stack/skills/ms-communications/SKILL.md

name, description, disable-model-invocation

name	description	disable-model-invocation
ms-communications	Use this skill whenever sending a message to, or receiving one from, another Mosaic agent.	false

ms-communications

Agent-to-agent messaging: one send path per transport, a required sender header, honest triage. Messages are transport. The durable record lives in run records, issues, and SESSIONS.md, never in a pane that scrolls away or a thread that lives only in T3's database.

Channel

Pick the transport by where the recipient runs. Each has one send path.

Recipient	Send path	Guide
A T3 Code thread (Mosaic development agents while development runs in T3)	t3_send_message / t3_create_thread from the t3 MCP server	docs/guides/T3-AGENT-COMMS.md
A tmux seat (fleet seats, pane-hosted agents)	tools/tmux/agent-send.sh	tools/tmux/README.md

• T3 threads are a temporary channel. Jason, 2026-09-26: Mosaic Stack development agents talk through T3 agent comms for now; Mosaic Stack will replace it with its own internal comms. Use the T3 tools as documented and do not design Mosaic features against them.
• Harness-native cross-session messaging (Claude Code's SendMessage and ListAgents, or any equivalent built into a harness) is not a Mosaic channel. Jason, 2026-09-12: Mosaic Stack develops and uses its own cross-harness comms; a harness feature may be used only as a stated stopgap when both paths above are unreachable, and never designed against. The t3 MCP server is not harness-native. It reaches Claude, Codex, and OpenCode threads alike.
• Your own session output is not a send path. A reply composed as assistant prose, however well formatted, delivers nothing to the recipient; a hand-written header in prose is decoration, not delivery. A reply exists only once the send tool has run and returned its receipt: a turnId from the T3 tools, exit code 0 from agent-send.sh. No receipt, no send.

T3 threads

Full mechanics, including setup checks, thread lookup, and upkeep, are in docs/guides/T3-AGENT-COMMS.md. Read it before your first T3 send. The parts that carry the protocol:

[from: <sender-role> (<sender-thread-id>) -> to: <recipient-role> (<recipient-thread-id>)]
[from: <sender-role> (<id>) -> to: <recipient-role> (<id>) class=<CLASS>]    # with triage class

• You write the header yourself as the first line of the prompt. T3 delivers it as a user prompt, so the header is the only sign an agent sent it.
• Find thread IDs with t3_list_threads on the mosaic-stack project; threads carry the agent's name as title. Never invent an ID; write thread-id: unknown instead.
• Always pass idempotencyKey (<lane>-<purpose>-<date>).
• Replies and notices go out with wait off. Use wait: true only when you cannot continue without the answer. Two agents waiting on each other block until timeout.

tmux seats

tools/tmux/agent-send.sh is the only tmux send path. It prepends the preamble, submits reliably (bracketed paste, Enter flush, draft detection), and ships itself over ssh for remote targets. Never raw tmux send-keys; that is how messages die as unsubmitted drafts.

Preamble is prepended to the message when using the agent-send.sh script. Check the script for usage instructions.

[<src_host>:<src_session> -> <dst_host>:<dst_session>] <message>
[<src> -> <dst> class=<CLASS>] <message>     # with triage class

• Non-Fleet seats use the default socket.
• Fleet seats use the named socket: -L mosaic-fleet (or MOSAIC_TMUX_SOCKET). Fleet traffic stays off the user's default tmux server.
• Address durable fleet seats exactly: =coder0, not a prefix that might match two sessions.
• Tool spec and internals: tools/tmux/README.md
• host is hostname -s of the sender's machine; session is the tmux session name. agent-send.sh writes the preamble for you. Never write the bracket line yourself.

Both transports

1. Replying? Flip it: [<dst> -> <src>] .... Answer under your own lane. On T3, send to the sender's thread ID with the header flipped. On tmux, aim agent-send.sh -s <src_session> -C <class> at the sender and the tool writes the flipped preamble.
2. A header-less cross-agent message is malformed. If you receive one, ask the sender to resend before acting on it. A T3 prompt with no header and no claim to come from an agent is from Jason.

Triage classes

Class	Meaning	Recipient behavior
(absent)	fail-safe default	treat as actionable
actionable	decision, blocker, or gate	act, then reply
human	from a human operator	deliver; respond promptly
reaction	emoji or ack	note it; no reply expected
terminal-log	log-only noise	file it; never act
digest	machine-wake, coalescible	batch; wake and continue

Class honestly. Never downgrade a question you want answered to terminal-log.

Etiquette

1. Write for a context-wiped reader. Preamble plus body must carry the ask, the evidence (run id, issue number, path), and any deadline. The recipient has no "as I mentioned earlier".
2. One topic per message. Two asks in one paste is how the second gets lost.
3. Reply, even when the reply is "ACK, on it" or "cannot, reason follows". Silence is not an ack. A refusal with a reason is recoverable; a guess is not.
4. No secrets. Messages land in scrollback, logs, T3's database, and possibly comms daemons.
5. Waiting on a condition? Arm agent-watch on the condition, not a poll of a colleague's pane or thread. Waiting on a seat? Message them (see ms-watch).
6. Every T3 message starts or steers a turn in the recipient and costs tokens. Do not answer an ACK or a reaction with another ACK.

Receiving

1. Read the header first. Confirm you are the recipient. Note the sender and, on T3, the sender's thread ID.
2. Triage by class (table above). actionable or absent: act now, or reply why not.
3. Reply by sending on the transport the message came in on: t3_send_message to the sender's thread, or agent-send.sh aimed at the sender's session. Cite the run id or issue you acted on. Formatting the reply into your own output without running the tool leaves the sender with nothing; that is a dropped reply, not a late one.

Delivery mechanics

• T3: a send returns threadId, turnId, and turn.state. A returned turnId is the receipt. A tool error or a missing token means no delivery; run the status check in the T3 guide and diagnose.
• tmux exit codes: 0 delivered or queued, 1 target not found, 2 still draft, 3 usage error, 4 ambiguous socket (the session name exists on more than one tmux server; disambiguate with -L).
• A refusal is evidence. Diagnose it; do not route around it with raw send-keys.
• rc=2 from an agent-watch delivery means the text reached your pane as a draft. Go read the pane; auto-submit-drafts.sh flushes stable drafts.

When not to message

• Waiting on yourself: do the next thing.
• Facts that must survive the exchange belong in the run record, the issue, or SESSIONS.md. A message that matters gets persisted where the record lives.