Correct in-node accessor + deferral comment claims

The persist() example in the queryable observer pattern docs was
reading state.invocation_id, but a default State has no such field.
Switch the snippet to bind invocation_id from
current_invocation_id() (the supported in-node accessor) with a
brief note that it is guaranteed non-None inside a node body.

The 0048 fixture-deferral comment in test_fixture_parsing.py
claimed unit tests covered per-attempt scoping under retry and
per-async-context scoping under fan-out. Neither is true: there
are no retry-attempt tests in test_observability_metadata.py, and
the fan-out coverage lives in the runtime conformance harness via
the predecessor proposal 0034/0040 fixtures, not as unit tests
here. Rewrite the comment to be honest about what each pin
actually covers and to flag the retry-side gap.

Author: chris-colinsky

docs/concepts/observability.md

@@ -577,15 +577,19 @@ release the bucket via the §9.4 `drop` discipline:
 
 ```python
 async def persist(state: PipelineState) -> Mapping[str, Any]:
+    # current_invocation_id() returns the engine-minted (or
+    # caller-supplied) id of the active invocation; never None
+    # inside a node body.
+    invocation_id = current_invocation_id()
     # 1. Wait for every event under this invocation_id to dispatch
     #    to every attached observer; bounded by the timeout.
-    await graph.drain_events_for(state.invocation_id, timeout=2.0)
+    await graph.drain_events_for(invocation_id, timeout=2.0)
     # 2. Read the bucket — the accumulator's view now reflects the
     #    full event stream for this invocation.
-    usage_records = accumulator.get_bucket(state.invocation_id)
+    usage_records = accumulator.get_bucket(invocation_id)
     # 3. Release the bucket per §9.4. Skip this step only if the
     #    accumulator is intentionally session-scoped across resumes.
-    accumulator.drop(state.invocation_id)
+    accumulator.drop(invocation_id)
     # ...
 ```
 

tests/conformance/test_fixture_parsing.py

@@ -277,10 +277,18 @@ def _id(case: tuple[str, Path]) -> str:
     # ``current_invocation_metadata`` plus the §9 queryable observer
     # pattern (convention-only); v0.12.0 adds ``get_invocation_metadata``
     # as the canonical alias and the §9 documentation. Behavior is
-    # pinned by ``tests/unit/test_observability_metadata.py`` (read
-    # roundtrip + per-async-context scoping under fan-out + per-attempt
-    # scoping under retry + outside-invocation empty). Fixture-shape
-    # activation is queued for a future PR.
+    # pinned by:
+    #   - ``tests/unit/test_observability_metadata.py``: read
+    #     roundtrip + alias identity + mid-invocation augmentation
+    #     visible to next node + outside-invocation empty.
+    #   - Predecessor proposal 0034/0040 conformance fixtures
+    #     (observability/026, 027, 029, 030, 034 — already
+    #     implemented and exercised by the runtime harness) cover
+    #     per-async-context scoping under fan-out + parallel-branches.
+    #   - Per-attempt scoping under retry is the OPEN gap documented
+    #     on the 0048 manifest entry (status = "partial"); pinning
+    #     lands in the follow-on retry-metadata-reset PR.
+    # Fixture-shape activation is queued for a future PR.
     "observability/043-get-invocation-metadata-roundtrip": (
         "Proposal 0048 fixture-shape models pending; contract pinned by unit tests"
     ),