Refill Ghostty prewarm pool after consumption

[almogdepaz]

Summary

• schedule a deferred Ghostty prewarm refill after a prewarmed instance is consumed
• keep take() as a pure consume operation so refill does not start wasm work in the terminal-open stack
• preserve immediate-prewarm debug/onReady instrumentation from Prewarm Ghostty terminals immediately #186
• clean up perf-* sessions in terminal-load-perf.ts so repeated measurements do not exhaust broker fds

Verification

• bun run typecheck
• bun test tests/unit/ghostty-prewarm-pool.test.ts tests/unit/ghostty-prewarm-debug.test.ts
• bun test tests/unit/terminal-load-perf.test.ts tests/unit/ghostty-prewarm-pool.test.ts tests/unit/ghostty-prewarm-debug.test.ts
• bunx playwright test tests/e2e/grid.e2e.ts --project=desktop
• local server-only deploy with --broker=no
• browser grid smoke: 2 cells hydrated/live, no console errors or failed requests
• combined n20 perf: grid prewarm hits 40/40, grid Ghostty create p95 0.1ms, grid reveal p50/p95 197.6/218.5ms, page console errors 0, remaining perf sessions 0

Stacked on #186 (prewarm-ghostty-immediately). Retarget/rebase to main after #186 merges.

[almogdepaz]

reviewed the PR #187 diff.

no blocking findings.

findings:

• low / nonblocking — public/ghostty-prewarm-pool.ts:25 and public/ghostty-prewarm-pool.ts:29: scheduleGhosttyPrewarmRefill drops the promise returned by options.prewarm() instead of routing rejection to onError. the current app call passes GhosttyPrewarmPool.prewarm(), which catches create failures internally, so this is not a merge blocker. but since the helper is exported and its API accepts an arbitrary async prewarm, a future caller can produce an unhandled rejection. i'd wrap the call once and attach .catch(onError), plus add a rejected-prewarm unit test.

nonblocking observations:

• scripts/terminal-load-perf.ts:252-271 cleanup is scoped and preserves cleanup progress after individual kill failures; tests cover reverse order and failure continuation.
• status check Tests is green per gh pr view.
• merge risk is mostly stack management: this is based on prewarm-ghostty-immediately / Prewarm Ghostty terminals immediately #186, so retarget/rebase after Prewarm Ghostty terminals immediately #186 merges.

[almogdepaz]

addressed the low/nonblocking refill error-handling finding in 3ac4c7c.

• scheduleGhosttyPrewarmRefill now routes async prewarm() rejections to onError
• also catches synchronous prewarm() throws defensively
• added regression coverage: refill scheduling reports asynchronous prewarm failures

verification:

• bun test tests/unit/ghostty-prewarm-pool.test.ts tests/unit/ghostty-prewarm-debug.test.ts
• bun run typecheck
• git diff --check