Add ordered build-local loader and record staged apply decision

plans/phase3-staged-apply-decision.md

@@ -0,0 +1,32 @@
+# Phase 3 — decision required before live module replacement
+
+COMMON.md says: "If you hit a decision that changes user-visible behaviour or
+risks data loss that the documents do not answer, write QUESTION ... and end your
+turn instead." This concerns §2c.5's instruction to switch stale modules when
+new bytes arrive, after a new build has booted using a same-contract fallback.
+
+Concrete finding: direct-media.js creates private rooms, pending, transfers and
+waiting maps at module evaluation (lines 4–6). Its public API has no busy,
+dispose or state handoff method. Re-evaluation replaces window.DirectMedia,
+while WebRTC callbacks/workers still close over the old maps. Later messages
+routed by app.js through the new DirectMedia.handle can no longer find those
+in-flight transfers. p2p-client.js similarly replaces its public singleton but
+retains old sockets, timers and its visibility listener; P2PTransfer exposes
+start/download without disposal. Matching contract numbers do not establish
+safe runtime state migration. Piano/MIDI/floating-window UI also retains closures.
+
+Recommended owner decision: background-download and verify the new URLs
+immediately, but pin an already-executing stale module until its feature session
+closes and can be safely recreated. Keep P2P/direct instances until the next
+explicit user-initiated, playback-guarded page reload. Groups never executed use
+the newest cached version immediately. In Phase 4, introduce explicit teardown
+and state handoff seams before enabling live replacement of these instances.
+This narrows "switch when the new one arrives" for stateful modules; it requires
+owner approval rather than silently claiming that caching new bytes replaces
+running code.
+
+Completed safe prerequisites: plan commit 895f20a; pure contract fallback and
+background-group synchronization commit f804a23; ordered build-local loader with
+unit tests (not yet wired into index.html). No layout or feature was removed
+from the current eager path. Full browser/layout/performance acceptance remains
+outstanding. This is a QUESTION checkpoint, not a completed phase report.