Recover a guessed stream's channels + bit depth by correlation too (step b)

Extends the two-path correlation from rate-only to the full layout, removing the
"channels/bit-depth assumed = device" limitation. correlate_format tries each
candidate de-interleaving (float32 / int16; mono..7.1) of the hook capture, runs
the rate correlation per layout, and keeps whichever aligns with the loopback;
a wrong de-interleaving is noise and won't.

The catch: the hook can't know a guessed stream's real frame size, so its verify
tap pads each render buffer to the device block -- which over-reads stale staging
bytes for a stream with fewer channels/bits, scrambling the audio. So the tap is
now self-describing: it prefixes each buffer with its frame count
([count][count*device_block bytes]), and the host strips the padding per candidate
layout (take the real count*real_block of each chunk) before de-interleaving.

- audio_correlate.hpp: ChunkedCapture + chunk-aware correlate_format + candidate
  layouts; absolute-margin confidence gate (the true layout scores ~1.0, a truly
  ambiguous alternative within ~0.001 -- 2ch@R == 1ch@2R for identical channels --
  is correctly left unconfident).
- audio_hook.cpp: chunked verify tap (free-space-checked so framing can't tear).
- audio_format_verifier: parse chunks; recover_layout path. AudioMirror now corrects
  the full format.
- audio_correlation_test: layout recovery from padded chunks (stereo float, 16-bit
  PCM, 5.1, mono). audio_verify_test gains scenario (b): 2ch on a multichannel
  endpoint with distinct per-channel content (new env-gated ToneSource mode) ->
  recovers ch=2/32-bit float end-to-end.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

host/src/audio/audio_format_verifier.cpp

@@ -99,6 +99,35 @@ void drain_ring(AudioRingHeader& ring, std::vector<BYTE>& scratch)
 	}
 }
 
+// Parse the hook's self-describing verify stream -- a sequence of [u32 frame-count][count*stride
+// bytes] chunks -- into a ChunkedCapture. `stride` is the device block_align (what the hook padded
+// each buffer to). Stops at the first truncated/garbled record.
+ChunkedCapture parse_chunks(const std::vector<BYTE>& raw, unsigned stride)
+{
+	ChunkedCapture cap;
+	cap.stride = stride;
+	if (stride == 0)
+	{
+		return cap;
+	}
+	std::size_t off = 0;
+	while (off + sizeof(std::uint32_t) <= raw.size())
+	{
+		std::uint32_t count = 0;
+		std::memcpy(&count, raw.data() + off, sizeof(count));
+		off += sizeof(count);
+		const std::size_t payload = static_cast<std::size_t>(count) * stride;
+		if (count == 0 || off + payload > raw.size())
+		{
+			break; // truncated or garbled -> stop
+		}
+		cap.counts.push_back(count);
+		cap.bytes.insert(cap.bytes.end(), raw.data() + off, raw.data() + off + payload);
+		off += payload;
+	}
+	return cap;
+}
+
 } // namespace
 
 FormatVerification verify_stream_format(DWORD pid, AudioRingHeader* ring, unsigned window_ms, bool recover_layout)
@@ -156,31 +185,53 @@ FormatVerification verify_stream_format(DWORD pid, AudioRingHeader* ring, unsign
 	ring->verify_capture.store(0, std::memory_order_release);
 	drain_ring(*ring, scratch); // leave the ring clean for the real capture that follows
 
-	// The hook bytes are at the guessed layout = the device channels/bits (the assumption the
-	// cadence path also makes). Decode both captures with that layout and correlate.
-	const std::vector<float> hook_mono = to_mono(hook_bytes, dev);
+	// The loopback is at the KNOWN device layout. Decode it to mono ground truth. The hook stream
+	// is self-describing chunks ([count][padded payload]); parse them at the device block.
 	const std::vector<float> loop_mono = to_mono(loop_bytes, dev);
+	const unsigned dev_block = dev_wfx->nBlockAlign;
+	const ChunkedCapture cap = parse_chunks(hook_bytes, dev_block);
+	const std::size_t need = dev.rate / 5; // require >= ~200 ms of usable audio on both sides
+	const std::size_t hook_frames = dev_block != 0 ? cap.bytes.size() / dev_block : 0;
 	CoTaskMemFree(dev_wfx);
 
 	if (const char* dbg = std::getenv("COOP_VERIFY_DEBUG"); dbg != nullptr && dbg[0] == '1')
 	{
-		std::fprintf(stderr, "[verify] dev=%uHz/%uch/%ubit tag=%u hook_frames=%zu loop_frames=%zu\n", dev.rate,
-		             dev.channels, dev.bits, dev.tag, hook_mono.size(), loop_mono.size());
+		std::fprintf(stderr, "[verify] dev=%uHz/%uch/%ubit blk=%u chunks=%zu hook_frames=%zu loop=%zu layout=%d\n",
+		             dev.rate, dev.channels, dev.bits, dev_block, cap.counts.size(), hook_frames, loop_mono.size(),
+		             recover_layout ? 1 : 0);
 	}
-	const std::size_t need = dev.rate / 5; // require >= ~200 ms of usable audio on both sides
-	if (hook_mono.size() < need || loop_mono.size() < need)
+	if (loop_mono.size() < need || hook_frames < need)
 	{
 		return result; // not enough non-silent audio captured (game quiet, or stream wasn't a guess)
 	}
 
-	const RateCorrelation rc = correlate_rate(hook_mono, loop_mono, dev.rate, standard_audio_rates());
-	result.ok = rc.ok;
-	result.rate = rc.rate;
-	result.score = rc.score;
-	// Channels/bit-depth stay the device assumption here; step (b) recovers them.
-	result.channels = dev.channels;
-	result.bits = dev.bits;
-	result.format_tag = dev.tag;
+	if (recover_layout)
+	{
+		// Step (b): recover channels + bit depth too, by trying candidate de-interleavings of the
+		// (de-padded) hook bytes and keeping whichever (layout, rate) correlates with the loopback.
+		const FormatCorrelation fc =
+		    correlate_format(cap, loop_mono, dev.rate, standard_audio_rates(), standard_audio_layouts());
+		result.ok = fc.ok;
+		result.rate = fc.rate;
+		result.score = fc.score;
+		result.layout_ok = fc.ok;
+		result.channels = fc.channels;
+		result.bits = fc.bits;
+		result.format_tag = fc.tag;
+	}
+	else
+	{
+		// Step (a): rate only, assuming the hook layout matches the device (common stereo case), so
+		// the de-padded payload is already clean device-layout audio.
+		const std::vector<float> hook_mono = to_mono(cap.bytes, dev);
+		const RateCorrelation rc = correlate_rate(hook_mono, loop_mono, dev.rate, standard_audio_rates());
+		result.ok = rc.ok;
+		result.rate = rc.rate;
+		result.score = rc.score;
+		result.channels = dev.channels;
+		result.bits = dev.bits;
+		result.format_tag = dev.tag;
+	}
 	return result;
 }