fix(run): await capped browser close on shutdown so Chromium isn't orphaned

[JonasJesus42]

Problem

The shutdown handler in runCommand (SIGINT / SIGTERM / global timeout) did:

if (browser) browser.close().catch(() => undefined); // fire-and-forget
process.exit(130);                                    // kills Node immediately

process.exit is synchronous, so Node died before the async browser.close() ever completed — orphaning the Chromium subprocess on every Ctrl-C or global-timeout shutdown. Under repeated or parallel runs (e.g. inside Conductor) these orphaned browsers accumulate and feed the memory pressure that drives the OS OOM killer to SIGKILL sibling processes (exit 137).

Fix

Make shutdown async and await a capped browser.close() (3s race) before process.exit(130). browser.close() terminates the Chromium subprocess; awaiting it ensures that actually happens, while the cap guarantees a wedged Chromium can't block the exit. Signal and timeout callers invoke it as void shutdown(...). The double-signal fast path (hard exit on 2nd Ctrl-C) is preserved.

Verification

• bun run check (tsc) passes.
• Manual: Ctrl-C mid-run, then ps aux | grep -iE "Chromium|headless_shell" — no orphaned processes remain.

Part of the memory-pressure / OOM series (see #173, #174).

🤖 Generated with Claude Code

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Summary by cubic

Await a capped browser close (3s max) during shutdown so Chromium isn’t orphaned after SIGINT/SIGTERM/global timeout. This stops zombie browsers from piling up and reduces OOM kills during repeated or parallel runs.

• Bug Fixes
  • Made shutdown async and await browser.close() with a 3s race to avoid blocking on a wedged Chromium.
  • Updated signal/timeout handlers to call shutdown asynchronously; preserved the fast hard-exit on a second signal.

^{Written for commit b8cb3f3. Summary will update on new commits.}