diff --git a/docs/ARCHITECTURE_RESILIENCE_REVIEW.md b/docs/ARCHITECTURE_RESILIENCE_REVIEW.md
index e482ae2..d623c57 100644
--- a/docs/ARCHITECTURE_RESILIENCE_REVIEW.md
+++ b/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
 
diff --git a/docs/PHASE_1_SUBSYSTEM_BOUNDARIES_DESIGN.md b/docs/PHASE_1_SUBSYSTEM_BOUNDARIES_DESIGN.md
index 3f54f18..829f118 100644
--- a/docs/PHASE_1_SUBSYSTEM_BOUNDARIES_DESIGN.md
+++ b/docs/PHASE_1_SUBSYSTEM_BOUNDARIES_DESIGN.md
@@ -504,7 +504,8 @@ Core responsibilities:
 
 - `LoadConfig()`
 - `LoadPersistentState()`
-- `SavePersistentStateSnapshot(...)`
+- `BuildPersistentStateSnapshot(...)`
+- `RequestPersistence(...)`
 - `GetStoredLayerStack()`
 - `SetStoredLayerStack(...)`
 - `GetStackPresetNames()`
diff --git a/docs/PHASE_3_LIVE_STATE_SERVICE_COORDINATION_DESIGN.md b/docs/PHASE_3_LIVE_STATE_SERVICE_COORDINATION_DESIGN.md
index 7b795e8..c3c1569 100644
--- a/docs/PHASE_3_LIVE_STATE_SERVICE_COORDINATION_DESIGN.md
+++ b/docs/PHASE_3_LIVE_STATE_SERVICE_COORDINATION_DESIGN.md
@@ -35,7 +35,7 @@ The main problems Phase 3 addressed:
 - transient OSC overlay state and persisted committed state needed a named reconciliation boundary
 - `RenderEngine` needed to move final frame-state selection and value composition out of drawing code
 - service-side queues for pending OSC updates and completed OSC commits needed a bridge outside `OpenGLComposite`
-- `RuntimeStore` still performs synchronous persistence directly from many state mutation paths
+- Phase 6 has since moved runtime-state persistence requests onto a debounced background writer
 - `RuntimeUpdateController` still exists partly as compatibility glue between synchronous coordinator results and event-driven effects
 
 ## Goals
@@ -46,7 +46,7 @@ Phase 3 should establish:
 - service-facing event bridges for OSC overlay updates and overlay commit completions
 - a narrower `OpenGLComposite::renderEffect()` that renders a prepared read model instead of orchestrating runtime/service state
 - a clear owner for final render-layer state resolution before it reaches GL drawing
-- a contained persistence request model that prepares for the later background writer phase
+- a contained persistence request model that later Phase 6 connected to the background writer
 - tests for live-state composition, overlay settlement, and service-to-runtime event behavior without GL or DeckLink
 
 ## Non-Goals
@@ -153,7 +153,7 @@ Non-responsibilities:
 | render asks for overlay commit requests | `OscOverlaySettled` or direct coordinator command plus event publication | Commit request creation should leave `renderEffect()` and live near the live-state owner. |
 | completed OSC commits drained by `OpenGLComposite` | `RuntimeMutationAccepted` / completion event -> live-state commit completion | Completed commit routing should be event-driven or owned by live-state service bridge. |
 | `RenderFrameStateResolver::Resolve(...)` | `RenderStateComposer::BuildFrameState(...)` | Keep final state composition testable without GL. |
-| direct persistence writes from store mutations | `RuntimePersistenceRequested` as the durable write trigger | Background writer lands later; Phase 3 should make request boundaries clear. |
+| direct persistence writes from store mutations | `RuntimePersistenceRequested` as the durable write trigger | Phase 6 later connected this request boundary to the background writer. |
 | runtime-state broadcast side effects | `RuntimeStateBroadcastRequested` plus optional completed/failed observations | Keep broadcast delivery in services and presentation ownership in runtime presentation. |
 
 ## Runtime Store Scope In Phase 3
@@ -164,7 +164,7 @@ Target responsibilities:
 
 - initialize runtime config and persistent state
 - expose durable layer/package/config read models
-- own saved layer stack and preset serialization until the background writer phase
+- own saved layer stack and preset serialization while exposing snapshots for the background writer
 - publish or support immutable render/presentation snapshots
 
 Avoid adding:
@@ -231,16 +231,16 @@ Avoid:
 
 ## Persistence Position
 
-Phase 3 should not implement the background writer, but it should prepare for it.
+Phase 3 did not implement the background writer, but it prepared the request boundary that Phase 6 now uses.
 
 Target behavior by Phase 3 exit:
 
 - state mutations publish `RuntimePersistenceRequested`
 - persistence can be observed and tested as an event side effect
-- synchronous `SavePersistentState()` remains allowed as an implementation detail inside `RuntimeStore`
+- disk writes are not inferred by callers; later Phase 6 routes accepted durable mutations through `RuntimePersistenceRequested` and the background writer
 - callers outside the store/coordinator should not infer disk writes from mutation categories
 
-This keeps Phase 6 smaller: the background snapshot writer can subscribe to persistence requests and consume a stored-state snapshot rather than rediscovering mutation policy.
+This kept Phase 6 smaller: the background snapshot writer consumes persistence requests and stored-state snapshots rather than rediscovering mutation policy.
 
 ## Migration Plan
 
@@ -348,7 +348,7 @@ The current groundwork is intended to let these lanes proceed in parallel with l
 | B. Render-state composition | `runtime/live/RenderStateComposer.*`, `gl/frame/RenderFrameStateResolver.*`, `gl/RenderEngine.*` | Implemented for Phase 3: value composition and frame-state selection sit outside GL drawing while GL calls remain in `RenderEngine`. |
 | C. Service bridge | `control/RuntimeServices.*`, `control/RuntimeServiceLiveBridge.*`, `control/ControlServices.*` | Implemented for Phase 3: `OpenGLComposite::renderEffect()` no longer drains OSC update/completion queues directly. |
 | D. App-frame orchestration | `gl/composite/OpenGLComposite.*`, `gl/frame/RuntimeUpdateController.*` | Implemented for Phase 3: render-effect glue is a narrow runtime-work, frame-input, render-frame sequence. |
-| E. Persistence boundary | `runtime/coordination/RuntimeCoordinator.*`, `runtime/store/*`, event tests | Implemented for Phase 3: persistence request publication is explicit and ready for a later background writer. |
+| E. Persistence boundary | `runtime/coordination/RuntimeCoordinator.*`, `runtime/store/*`, event tests | Implemented for Phase 3: persistence request publication is explicit. Phase 6 later wired those requests to the background writer. |
 
 ## Phase 3 Exit Criteria
 
@@ -368,7 +368,7 @@ Phase 3 can be considered complete once the project can say:
 - Should the new live-state owner live under `runtime/`, `gl/`, or a new `renderstate/` boundary?
 - Should smoothing policy be owned by live state, render-state composition, or render settings?
 - Should overlay commit completion be represented as a new typed event, or derived from existing accepted mutation events with route/generation metadata?
-- How much of persistence should remain synchronous until Phase 6?
+- Should preset save remain synchronous after Phase 6, or eventually move behind a completion-based async request?
 
 ## Short Version