Audio: detect a pre-existing render stream's true sample rate (fix pitch)

Hooked audio mirroring played back pitch-shifted on games we inject into
that render at a non-device sample rate (e.g. Godot/Brotato render 44100 Hz
on a 48000 Hz endpoint via WASAPI AUTOCONVERTPCM). We attach to an
already-running game, so the render-hook never saw its IAudioClient::
Initialize and assumed the device mix format -- right channels/bits, wrong
rate -- so 44100 audio was rendered as 48000 (+~1.5 semitones).

Fix: treat a pre-existing client's format as a guess and measure its true
sample rate from the render cadence (frames/sec over a steady-state window,
snapped to the nearest standard rate) before publishing it, deferring
capture until verified. Discard the first measurement window so the
buffer-fill burst at attach time doesn't over-count. Streams created after
we inject still carry their exact Initialize format.

Channels/bit-depth genuinely can't be recovered for a pre-existing client:
AUTOCONVERTPCM hands GetBuffer a fixed staging buffer (no buffer stride to
measure -- confirmed empirically) and WASAPI exposes no API for the format.
They stay the device-mix guess, which is correct for the common case
(engines render stereo float, matching the endpoint). To keep a wrong guess
safe, a VirtualQuery clamp stops the capture copy from ever over-reading the
source buffer when the guessed bytes/frame is too large.

Surface all of this: a per-stream AudioFormatState (known / measuring /
measured rate (ch/bits assumed)) in HookStatus, shown in the Audio panel for
the hooked path and as "device endpoint (known)" for loopback; clear hook
logs; and enriched mirror status strings. Documented in README (Limitations
+ Lessons learned). The loopback fallback was always correct (post-mix at
the device format).

Tests: extract a shared, configurable ToneSource (used by coop_tone and the
hook self-test); coop_tone takes rate/channels/bits/format args. Rewrite
audio_hook_test to a format matrix x both code paths -- see-init (exact) and
guess (rate measured) -- plus a byte-incompatible guess that asserts the
clamp keeps capture safe. The matrix caught the attach-burst over-count.
audio_loopback_test now spawns coop_tone at several source formats to
confirm loopback is format-agnostic. 11/11 x64 + 3/3 x86 pass.

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

host/src/audio_panel.cpp

@@ -14,6 +14,10 @@ namespace coop
 namespace
 {
 
+const ImVec4 kGreen(0.4f, 1.0f, 0.4f, 1.0f);
+const ImVec4 kAmber(1.0f, 0.8f, 0.3f, 1.0f);
+const ImVec4 kRed(1.0f, 0.45f, 0.4f, 1.0f);
+
 const char* format_tag_name(std::uint32_t tag)
 {
 	switch (tag)
@@ -29,6 +33,36 @@ const char* format_tag_name(std::uint32_t tag)
 	}
 }
 
+// How the hooked backend learned a stream's format (drives the pitch correctness).
+const char* audio_format_state_name(std::uint32_t state)
+{
+	switch (state)
+	{
+	case AudioFormat_Exact:
+		return "known (from game)";
+	case AudioFormat_Measuring:
+		return "measuring rate...";
+	case AudioFormat_Measured:
+		return "measured rate (ch/bits assumed)";
+	default:
+		return "unknown";
+	}
+}
+
+ImVec4 audio_format_state_color(std::uint32_t state)
+{
+	switch (state)
+	{
+	case AudioFormat_Exact:
+	case AudioFormat_Measured:
+		return kGreen; // format trustworthy -> correct pitch
+	case AudioFormat_Measuring:
+		return kAmber; // still verifying the rate
+	default:
+		return kRed; // unknown
+	}
+}
+
 } // namespace
 
 void AudioPanel::draw_ui(const HookStatusView& status, bool debug_details)
@@ -71,12 +105,25 @@ void AudioPanel::draw_ui(const HookStatusView& status, bool debug_details)
 	{
 		const AudioMirror::Source src = mirror_.source();
 		const bool hooked = src == AudioMirror::Source::Hooked;
-		ImGui::TextColored(ImVec4(0.4f, 1.0f, 0.4f, 1.0f), "Mirroring  %u Hz, %u ch",
-		                   mirror_.sample_rate(), mirror_.channels());
+		ImGui::TextColored(kGreen, "Mirroring  %u Hz, %u ch", mirror_.sample_rate(), mirror_.channels());
 		ImGui::Text("Source:");
 		ImGui::SameLine();
-		ImGui::TextColored(hooked ? ImVec4(0.4f, 1.0f, 0.4f, 1.0f) : ImVec4(1.0f, 0.8f, 0.3f, 1.0f), "%s",
-		                   mirror_.source_name());
+		ImGui::TextColored(hooked ? kGreen : kAmber, "%s", mirror_.source_name());
+
+		// Where the rendered format came from -- so it's clear the playback pitch is right.
+		// Hooked: the primary stream's provenance (exact / measured). Loopback: the audio is
+		// captured post-mix at the device endpoint format, so it's always known-correct.
+		ImGui::Text("Format:");
+		ImGui::SameLine();
+		if (hooked)
+		{
+			const std::uint32_t st = status.audio_streams[0].format_state; // [0] is the primary
+			ImGui::TextColored(audio_format_state_color(st), "%s", audio_format_state_name(st));
+		}
+		else
+		{
+			ImGui::TextColored(kGreen, "device endpoint (known, post-mix)");
+		}
 		ImGui::Text("Buffered: %4u ms", mirror_.buffered_ms());
 	}
 	const std::string mirror_status = mirror_.status();
@@ -132,11 +179,12 @@ void AudioPanel::draw_ui(const HookStatusView& status, bool debug_details)
 	const double now = ImGui::GetTime();
 	const bool resample = (now - rate_base_time_) >= 0.5; // recompute frames/s ~2x a second
 	if (rows > 0 &&
-	    ImGui::BeginTable("audio_streams", 5, ImGuiTableFlags_Borders | ImGuiTableFlags_SizingFixedFit))
+	    ImGui::BeginTable("audio_streams", 6, ImGuiTableFlags_Borders | ImGuiTableFlags_SizingFixedFit))
 	{
 		ImGui::TableSetupColumn("#");
 		ImGui::TableSetupColumn("role");
 		ImGui::TableSetupColumn("format");
+		ImGui::TableSetupColumn("source");
 		ImGui::TableSetupColumn("frames");
 		ImGui::TableSetupColumn("live");
 		ImGui::TableHeadersRow();
@@ -170,6 +218,9 @@ void AudioPanel::draw_ui(const HookStatusView& status, bool debug_details)
 			ImGui::Text("%u Hz %uch %u-bit %s", s.sample_rate, s.channels, s.bits,
 			            format_tag_name(s.format_tag));
 			ImGui::TableNextColumn();
+			ImGui::TextColored(audio_format_state_color(s.format_state), "%s",
+			                   audio_format_state_name(s.format_state));
+			ImGui::TableNextColumn();
 			ImGui::Text("%llu", static_cast<unsigned long long>(s.frames_rendered));
 			ImGui::TableNextColumn();
 			if (live)