Phase 6: Add WAV clips, graph playback and bounded recording

docs/decisions/0005-preloaded-audio-and-recording.md

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+# 0005: Preloaded WAV clips and control-thread recording consumer
+
+Status: accepted for Phase 6.
+
+Use a small bounded C99 WAV decoder/writer for PCM16/24/32 and IEEE float32,
+mono/stereo, instead of adding libsndfile in this milestone. This avoids a new
+build/runtime/license dependency, keeps the supported format surface explicit,
+and enables malformed-input tests. It also limits format coverage; a future
+codec library needs its own dependency and licensing review.
+
+Compile musical clip ranges and decoded, shared-per-path mono buffers while
+stopped. The callback renders the timeline into a preallocated buffer consumed
+by an explicit graph source node, preserving graph routing rather than mixing
+outside the graph. The old snapshot remains until candidate preparation succeeds.
+All track clips currently share one source; per-track routing/mixing is deferred.
+
+Use a bounded SPSC ring for callback input capture, with release/acquire index
+publication and a GUI/control-thread consumer. This adds no worker-thread
+dependency; a two-second ring tolerates normal 100 ms polling but exposes
+overflow if the GUI or disk stalls. Sticky errors prevent silent time compression.
+Finalization requires callback quiescence. Future long-session/background I/O
+work can reuse the ring contract with a dedicated consumer.
+
+Store external absolute paths in version 2 metadata and retain version 1 loads.
+Missing/unreadable assets are reported silence, with explicit relinking; portable
+bundles and content-addressed assets are deferred. See AUDIO_FILES.md for limits.