feat(framework/tools): inter-agent tmux comms — agent-send.sh + standard

Adds tools/tmux/ to the framework source (previously only present in installed
~/.config/mosaic copies, never committed):

- agent-send.sh: inter-agent messaging wrapper. Prepends the canonical
  addressing preamble [<src_host>:<src_session> -> <dst_host>:<dst_session>]
  (auto-detecting the sender), and delivers reliably to local OR remote panes.
  Remote delivery ships send-message.sh over ssh and runs it local to the target
  pane, sidestepping the ssh->nested-tmux Enter/C-m submission swallow; the
  remote needs only bash+tmux+base64 (no framework install required there).
- send-message.sh: low-level reliable single-pane submitter (bracketed paste +
  Enter-flush + draft detection). Adds a -b base64 input for ssh-safe transport.
- README.md: documents the addressing standard (replies flip the preamble) and
  the submission gotcha the helper exists to solve.

Propagates to each host via install.sh rsync on next framework upgrade.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/mosaic/framework/tools/tmux/README.md

@@ -0,0 +1,78 @@
+# Inter-Agent tmux Comms — Standard & Tooling
+
+Reliable, self-identifying messaging between Mosaic agents running in tmux panes
+(Claude Code / Codex / OpenCode REPLs), across hosts.
+
+## The addressing standard (required)
+
+Every cross-agent tmux message MUST begin with an addressing preamble:
+
+```
+[<src_host>:<src_session> -> <dst_host>:<dst_session>] <message>
+```
+
+- `host` = `hostname -s` of the machine the agent runs on (e.g. `web1`, `sb-it-mgr-0-lt`).
+- `session` = the tmux session name (e.g. `mos-claude`, `rev0-4`, `installer-1`).
+- **Replies FLIP the preamble**: the recipient answers with `[<dst> -> <src>] ...`.
+
+Why: a fresh or context-wiped agent always knows who sent a message and to whom.
+No ambiguity about origin or lane after a tmux wipe / session restart.
+
+Example exchange:
+
+```
+[web1:mos-claude -> sb-it-mgr-0-lt:installer-1] status on #29?
+[sb-it-mgr-0-lt:installer-1 -> web1:mos-claude] Q2 done, opening PR #34.
+```
+
+## The helper: `agent-send.sh`
+
+Prepends the preamble automatically (auto-detecting your own `host:session`) and
+delivers reliably to local OR remote panes.
+
+```bash
+# Local target (same host)
+agent-send.sh -s <dst_session> -m "message"
+
+# Remote target (over ssh)
+agent-send.sh -H user@host -s <dst_session> -m "message"
+
+# From a file / stdin
+agent-send.sh -H user@host -s <dst_session> -f msg.txt
+echo "msg" | agent-send.sh -s <dst_session>
+```
+
+Key flags: `-s` dst session (required) · `-H` ssh target for remote · `-n` dst
+hostname for the preamble (else auto-resolved) · `-m`/`-f`/stdin body · `-S`
+override source label · `-v` verbose · `-r N` Enter-flush attempts.
+
+## Why a helper exists (the submission gotcha)
+
+Pasting into an interactive REPL via raw `tmux send-keys` is unreliable: a
+trailing `Enter` is frequently swallowed and the message sits as an **unsubmitted
+draft** ("Press up to edit queued messages"). Over an `ssh -> nested tmux` hop the
+plain `Enter` keyname often does not register at all — `C-m` is needed.
+
+`send-message.sh` solves this for a **local** pane: bracketed-paste the body
+(so multi-line content doesn't submit early), pause, then send `Enter` as its own
+keystroke and flush with a second, verifying against a draft heuristic.
+
+`agent-send.sh` solves the **remote** case by _shipping `send-message.sh` over ssh_
+(`ssh host bash -s -- ... < send-message.sh`) and running it local to the target
+pane — so the reliable send-keys always happens on the pane's own host. The remote
+needs only `bash` + `tmux` + `base64`; **no mosaic install required there**. The
+message crosses the wire as base64 (`-b`) to avoid all shell-quoting hazards.
+
+## Files
+
+- `agent-send.sh` — inter-agent wrapper (preamble + local/remote dispatch).
+- `send-message.sh` — low-level reliable single-pane submitter (`-b` base64 input).
+
+## Distribution
+
+These live in the installed framework copy at
+`~/.config/mosaic/tools/tmux/`. `install.sh` rsyncs the framework **source tree**
+to each host, so to propagate permanently, land both files in the framework
+source repo and re-run the installer on each host. Until then, `agent-send.sh`
+already works against any reachable host because it ships `send-message.sh` over
+ssh per-send — no pre-install on the target host is needed to _send to_ it.