Small follow-ups after 0.19.0 (audit P3s, test gaps, doc nits) #1815

Small follow-ups carried over from #1779 after llamadart 0.19.0 (published 2026-11-08), plus non-blocking notes from the #1808 and #1812 audits. P3s, test gaps and doc nits only; bugs and P1/P2 get their own issues.

Open

• Echo Chrome supervisor output and accept mixed pass/fail summary #1796 audit: with fd 1 closed, the supervise_chrome echo writes into events.jsonl (behaviour bug, not reachable from CI). (PR #1828, pending merge)
• Qwen3.5-VL thinking check (CPU and GPU) → LiteRT-LM Qwen3.5 bundles never emit thinking (embedded template pre-closes <think>), failing litert-lm-chat-features-smoke on CPU and GPU #1827
• macOS support in litert_lm_library_smoke.dart. (PR #1828, pending merge)
• Model-store test: floor against Flutter 3.38. (PR #1828, pending merge)
• llamadart-native v0.9.0 release isn't immutable → moved to Make published releases immutable (v0.9.0 is mutable) llamadart-native#186 (maintainer settings change).
• Docs changelog bridge bullet tense ("Aligned …") — won't fix: released sections stay as published (AGENTS.md).
• update_core_changelog_native_pin guard tests — Pin the native pin changelog over-consumption guards with tests #1826.
• Column-0 #… continuation line stops the pin-bullet match early — Stop native pin changelog continuation only at real Markdown headings #1835 (accepted gap: no tab-after-hash test).
• capability_coverage.json embeddings note unasserted — won't fix: no consumer reads pack notes; its facts are tested where used (Drop the unused desktop libLiteRt and sweep LiteRT-LM follow-ups from #1815 #1819).

Done

• Sweep 0.19 test and tooling follow-ups from #1779 #1794 audit: run_local_e2e.dart SHA256 message, host-history test covers Windows — Sweep #1815 tooling, test and migration-doc follow-ups (A) #1817; pin-sync bullet replacement — Fix multi-line native pin changelog replacement and stale model-store CI comment #1818.
• Echo Chrome supervisor output and accept mixed pass/fail summary #1796 audit: blocking-restore test covers fd 2 — Sweep #1815 tooling, test and migration-doc follow-ups (A) #1817.
• Sweep #1779 test and tooling follow-ups (#1805, #1807 audits) #1810 audit: browser-default test, Safari driver stderr fd/timeout — Sweep #1815 tooling, test and migration-doc follow-ups (A) #1817.
• Stale ci.yml comment — Fix multi-line native pin changelog replacement and stale model-store CI comment #1818.
• MIGRATION.md 0.18.x -> 0.19.0 section — Sweep #1815 tooling, test and migration-doc follow-ups (A) #1817.
• libLiteRt dropped from Linux/Windows bundles; older custom runtimes still preload it — Drop the unused desktop libLiteRt and sweep LiteRT-LM follow-ups from #1815 #1819.
• S24 runtime-tag allow-list (v0.19.1, v0.19.1-1) — Drop the unused desktop libLiteRt and sweep LiteRT-LM follow-ups from #1815 #1819.
• Windows .xnnpack_cache teardown fallback unit-tested; suite root left on Windows (won't fix: after-exit reaper didn't work on CI) — Drop the unused desktop libLiteRt and sweep LiteRT-LM follow-ups from #1815 #1819.
• checkLoad legacy-override limitation documented — Drop the unused desktop libLiteRt and sweep LiteRT-LM follow-ups from #1815 #1819.
• LiteRT-LM dispose timeout (LiteRT-LM dispose can exceed the 5 s native free timeout on Linux CI #1814) — Wait for started LiteRT-LM native teardown instead of timing it out #1820.
• Custom v0.19.0/v0.19.1 desktop runtimes indistinguishable: marker shipped in Export an in-process LiteRT marker from the runtime bridge litert-lm-native#115/Sync WebGPU bridge assets to llama.cpp b9016 #117; release and llamadart gate tracked in Plan: LiteRT-LM in-process marker (litert-lm-native v0.19.1-2) and llamadart desktop embeddings gate #1824.