Pin the lazy-grammar pause and the Seed-OSS call-name constraint in tests - #1963

Summary

• Pins that a lazy grammar stays paused through a thinking budget even when its root is think-body or seed-thought (Keep the response-format grammar applied through a budgeted forced-open thought #1956 audit, mutant F).
• Makes the Seed-OSS required-grammar rejection after a forced close name its constraint: a complete scope calling an unknown tool (Keep the Seed-OSS required-call grammar applied through a budgeted thought #1962 audit).

Tracks #1950; does not close it.

Production-readiness scope

• User-facing scope: None; test-only.
• Supported platforms/paths: Dart VM (stories15M integration test runs on every OS; the unit test on Linux).
• Unsupported or intentionally unavailable paths: N/A.
• Out of scope / follow-ups: None.

Completeness checklist

• Declared scope is fully implemented, or explicitly reduced above.
• Unsupported platform/option combinations fail loudly: N/A, no runtime change.
• Public API docs, README/website docs, examples, support matrices, and changelog: N/A, test-only.
• Regression coverage covers the audit gaps below.
• Validation coverage registry: N/A, no capability change.
• Security/privacy review: no secrets or paths added.
• Follow-up work: None.

PR type guidance

• Bugfix PR: N/A, test-only; closes two audit test gaps.

Mutation results

The old assertion lacked the closing </seed:tool_call>, so it was rejected as incomplete under either mutation. The new input is a complete scope with the right location parameter and a wrong function name (get_time).

Test Plan

• dart run tool/prepare_workspace.dart
• dart format --output=none --set-exit-if-changed . (touched files)
• dart analyze
• dart test -p vm -j 1 --exclude-tags local-only : touched files only locally (TMPDIR isolated); full lane in CI
• dart test -p chrome --exclude-tags local-only N/A, VM-only tests
• coverage-lib N/A, no lib/ change
• Other: dart tool/ci/test_shards.dart hosts on both files (integration: every OS; unit: Linux only)

Matrix Evidence

Review Notes

• Independent review status: PASS (fresh Opus audit at 2b51d2f; one P3 logged in 0.19.8 audit follow-ups #1950)
• CI status / head SHA: green, run 43275159551 (16 pass, 15 skipped) / 2b51d2f

High-risk regression review

• Classification: high-risk (surface structuredOutput, from test paths only; no production file changes)
• Implementation task: lane-1950-tbtests
• Independent blocking QA task: fresh auditor, PASS, 0 P1/P2; evidence exit 2 (externalPrerequisitesUnavailable)
• Exact head / current base: 2b51d2f / ec62e97
• Production-branch deletion, bypass, or miswire proof: the mutation table; both tests fail when the guarded production line is removed
• Affected-family real-model/artifact evidence: stories15M (lazy pause); Seed-OSS family covered by grammar recognizer
• Explicit unavailable-family or other N/A evidence: N/A
• Known PR-caused P1 regressions: 0
• Unresolved review threads: 0