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/TODO.md

@@ -44,25 +44,41 @@ verified (PR https://git.jayfield.org/jens/JaySynth/pulls/1).
   `noteOn` with no matching `noteOff`) is untested.
 - [ ] **Polyphony/multiple simultaneous notes untested** - only ever a single
   held note in all smoke tests so far.
+- [ ] **`tests/run_tests.sh` never asserts specific expected values for
+  `PluginHost::load()`/`getNumInputChannels()`/`getNumOutputChannels()`/
+  `getNumParameters()`** - every test exercises them (they're printed in
+  the load banner), but nothing pins e.g. "JaySynth must report exactly
+  0 in / 2 out / 140 parameters," so a regression there would only be
+  caught if it also broke something else. Same underlying gap as "no
+  automated regression baseline comparison" above, just called out
+  separately since it's about the load-time metadata rather than the
+  rendered audio. See `tests/README.md`'s `PluginHost` coverage table.
 
 ## Investigate
 
-- [ ] **JaySynth's compiled VST2 wrapper never advertises chunk support to
-  the host, so real `.fxp`/`.fxb` sample files silently have no effect when
-  loaded generically.** Found while building `tests/run_tests.sh`: loading
-  a bundled sample under `extras/sounds/` via `--patch` produces byte-
-  identical output to not loading anything (confirmed by diffing
-  `--printParams`). The files are legitimately in VST2's opaque-chunk
-  ("FPCh") format, but JUCE 3.1.1's plugin-side VST wrapper
-  (`juce_VST_Wrapper.cpp`, compiled into `JaySynth.so`) never sets
-  `effFlagsProgramChunks` on the `AEffect` struct, so JUCE's own host-side
-  `VSTPluginInstance::usesChunks()` returns false and silently no-ops both
-  load and save. Not one of the tracked `TODO.md` (repo root) findings, and
-  not attempted here - fixing it means patching JUCE's own VST wrapper,
-  a bigger and riskier change than this pass's scope. See
-  `tests/README.md` for the full writeup; `tests/run_tests.sh`'s round-trip
-  tests work around it by using `testhost`'s own save output as the
-  fixture instead of an external sample file.
+- [ ] **Bundled sample `.fxp` files under `extras/sounds/` silently have no
+  effect when loaded via `--patch`** (confirmed by diffing `--printParams`
+  output with and without `--patch` - zero parameters differ), even though
+  loading doesn't crash. **Correction**: an earlier version of this entry
+  claimed this was because JaySynth's compiled VST2 wrapper never sets
+  `effFlagsProgramChunks`, so JUCE's host-side `usesChunks()` would see
+  false and skip the chunk mechanism entirely. That diagnosis was wrong -
+  disproved directly: `--saveBank`/`--savePatch` (the exact same generic
+  `AudioProcessor::getStateInformation` path) produce real `FBCh`/`FPCh`-
+  magic, GZIP-compressed-XML files (confirmed via hex dump and by feeding
+  the raw inner chunk bytes straight to `effSetChunk` via the new
+  `Vst2RawChunk` bypass, added specifically to rule this out - still no
+  effect). So `usesChunks()` genuinely is true, and `test_chunk_roundtrip`
+  in `tests/run_tests.sh` proves the real `bankEncodeXml`/`bankDecodeXml`
+  path round-trips correctly for files this build produces. The actual
+  cause of the *external* sample files failing is still unidentified -
+  most likely those specific (10+ year old) files use a compression or
+  XML-schema shape that `JaySynthAudioProcessor::setCurrentProgramState-
+  Information`/`getXmlFromBinary` no longer parses, not a host/plugin
+  capability mismatch. Not one of the tracked repo-root `TODO.md` findings.
+  Worth a closer look at some point (e.g. hex-diff one of these files'
+  decompressed XML against what this build produces), but not chased
+  further here. See `tests/README.md`'s "corrected finding" note.
 - [ ] **DPF-based plugins print a non-fatal assertion on load.** All three
   Zam*-vst.so plugins tested (built with the DISTRHO Plugin Framework) print
   `assertion failure: "fIsActive" in .../DistrhoPluginInternal.hpp` during