workflow-fix: add gate-id-uniqueness check to workflow_lint.py

Overview / Motivation

Auto-filed by the workflow-fix-on-bug protocol from a Claude r1 code-reviewer follow-up surfaced on task #694 (emitting agent: code-reviewer).

Goal

Add a gate-id-uniqueness check to scripts/workflow_lint.py so that a duplicate id: value across gates.{inline, park_and_wait, conditional} in .claude/workflow.yaml is caught mechanically rather than relying on a human / Claude code-reviewer noticing it.

Workflow gap

• Bug observed: task #694 round 1 added a new related_work_positioning conditional gate with id: 15, which was already held by the existing concern_deferral_request gate (line 403). Both workflow_lint.py --default and --check-asks PASSed (the id: field is never read for gate resolution, so functionally nothing broke); the duplicate id only surfaced via the Claude code-reviewer's manual inspection.
• Why it is a workflow gap: the id: field is conventionally unique-per-gate-list across the workflow.yaml gates.* blocks (the existing ids 1-16 are all unique pre-#694), and the next future addition of a gates.{inline, park_and_wait, conditional} entry SHOULD be checked mechanically against reusing an existing id. Letting a duplicate id slip past lint into main again is a known recurring failure mode (Claude's verdict: "this slipped past every existing gate precisely because no check validates id").
• Confidence (emitter): medium

Proposed change (candidate diff sketch — refine in planning)

Add a check function to scripts/workflow_lint.py (next to the existing --check-asks / --check-tables / --check-references checks) that:

1. Parses .claude/workflow.yaml.
2. Collects ALL id: values across gates.inline, gates.park_and_wait, and gates.conditional.
3. FAILs with a clear error if any id appears more than once, naming the offending gate-name pairs.
4. Bundles into the no-flags default run (so uv run python scripts/workflow_lint.py catches it without a flag).

Also: add a tests/test_workflow_lint.py::test_workflow_lint_check_gate_ids_unique_exits_zero test (mirroring the existing test_workflow_lint_check_asks_exits_zero shape) to pin the check.

Scope / surfaces

• Primary targets: scripts/workflow_lint.py + tests/test_workflow_lint.py
• Grep before editing to understand the existing check structure: grep -n 'def check_' scripts/workflow_lint.py

Constraints / invariants

• Workflow-helper script + test — scripts/workflow_lint.py is in-scope per workflow-fix-on-bug.md § Workflow surface.
• uv run ruff check . on touched files PASSes; existing workflow_lint.py --default + --check-asks baseline PASSes.
• The new check is bundled into the default run (no separate flag required to invoke).
• Must run cleanly on the current workflow.yaml after task #694's gate id renumber (id 15 → 17 for related_work_positioning); the existing ids 1-14, 16, 17 are all unique.

Provenance

• workflow_fix_target: scripts/workflow_lint.py
• fingerprint: 573498928966

(Surfaced as Claude code-reviewer r1 Minor finding + follow-up suggestion on task #694 — verbatim: "I also surfaced a follow-up suggesting a workflow_lint.py gate-id-uniqueness check, since this slipped past every existing gate precisely because no check validates id.")