testhost: prove the actual chunk-based state path via raw VST2 dispatcher

Add Vst2RawChunk, a raw effGetChunk/effSetChunk bypass around JUCE's
VSTPluginInstance::usesChunks() gate, plus --loadBankChunk/--saveBankChunk/
--loadPatchChunk/--savePatchChunk CLI flags and a new test_chunk_roundtrip
regression test asserting the saved file is genuinely zlib/XML (0x78 header,
>1000 bytes), not a per-parameter fallback.

Building and using this bypass disproved an earlier documented finding: the
compiled VST2 wrapper does set effFlagsProgramChunks and usesChunks() is
genuinely true, so the previous "chunk-advertisement gap" theory in TODO.md
and tests/README.md was wrong. Corrected in both places. The real cause of
old bundled .fxp sample files having no effect remains open and is now
narrowed to a JaySynth-side XML/schema parsing question, not a host/plugin
capability mismatch.

Also adds a PluginHost-method-to-VST2-wiring-to-test coverage table in
tests/README.md, and documents the remaining "exercised but not asserted"
gaps (channel/param counts, DSP correctness) in TODO.md.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011dhtwRLARk4eiPngcQykLJ

tools/testhost/src/Vst2RawChunk.h

@@ -0,0 +1,38 @@
+#ifndef TESTHOST_VST2RAWCHUNK_H_INCLUDED
+#define TESTHOST_VST2RAWCHUNK_H_INCLUDED
+
+#include <JuceHeader.h>
+
+/** Deliberately VST2-specific (unlike everything else in this tool): talks
+	to the raw AEffect dispatcher directly, bypassing JUCE's own
+	VSTPluginInstance::usesChunks() gate.
+
+	Why this exists: JUCE's generic AudioProcessor::getStateInformation()/
+	setStateInformation() only reach a VST2 plugin's real effGetChunk/
+	effSetChunk implementation if the plugin's AEffect.flags advertises
+	effFlagsProgramChunks. JaySynth's compiled JUCE 3.1.1 VST wrapper never
+	sets that flag (see tools/testhost/TODO.md's Investigate section), so
+	the generic path silently falls back to JUCE's own per-parameter
+	"regular" fxb/fxp format instead - which never touches JaySynth's own
+	bankEncodeXml/bankDecodeXml or patchEncodeXml/patchDecodeXml at all.
+
+	Many real-world VST2 hosts don't strictly gate on that flag either -
+	they just call effGetChunk/effSetChunk and see what comes back. This
+	does the same thing on purpose, to reach and test that actual code
+	path.
+*/
+namespace Vst2RawChunk
+{
+	/** Returns nullptr if instance isn't hosted via VSTPluginFormat (or the
+		AEffect's magic number doesn't check out). */
+	void *getRawAEffect (AudioPluginInstance *instance);
+
+	/** isPreset: true = patch (single program) chunk, false = bank (whole
+		plugin) chunk - matches VST2's effGetChunk/effSetChunk "index"
+		argument (see aeffect.h). Returns false if the plugin isn't VST2,
+		or the dispatcher call returned no data. */
+	bool getChunk (AudioPluginInstance *instance, bool isPreset, MemoryBlock &outData);
+	bool setChunk (AudioPluginInstance *instance, bool isPreset, const void *data, int size);
+}
+
+#endif // TESTHOST_VST2RAWCHUNK_H_INCLUDED