Docs update

docs/ARCHITECTURE_RESILIENCE_REVIEW.md

@@ -10,7 +10,7 @@ Phase checklist:
 - [x] Finish live-state and service-facing coordination
 - [x] Make the render thread the sole GL owner
 - [x] Refactor live state layering into an explicit composition model
-- [ ] Move persistence onto a background snapshot writer
+- [x] Move persistence onto a background snapshot writer
 - [ ] Make DeckLink/backend lifecycle explicit with a state machine
 - [ ] Add structured health, telemetry, and operational reporting
 
@@ -21,7 +21,7 @@ Checklist note:
 - The checked Phase 3 item means the render-facing state path now has named live-state, composition, frame-state, resolver, and service-bridge boundaries. `OpenGLComposite::renderEffect()` is reduced to runtime work, frame input construction, and frame rendering.
 - The checked Phase 4 item means normal runtime GL work is now owned by a dedicated `RenderEngine` render thread. Input upload, output render, preview, screenshot capture, render-local resets, and shader application enter through render-thread queue/request paths instead of caller-thread context borrowing. The remaining output timing risk is callback-coupled synchronous output production, which is intentionally tracked for the later DeckLink/backend lifecycle and playout-queue work.
 - The checked Phase 5 item means persisted, committed/session, transient automation, and render-local state are explicitly named. `CommittedLiveState` physically owns current session layer state, `RuntimeLiveState` owns transient OSC overlays, `RenderStateComposer` consumes a layered input contract, and reset/reload/preset overlay invalidation is centralized and covered by non-GL tests.
-- It does not mean the whole app is fully extracted. Background persistence, backend lifecycle/playout queue policy, and richer telemetry continue through later phases.
+- It does not mean the whole app is fully extracted. Backend lifecycle/playout queue policy and richer telemetry continue through later phases.
 
 ## Timing Review
 
@@ -575,18 +575,19 @@ Expected benefits:
 
 ### Phase 6. Move persistence onto a background snapshot writer
 
-After the state model is explicit, persistence should become a background concern rather than a synchronous side effect of mutations.
+Status: complete. Runtime-state persistence is now a background concern rather than a synchronous side effect of mutations.
 
 Dedicated design note:
 
 - [PHASE_6_BACKGROUND_PERSISTENCE_DESIGN.md](/c:/Users/Aiden/Documents/GitHub/video-shader-toys/docs/PHASE_6_BACKGROUND_PERSISTENCE_DESIGN.md)
 
-Target behavior:
+Implemented behavior:
 
 - mutations update authoritative in-memory stored state
 - persistence requests are queued
 - disk writes are debounced and coalesced
-- writes are atomic and versioned where practical
+- writes use temp-file replacement where practical
+- shutdown flush behavior is explicit and tested
 
 Why this phase comes after state splitting:
 
@@ -688,7 +689,7 @@ This order tries to avoid doing foundational work twice.
 - The event model comes before major subsystem extraction so coordination patterns stabilize early.
 - runtime state ownership is split before render isolation so the render thread does not inherit a monolithic state model.
 - Live state layering is formalized only after render ownership is clearer.
-- Persistence is moved later so it can target the final state model rather than the current one.
+- Persistence moved after the state model split so it could target the durable snapshot model rather than an older mixed-responsibility runtime object.
 - Telemetry is intentionally late so it instruments the architecture that survives the refactor.
 
 ## Short Version
@@ -700,7 +701,7 @@ The app is in a much better place than it was before the OSC timing work. The sh
 3. split state ownership
 4. isolate rendering
 5. formalize layered live state
-6. background persistence
+6. complete background persistence
 7. explicit backend lifecycle
 8. health and telemetry