[leehack]

Summary

• Pins litert-lm-native v0.19.1-3 (owner PR #118, owner commit ed8ffe33), which no longer ships the unused LiteRT Metal accelerator on iOS and macOS.
• Root cause: v0.19 Apple LiteRtLm links its GPU accelerator statically (iOS Metal, macOS WebGPU). LiteRT's gpu_registry searches shared libraries only when no static one registered, so LiteRtMetalAccelerator was never opened.
• Drops the LiteRtMetalAccelerator target from the Apple companion Package.swift and its entries from the hook pins, macOS runtime inventory and prepare script; sync_native_release_pins.py learns the v0.19 Metal transition (kept while every iOS bundle ships it, removed once none does, refused if only some do).
• Admits v0.19.1-3 in the LiteRT-LM library smoke and the S24 binding: its Android arm64 archive is byte-identical to v0.19.1-2 (all files, SHA-256 compared).
• Closes #1798.

Size	Before (v0.19.1-2)	After (v0.19.1-3)
macOS hook dir litert_lm/<ver>/macos/arm64	86,528 KiB	78,044 KiB
macOS libLiteRtMetalAccelerator.dylib	8,685,472 B	removed
iOS LiteRtMetalAccelerator.framework	8,145,344 B device / 7,293,672 B simulator	removed
SwiftPM LiteRtMetalAccelerator xcframework zip	8,404,372 B	removed
runtime tarball macOS / iOS device / iOS sim	30,092,586 / 33,222,309 / 33,861,362 B	26,836,736 / 28,042,822 / 28,769,500 B

Production-readiness scope

• User-facing scope: smaller iOS apps and macOS hook bundle; GPU generation unchanged; iOS LiteRT-LM frameworks no longer carry the User Defaults required-reason API.
• Supported platforms/paths: iOS and macOS Apple LiteRT-LM (hook and SwiftPM companion). Other platforms only get the new tag.
• Unsupported or intentionally unavailable paths: iOS physical-device GPU is NOT qualified (no physical device available); only the iOS simulator Metal path was exercised. Custom LLAMADART_LITERT_LM_LIB_DIR runtimes older than v0.19.1-3 still load; the Metal accelerator is no longer required from them.
• Out of scope / follow-ups: #1911 (other macOS/iOS libraries that text GPU never opens).

Completeness checklist

• Declared scope is fully implemented, or explicitly reduced above.
• Unsupported platform/option combinations fail loudly with actionable diagnostics or are clearly documented as unavailable.
• Public API docs, README/website docs, examples, support matrices, and changelog entries are updated where relevant.
• Regression coverage covers the original issue plus key negative/version-skew paths where relevant.
• Public capability changes update the validation coverage registry with a pack or a reasoned, issue-linked exemption; inventory checks pass (N/A: no capability change; validation_coverage_test.dart passes).
• Security/privacy review completed: no secrets, bearer tokens, signed URLs, or raw secret-bearing paths leak through logs, cache keys, metadata, errors, or snapshots.
• Follow-up work that is useful but not required for this PR is tracked in GitHub Issues: #1911.

PR type guidance

• Bugfix PR: root cause above. Regression coverage: updated pin, inventory, Package.swift and prepare-script tests plus sync-script transition tests (tool/native/test_sync_native_release_pins.py). Affected platforms: iOS and macOS.

Test Plan

• dart run tool/prepare_workspace.dart
• dart format --output=none --set-exit-if-changed .
• dart analyze
• dart test -p vm -j 1 --exclude-tags local-only (only the 6 Windows registry tests fail locally: pwsh is not installed here)
• dart test -p chrome --exclude-tags local-only
• coverage-lib: 93.67% lines
• Other: check_native_release_digests.dart (8 LiteRT-LM bundles match v0.19.1-3), verify_release_docs_versions.dart (reports the expected pending companion bump), (cd packages/llamadart_litert_lm_flutter && flutter test), owner CI run 42858395264 and release run 42879370634

Matrix Evidence

Matrix row	Scope covered	Platform / model / backend	Result	Evidence / notes
native-sync-python-suites	pin sync policy, header and binding sync suites	macOS, Python 3.13	PASS	162 pin-sync tests plus the other three suites
coverage-lib	lib/ line coverage	macOS VM	PASS	93.67% (33,570/35,837)
litert-lm-chat-features-smoke	real .litertlm chat, tool loop, thinking	macOS arm64, Qwen3-0.6B, --backend gpu, hook cache v0.19.1-3	PASS	log registers GPU WebGPU statically; no Metal file in the hook cache
macos-arm64-runtime-smoke	LiteRT-LM GPU from the owner candidate	macOS arm64, Qwen3-0.6B, litert_lm_chat_smoke.py --backend gpu	PASS	answer "4", candidate from run 42858395264
ios-simulator-smoke	LiteRtLm framework Metal generation without the accelerator	iOS 26.5 simulator (iPhone 17 Pro), Qwen3-0.6B, gpu	PASS	static GPU Metal registered, Metal device created, reply "42"; evidence in llamadart-evidence/litert-lm-native-118/
ios-arm64-device-smoke	iOS device	none	N/A	no physical device; device GPU not qualified
release-companion-pub-gate	companion pub availability	n/a	N/A	companion not released here; verify_release_docs_versions.dart reports the pending bump for release prep

Review Notes

• Independent review status: PASS at 6a0d0f9a (fresh auditor session, 0 P1/P2). The audit also checked a merge with current main 2cfb9361: it merges cleanly, analyze is clean, and 2711 targeted tests pass. Evidence: llamadart-evidence/pr-1913/; evaluator exit 2.
• CI status / head SHA: green (38 pass, 8 skipped) at head 752b027fbb1d5b4481f78084901ca484a4f08513, a merge of main 2cfb9361 into the audited 6a0d0f9a. The merge was needed because GitHub ignores the changelogs' union merge driver. The delta re-audit passed: only the union-merged changelogs differ, all mutants were re-run, and the evaluator exits 2.

High-risk regression review

• Classification: high-risk (artifactConsumer, backendRuntime)
• Implementation task: this PR (draft)
• Independent blocking QA task: PASS at 6a0d0f9a, 0 P1/P2. Maintainer merge approval given ("Merge Drop the unused LiteRT-LM Metal accelerator from Apple bundles #1913").
• Exact head / current base: 6a0d0f9a1a1539a1f65a50b1078d80c490c21403 / 33e00f5a7a
• Production-branch deletion, bypass, or miswire proof: the auditor killed 8/8 Dart mutants and 8/9 sync-script mutants; M9 is equivalent in practice and logged on 0.19.x audit follow-ups (index) #1861; the removed inventory entries are covered by the updated hook, Package.swift and prepare-script tests
• Affected-family real-model/artifact evidence: Qwen3-0.6B .litertlm on macOS GPU and the iOS simulator against the owner candidate and published v0.19.1-3 inventory; Metal absence verified in the published tarballs
• Explicit unavailable-family or other N/A evidence: iOS physical-device GPU unavailable (no device)
• Known PR-caused P1 regressions: 0
• Unresolved review threads: 0

[github-actions]

Chat app preview removed for leehack/llamadart-chat-pr-1913.