Fix cross-rate Preserve splices, re-stamp on host-rate change, name the rate refusal

The splice crossfade now counts output frames and stops before the ring's far end (this also fixes a lap at matched rate). The search strides by the rate ratio. The editor takes its time base from its own decode. Same-rate output is pinned to hashes from before the change.

src/shell/instrument/instrument_bake.cpp

@@ -128,14 +128,16 @@ BakeChainResult runBake(ReaSamplerProcessor& processor) {
 
     // The snapshot comes first: the default program's window is derived from the sound it
     // carries (a Gate release, a Trigger play span), not from a constant.
-    std::optional<SampleData> snapshot = processor.bakeSnapshot(sampleRate);
-    if (!snapshot) return fail("the loaded capture could not be decoded for the render");
+    ReaSamplerProcessor::BuiltCapture built = processor.bakeSnapshot(sampleRate);
+    if (built.rateRefused) return fail("cannot render: " + sourceRateRefusalText());
+    if (!built.sample) return fail("the loaded capture could not be decoded for the render");
+    SampleData& snapshot = *built.sample;
 
     // The note fires at the velocity the user has been auditioning at: three velocity curves
     // are live, so a sound dialed at 127 does not bake as one dialed at 40.
     const Velocity velocity = Velocity::of(processor.previewVelocity());
     const instrument::bake::PlannedBake planned = planBake(
-        resolveNote(defaultBakeProgram(*snapshot, sampleRate, dialed.bakeHold, velocity),
+        resolveNote(defaultBakeProgram(snapshot, sampleRate, dialed.bakeHold, velocity),
                     *tempo),
         sampleRate, rootNote);
     if (!planned.plan) {
@@ -146,7 +148,7 @@ BakeChainResult runBake(ReaSamplerProcessor& processor) {
     const instrument::bake::BakePlan& plan = *planned.plan;
 
     const instrument::bake::BakeAudio audio =
-        renderBake(std::move(*snapshot), plan, processor.masterGainLinear(),
+        renderBake(std::move(snapshot), plan, processor.masterGainLinear(),
                    dialed.limiterEnabled);
     if (audio.empty()) return fail("the offline pass produced no audio");