Further lifecycle/safety hardening of the local provider:
- Tear the instance down when the initialize handshake is aborted, so a
poisoned pending `ready` can't make later queries for that workspace re-wait.
- Make the serialized-queue wait itself abortable, so a query blocked behind
hung earlier work can still observe its own timeout.
- Spawn the server detached and signal the whole process group on teardown, so
helper processes (e.g. tsserver) can't outlive dispose().
- Open the source with O_NOFOLLOW and cap the read at maxDocumentBytes+1, closing
the symlink-swap and concurrent-grow windows the fd-based read left open.
- Honor an already-aborted signal before any host I/O or startup.
- Validate maxStderrBytes positive at load; surface the retained stderr tail in
the "language server exited" error so a fatal startup diagnostic is visible.
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