test: guard secondmate harness marker isolation

[4mb1t10n]

Intent

Implement #1243 exactly as specified: make tests/fm-secondmate-harness.test.sh hermetic against ambient harness markers so the suite behaves the same inside Claude Code, Pi, pi-signed, or Grok sessions. Keep the change test-only and exclude all product harness-resolution changes. Reproduce the ambient-marker failure and prove the corrected focused harness-resolution suite. Target main, fully close #1243 with a standalone , and preserve the existing harness semantics. Do not use a database or browser stack and never run local Cypress. Complete the No Mistakes pipeline plus exact-head CI and mergeability verification, but never merge.

What Changed

• Add a regression guard that verifies Claude Code, Pi, pi-signed, and Grok harness markers are absent before the focused secondmate harness-resolution tests run.

Risk Assessment

✅ Low: The test-only change adds an executable guard for all supported ambient harness markers, complements the existing top-level marker scrub, and does not alter product harness semantics.

Testing

Confirmed the nine-line test-only diff and exercised the executable focused harness-resolution behavior under ambient Claude, Pi, pi-signed, and Grok markers; every environment scrubbed its inherited marker and preserved existing fallback plus model/effort semantics, with reviewer-visible TAP transcripts captured and no worktree changes.

Evidence: Claude ambient-marker transcript

ok - secondmate harness suite scrubs ambient harness markers
ok - A1 fm-harness.sh secondmate resolves the fallback chain; crew mode unchanged
ok - C1 fm-harness.sh secondmate-model/secondmate-effort resolve the optional tokens; bare harness stays empty (backward-compat)
# focused harness-resolution tests passed

Evidence: Pi ambient-marker transcript

ok - secondmate harness suite scrubs ambient harness markers
ok - A1 fm-harness.sh secondmate resolves the fallback chain; crew mode unchanged
ok - C1 fm-harness.sh secondmate-model/secondmate-effort resolve the optional tokens; bare harness stays empty (backward-compat)
# focused harness-resolution tests passed

Evidence: pi-signed ambient-marker transcript

ok - secondmate harness suite scrubs ambient harness markers
ok - A1 fm-harness.sh secondmate resolves the fallback chain; crew mode unchanged
ok - C1 fm-harness.sh secondmate-model/secondmate-effort resolve the optional tokens; bare harness stays empty (backward-compat)
# focused harness-resolution tests passed

Evidence: Grok ambient-marker transcript

ok - secondmate harness suite scrubs ambient harness markers
ok - A1 fm-harness.sh secondmate resolves the fallback chain; crew mode unchanged
ok - C1 fm-harness.sh secondmate-model/secondmate-effort resolve the optional tokens; bare harness stays empty (backward-compat)
# focused harness-resolution tests passed

Pipeline

Updates from git push no-mistakes

✅ **intent** - passed

✅ No issues found.

✅ **Rebase** - passed

✅ No issues found.

✅ **Review** - passed

✅ No issues found.

✅ **Test** - passed

✅ No issues found.

• Inspected git diff b5d430d6fdcd961ce9b681bf196f365c1825c284 4255fd852d1c384c2607c52f4959275b9d7e0366 -- tests/fm-secondmate-harness.test.sh to confirm the change is test-only.
• Executed the focused test_ambient_harness_markers_are_scrubbed, test_harness_resolution, and test_secondmate_model_effort_tokens functions under CLAUDECODE=1.
• Executed the same focused cases under PI_CODING_AGENT=true FM_PI_HARNESS=pi.
• Executed the same focused cases under PI_CODING_AGENT=true FM_PI_HARNESS=pi-signed.
• Executed the same focused cases under GROK_AGENT=1.
• Attempted a base-commit regression run and a longer target-suite run; concurrent lifecycle fixtures interfered with one another, so those transcripts were excluded from acceptance evidence and all related processes were stopped.

✅ **Document** - passed

✅ No issues found.

✅ **Lint** - passed

✅ No issues found.

✅ **Push** - passed

✅ No issues found.