docs update

docs/NEW_RENDER_CADENCE_APP_PLAN.md

@@ -1,5 +1,7 @@
 # New Render Cadence App Plan
 
+Status: historical implementation plan. `apps/RenderCadenceCompositor` now exists; use [apps/RenderCadenceCompositor/README.md](../apps/RenderCadenceCompositor/README.md) and [Render Cadence Golden Rules](RENDER_CADENCE_GOLDEN_RULES.md) as the current implementation contract.
+
 This plan describes a new application folder that rebuilds the output path from the proven `DeckLinkRenderCadenceProbe` architecture, but as a maintainable app foundation rather than a monolithic probe file.
 
 The first goal is not to port the current compositor feature set. The first goal is to reproduce the probe's smooth 59.94/60 fps DeckLink output with clean module boundaries, tests where possible, and a structure that can later accept the shader/runtime/control systems without compromising timing.
@@ -43,7 +45,7 @@ Render cadence thread
 
 System frame exchange
   -> owns Free / Rendering / Completed / Scheduled slots
-  -> latest-N semantics for completed unscheduled frames
+  -> bounded FIFO reserve for completed unscheduled frames
   -> protects scheduled frames until DeckLink completion
 
 DeckLink output thread
@@ -63,7 +65,7 @@ Everything else must fit around that spine.
 - Completion callbacks never render.
 - No synchronous render request exists in the output path.
 - Preview, screenshot, input upload, shader rebuild, and runtime control cannot run ahead of a due output frame.
-- Completed unscheduled frames are latest-N and disposable.
+- Completed unscheduled frames are a bounded FIFO reserve; overflow drops are counted separately from DeckLink drops.
 - Scheduled frames are protected until DeckLink completion.
 - Startup warms up real rendered frames before scheduled playback starts.
 
@@ -77,7 +79,7 @@ Keep these behaviors from `DeckLinkRenderCadenceProbe`:
 - PBO ring readback
 - non-blocking fence polling with zero timeout
 - system-memory slots with `Free`, `Rendering`, `Completed`, `Scheduled`
-- drop oldest completed unscheduled frame if render needs space
+- preserve completed frames waiting for playout; drop/count the oldest completed frame only if the bounded reserve overflows
 - DeckLink playout thread only schedules completed frames
 - warmup completed frames before `StartScheduledPlayback()`
 - one-line-per-second timing telemetry
@@ -430,7 +432,7 @@ Feature set:
 - simple motion renderer
 - BGRA8 only
 - PBO async readback
-- latest-N system-memory frame exchange
+- bounded FIFO system-memory frame exchange
 - warmup before playback
 - one-line telemetry