[ShryukGrandhi]

Summary

Most of #765 is already handled on main. readSessionBrokerHealth goes through probeSessionBrokerHealth, which reads a bounded body and decodes it with parseSessionBrokerHealth (exact keys, ok: true, safe integers, strings, and the legacy paths shape). The one acceptance criterion still open was the PID: the decoder used the generic safe-integer check with a minimum of 0, so a health payload with "pid": 0 decoded as healthy. process.kill(0, ...) signals the caller's whole process group, so a zero PID should never get through.

Changes

• parseSessionBrokerHealth now requires pid to be a safe integer >= 1. That matches the check the launch-metadata decoder already does. The other counters still accept 0.
• Extended the health decoder test to reject zero, negative, fractional, string, and unsafe (MAX_SAFE_INTEGER + 1) PIDs.
• Added a patch Changeset.

The restart path in hunk daemon restart (daemonCommands.ts) signals only the PID from the validated launch metadata (parseSessionBrokerLaunchMetadata, which also requires a minimum of 1). It never uses the health payload's PID, so no restart code changes were needed.

Testing

• bun test packages/hunk/src/session/broker/brokerLauncher.test.ts: the new pid: 0 case fails before the fix and passes after it.
• bun test packages/hunk/src/session: 443 pass, 1 fail. The failing test is a timing-sensitive daemon-server test (keeps a silent session past the stale TTL...). It is not related to this change: it and other daemon-server tests also failed intermittently on unmodified main on the same machine.
• bun run typecheck, oxlint, and oxfmt on the touched files are clean.
• Tested on macOS arm64 only.

Fixes #765

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