diff --git a/docs/SESSIONS.md b/docs/SESSIONS.md
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+++ b/docs/SESSIONS.md
@@ -8,3 +8,4 @@ are never rewritten or removed; corrections are new entries.
 |---|---|---|---|
 | 2026-09-03 | assistant (conductor + worker) | POC through M12: containerized pi proof, config layer, missions/tasks, release model, adapter seam, workspaces/capabilities, named sessions, retention, session forking, conductor auto-apply, roles/ convention | 13 tags; suites 24/58/14 + 17 conductor + verify green; releases 0.0.1–0.0.7; issues #1–#34 closed |
 | 2026-09-03 | assistant (conductor) | User layer: profile updates (pets, family), ms-user skill review/revision (confirmation rules merged, propose-not-apply, missing-file flow, privacy scope, dispatch = all of user/, rule 9 scratch-file constraint), USER.md.bak removed | skills/ms-user/SKILL.md rewritten; ~/.mosaic-dev/user/USER.md updated (Family, Pets); USER.md.bak deleted |
+| 2026-09-03 | assistant | ms-communications skill: inter-agent messaging protocol consolidated from tools/tmux/README.md and agent-send.sh (channel, preamble grammar, flip-on-reply, triage classes, etiquette, receiving protocol, delivery mechanics) | skills/ms-communications/SKILL.md created; unslop-check clean |
diff --git a/skills/ms-communications/SKILL.md b/skills/ms-communications/SKILL.md
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+---
+name: ms-communications
+description: Use this skill whenever sending a message to, or receiving one from, another Mosaic agent.
+disable-model-invocation: false
+---
+
+# ms-communications
+
+Agent-to-agent messaging: one channel, one addressing grammar, honest triage.
+Messages are transport. The durable record lives in run records, issues, and
+SESSIONS.md, never in a pane that scrolls away.
+
+## Channel
+
+- `tools/tmux/agent-send.sh` is the only 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.
+- Non-Fleet seats use the default docket.
+- 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`.
+
+## Preamble (required)
+
+```
+[<src_host>:<src_session> -> <dst_host>:<dst_session>] <message>
+[<src> -> <dst> class=<CLASS>] <message>     # with triage class
+```
+
+`host` is `hostname -s` of the sender's machine; `session` is the tmux session
+name. `agent-send.sh` writes the preamble for you. Two rules carry the protocol:
+
+1. Replying? Flip it: `[<dst> -> <src>] ...`. Answer under your own lane.
+2. A preamble-less cross-agent message is malformed. If you receive one, ask
+   the sender to resend before acting on it.
+
+## 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, and possibly comms daemons.
+5. Waiting on a condition? Arm `agent-watch` on the condition, not a poll of a
+   colleague's pane. Waiting on a seat? Message them (see ms-agent-watch).
+
+## Receiving
+
+1. Read the preamble first. Confirm you are the `dst`. Note the `src`.
+2. Triage by class (table above). `actionable` or absent: act now, or reply why not.
+3. Reply with the preamble flipped. Cite the run id or issue you acted on.
+
+## Delivery mechanics
+
+- 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.