fix(preview): relaunch the shared browser after it disconnects (#146)

[truffle-dev]

Closes #146.

The bug

getOrCreateBrowser and getOrCreatePreviewContext in src/ui/preview.ts both return their cached handle unconditionally (if (browser) return browser, if (currentContext) return currentContext). When the shared Chromium process dies out of band — a renderer crash that propagates to the browser process, an OOM kill, or an external process sweep — the Browser disconnects but the module-level reference stays non-null. Every later phantom_preview_page and browser_* call then hands back a dead handle, so the whole tool surface fails with Target/Page crashed or ...has been closed for the rest of the process lifetime, with no recovery short of a restart.

I hit both faces of this while using the browser tools (the ...has been closed mode and the Page crashed mode are the same root cause — a disconnected shared browser that is never re-created); the issue thread has the process-level evidence (orphaned chrome-headless-shell processes from prior sessions, a crashed renderer that is never relaunched).

The fix

Gate both warm-cache returns on liveness:

• getOrCreateBrowser checks browser.isConnected() and, if false, drops the stale reference so the existing launch path relaunches a fresh process.
• getOrCreatePreviewContext checks the context's browser via currentContext.browser()?.isConnected() and, if dead, drops the cached context so it rebuilds on the relaunched browser instead of returning a corpse.

Recovery is lazy (on the next call), which matches the module's existing lazy-singleton shape and needs no disconnected-event listener lifecycle to manage. The launch-failure recovery (try/finally clearing browserPromise), the shuttingDown guard, and cookie rotation are all unchanged.

Tests

Two regression tests in preview-correctness.test.ts drive the crash path with a fake browser whose __disconnect() flips isConnected() to false without going through close() (simulating an out-of-band death): one asserts getOrCreateBrowser relaunches, one asserts getOrCreatePreviewContext rebuilds on a fresh browser. The fakes gain isConnected() and context.browser() to cover the new call surface.

bun test src/ui/__tests__/preview-correctness.test.ts   # 10 pass, 0 fail
bun test src/ui/                                         # 358 pass, 10 skip, 0 fail
bunx tsc --noEmit                                        # clean
bunx biome check src/ui/preview.ts src/ui/__tests__/preview-correctness.test.ts  # clean