not composed:
+            return
+        rejected = ", ".join(f"'{c}'" for c in composed)
+        raise ValueError(
+            f"Only predefined semantic-layer measures can be queried on this "
+            f"connection (query_policy: semantic-layer-only); filters may not "
+            f"compose aggregate expressions: {rejected}. Filter on declared "
+            f"dimensions or columns, or compare a predefined measure by name "
+            f"(e.g. 'orders.revenue > 100')."
+        )
+
     def _collect_colliding_predefined_names(self, raw: list[str | dict]) -> set[str]:
         counts: Counter[str] = Counter()
         for item in raw: