Phase 32: add MIDI track CLAP, VST2 and VST3 instruments

docs/decisions/0011-midi-track-instruments.md

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+# 0011 — Prepared MIDI track instruments
+
+Accepted for Phase 32. Extend the modern C99 adapters with zero-audio-input,
+mono-output instruments and one event input. Keep graph effects separate from
+track bindings. Each assigned track owns one prepared instance; the existing
+instrument source sums their mixed output and the sine output of unassigned
+tracks. A stable saved live target prevents accidental broadcast/double playback.
+
+Bindings are copied metadata in the project/history model, serialized in v12.
+Loading metadata never executes modules. GUI edits prepare a candidate before
+publication, preserving the previous project on missing/invalid binaries. Existing
+quiescent plan retirement owns destruction; no module operation belongs in audio.
+
+Preallocate 256-frame audio scratch and 256 incoming events per chunk. Stable
+insertion orders reset, scheduled off/on and live events without callback sort or
+allocation. VST3 translates into a bounded 2304-event IEventList (2048 possible
+held keys plus 256 incoming events); panic expands held keys to note-offs. CLAP
+prefers MIDI where supported, otherwise native note events; VST2 uses MIDI ABI
+messages. Native CLAP and VST3 currently omit controller mapping. Existing
+32 simultaneous scheduled notes and 4096 stored notes remain validation bounds.
+
+Discontinuities send all-off and chase spanning notes with fresh note-ons.
+Panic suppresses already-started scheduled notes. Neither operation promises
+opaque DSP reconstruction or removal of release tails. Overflow/process errors
+silence the block and arm reset for the following render. Hosts cannot guarantee
+that third-party processing is realtime safe. Qualification covers original ABI
+fixtures; arbitrary third-party plugins, physical audio and MIDI remain unverified.