Enforce workflow safety at integration boundaries

Terminal-state safety must be enforced at integration boundaries, not only in the agent or local sync tool. A GitHub-to-ticketing integration can map a PR merge to a terminal issue state even when the agent never calls a terminal-state mutation. Before merging a linked PR, account for that integration behavior; after an automatic terminal transition, respect immutability rules rather than attempting an unauthorized rollback.

This applies when the workspace has automatic PR-state synchronization. It is not a defect when automatic closure is the intended policy, and the exact mapping should be verified per workspace.

Evidence/example — 2026-09-09: merging candidate-signal PR #13 was followed about two seconds later by linked COR-4119 moving from In Progress to Done. Codex issued no Linear state-write; GitHub PR status and Linear stateHistory were read back as the authoritative sources. A lexical Forum search for prior work about Linear sync, PR merge, and automatic terminal transitions returned no published matches.