BrowserManager only re-launched chromium when the cached handle was
None. A crash mid-pass left the handle Some pointing at a dead
process — every subsequent acquire returned the zombie Browser, and
every nav cascaded CDP errors until the idle reaper fired.
Add BrowserManager::invalidate(): take the inner mutex, drop the
handle (closing it if present), and signal the next acquire to
relaunch. Idempotent — invalidating an empty handle is a no-op.
Wire detection via NavError::is_likely_browser_dead and a
chain-walking anyhow_looks_browser_dead helper: substring-match
common channel/connection/transport/WebSocket markers and surface
NavError::Timeout as "presumed dead." Apply at both error
boundaries — RealChapterDispatcher::dispatch and
RealMetadataPass::run.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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