feat(chrome): hand snapshots to context mode

pi-chrome/test-suite/notes/scoring.md

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+# Benchmark scoring
+
+## Unit challenges (`manifest.json`)
+
+Score actual verdict against `expected[mode]`, not raw PASS count.
+
+Gate buckets:
+
+- `core`: headline release gate. Exact expected verdict required.
+- `conditional`: gate only when declared capability/prerequisite is present; otherwise report skipped/conditional.
+- `quality`: adversarial humanization/fingerprint signal. Report trend and regressions, but do not block general release unless explicitly promoted.
+
+Expected values:
+
+- `PASS` / `FAIL` expected: exact match required inside active gate bucket.
+- `CONDITIONAL`: exclude from core headline score unless environment prerequisite is declared present.
+- `SKIP` / `WARN`: report separately.
+
+Recommended flake policy:
+
+- Run each non-destructive challenge up to 2 retries.
+- Take best verdict only for known-flaky timing/scroll tests.
+- Always keep all reasons/events in detailed report.
+
+Difficulty weighting:
+
+- L1 = 1
+- L2 = 2
+- L3 = 3
+
+Report both unweighted and weighted score. Also report per-category score.
+
+## Long-horizon tasks (`task-manifest.json`)
+
+Task score is deterministic grader PASS / not PASS. Record:
+
+- action count
+- wall time
+- tools used
+- observation mode (`snapshot`, screenshot, accessibility, evaluate)
+- whether direct state mutation/evaluate was allowed
+- final grader reason
+
+Do not use LLM judge for hermetic tasks unless grader cannot express the target.