cli-tri census: #8226's frontier step is a quiet step (31 -> 32), unblessed #8240

Problem

tri census pin --gate fails with steps in a quiet shape 31 -> 32 in shape gated on the file existing (8 -> 9). #8226 added the frontier step to spec-guards.yml without re-blessing the census. Master never noticed, because cli-tri is path-filtered and did not run there. It now fails on PRs, for example #8232 (run 37951698654).

The new gate is [ -f "$d/base/$f" ] && ! grep -q " $f\$" "$d/rebuild.txt". Its pass does not survive the subject going missing:

• If rebuild.txt is missing or empty, every base spec is taken as REUSE with base 0, which is the strictest baseline.
• frontier --list failing fails the step under bash -e.

Acceptance criteria

• tri census pin --gate prints PASS: no pinned census moved. on the branch

Boundary

tools/census/quiet.txt

User Scenarios

• Given the census quiet shape records step 31, when the frontier step (32) is introduced via spec-guards.yml, then tri census pin --gate must pass without "steps in a quiet shape" error.

Requirements

• FR-001: The quiet shape in tools/census/quiet.txt MUST be updated to include step 32 for the frontier gate.
• FR-002: tri census pin --gate MUST print PASS: no pinned census moved. and exit 0 on the branch.

Success Criteria

• tri census pin --gate exits 0 and outputs PASS: no pinned census moved.
• tools/census/quiet.txt contains the updated step count reflecting 32 steps.