C API: follow-ups from the FFI audit (ABI version, options handle, last-error, handled-error entry point) #39

The C API audit (docs/ffi-audit.md, #21) produced a prioritised change list; the generated-header ABI gate is in place but these items are still open:

1. An ABI/version query so hosts can check compatibility at load time.
2. A launch options handle (data directory, native-crash capture on/off, scrubbing, rate limiting, release health, launch-recovery budget, flush-at-exit) instead of the current endpoint-only variant. The data directory is the blocker for mobile hosts.
3. A last-error retrieval entry point (thread-local message for the most recent non-OK status).
4. A handled-error entry point that accepts host-supplied frames (the existing exception call is a lossy message capture with a Rust backtrace).
5. Expose shutdown, the opt-in termination flush (feat: defined shutdown/flush contract and opt-in SIGTERM/SIGINT flush (#8) #31) and a storage-status / degraded-state accessor (feat: defined data-directory fallbacks and in-memory mode for read-only/ephemeral file systems (#9) #24).
6. Header documentation pass: the generated # Safety text states the Rust unsafety rule for string pointers, not the success-path nullability rules documented in the audit.

Freeze the surface only after these land.

🤖 Generated with Claude Code