Context

PR #2191 wholesale-restored multiple files from pre-v2026.3.1. This captures the remaining medium-priority improvements that don't warrant individual issues.

Audit report: hq/engineering/notes/post-remediation-audit-b3b4.md

Findings

doctor.ts (2 lost checks)

1. noteStartupOptimizationHints() — v2026.3.1 added startup optimization hints check. Module (doctor-performance.js) exists and already exports it. Just needs import + call.
2. noteOpenAIOAuthTlsPrerequisites() — v2026.3.2 added OpenAI OAuth TLS prerequisites check. Module (oauth-tls-preflight.ts) exists. Needs import + call.

routes.ts (1 perf improvement)

3. Conditional loadPlugins for health --json — change loadPlugins type from boolean to boolean | ((argv: string[]) => boolean). Set routeHealth.loadPlugins = (argv) => !hasFlag(argv, "--json"). Skips local plugin metadata loading for JSON health checks.

acp/client.ts (1 platform fix)

4. Wire resolveAcpClientSpawnInvocation into startAcpServer — the function exists at HEAD but is unused. The spawn call still uses raw serverCommand/effectiveArgs instead of the resolved invocation. Needed for Windows .cmd shim handling and windowsHide.

sessions.ts (1 UI fix)

5. CONTROL_UI session listing filter — prevents the gateway's control panel from appearing in session listings. Uses GATEWAY_CLIENT_IDS constant.

config/defaults.ts (1 feature)

6. Anthropic cache retention default — set cacheRetention: "short" when primary model targets Anthropic. Useful even without model catalog.

doctor-legacy-config.ts (1 DRY refactor)

7. Replace inline Slack migration message strings with formatSlackStreamModeMigrationMessage() and formatSlackStreamingBooleanMigrationMessage() from ../config/discord-preview-streaming.js. Module exists in fork.

Exit Criterion

All 7 improvements applied where dependency modules exist. No new suppressions.