feat(tess): add configurable Pi interaction service (#728)

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

@@ -12,6 +12,8 @@ exact-match session.
 
 - `mosaic-tmux-holder.service` — user-mode holder that owns the named tmux server.
 - `mosaic-agent@.service` — user-mode template for one reusable agent session.
+- `mosaic-interaction-agent@.service` — generic Pi operator-interaction template
+  that fails fast when its pinned runtime policy is incomplete or changed.
 - `test-fleet-units.sh` — validates unit syntax and required relationships.
 
 The agent template calls:
@@ -45,12 +47,22 @@ MOSAIC_AGENT_WORKDIR=$HOME/src/your-project
 ```bash
 mkdir -p ~/.config/systemd/user ~/.config/mosaic/tools/fleet ~/.config/mosaic/fleet/agents
 cp packages/mosaic/framework/systemd/user/mosaic-*.service ~/.config/systemd/user/
-cp packages/mosaic/framework/tools/fleet/start-agent-session.sh ~/.config/mosaic/tools/fleet/
-chmod +x ~/.config/mosaic/tools/fleet/start-agent-session.sh
+cp packages/mosaic/framework/tools/fleet/*.sh ~/.config/mosaic/tools/fleet/
+chmod +x ~/.config/mosaic/tools/fleet/*.sh
 systemctl --user daemon-reload
 systemctl --user start mosaic-tmux-holder.service
 systemctl --user start mosaic-agent@canary.service
 tmux -L mosaic-fleet ls
+
+# For an operator-interaction service, the roster/env identity selects the
+# generic unit instance; no service source is renamed for an instance.
+systemctl --user start mosaic-interaction-agent@<agent-name>.service
+MOSAIC_AGENT_NAME=<agent-name> \
+MOSAIC_AGENT_RUNTIME=pi \
+MOSAIC_AGENT_MODEL=openai/gpt-5.6-sol \
+MOSAIC_AGENT_REASONING=high \
+MOSAIC_AGENT_TOOL_POLICY=operator-interaction \
+  ~/.config/mosaic/tools/fleet/print-interaction-effective-policy.sh
 ```
 
 Do not use `tmux kill-server` without `-L mosaic-fleet`; this pattern is meant