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

src/shell/instrument/instrument_bake.h

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+// instrument_bake — the instrument's half of the resample chain: render the dialed sound
+// offline, stage it outside the bank, ask the extension to bank it, then re-point and go
+// neutral. UI thread only; nothing here is on any audio path.
+//
+// The extension is REQUIRED. Without it the bank has no writer, so the affordance reads
+// Disabled and this refuses rather than half-baking.
+
+#pragma once
+
+#include <string>
+
+namespace reasampler::vst {
+
+class ReaSamplerProcessor;
+class ReaperBridge;
+
+// Whether a bake can run at all right now: a REAPER host, and the extension's bake action
+// registered. Cheap enough for the editor's sync tick, which is where the button's paint
+// state is decided — the control must never be enabled and then refuse.
+bool bakeAvailable(ReaperBridge& bridge);
+
+struct BakeChainResult {
+    bool ok = false;
+    std::string message;  // always populated — the editor prints it either way
+};
+
+// Runs the whole chain against `processor`. On failure NOTHING has changed: no temp file
+// survives, no bank entry was added, no assign was written, and the dialed state is
+// exactly as it was before the click.
+//
+// MUST NOT be called from a mouse handler. It invokes a REAPER action synchronously — an
+// offline landing nested inside a click, with the mouse captured, re-pointing the very
+// instance whose frame is on the stack. The editor defers it to its own timer tick.
+BakeChainResult runBake(ReaSamplerProcessor& processor);
+
+}  // namespace reasampler::vst