Activate proposal 0049 conformance fixtures 050-056 (#139)

* Activate proposal 0049 conformance fixtures 050-056

Adds harness support for the typed_event_collector directive introduced
by proposal 0049's seven conformance fixtures (050-056). The directive
declares one or more typed event collectors with optional filter_event_type
and include_caller_metadata flags; the parser aggregates the latter into
the provider's populate_caller_metadata kwarg.

Adds eight assertion shape handlers consumed by the fixtures:
contains_event, contains_exactly_one_event_of_type,
contains_event_of_type, contains_exactly_n_events_of_type,
does_not_contain_event_of_type, captured_event_field_values_cover,
every_captured_event_has, relative_order_of_events_matching. The
captured_event_field_values_cover shape uses set equality (matching
the spec text's "cover" semantic) rather than sorted-by-str (which
silently masks None-vs-primitive ordering ambiguity). An unknown-key
guard rejects fixture typos before any assertion runs.

Three graph builders cover the fixture topologies: a simple entry-ask-END
shape (050, 051, 052, 053, 056), a fan-out builder (054), and a
parallel-branches builder (055). The failure-path runner (053) sources
the calling-node NodeEvent from an unfiltered named collector when one
exists; otherwise attaches an AllEventsCollector specifically for that
assertion. The cause-chain walk handles the NodeException wrapper the
engine layers over the underlying ProviderUnavailable.

Adds tests/conformance/test_typed_event_harness.py with 31 unit tests
covering the harness helpers' edge cases: typo detection in assertion
keys, set-equality semantics, namespace tuple-vs-list normalization,
usage Mapping-vs-Usage comparison, cause-chain walking, populate_caller_metadata
aggregation, and the mock_model resolution. These would otherwise only
surface when a future fixture trips them.

Flips conformance.toml's [proposals."0049"] from not-yet to implemented
since 0.13.0. The leading-comment block notes that the OTel + Langfuse
observers continue driving their span / generation surface off the
sentinel NodeEvent pair during the dual-emit transition window;
type-discrimination migration of those observers waits on the
request-side-fields extension currently being drafted.

* Address PR review feedback on typed-event harness

Two distinct issues across five review threads:

1. Three sites used a truthy check on caller_metadata (if metadata:)
   that collapsed an explicit empty mapping (caller_metadata: {}) to
   the "no metadata key" case and dropped the metadata= kwarg from
   graph.invoke(). Switched all three sites
   (_invoke_typed_fixture, _run_typed_event_fanout_case,
   _run_typed_event_branches_case) to is-not-None checks so empty
   mappings flow through to the engine.

2. Two harness helpers (_event_fields_match and the
   every_captured_event_has branch in _assert_observer_expectations)
   used getattr(event, name, None), conflating a missing attribute
   with an attribute present and set to None. A fixture-side
   field-name typo (node_nam vs node_name) would silently match
   against any None expectation. Added hasattr() preambles that
   raise AssertionError naming the missing field, since upstream
   type filtering guarantees attribute presence on the captured
   set.

Two new harness unit tests pin the missing-attribute contract: a
typo'd field on _event_fields_match raises a clear error, and the
every_captured_event_has branch does the same.

Author: chris-colinsky

conformance.toml

@@ -295,10 +295,19 @@ status = "implemented"
 since = "0.12.0"
 
 # Spec v0.41.0 (proposal 0049).  Typed LLM Completion Event — first
-# typed event variant on the observer event union.  Queued for
-# v0.13.0 alongside 0047.
+# typed event variant on the observer event union.  Shipped in
+# v0.13.0: provider dual-emits the typed event alongside the sentinel
+# NodeEvent pair (success-only per spec scope); LlmCompletionEvent
+# carries identity/scoping/outcome fields per the spec field table.
+# Conformance fixtures 050-056 activated by the typed_event_collector
+# harness directive.  The OTel + Langfuse observers continue to drive
+# their §5.5 / §8.4.4 surface off the sentinel NodeEvent pair during
+# the dual-emit transition window; type-discrimination migration
+# lands once the follow-on request-side-fields extension (proposal
+# 0057) ships.
 [proposals."0049"]
-status = "not-yet"
+status = "implemented"
+since = "0.13.0"
 
 # Spec v0.42.0 (proposal 0050).  Retry & degradation primitives —
 # failure-isolation middleware + call-level retry.  Queued for