feat(fleet): enforce generated environment boundary (#772)

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

@@ -24,45 +24,56 @@ The agent template calls:
 
 which starts or reuses a tmux session on `MOSAIC_TMUX_SOCKET`.
 
-## Local customization
+## Generated environment and local data
 
-Per-agent overrides live outside the package in:
+The roster-derived projection is written outside the package at:
 
 ```text
-~/.config/mosaic/fleet/agents/<agent>.env
+~/.config/mosaic/fleet/agents/<agent>.env.generated
 ```
 
-Example:
+Systemd does not read either environment file. It starts the launcher with a fixed cleared bootstrap
+environment; before it creates, queries, or stops an exact agent tmux session, `start-agent-session.sh`
+strictly parses the generated projection and the optional local data file:
 
-```dotenv
-MOSAIC_TMUX_SOCKET=mosaic-fleet
-MOSAIC_AGENT_RUNTIME=claude
-MOSAIC_AGENT_WORKDIR=$HOME/src/your-project
-# Optional escape hatch for PoC/canary agents:
-# MOSAIC_AGENT_COMMAND=mosaic yolo claude
+```text
+~/.config/mosaic/fleet/agents/<agent>.env.local
 ```
 
+The local file may contain only safe machine-specific data (`MOSAIC_RUNTIME_BIN`, heartbeat paths or
+interval, and Claude configuration paths). It cannot override roster-derived keys, carry a command,
+or contain secret-like/unknown keys. Both files must be private regular files. Do not hand-edit the
+generated projection; update the roster and regenerate it instead. A legacy `<agent>.env` is
+consumed only for regeneration, strict relocation, or private quarantine and is never launch input.
+
+See `docs/fleet/reference/generated-env-boundary.md` for the full contract.
+
 ## Manual canary sequence
 
-```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/*.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
+Use the roster and the supported installer; do not pre-create the agent environment directory or
+edit a generated projection. `mosaic fleet install` validates the roster, installs the units and
+helpers, and writes private roster-derived projections before any service is started.
 
-# For an operator-interaction service, the roster/env identity selects the
-# generic unit instance; no service source is renamed for an instance.
+```bash
+# Create a site-owned canary roster. Inspect an existing roster before using --force.
+mosaic fleet init --profile minimal --write
+mosaic fleet install
+systemctl --user daemon-reload
+mosaic fleet start canary-pi
+tmux -L mosaic-fleet ls
+```
+
+For an operator-interaction service, first put `<agent-name>` in the roster with the pinned Pi
+runtime, model, reasoning, and `operator-interaction` tool policy. Re-run `mosaic fleet install` after
+that roster change so it writes `<agent-name>.env.generated`; ambient `MOSAIC_AGENT_*` values are not
+launch authority. The generic unit instance uses that generated identity, and no service source is
+renamed for an instance:
+
+```bash
+mosaic fleet install
+systemctl --user daemon-reload
 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
+~/.config/mosaic/tools/fleet/print-interaction-effective-policy.sh <agent-name>
 ```
 
 Do not use `tmux kill-server` without `-L mosaic-fleet`; this pattern is meant