AgentHub Adds Expiring Handoff Notes

This is a small feature with outsized reliability value: stale handoff notes are a major failure mode in multi-agent coding, and failing closed is safer than confidently applying obsolete context.

• –Commit pinning gives agents a verifiable snapshot instead of trusting prose.
• –Expiry dates turn handoffs into time-bounded contracts rather than permanent instructions.
• –Drift detection can prevent agents from overwriting newer work or repeating already-resolved mistakes.
• –The feature complements AgentHub’s broader shared-context and subscription-routing workflow.
• –Teams still need tests, clean worktrees, and explicit ownership boundaries; expiry metadata reduces coordination risk but does not eliminate it.