cluster-PR mode gates only the first issue — move SEEN_ISSUES parsing ahead of the actionability gate in idd-implement / idd-plan / idd-all

[kiki830621]

Problem

idd-implement runs the actionability gate (Step 0.35, since 3.1.0) on the scalar $NUMBER. In cluster-PR mode (/idd-implement #34 #36 #38 --pr, v2.34.0+) the issue set SEEN_ISSUES is only parsed later in Step 0.5, so the second and later issues are never gated: an issue carrying parking-lot or a non-empty ### Blocking is still branched, written into the shared Implementation Plan comment and taken into the TDD loop. The same holds for idd-plan and idd-all cluster paths.

This is pre-existing — round 2 of PR #318 gated the same scalar from Step 2.5 — but spec R2 / R5 of actionability-gate assert coverage the cluster path does not have. The reference now states the gap explicitly and points here.

Source

• Verify report on PR feat: actionability gate round 2 — prefix tier + deferral vocabulary, wired into all four consumers (#316) #318 (round 3), row 9 / follow-up row 16 (requirements HIGH-1, DA adjudication: pre-existing, MEDIUM).
• Contract: plugins/issue-driven-dev/references/actionability-gate.md §Consumer contract.

Expected

Issue-set parsing (SEEN_ISSUES / ISSUE_COUNT / CLUSTER_MODE) moves ahead of the gate; the gate runs once per issue (for NUMBER in "${!SEEN_ISSUES[@]}"), and any VEXIT=1 stops the whole cluster before any branch or egress. The line-order test in scripts/tests/actionability-gate/test.sh gains a cluster assertion.

Acceptance criteria

• idd-implement, idd-plan, idd-all gate every issue of a cluster before the first side effect
• one withheld issue aborts the cluster with all reasons printed
• test pins the order for the cluster path
• reference's "cluster path gates the first issue only" sentence removed

Complexity

Plan — three skills, an argument-parsing reorder with ordering constraints, no new published API.