NodeBridge should reset process after stdin write failures

[bbopen]

Problem

send() catches IPC write errors (e.g., EPIPE) and throws, but leaves this.child intact. Subsequent calls keep trying to write to the same broken stdin without reinitializing, causing repeated failures instead of recovering.

Evidence

• src/runtime/node.ts: in send(), write errors clear the pending entry but do not reset this.child, initPromise, or bridgeInfo.

Acceptance criteria

• On stdin write failure, clear the current child process, reset initPromise/bridgeInfo, and ensure the next call reinitializes.
• Add a regression test using a fixture that closes stdin or triggers EPIPE.

[bbopen]

Fixed in PR #160: ProcessIO now calls markForRestart() after stdin write failures, ensuring the next request uses a fresh process.