[leehack]

Summary

• Repins LiteRT-LM to litert-lm-native v0.19.1-5 (prerelease promoted from prepare-only run 43521953259). Android arm64/x64 libLiteRtLm.so links the WebGPU top-k sampler again (litert-lm-native#121).
• Fixes #1998: on the WebGPU/Vulkan route (no loadable OpenCL) a GPU engine loaded and then failed at the first token with "Can not find OpenCL library on this device" (0.18.0 through 0.19.9). Plan: #1995.
• Pins written by sync_native_release_pins.py --litert-lm-tag v0.19.1-5; hand edits: library smoke admission, tag literals in tests, two SKILL.md, README and website pin text, maintainer sync note, S24 qualifier admission, changelog and known-platform-issues.
• Release prep, not this PR: llamadart_litert_lm_flutter 0.19.10 with floor llamadart: '>=0.19.10 <0.20.0' (cores up to 0.19.9 treat a -5 companion as a different build). verify_release_docs_versions.dart reports that bump as pending, as expected.

Production-readiness scope

• User-facing scope: Android LiteRT-LM GPU generation works without a loadable OpenCL library; apps on 0.19.10 get the fixed runtime (Android has no runtime override, so no code guard is needed).
• Supported platforms/paths: Android arm64 (S24 evidence below), Android x64 (same fix, no device run), all other LiteRT-LM platforms get the new pin with no inventory change.
• Unsupported or intentionally unavailable paths: Adreno 750's 128 MiB WebGPU binding limit still rejects larger Qwen3 weight buffers; OpenCL stays the recommended route (installation.md unchanged). Older releases cannot be patched: known-platform-issues.md gives them the workaround (declare libOpenCL.so or ComputeDevice.cpu).
• Out of scope / follow-ups: Pixel (Mali) WebGPU run (W2c) was not run; companion version bump at release prep.

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. The harness test "binding admits only the listed runtime tags, including the pin" fails when the pin moves without S24 admission; v0.19.1-6 is the rejected example. Rolling the pin back to -4 is refused by the sync tool (same-channel rollback).
• N/A: no public capability change, so no capability_coverage.json change.
• Security/privacy review completed: no secrets, tokens or signed URLs added.
• Follow-up work tracked: companion bump in #1995.

PR type guidance

• Bugfix PR: root cause is the missing WebGPU sampler in the Android libLiteRtLm.so since 0.18.0, fixed in the owner runtime; the regression test is the on-device W1c run below plus the pin-admission harness test. Affected platform: Android (arm64 verified).

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 (isolated TMPDIR; 14478 passed)
• dart test -p chrome --exclude-tags local-only (4900 passed)
• coverage-lib: 93.93% line coverage
• Other: check_native_release_digests.dart, the four native Python suites, dart test -p vm test/unit/tooling/ and test/unit/hook, packages/llamadart_validation tests and Python suite, companion flutter test, ./tool/docs/build_site.sh, local LiteRT-LM smoke

Matrix Evidence

Matrix row	Scope covered	Platform / model / backend	Result	Evidence / notes
static-format-analyze	format, analyzer, boundaries	macOS, Flutter 3.47.1	PASS	check_platform_boundaries.dart clean
root-vm	VM unit/integration	macOS arm64	PASS	14478 tests
coverage-lib	lib/ line coverage	macOS arm64	PASS	93.93%
native-release-digests	8 LiteRT-LM archive digests vs the v0.19.1-5 release	network	PASS
native-sync-python-suites	pin policy, header, binding suites	Python 3.15	PASS	167 + 14 + 23 + 5 tests
native-hook-bundles	hook, bundle selection, companions	macOS arm64	PASS	test/unit/hook
release-doc-version-consistency	install snippets, companion pins	n/a	PASS	companion 0.19.10 reported pending, by design
docs-site	website build, links	n/a	PASS	build_site.sh exit 0
litert-lm-engine-smoke	LiteRT-LM load and generate	macOS arm64, Qwen3 0.6B, cpu	PASS	RESULT litert_lm_engine; library smoke resolves .dart_tool/llamadart/litert_lm/0.19.1-5 and prints its symbols
validation-harness	S24 binding admission and harness	macOS arm64	PASS locally, see below	package suite 642 tests, Python 47 tests
litert-lm-json-schema	Gemma 4 E2B GPU schema checks, Android S24	Test Lab SC-51E / API 36, Adreno 750	PASS (pre-release bytes)	W1c-prep (WebGPU route: Adreno 750 adapter selected, 0 OpenCL sampler loads, 5 cases) and C2-prep (OpenCL route, 1 OpenCL sampler load); the prep APKs carry 9926197b, the stripped form of the published archive's libLiteRtLm.so (cc8de93e, archive 09da4ead); the S24 qualifier APK carries cc8de93e unstripped
S24 20-case LiteRT qualifier	native/public graph on the new Android bytes	Test Lab SC-51E / API 36	PASS	matrix 8700956042671373601, 20/20

Qualifier admission

v0.19.1-5 changes the Android libLiteRtLm.so, so S24 admission needed the 20-case LiteRT qualifier again, as #1830 did for v0.19.1-2. Run pr2003-litert0191-5-s24-20261114 (Test Lab matrix 8700956042671373601, source 73b2a2fe): 20/20 PASS, six lifetimes closed, completion present, full LITERT_CL delegation (1306/1306 decode, 1358/1358 prefill), no CPU fallback, same four legacy semantic failures as v0.19.1. Details in doc/litert_lm_v1_adoption.md.

Review Notes

• Independent review status: pending (high-risk audit of the exact head required before ready)
• CI status / head SHA: full CI on 5d3b2326, see checks

High-risk regression review

• Classification: high-risk (surfaces: artifactConsumer, backendRuntime)
• Implementation task: this lane (worker)
• Independent blocking QA task: pending
• Exact head / current base: pending
• Production-branch deletion, bypass, or miswire proof: pending audit; mutation: reverting the pin to v0.19.1-4 is rejected by the sync tool and the failure W1 recorded returns
• Affected-family real-model/artifact evidence: W1c-prep and C2-prep on S24 (Gemma 4 E2B GPU); S24 qualifier 20/20; macOS Qwen3 0.6B CPU smoke passed. Pixel (Mali) not run.
• Explicit unavailable-family or other N/A evidence: Android x64 has no device run
• Known PR-caused P1 regressions: 0
• Unresolved review threads: 0