[AZ-381] Fix ISam2GraphHandleImpl missing get_pose_key + comments

F1 (High/Architecture) from cumulative review of batches 01-22:
`ISam2GraphHandleImpl` did not satisfy C4's `ISam2GraphHandle`
Protocol stub (AZ-355) because it lacked `get_pose_key`.
`pose_factory`'s isinstance gate would have raised at composition.
Two Protocols (C4 minimal consumer cut, C5 richer producer surface)
are intentional per AZ-355 Risk 1 — the impl just needed to expose
the canonical name. Delegates to estimator.key_for_frame.

Added cross-component conformance test asserting the C5 impl
satisfies both Protocols, so future drift trips a unit test.

F2 (Medium/Maintainability): added justifying comments at four
`except: pass` sites in runtime_root, c8_fc_adapter (ap + inav),
and c13_fdr writer. No behavioral change.

Updated cumulative review report verdict from FAIL to PASS and
recorded a post-mortem on the initial misframing
(treated the dual-Protocol design as duplication on first read).

Autodev state: batch 22 done, cumulative-review PASS,
ready for batch 23.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/gps_denied_onboard/components/c13_fdr/writer.py

@@ -539,6 +539,10 @@ class FileFdrWriter:
             if seg_path.exists() and seg_path.stat().st_size == 0:
                 seg_path.unlink()
         except OSError:
+            # Rollback unlink is best-effort: a zero-byte stray segment is
+            # harmless (the next open_flight scans + skips empty segments),
+            # so any unlink failure here MUST NOT mask the underlying
+            # FdrOpenError that this _fail_open call is about to raise.
             pass
         self._release_filelock()
         self._started = False