feat(fleet): add durable tmux fleet poc

packages/mosaic/framework/systemd/user/README.md

@@ -3,6 +3,11 @@
 This directory contains the first durable tmux-backed fleet primitives for the
 Mosaic software-factory model.
 
+The lifecycle model follows the organization-neutral AI Guide playbook
+`mosaicstack/aiguide:playbooks/tmux-fleet.md` (commit `2a0b0b5`): a dedicated
+holder owns the tmux server/socket; agent units join it and stop only their own
+exact-match session.
+
 ## Layout
 
 - `mosaic-tmux-holder.service` — user-mode holder that owns the named tmux server.

packages/mosaic/framework/systemd/user/mosaic-agent@.service

@@ -14,7 +14,7 @@ Environment=MOSAIC_AGENT_RUNTIME=pi
 Environment=MOSAIC_AGENT_WORKDIR=%h
 EnvironmentFile=-%h/.config/mosaic/fleet/agents/%i.env
 ExecStart=/bin/bash %h/.config/mosaic/tools/fleet/start-agent-session.sh %i
-ExecStop=-/bin/bash -lc 'tmux -L "${MOSAIC_TMUX_SOCKET:-mosaic-factory}" kill-session -t "=%i:0.0"'
+ExecStop=-/bin/bash -lc 'tmux -L "${MOSAIC_TMUX_SOCKET:-mosaic-factory}" kill-session -t "=%i"'
 
 [Install]
 WantedBy=default.target

packages/mosaic/framework/systemd/user/test-fleet-units.sh

@@ -18,6 +18,7 @@ grep -qF 'tmux -L' "$HOLDER" || fail "holder does not use named tmux socket"
 grep -qF '_holder' "$HOLDER" || fail "holder session is not explicit"
 grep -qF 'Requires=mosaic-tmux-holder.service' "$AGENT" || fail "agent does not require holder"
 grep -qF 'start-agent-session.sh' "$AGENT" || fail "agent unit does not call start-agent-session.sh"
+grep -qF 'kill-session -t "=%i"' "$AGENT" || fail "agent stop does not exact-match its session"
 
 if command -v systemd-analyze >/dev/null 2>&1; then
   systemd-analyze verify --user "$HOLDER" "$AGENT" >/tmp/mosaic-fleet-systemd-verify.log 2>&1 || {

scratchpads/2026-06-19-tmux-fleet-durable-install-plan.md

@@ -6,6 +6,8 @@
 
 **Architecture:** Mosaic should ship generic tmux fleet primitives in the framework, then layer local rosters through configuration. The holder service owns the tmux socket; each agent service joins the holder-owned server and runs `mosaic yolo <runtime>`. The orchestrator addresses agents through `mosaic agent ...` abstractions so tmux can later be replaced by Matrix-backed agent comms without changing mission flow.
 
+**Reference:** AI Guide `playbooks/tmux-fleet.md` at commit `2a0b0b5` documents the organization-neutral holder-service pattern, exact-match `=<name>` stop targets, and coupled-server cutover/verification sequence. The Stack implementation should treat that as the lifecycle model and keep concrete Mosaic unit/tooling details here.
+
 **Tech Stack:** Bash, tmux, user systemd units, Mosaic CLI/framework installer, JSON/YAML roster config, existing `packages/mosaic/framework/tools/tmux/{agent-send.sh,send-message.sh}`.
 
 ---