Run P0.3 exact Specialist-to-Leader Matrix handoff probe

[shenjiecode]

Goal

Run the remaining P0.3 exact Specialist-to-Leader Matrix handoff probe on the pinned AgentTeams v1.2.0 stack.

Required proof

• Human event visibly mentions only the Specialist; the stock Leader remains idle for that event.
• Specialist sends a bounded, ordinary-client-readable handoff with an exact namespaced structured reference binding workId, source roomId/eventId, authenticated sender, and current Leader recipient.
• Matrix send returns the sender-side event ID/transaction acknowledgement.
• An independently authenticated Leader observation/receipt proves the same handoff event and current IDs; sender acknowledgement is not used as Leader receipt.
• Retrying the same Matrix transaction ID returns the same event and does not create a second visible handoff.
• Malformed, cross-room, wrong-source, wrong-sender, wrong-recipient, and non-bound references fail closed without a new Work or handoff event.
• Handoff is agent communication and does not admit a new Human Work.
• Exact temporary Team/Worker/room/alias/storage/observability cleanup is verified.

Scope

Probe/support code, deterministic contract tests, and a dated run plan only. Do not implement the target PostgreSQL Work/outbox or product admission path. Do not disable requireMention, use hidden/frontend relays, impersonate Human, or treat model prose as authority.