Ξ-W2-T1: the resample bake chain — instrument renders, extension banks, one click re-points and resets

src/core/instrument/bake/CLAUDE.md

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+# src/core/instrument/bake — the resample bake's pure half
+
+## Scope
+
+The offline pass that turns the dialed instrument into a file, and the reset that hands the
+instrument back neutral afterwards. A fifth peer of `engine/` / `map/` / `note/` / `ui/`
+under `core/instrument/`, pure by the same rule — no REAPER types, no VST3 types, no host.
+
+It is neither engine (it owns no voice), mapping (it resolves no capture), nor note (it
+holds no program): it is the *composition* of the three into one render, plus the one
+decision about what the render made obsolete.
+
+## Invariants
+
+- **The bake renders on its OWN engine, never the live one.** `renderBake` takes its
+  `SampleData` BY VALUE and detaches `SampleData::live` before constructing a `VoiceEngine`
+  for the render alone. Two consequences, both load-bearing: the audio thread's live block
+  can neither be observed nor disturbed by a bake, and a repeated bake of one dialed sound
+  is byte-identical because nothing outside the passed value can vary between runs.
+- **The window bounds the render; the envelope does not.** Termination is structural — the
+  loop runs to `BakePlan::totalFrames` and stops. That is why a Gate bake with a sustain
+  loop active terminates: the gate is released at `noteOffFrame` so the tail is real, but
+  even a pathological envelope cannot run past the window.
+- **The block size is fixed here, not taken from the host.** A block boundary is where the
+  engine re-observes state, so pinning it is part of what makes two bakes on two hosts
+  produce the same bytes.
+- **A degenerate window is refused, not rendered.** `planBake` returns nullopt for a
+  collapsed window, a non-positive rate, or a window that rounds to no frames.
+- **The reset's survive list is written out; everything else defaults.** `resetAfterBake`
+  starts from a default-constructed parameter set and copies back only the mapping facts.
+  A parameter added later therefore resets by default — the safe direction, since
+  under-resetting applies the same processing twice while over-resetting costs a re-dial.
+  A new mapping fact must be added to the copy list explicitly.
+
+## Modules
+
+- `bake_plan` — `defaultBakeProgram` (the program a bake uses until the capture-signal
+  popup ships; its release tail exists so the bake is not truncated at note-off),
+  `BakePlan` (the frame window plus its two event frames), and `planBake`, the one
+  `ResolvedNote` + rate -> frames resolution.
+- `bake_render` — `BakeAudio` and `renderBake`: the programmed note through the sample's
+  own voice path, summed into an interleaved buffer at the source's own channel count.
+- `bake_reset` — `BakeReset` and `resetAfterBake`: the ratified reset scope, answered for
+  both the parameter set and the post-mixer master gain.
+
+## Gotchas
+
+- Frame 0 of the render is the start of the CAPTURED FILE, not note-on. A capture that
+  opens before the note has `noteOnFrame > 0` and silence ahead of it.
+- The render's channel count is the loaded `SampleData`'s, which is already the instance's
+  channel-mode decision — a mono-mode instance bakes mono, and that is faithful, not a fold.