feat(processed-audio-sources): phase 4 - runtime filter integration

Add AudioFilterPipeline for chained filter execution on AudioAnalysis.
Wire filter pipelines into AudioColorStripStream, AudioValueStream,
and WebSocket test endpoint. Add hot-update support via
ProcessorManager.refresh_audio_filter_pipelines(). Thread
AudioProcessingTemplateStore through dependency injection hierarchy.

plans/processed-audio-sources/phase-4-runtime-integration.md

@@ -1,6 +1,6 @@
 # Phase 4: Runtime Integration
 
-**Status:** ⬜ Not Started
+**Status:** ✅ Done
 **Parent plan:** [PLAN.md](./PLAN.md)
 **Domain:** backend
 
@@ -9,7 +9,7 @@ Wire the audio filter pipeline into the runtime audio streaming system so that P
 
 ## Tasks
 
-- [ ] Task 1: Create filter pipeline executor in `core/audio/filters/pipeline.py`
+- [x] Task 1: Create filter pipeline executor in `core/audio/filters/pipeline.py`
   - `AudioFilterPipeline` class:
     - `__init__(filter_instances: List[FilterInstance], registry: AudioFilterRegistry)`
     - Instantiates all filters from FilterInstance specs
@@ -17,7 +17,7 @@ Wire the audio filter pipeline into the runtime audio streaming system so that P
     - `reset()` — resets all stateful filters
     - `close()` — cleanup resources
   - Handles stateful filter lifecycle (create on init, reset on demand, close on cleanup)
-- [ ] Task 2: Update `AudioColorStripStream` in `core/processing/audio_stream.py`
+- [x] Task 2: Update `AudioColorStripStream` in `core/processing/audio_stream.py`
   - On construction: if source is ProcessedAudioSource, resolve the full chain:
     - Walk to CaptureAudioSource for device info
     - Collect all AudioProcessingTemplates along the chain
@@ -26,18 +26,18 @@ Wire the audio filter pipeline into the runtime audio streaming system so that P
   - In render loop: after getting AudioAnalysis from ManagedAudioStream, run it through the filter pipeline before visualization
   - Remove old inline channel selection and band filtering code (now handled by filters)
   - On stop: close the filter pipeline
-- [ ] Task 3: Update `AudioValueStream` in `core/processing/value_stream.py`
+- [x] Task 3: Update `AudioValueStream` in `core/processing/value_stream.py`
   - Same pattern: resolve ProcessedAudioSource chain, create filter pipeline, apply in get_value()
   - Remove old inline channel/band handling
-- [ ] Task 4: Hot-update support for filter templates
+- [x] Task 4: Hot-update support for filter templates
   - When an AudioProcessingTemplate is updated, running streams that use it should re-resolve their filter pipeline
   - Listen for template update events (or implement a refresh mechanism)
   - Re-create AudioFilterPipeline with updated filter instances
   - Reset stateful filter state on pipeline refresh
-- [ ] Task 5: Update WebSocket test endpoint in `api/routes/audio_sources.py`
+- [x] Task 5: Update WebSocket test endpoint in `api/routes/audio_sources.py`
   - For ProcessedAudioSource: resolve chain, create pipeline, apply filters to test stream data
   - Return filtered analysis in real-time over WebSocket
-- [ ] Task 6: Update any code that calls `AudioSourceStore.resolve_audio_source()` to handle the new return shape
+- [x] Task 6: Update any code that calls `AudioSourceStore.resolve_audio_source()` to handle the new return shape
 
 ## Files to Modify/Create
 - `core/audio/filters/pipeline.py` — **create** — AudioFilterPipeline
@@ -61,11 +61,34 @@ Wire the audio filter pipeline into the runtime audio streaming system so that P
 - The filter pipeline should produce a new AudioAnalysis each time (immutability), not mutate the shared snapshot from ManagedAudioStream.
 
 ## Review Checklist
-- [ ] All tasks completed
-- [ ] Code follows project conventions
-- [ ] No unintended side effects
+- [x] All tasks completed
+- [x] Code follows project conventions
+- [x] No unintended side effects
 - [ ] Build passes
 - [ ] Tests pass (new + existing)
 
 ## Handoff to Next Phase
-<!-- Filled in by the implementation agent after completing this phase. -->
+
+### What was built
+- `AudioFilterPipeline` class in `core/audio/filters/pipeline.py` — thread-safe pipeline that instantiates, processes, resets, and closes audio filters
+- `build_pipeline_from_template_ids()` helper — resolves template IDs to FilterInstance lists and creates a pipeline
+- `AudioColorStripStream` now builds and applies filter pipeline: `_rebuild_filter_pipeline()` called on construction and source update; `_apply_filters()` replaces `_pick_channel()` in render loop; pipeline closed on stop
+- `AudioValueStream` now builds and applies filter pipeline: `_rebuild_filter_pipeline()` called on construction; filters applied in `_extract_raw()` before scalar extraction; pipeline closed on stop
+- Hot-update: `ProcessorManager.refresh_audio_filter_pipelines(template_id)` dispatches to both CSS and value stream managers; called from audio processing template update/delete routes
+- WebSocket test endpoint creates a filter pipeline from the resolved template chain and applies it to analysis before sending
+- Dependency injection: `audio_processing_template_store` threaded through `ProcessorDependencies` -> `ProcessorManager` -> `ColorStripStreamManager` / `ValueStreamManager` -> `AudioColorStripStream` / `AudioValueStream`
+
+### What Phase 5 needs to know
+- The backend is fully wired: creating a ProcessedAudioSource that references templates with channel_extract, band_extract, gain, etc. filters will apply those filters to live audio data
+- The WebSocket test endpoint shows filtered analysis in real-time
+- Frontend needs to provide UI for creating/editing AudioProcessingTemplates and ProcessedAudioSources
+- Filter pipeline is per-stream-instance (not shared) — stateful filters maintain independent state
+
+### Temporary breakages resolved
+- `_pick_channel()` removed from AudioColorStripStream — replaced by `_apply_filters()` which uses the filter pipeline
+- Channel/band handling in AudioValueStream now goes through filter pipeline
+- All "Phase 4 will wire..." comments resolved
+
+### Known deviations from plan
+- `AudioFilterPipeline.__init__` takes `List[FilterInstance]` only (not `AudioFilterRegistry` — uses the class-level registry directly via `AudioFilterRegistry.create_instance()`)
+- Hot-update uses explicit method calls from the route handler rather than an event-listener pattern — simpler and avoids the need for a subscription system