docs(01-04): complete offscreen port keepalive + OFFSCREEN_READY handshake plan

- Add 01-04-SUMMARY.md with TDD RED/GREEN/REFACTOR gate records,
  acceptance grep gates, threat mitigations (T-1-04, T-1-NEW-04-01),
  Plan 05 SW-side handoff (REQUIRED sender.id === chrome.runtime.id
  check), and 1 Rule 1 deviation documented
- Advance STATE.md Plan counter 4 → 5, progress 43% → 57%
- Append 3 decisions to STATE.md Accumulated Context
- Update ROADMAP.md: 01-04-PLAN checkbox → [x], phase progress row 3/7 → 4/7

REQ-video-ring-buffer NOT marked complete — still pending Plan 07
ffprobe D-12 gate per the requirement's traceability.

.planning/STATE.md

@@ -3,15 +3,15 @@ gsd_state_version: 1.0
 milestone: v2.0.0
 milestone_name: milestone
 status: executing
-stopped_at: Completed Plan 01-03 — recorder.ts ring-buffer + codec strict-mode GREEN; Plan 04 next (port keepalive + REQUEST_BUFFER wiring)
-last_updated: "2026-05-15T15:41:54.994Z"
+stopped_at: Completed Plan 01-04 — port keepalive + OFFSCREEN_READY handshake GREEN (9/9 tests pass); Plan 05 next (SW shrink + onConnect host with T-1-04 sender check)
+last_updated: "2026-05-15T15:53:24.264Z"
 last_activity: 2026-05-15
 progress:
   total_phases: 5
   completed_phases: 0
   total_plans: 7
-  completed_plans: 3
-  percent: 43
+  completed_plans: 4
+  percent: 57
 ---
 
 # Project State
@@ -28,12 +28,12 @@ no server, no password leaks.
 ## Current Position
 
 Phase: 1 (Stabilize Video Pipeline) — EXECUTING
-Plan: 4 of 7
+Plan: 5 of 7
 Status: Ready to execute
 Last activity: 2026-05-15
 REQUIREMENTS.md, ROADMAP.md, STATE.md written)
 
-Progress: [████░░░░░░] 43%
+Progress: [██████░░░░] 57%
 
 ## Performance Metrics
 
@@ -62,6 +62,7 @@ Progress: [████░░░░░░] 43%
 | Phase 01 P01 | 4min | 6 tasks | 6 files |
 | Phase 01 P02 | 4min | 5 tasks | 8 files |
 | Phase 1 P03 | 8min | 3 tasks | 5 files |
+| Phase 01 P04 | 4min | 3 tasks | 1 files |
 
 ## Accumulated Context
 
@@ -88,6 +89,9 @@ current work:
 - [Phase 01-03]: Bundled OffscreenLogger into Task 2 commit (Rule 3 blocking dependency — recorder.ts cannot typecheck without the import)
 - [Phase 01-03]: Defensive bootstrap guard (typeof chrome check) lets pure ring-buffer test import recorder module without chrome stub
 - [Phase 01-03]: Removed SW-side VIDEO_CHUNK/VIDEO_CHUNK_SAVED branches + IndexedDB helpers inline (tsc-clean requires; Plan 05 owns remaining SW shrink)
+- [Phase 01-04]: Kept Plan 03's defensive bootstrap guard (typeof chrome / per-API existence checks) instead of Plan 04's verbatim unguarded block — Plan 04's verbatim block regressed ring-buffer and codec-check tests (they don't stub full chrome surface); restored guard preserves Plan 02 RED contract while satisfying Plan 04's new GREEN contract. Rule 1 deviation.
+- [Phase 01-04]: T-1-04 SW-side sender check documented redundantly (4 places in recorder.ts) for Plan 05 executor visibility — Offscreen is trusting party; SW is validating party. Documenting in module header, port-name constant, threat-mitigation comment near bootstrap, and inline at connectPort makes the contract impossible to miss when grepping for T-1-04 during Plan 05.
+- [Phase 01-04]: REFACTOR pass NOT skipped: stale 'Plan 04 wires this' comments replaced with actual D-17/Pattern 5 citations — Forward-pointing TODO-style comments became misleading after the work landed; minimal correctness-preserving comment update with all 9 tests still GREEN.
 
 ### Pending Todos
 
@@ -110,7 +114,7 @@ Items acknowledged and carried forward from previous milestone close:
 
 ## Session Continuity
 
-Last session: 2026-05-15T15:41:54.976Z
-Stopped at: Completed Plan 01-03 — recorder.ts ring-buffer + codec strict-mode GREEN; Plan 04 next (port keepalive + REQUEST_BUFFER wiring)
+Last session: 2026-05-15T15:53:12.593Z
+Stopped at: Completed Plan 01-04 — port keepalive + OFFSCREEN_READY handshake GREEN (9/9 tests pass); Plan 05 next (SW shrink + onConnect host with T-1-04 sender check)
 intel synthesis. Coverage validated: 11/11 v1 REQs mapped.
-Resume file: .planning/phases/01-stabilize-video-pipeline/01-04-PLAN.md
+Resume file: .planning/phases/01-stabilize-video-pipeline/01-05-PLAN.md