refactor(mediabunny): [PKG-MB-08] checkpoint typed entry and compatible media declarations

refactor/risks.json

@@ -3679,13 +3679,15 @@
         "PKG-MB-08",
         "PKG-MB-10"
       ],
-      "compatibleResolution": "Preserve optional whole-factory and exact Canvas assignment, model explicit shim capabilities separately and verify historical default namespace and callable consumers.",
+      "compatibleResolution": "Preserve optional whole-factory and exact Canvas assignment, model explicit shim capabilities separately and verify historical default namespace and callable consumers. MB-08 entry checkpoint preserves exact optional factory/Canvas assignment, adds opt-in checked media types without SDK imports, and fixes classic legacy/NodeNext ESM resolution. Seventeen installed compiler cases plus runtime exports passed against two frozen releases and candidate; seven candidate cases reject fifteen invalid uses each. Type facade/runtime export part is verified; final MB-08 capability and MB-10 distribution gates remain open.",
       "closureCriteria": "Actual installed old/candidate compiler and runtime export matrices pass with negative controls; any incompatible declaration generation requires an explicit decision.",
       "status": "open",
       "evidence": [
         "refactor/baselines/mb-release.json",
         "refactor/baselines/mb-contract.md",
-        "refactor/changes/2026-09-12-PKG-MB-01-contract.md"
+        "refactor/changes/2026-09-12-PKG-MB-01-contract.md",
+        "refactor/changes/2026-09-12-PKG-MB-08-entry-checkpoint.md",
+        "refactor/baselines/mb-entry-checkpoint.json"
       ]
     },
     {
@@ -3715,13 +3717,14 @@
         "PKG-MB-04",
         "PKG-MB-09"
       ],
-      "compatibleResolution": "Use explicit coordinated readiness and failure state, preserving valid event order while preventing duplicate or stale callbacks; evaluate trackless behavior separately from normal media. MB-04 coordinates metadata once, suppresses stale readiness and rejects trackless input before decoder setup. Existing-track unsupported-codec behavior and full native combinations remain MB-05/06/09; risk stays open.",
+      "compatibleResolution": "Use explicit coordinated readiness and failure state, preserving valid event order while preventing duplicate or stale callbacks; evaluate trackless behavior separately from normal media. MB-04 coordinates metadata once, suppresses stale readiness and rejects trackless input before decoder setup. Existing-track unsupported-codec behavior and full native combinations remain MB-05/06/09; risk stays open. MB-08 entry checkpoint reproduces remaining false readiness in both previous and candidate builds: actual SDK-parsed video-only MP4 with controlled canDecode=false and AudioContext yields null audio/video sinks but readyState 4 and all readiness events, including replaceTracks. Keep open for the next MB-08 capability implementation; this controlled case is not native decoding evidence.",
       "closureCriteria": "Candidate metadata/data/canplay ordering and counts pass normal, absent-track and failure interleavings in native browsers and controlled race tests.",
       "evidence": [
         "refactor/changes/2026-09-12-PKG-MB-02-baseline.md",
         "refactor/baselines/mb-behavior-validation.json",
         "refactor/changes/2026-09-12-PKG-MB-04-coordination.md",
-        "refactor/baselines/mb-coordination-validation.json"
+        "refactor/baselines/mb-coordination-validation.json",
+        "refactor/baselines/mb-entry-checkpoint.json"
       ]
     }
   ]