test: pin that a public-review stage never dispatches through the CoS runner (#6105)

[atomantic]

Summary

A public-review stage is direct-only — spawnAgentForTask forces it off the CoS runner with one expression, and nothing pinned it:

const dispatchUseRunner = publicReview ? false : useRunner;

That line is load-bearing because the two halves of a vendor's no-tool posture are enforced in different places. The argv is declared on the vendor row and resolved inside buildVendorSpawnConfig, so it survives any dispatch path — but OpenCode's posture lives entirely in the config content buildCliChildEnv writes from the safetyProfile it is handed, and the runner payload (composeProviderEnv at spawnAgentViaRunner) carries no safetyProfile. A stage that reached the runner would still look enforced (right flag, right provider, gate passed) while running tool-enabled against contributor-authored PR text. Silent, and green in CI.

No production change — the routing itself is what gets pinned. Threading safetyProfile into the runner payload as a belt was considered and declined: it would make routing a public-review stage through the shared runner look supported, and the runner may inherit ambient tool configuration.

What changed

server/services/agentLifecycle.postureGate.test.js only:

• Extended the mock set so a public-review spawn actually reaches the dispatch — PATHS.cosAgents re-rooted at a temp dir via the existing makePathsProxy helper, plus stubs for the leaves between workspace prep and dispatch (readPublicReviewInputSnapshot, buildAgentPrompt, createAgentRun, buildCliSpawnConfig, workspaceContext.snapshotOnRepoSwitch, the two agentPromptBuilder predicates the registerAgent projection reads). The orchestrator itself stays the production one.
• New case: a public-review stage with runner mode on still goes to spawnDirectly, carrying its safetyProfile, and spawnAgentViaRunner is never called.
• New control: with the same mock set, an ordinary task does reach the runner — so the negative above cannot pass merely because runner mode never took effect.
• De-vacuumed the sibling case. spawns a public-review stage on a TUI provider headless, never as a PTY session passed its negatives because the flow never reached a spawner at all. It now runs to the dispatch and asserts spawnDirectly was called.

Test plan

• server/services/agentLifecycle.postureGate.test.js — 7 passed.
• Mutation-checked: changing dispatchUseRunner to plain useRunner turns the new case red on the assertion that names the invariant (expected spawnAgentViaRunner not to be called, 1 call), and green again on restore. The control and the other five cases stay green either way, so the failure points at the routing rather than at the scaffold.
• Full server suite (cd server && npm test): 1917 files passed, 38719 tests passed, 14 skipped.

Closes #6105

https://claude.ai/code/session_01RA3pD5YM2dukQwbZ3pC6WA