Feat/wsola tests

.claude/skills/audio-nodes/SKILL.md

@@ -331,6 +331,16 @@ Do **not** gate `GraphObject::process()` on `isProcessable()` of inputs: CONDITI
 
 Tail-bearing nodes (Delay/Convolver/Biquad) need no special handling: while connected they stay `CONDITIONAL_PROCESSABLE`; after disconnect they stay `isProcessable()` via the tail override until the impulse decays, so settle does not zero them mid-tail.
 
+### WSOLA (pitchCorrection) source invariants
+Hard-won invariants for `AudioBufferBaseSourceNode::processWithPitchCorrection` and back-to-back scheduled joins (`b2.start(t1 + D/pr)`, join compensation L = 0):
+
+- **Feed real PCM only.** Never let `updatePlaybackInfo`-zeroed start-quantum frames enter the WSOLA analysis queue; mid-quantum starts must instead shift WSOLA's rendered output into `startOffset` after synthesis.
+- **EOF drain.** After natural PCM EOF, keep calling `drainOutput` for full quanta while it fills them; stop when a quantum is under-filled (stretcher dry).
+- **WSOLA whenever `pitchCorrection` is on.** Including `playbackRate == 1` — do not bypass to the non-WSOLA path at unity rate (buffer-source priming may still skip `|rate| == 1`).
+- **Queue EOF needs `endOfStream()`.** An empty queue without that signal is only an underrun; with it, the base drain path runs even when `isEmpty()`.
+
+`AudioFileSourceNode` still has its own prime/drain path (not yet shared).
+
 ---
 
 ## Implementing a New Node — Checklist

.claude/skills/utilities/SKILL.md

@@ -231,6 +231,22 @@ Higher-level DSP blocks. Read each header before use.
 
 ---
 
+### `WsolaTimeStretcher.h` — pitch-preserving time stretch
+
+Needs ~`getRequiredInputFrames()` of PCM in its internal queue before the first OLA
+iteration.
+
+- **File / AudioTag:** early `SeekDecoderDaemon` fills the SPSC; construction
+  `primeWsolaInputFromDecoder()` waits until the analysis queue is full (no wall-clock
+  deadline). No first-quantum warmup — process only feeds the current quantum.
+- **Buffer sources:** `AudioBufferSourceNode::start` calls `primeWsolaInput()` after
+  setting `vReadIndex_` (advances cursor by frames fed). Prefill happens only there;
+  `processWithPitchCorrection` feeds one quantum's input. Compare cold-start with DC
+  ones sample + abs/relative first-sound logs in `WsolaTimeStretcher`. Scratch sized
+  with `scratchBufferFrames(sampleRate)`.
+
+---
+
 ### `SpectrumAnalyser.h` — shared windowed-FFT magnitude spectrum
 
 Owns FFT scratch state (Blackman window, temp array, complex scratch, magnitude