feat(capabilities): compound capability predicates (66b)

[discreteds]

Backlog item 66b — compound capability predicates. Adds a structured, enumerable predicate over the bound operation call to CapabilityFact, evaluated by a new collecting API violations_for(bound_call) -> frozenset[CapabilityFact], alongside an unchanged capability_for.

What

• Predicate model (schema.py): ClauseOp (EQ/IN/IS_SET/IS_NULL/IS_LITERAL/MATCHES_CLASS), Clause, Predicate (canonical-ordered, order-insensitive eq/hash), and CapabilityFact.predicate with registration validation (BUILD-only, value-agnostic, GATE-only, UNSUPPORTED/EXPR_CAPABLE only, param-is-a-clause-root).
• Predicate engine (predicates.py): BoundCall, bind_expression_call, path resolution (declared-field/enum/mapping traversal, loud ValueError on missing, root LiteralNode unwrap), clause evaluation (§4.4 dynamic-arg semantics), and a sound subsumption/overlap lattice.
• Registry (registry.py): a separate _predicate_facts store (predicate facts carry option_value=None/value_class=None and must not collide with value-agnostic facts), violations_for, a registration-time conflict check (block-vs-permit, dialect-scope-compatible, strict-subsumption resolves), and snapshot/restore/reset coverage.
• Gate integration: both unified visitors call violations_for once per call, in addition to the existing per-param loops.
• Consumer audit: fact_sort_key totals over predicate facts; the argument-probe filter excludes them.

Design decisions (spec rev 3, post adversarial review)

• IS_SET is pure §4.2 value semantics (the §5 "reads supplied" conjunction made the subsumption lattice unsound); BoundCall.supplied is still recorded.
• violations_for collects only UNSUPPORTED GATE predicate facts; EXPR_CAPABLE participates in the conflict check only.
• §6 cross-product compound-cell enumeration deferred per §7 (no consumer yet) — flagged, not hidden; an invariant test documents zero production predicate facts.

Verification

• Full suite: 22348 passed, 0 failed (81 skipped, 3708 xfailed).
• ruff:check clean.
• mypy: 97 pre-existing import-untyped errors, none in changed files.

Spec: 2026-07-28-compound-capability-predicates-design.md; plan: 2026-08-15-compound-capability-predicates.md.