Module validate 

Pre-flight environment check for the thin-rebuild pipeline.

Catches the “fat build was for one toolchain, the dev loop is now using another” class of breakage before subsecond::apply_patch runs and segfaults the device. The check is deliberately small — we only assert what’s necessary to keep the same captured rustc invocation viable:

1. The current rustc still supports the target triple the fat build was for. If a rustup toolchain change between the fat build and the first edit dropped the Android target, we want a clear error here, not a cryptic linker failure later.

Things we deliberately do NOT validate:

• Exact rustc version match. Patch dylibs survive across patch-level rustc bumps in practice (subsecond is pretty tolerant); demanding strict equality would break workflows where rustup update is a frequent occurrence. Major version regressions WILL be surfaced by the thin rebuild itself (rustc returns non-zero), so we let that path do the talking.

• Sysroot stability. Same reasoning — rustc verifies its own sysroot at compile time. We don’t add a redundant probe.

Functions

ensure_target_supported

Spawn rustc --print=target-list and verify triple shows up. Synchronous on purpose — runs once per dev-server boot, not per patch.

extract_target_triple

Pull the value passed to --target (or --target=...) out of a rustc argv. Pure helper — same shape as extract_crate_name in the shim.

validate_environment

Run the pre-flight checks. Returns Ok(()) if it’s safe to call thin_rebuild; otherwise Err with a message a human can act on.