[leehack]

Summary

• 0.19.x audit follow-ups (index) #1861 items from the Name the bundle template in a failed C API 1.0 LiteRT-LM chat send #1875 audit: pin the C API 1.0 send-failure message text, restore isA<LlamaException>() for the stage-16 variant, and keep the native stack trace when LiteRtLmV1Turn._start wraps a failure (Error.throwWithStackTrace).
• Stacked on #1875 (head 03d50e4); retarget to main once it merges.

Production-readiness scope

• User-facing scope: None; tests and error plumbing only.
• Supported platforms/paths: LiteRT-LM C API 1.0 (macOS/Linux VM)
• Unsupported or intentionally unavailable paths: N/A
• Out of scope / follow-ups: Refs #1861 (tick after merge); plan #1874.

Test Plan

• dart format --output=none --set-exit-if-changed and dart analyze on touched dirs
• TMPDIR=$(mktemp -d) dart test -p vm -j 1 test/unit/backends/litert_lm/litert_lm_v1_conversation_test.dart (45 pass)
• Full CI: stacked or not on main, run via workflow_dispatch of ci.yml (see comment)

Review Notes

• Mutants: wrap using toString() fails the text test; dropping throwWithStackTrace fails the new trace assertion (failed first); non-LlamaException at stage 16 fails the restored assertion

High-risk regression review

• Classification: high-risk (backendRuntime)
• Implementation task: this PR
• Independent blocking QA task: pending

[leehack]

Landed on main via batch integration PR #1895 (rebase merge, main ba4e0e1b; tree identical to the audited integration head 5ffd1224).