vlm-benchmark

name	vlm-benchmark
description	Benchmark an optimization (PR or branch) on a Device Farm device via the vlm-benchmark framework — baseline vs optimized, quality-regression-aware.
argument-hint	<PR#|PR-url|branch> [--device s25|pixel9|s26|iphone17…] [--model qwen3.5-q8|gemma4-q4|<label>] [--preset full|base|smoke] [--runs 2] [--mmproj both|gpu]

VLM Benchmark — on-device optimization A/B

Benchmark an optimization change (a PR or branch, in the addon or the qvac-fabric) on a specific AWS Device Farm device, using the packages/llm-llamacpp/benchmarks/vlm-benchmark framework. It builds the change from source, runs a baseline vs optimized A/B on the device (N runs each), pairs them by CPU fingerprint, and reports speed and quality — with quality regression as the primary gate. This codifies the QVAC-21320 / QVAC-21297 methodology.

Scope: Qwen3.5-0.8B VLM, projector mmproj CPU-vs-GPU (mmproj=both) by default. The model is selectable (--model) — the framework already ships multiple VLMs (Qwen3.5 f16/q8, Gemma-4-E2B) and a new one can be added to config.cjs; Qwen3.5-q8 is just the default. Device Farm only (no local ADB run yet). Thermal / cross-unit variance is handled by CPU-fingerprint matching over multiple runs, not interleaving.

Source safety (read-only target). This skill never modifies the PR or branch under test. It only reads the target — gh pr view / gh pr diff / git diff — to resolve its ref/commit and classify the change. Every change (harness/config edits and the optimization itself — the fabric overlay REF or cherry-picked addon commits) is made only on the skill's own test/<slug> / test/<slug>-base refs. It never commits to, pushes to, or otherwise alters the source PR's branch, the fabric repo, or main.

Usage

/vlm-benchmark #2921
/vlm-benchmark https://github.com/tetherto/qvac/pull/2921
/vlm-benchmark https://github.com/tetherto/qvac-fabric-llm.cpp/pull/172 --model gemma4-q4 --device pixel9
/vlm-benchmark feat/QVAC-21297-opencl-vision-encoder --device s25 --preset full --runs 2
/vlm-benchmark feat/my-opt --mmproj both --preset base

Arguments

Arg	Required	Default	Meaning
target	yes	—	#<n> / PR URL → PR mode; otherwise a branch name
--device	no	s25	Device Farm phone as a matrix_mobile token: s25 (S25 Ultra / Adreno), pixel9 (Pixel 9 / Mali), s26 (S26 Ultra), iphone16 / iphone17 / iphone17pro. Passed as -f matrix_mobile=<token> at dispatch (Step 8) — the workflow resolves it to a single-device device_model filter. A friendly name ('Pixel 9') maps to its token (pixel9). Append -cpu/-gpu to force the model backend; bare token = the harness picks per --mmproj.
--model	no	qwen3.5-q8	Which VLM to benchmark — a config.cjs catalog label (qwen3.5-f16, qwen3.5-q8, gemma4-q4 = Gemma-4-E2B Q4) or a new one the skill adds (Step 6). A friendly value like gemma4/gemma4-e2b maps to the gemma4-q4 catalog entry. Default = MODEL_2 / current mmprojModel
--preset	no	full	full (5 tasks×5, sharpest — DEFAULT; but overruns the mobile session for mmproj=both → use only on desktop or mmproj=gpu, or raise mobile_timeout_min — see Step 8) · base (5 tasks×3 = the cognitive set with matrix_samples=3; the mobile mmproj=both choice) · smoke (textvqa×1, wiring check). Default to base on mobile mmproj=both.
--runs

Prerequisites & paths

The commands below use placeholders — resolve each once, up front, then substitute (don't assume hard-coded paths):

• gh CLI authenticated to tetherto/qvac (Actions dispatch + read); node on PATH (for match-devices.js).
• <qvac> — the local qvac main clone (origin = tetherto/qvac). Discover it, don't guess: run git worktree list from any qvac checkout → the first line's path is the main worktree. The session's current directory may be a read-only worktree — never build or push from it.
• <feature-branch> — the resolved target branch from Step 1 (the PR head branch, or the branch argument). The optimized ref is test/<slug>; the baseline ref is test/<slug>-base.
• <pr-repo> — the GitHub repo the PR lives in (resolved in Step 1): tetherto/qvac-fabric-llm.cpp for a fabric PR, tetherto/qvac for an addon PR. Used only to read the PR; Actions dispatch always targets tetherto/qvac.
• <slug> — the feature-branch basename (branch feat/QVAC-21297-opencl-vision-encoder → slug QVAC-21297-opencl-vision-encoder).
• <worktree> — the isolated worktree this run creates in Step 5: <qvac>/../wt-<slug> (a sibling of the clone — the repo's wt-<name> convention). All edits, build, and push happen here.
• <base> — the branch the worktree is cut from; chosen in Step 4 (origin/main, or the qvac feature branch related to the target).

Workflow

Step 1 — Resolve the target

• PR (#<n> or URL): resolve the repo from the target — a qvac-fabric-llm.cpp PR URL → tetherto/qvac-fabric-llm.cpp (a fabric PR); a qvac PR URL or a bare #<n> → tetherto/qvac (an addon PR). Then gh pr view <n> --repo <pr-repo> --json headRefName,commits,files,title,body → the head branch is the optimization. (<pr-repo> is only for reading the PR; all Actions dispatch in Steps 7–8 targets tetherto/qvac, where the workflow lives.)
• Branch: use it directly.
• Parse the flags off the tail (--device / --model / --mmproj / --preset / --runs); unset ones take their defaults, but --device/--model/--mmproj are reconciled against the PR in Step 3 before anything is built.

Step 2 — Detect the change scope (from the diff)

Run gh pr diff <n> --repo <pr-repo> (PR; <pr-repo> from Step 1) or git diff main...<branch> (branch). Classify:

• Addon change — touches packages/*/addon/** or addon JS/config. The optimization is the addon commit(s); baseline is the pre-optimization state (Steps 5–6 build it as <base> + harness edits, addon change omitted; the optimized ref adds the addon commits on top).
• Fabric change — the optimization is a qvac-fabric (tetherto/qvac-fabric-llm.cpp) commit (a fabric PR/commit, or a branch that bumps the fabric). The A/B uses a self-contained vcpkg overlay-port whose REF is the only delta: optimized overlay REF = the fabric PR/branch head commit; baseline overlay REF = the pre-change fabric commit (the PR's merge-base with its base, or the published registry version's commit). Both refs use the overlay — Step 6 covers creating the port and computing its SHA512 directly (no CI round-trip).
• Mixed / dependency — a PR that needs both (addon + a fabric overlay): apply both on the optimized build; the baseline strips only the optimization under test. Keep the optimization the sole delta between the two builds (isolation).

Step 3 — Reconcile the passed options against the PR

Before building, cross-check --device / --model / --mmproj against what the change actually targets, from the PR title/body/linked ticket + the diff-touched code:

• Device / backend — ggml-opencl / "OpenCL" / "Adreno" → an Adreno device (token s25); ggml-vulkan / "Vulkan" / "Mali" → a Mali device (token pixel9); "Metal" → iOS/desktop. Plus any explicit device/SoC mention in the PR (S25, Pixel 9, Adreno 830, Snapdragon) → its token.
• Model — a Qwen / Gemma / other model or projector mention.
• mmproj axis — whether it's a projector (mmproj) change vs an LLM change.

Then, per axis:

• (a) user did not pass it and the PR implies a value → adopt the PR's value and notify.
• (b) user passed it and it conflicts with the PR (e.g. --device pixel9 (Mali/Vulkan) on an Adreno/OpenCL-only fix — the change wouldn't even be exercised) → AskUserQuestion: proceed as passed / switch to the PR's value / cancel.
• (c) no PR signal → keep the passed value or the default.

Branch-mode targets with no PR: best-effort from the branch name / diff, else proceed with passed/defaults.

Step 4 — Choose <base>

• git -C <qvac> fetch origin
• Default: <base> = origin/main. The optimization is layered as the sole delta (fabric overlay REF / cherry-picked addon commits per Step 2), so the baseline stays clean regardless of base — this is the case for fabric PRs (target in tetherto/qvac-fabric-llm.cpp) and standard addon PRs alike.
• Exception — an existing qvac feature branch the target builds on: a branch-mode target that names a qvac branch, or an optimization explicitly stacked on another unmerged qvac feature branch → set <base> = that branch so the A/B builds on the same foundation.

The mmproj=both benchmark harness may not live on <base> yet — until it merges to main it lives on test/QVAC-21257-mmproj-gpu-benchmark-changes (the harness + addon instrumentation grafted cleanly onto main). Step 5 brings it in once the worktree exists. (Do not use the older feat/QVAC-21257-mmproj-gpu-config — it is ~100 commits behind main and does not merge cleanly.)

Step 5 — Create the isolated worktree + bring in the harness

Create the worktree from <qvac> (never the read-only session checkout or other in-use worktrees):

git -C <qvac> worktree add <worktree> -b test/<slug> <base>

(drop -b if test/<slug> already exists.) All later edits, build, and push happen inside <worktree>.

Bring in the mmproj=both harness. Check whether it is already present: git -C <worktree> show HEAD:packages/llm-llamacpp/benchmarks/vlm-benchmark/config.cjs contains mmprojGpu/mmprojModel and benchmarks/vlm-benchmark/match-devices.js exists.

• Present (<base> already carries it — e.g. once the harness has merged to main) → nothing to do.
• Absent → merge the grafted harness branch in — it sits directly on main, so this is a clean merge (no conflicts): git -C <worktree> merge --no-edit origin/test/QVAC-21257-mmproj-gpu-benchmark-changes It brings the mmproj=both axis (mmprojGpu/mmprojModel, legsFor, per-row vision_ms), the addon mmproj-use-gpu key + VisionEncodeMs instrumentation (which vision_ms depends on), match-devices.js, and the matrix_mmproj_gpu input + conditional targeted-android prebuild in benchmark-vlm-model-comparison.yml. (Never merge the old feat/QVAC-21257-mmproj-gpu-config: it trails main by ~100 commits, its addon C++ conflicts with main's ContextSlideOutcome refactor, and its matrix-s25/android_flagship_models wiring predates main's matrix_mobile/device_model.)

Two refs, one delta. The A/B is two refs that share identical harness config and differ only by the optimization. Build them in this order (Step 6 gives the exact edits):

1. baseline = test/<slug>-base = <base> (+ harness) + the harness/config edits, no optimization.
2. optimized = test/<slug> = the baseline plus the optimization only — fabric: point the self-contained packages/llm-llamacpp/vcpkg/ports/qvac-fabric overlay-port REF at the fabric commit with a computed SHA512 (Step 6); addon: cherry-pick / merge the PR/branch's addon commits on top.

(The QVAC-21297 run named these …-s25-stock / …-s25.)

Step 6 — Adjust the harness (notify the user, no approval)

Inside the worktree, make the edits and notify the user of each (file + what changed) — no approval needed, since it's an isolated branch/worktree:

• Optimization — apply the optimization per Step 2 (the sole delta between baseline and optimized):
  • Fabric — use a self-contained overlay-port at packages/llm-llamacpp/vcpkg/ports/qvac-fabric/. Copy portfile.cmake + vcpkg.json + android-vulkan-version.cmake from the registry port tetherto/qvac-registry-vcpkg:ports/qvac-fabric/ into that dir — for a Mali / Android-Vulkan target the port MUST carry android-vulkan-version.cmake + its Vulkan-C++-header provisioning (the port owns the Android vulkan.hpp, so the build works even on a fabric commit that predates a fabric-side Android Vulkan build fix — this is why the baseline builds cleanly). Add "overlay-ports": ["vcpkg/ports"] to packages/llm-llamacpp/vcpkg-configuration.json — main has no overlay-ports key, so add it as the first field (the path is relative to that file's dir → packages/llm-llamacpp/vcpkg/ports). In the portfile, change the registry's REF v${VERSION} to the fabric commit and set SHA512 to the hash computed directly (no CI round-trip; see SKILL-fabric-release.md Phase A). The fabric repo is private, so the archive fetch needs a token. Use curl on the /archive/<ref>.tar.gz URL — not gh api …/tarball/<ref>: the /tarball/ endpoint returns a differently-named top-level dir (owner-repo-shortsha vs repo-fullsha) → a different SHA512 that won't match what vcpkg fetches (and gh api can't write to a file without a redirect anyway). Commit-SHA /archive/ tarballs are byte-stable, so the computed hash equals vcpkg's fetch (validate once against a SHA512 already pinned in a known port):

    curl -fsSL -H "Authorization: Bearer $GH_TOKEN" https://github.com/tetherto/qvac-fabric-llm.cpp/archive/<ref>.tar.gz -o /tmp/f.tgz
    openssl dgst -sha512 /tmp/f.tgz     # or: vcpkg hash /tmp/f.tgz
    

    vcpkg_from_github(REPO tetherto/qvac-fabric-llm.cpp REF <fabric-commit> SHA512 <computed-sha512>)
    

    The baseline ref pins the pre-change fabric commit; the optimized ref pins the PR/branch commit — the overlay + is the only difference between them. (Fallback: if the computed hash is ever wrong, vcpkg prints the expected hash on the first failed fetch.)

Commit these harness edits on test/<slug> — this commit is the baseline state. Branch the baseline ref at it: git -C <worktree> branch test/<slug>-base. Then apply the optimization on test/<slug> (fabric: set the overlay-port REF+computed SHA512 to the optimized fabric commit; addon: cherry-pick / merge the PR's addon commits) and commit. The two refs now differ by exactly the optimization — nothing else.

Step 7 — Push the two refs (the one approval gate)

Notify the user of the exact pushes and ask for approval — noting they target separate test/<slug> refs (never main), so it's safe. Push both the optimized and baseline refs from Step 5:

git -C <worktree> push -u origin test/<slug>
git -C <worktree> push -u origin test/<slug>-base

Push only on approval.

Step 8 — Run baseline + optimized on Device Farm (--runs each)

Dispatch each ref --runs times — the optimized ref and the baseline ref from Step 5. <device> is the --device token (default s25); matrix_desktop=none forces zero desktop cells → the run is mobile-only, which triggers the targeted android-only prebuild (prebuild-candidate-mobile, built with the Vulkan SDK for Mali) and skips the heavy full-desktop prebuild + desktop legs. ⚠️ Use the literal none (any non-empty unknown token works), not an empty string — the workflow defaults an empty/unset matrix_desktop to linux-cpu (${MATRIX_DESKTOP:-linux-cpu}), which would run the full desktop prebuild and skip the targeted mobile build. matrix_sources=addon@candidate builds the addon from the dispatched ref so the ref's fabric overlay / addon commits actually take effect:

# optimized — dispatch --runs times
gh workflow run benchmark-vlm-model-comparison.yml --repo tetherto/qvac \
  --ref test/<slug> \
  -f matrix_sources=addon@candidate -f matrix_desktop=none \
  -f matrix_mobile=<device> -f matrix_preset=<preset> -f matrix_mode=two-models
# baseline — dispatch --runs times (identical inputs; only --ref differs)
gh workflow run benchmark-vlm-model-comparison.yml --repo tetherto/qvac \
  --ref test/<slug>-base \
  -f matrix_sources=addon@candidate -f matrix_desktop=none \
  -f matrix_mobile=<device> -f matrix_preset=<preset> -f matrix_mode=two-models

--preset → dispatch inputs. matrix_preset names a config.cjs preset (smoke, cognitive, full); there is no base preset, so map the arg:

• full → -f matrix_preset=full
• base → -f matrix_preset=cognitive -f matrix_samples=3 (the 5 VQA tasks × 3 = 15/cell, no OCR)
• smoke → -f matrix_preset=smoke

⚠️ Mobile session budget (critical for mmproj=both). On mobile, mmproj=both runs two cells (CPU + GPU) in one Device-Farm session → ~2× the inferences. full × mmproj=both overruns the ~30-min per-test ceiling: the CPU cell finishes but the GPU cell is cut off mid-run (matrix-mobile shows failure while matrix-combine still succeeds on partial data — the GPU cell's quality then covers only the first 1–2 tasks and is not comparable). So for a mobile mmproj=both verdict default to base, and/or raise the ceiling with -f mobile_timeout_min=<min> (e.g. 60; capped by the 120-min DF/GH job ceiling). full on mobile is safe only for mmproj=gpu (one cell) or with a raised timeout.

Default --runs 2 → 4 dispatches total (--runs = dispatches per ref, for CPU-fingerprint matching across units — not samples/task, which the preset governs). Device / preset / mode reach the phone via the matrix-mobile job's device_env (Step 6) — pass them as -f inputs, identical for both refs; only mmprojGpu (+ mmprojModel for --mmproj both) is baked into each ref's config.cjs. Monitor each run to completion (poll gh run view <id> --repo tetherto/qvac --json status,conclusion,jobs): the candidate prebuild (prebuild-candidate-mobile on a mobile-only run) is the early build signal; matrix-mobile is the on-device leg (skips if the prebuild fails). Record which run ID is baseline vs optimized — needed in Step 10.

Step 9 — Retrieve metrics

The raw [VLMROW]/[VLMSEG] markers a mobile run needs are in the console-logs-*-Android artifact — NOT in gh run view --log (they print to the on-device Android logcat, which Device Farm captures as an artifact). For each run, download it and keep the logcat as that run's marker file for Step 10:

gh run download <run-id> --repo tetherto/qvac --name console-logs-<pkg>-<device>-Android --dir <run-dir>
# → <run-dir>/Android/Android_logcat_full.txt holds the [VLMROW]/[VLMSEG] markers

Use a distinct <run-dir> per build+index (e.g. opt1/, base1/) so Step 10 can pair them, matching the run IDs recorded in Step 8. (On desktop legs the markers are on native stderr, so there the gh run view --log run log carries them; mobile does not.)

For the ready-made summary, read the vlm-matrix-consolidated-<run#> artifact (~2 KB markdown — full quality + speed + samples tables) or the identical matrix-combine job-log render:

• Quality: per-task textvqa / vizwiz / gqa / docvqa / ai2d + Overall % (equal-weight mean).
• Speed: mmproj-encode (from the addon vision_ms RuntimeStat), TTFT, wall; small/large resolution buckets; samples run / passed / failed.
• Confirm the projector routed to the intended backend from logcat — Adreno OpenCL: Adreno GPU version 830 found keeping OpenCL backend → using device GPUOpenCL; Mali Vulkan: found device description: Mali-G715 → removing OpenCL backend … rely on Vulkan/cpu only → using device Vulkan0 (Mali-G715).

Step 10 — Pair + detect quality regression (primary gate)

• Pair baseline↔optimized runs with benchmarks/vlm-benchmark/match-devices.js (build-invariant CPU mmproj-encode fingerprint → same-unit-equivalent), passing the per-run logs saved in Step 9 (--shipping = the baseline runs, --optimized = the optimized runs): node benchmarks/vlm-benchmark/match-devices.js --shipping base1/Android/Android_logcat_full.txt [base2/…] --optimized opt1/Android/Android_logcat_full.txt [opt2/…] (the per-run logcat files downloaded in Step 9).
• Quality Δ = (optimized − baseline) Overall %, plus per-task Δ. Flag ANY negative Δ (overall or any task) as a regression — this is the gate.
• With --mmproj both, also report the within-run GPU-vs-CPU quality Δ per build (the projector-backend regression — the QVAC-21297 case: stock GPU −4.1 pp → fixed GPU Δ0).
• full (5 tasks×5) gives the sharpest quality signal on desktop / mmproj=gpu. base (3 samples) is coarser and can noise-mask small regressions (QVAC-21320 saw the same Adreno bug read as base −4 pp vs full −18.8 pp) — but on mobile mmproj=both it is the verdict preset: full overruns the Device-Farm per-test window and truncates the GPU cell (Step 8), so a completed base beats a truncated full. Raise mobile_timeout_min if you must run full on mobile. smoke (1 sample) is a wiring check only — it cannot produce a quality verdict, so on smoke, skip the regression gate + the full Step 11 report and just confirm routing / GPU==CPU / 0 device-loss.

Step 11 — Report → write QVAC-<ticket>-benchmark-results.md

Write to QVAC-<ticket>-benchmark-results.md in the working dir where the prior docs live (repo root, alongside QVAC-21320-benchmark-results.md / QVAC-21297-benchmark-results.md). Derive <ticket> as the QVAC-\d+ match from the PR title (gh pr view <n> --repo <pr-repo> --json title) or the branch name; if there is no ticket, fall back to <slug>-benchmark-results.md and say so in the doc.

Never discard prior results — layer the newest on top (the shape QVAC-21320-benchmark-results.md already has: newest first, older sections below):

• Doc absent → create it in full with the Write tool, section-for-section per the template below.
• Doc present → do not overwrite. Read it, then insert THIS run at the top of the results (below the doc's title + goal/context paragraph, above the prior run) in order:
  1. Summary of the latest result — the > **Result:** … blockquote + the # Latest results … section (method one-liner, quality gate, CPU-matched table, recommendation) for this run.
  2. Latest result details — the # Detailed results block for this run.
  3. Results before that — the previously-latest content, demoted beneath: rename the prior # Latest results … heading to a dated/labelled # Previous results — <date/axis> and keep it and all older sections intact below (preserve verbatim; only demote headings / reorder).

Either way the skill does not commit/push the doc (see Notes).

Match the two reference docs section-for-section, in this order (copy their exact column/wording):

1. # QVAC-<ticket>: <one-line descriptor> (<device> / <SoC + backend>)
2. Goal / context paragraph (italic) — what the optimization is, the ticket goal, related-ticket links.
3. > **Result:** … blockquote — one-paragraph headline verdict (what the A/B proved, quality first).
4. ---
5. Headline section # Latest results — <compared axis> (<device>):
   • Method in one line (italic): N runs, Device Farm pool, baseline-vs-optimized definitions, model, mmproj mode, preset (tasks×samples, n=/cell), matched-by CPU fingerprint, link to CI runs.
   • Quality paragraph (the primary gate) — Overall Δ + notable per-task shifts.
   • Speed paragraph + the CPU-matched comparison table: | Metric | Baseline-CPU | Baseline-GPU | Optimized-CPU | Optimized-GPU | <opt vs base> | <opt vs shipping-CPU> | rows mmproj-encode (ms) · TTFT (ms) · wall (ms) · quality (Overall %); then a short column-meaning gloss.
   • Primary robust metric paragraph — the within-run CPU/GPU encode ratio (device variance cancels).
   • ## Recommendation — numbered, actionable verdict.
6. ---
7. # Detailed results:
   • ## Quality — lmms-eval overall % — per-task table | Build | Config | textvqa | vizwiz | gqa | docvqa | ai2d | Overall % | + a Δ-callout line (flag ANY negative per-task or overall Δ; note base-preset granularity if the preset is coarse).
   • ## Per-run summary — | Run | Build | CPU enc | GPU enc | GPU TTFT | within-run CPU/GPU | quality GPU vs CPU |, one row per run, run-ID linked.
   • ## Resolution dependence — small vs large mmproj-encode bucket table.
   • ## Caveats — decode-TPS artifact, peak-RSS not captured, CPU-fingerprint match %.
   • ## Setup & isolation — model/blobs, device + logcat backend-routing proof, baseline/optimized build definitions (overlay REF / addon commit), the isolation statement (optimization = sole delta).

QVAC-21320-benchmark-results.md and QVAC-21297-benchmark-results.md are the worked templates — copy their exact column headers and phrasing.

Notes

• Device Farm only — no local ADB run yet. Thermal / cross-unit variance is handled by CPU-fingerprint matching + N runs, not interleaving.
• Isolation — the optimization under test must be the ONLY delta between baseline and optimized builds. Don't drag in unrelated fabric/addon changes (e.g. keep OpenCL work free of Vulkan opts).
• Worktree — created from <qvac> (the main clone) at <worktree> = <qvac>/../wt-<slug> (the repo's wt-<name> convention; see Prerequisites). Never edit in the read-only session checkout or other in-use worktrees.
• Model support — config.cjs already ships multiple VLMs (Qwen3.5 f16/q8, Gemma-4-E2B); select via --model → mmprojModel (mmproj-compare) / models (two-models), and add a new one via hf() blob literals. No framework code change is needed to benchmark a different model.
• Approval policy — harness edits happen in the isolated worktree and are notify-only; the only approval gate is the push to origin (Step 7), and even that is a separate test/<slug>, never main.
• Harness source — until the mmproj benchmark tooling merges to main, it lives on test/QVAC-21257-mmproj-gpu-benchmark-changes (grafted cleanly onto main), merged in by Step 5. The older feat/QVAC-21257-mmproj-gpu-config is NOT usable — it trails main by ~100 commits and its addon C++ conflicts with main's ContextSlideOutcome refactor (the removed FullWipe). End state: once the grafted branch lands on main, drop the Step 5 merge and base directly on origin/main.
• Device targeting — a -f matrix_mobile=<token> dispatch input (s25/pixel9/s26/iphone*), not a branch edit. The context job resolves each token to device_model+device_manufacturer and the matrix-mobile job runs it as a single-device Device Farm filter (one phone per token).