RustTts is frozen pre-floravox: ABI mismatch on shipped DLL + floravox catch-up

[willwade]

Summary

The RustTts integration layer is frozen at 2026-08-21 (e80eca2) — the moment floravox landed in rust-tts-wrapper (first commit 2026-08-20). Everything since (floravox engine, lexicon routing, measured boundaries, floravox-core 0.8.x fixes) is absent. There is also a latent ABI mismatch shipping today.

Reference state: VoiceGarden-SPD consumes rust-tts-wrapper v0.5.2 (floravox-core 0.8.4, moving to 0.8.5) directly from the tagged git dep with floravox-lexicons.

Critical

1. ABI mismatch on tts_set_on_boundary

• VoiceGarden.UI.csproj:23 pins RustTtsWrapper.Bindings 0.3.20
• Our loader/thunk (updated in e80eca2) target the post-consolidation (rust-tts-wrapper#31) 7-arg callback: (word, charOffset, charLen, startS, endS, estimated, ud)
• The 0.3.20 DLL exports the same symbol with the old 4-arg signature: (word, startS, endS, ud)
• GetProcAddress succeeds (symbol name unchanged), so RustTtsLoader cannot detect it. The Rust side invokes the thunk with 4 args; charOffset / charLen / estimated are read from never-set registers → garbage offsets or crashes in the boundary lambda (TTSEngine.cpp:998)

Fix: bump NuGet to 0.5.0+ (consolidated signature verified) and add an ABI canary — e.g. resolve tts_set_on_mark (exists only ≥ 0.5.x) and refuse to load the DLL without it.

2. CI ships a nondeterministic DLL

• .github/workflows/msbuild.yml:228 grabs Get-ChildItem ~/.nuget/packages/rustttswrapper.bindings -Recurse -Filter rust_tts_wrapper.dll | Select -First 1 — whichever cached version sorts first, decoupled from the csproj pin
  Fix: pin the exact runtimes/win-{x64,x86}/native path from the referenced package version.

3. The NuGet package has no floravox

• rust-tts-wrapper publish.yml builds the Windows DLL with sapi,cloud,sherpaonnx only — no floravox, no floravox-lexicons. Even after a pin bump, SAPI cannot create a floravox engine.
• Also NuGet stops at 0.5.0 while the wrapper is at v0.5.2 — releases aren't published consistently.

Fix (wrapper side, tracked separately): add floravox-lexicons to the Windows NuGet build matrix, tag, publish.

Floravox catch-up (SPD parity)

Gap	SPD has	SAPI needs
Local engine	floravox engine via rust-tts-wrapper v0.5.2	Route piper-family voices to engine id floravox (needs wrapper NuGet fix above)
Word boundaries	Measured (floravox duration tensor)	Currently estimated-only via sherpaonnx path; TTSEngine.cpp:998 receives but ignores the estimated flag — use it to gate wpm/silence compensation
Bookmarks	marks → SPD events	tts_set_on_mark not resolved in RustTtsLoader.cpp — map it to SPEI_TTSBOOKMARK
Model install hardening	sidecar generate_sidecar() re-run, phoneme_id_map casefold, language_code sidecar (floravox 0.8.5)	Port equivalent logic to the UI model installer for local voices
Version hygiene	pinned tag + bump discipline	Pin NuGet to wrapper releases, note the mapping in release notes

Code nits

• RustTtsEngine.cpp:57-63 — hardcoded debug dump to C:\Users\WillWade\AppData\Local\Temp\vg_ssml_debug.txt on every SpeakSsml. Leftover debug; remove.
• TTSEngine.cpp:1037 — m_rustTtsUseSsml = false always, making the SpeakSsml path (lines 336/366) dead code — despite the integration plan calling the C++ BuildSSML() "superior" and c322489 adding PUA-sentinel SSML normalization. Decide: pass SSML for engines that support it (floravox, Azure), or delete the dead path.
• TTSEngine.cpp:1001 — boundaries with charOffset < 0 are dropped entirely; consider emitting audio-time-only events instead of losing them.

Suggested order

1. Remove debug file writes; fix CI DLL selection (trivial)
2. Bump NuGet 0.3.20 → 0.5.0+ and add the ABI canary in RustTtsLoader
3. Wrapper: Windows NuGet build with floravox-lexicons, tag, publish (blocks 4)
4. Route local voices through the floravox engine (measured boundaries + marks)
5. Port SPD installer hardening for local model sidecars

No architecture change required — the C-API-over-NuGet approach is correct for C++ (same reasoning as AVSynth's dylib). This is version rot plus a never-wired floravox path.