---
kind: guide
status: active
---

# Create, Inspect, Update, and Delete a Local Fleet Agent

Use the local roster-v2 control plane only. These commands change desired state and derived environment projections; they never start, stop, reconcile, inspect, or otherwise act on systemd, tmux, sessions, or runtimes.

## Read and plan first

```fleet-synopsis
mosaic fleet get <name>
mosaic fleet plan create --expected-generation <n> --agent '<json>'
mosaic fleet plan update <name> --expected-generation <n> --agent '<json>'
mosaic fleet plan delete <name> --expected-generation <n>
```

plan create takes the name from `--agent`. plan update and plan delete require the target name immediately after the operation. A plan is deterministic and side-effect free: it validates the complete proposed roster and projection targets without changing files. Use `--dry-run` on `create`, `update`, or `delete` for the same no-write result.

Every successful command prints JSON. `get` returns { "generation", "agent" }; mutation results contain `plan`, `applied`, `authoritativeRoster`, and `projections`.

## Create safely

```fleet-command
mosaic fleet create --expected-generation 7 --agent '{
  "name":"coder0",
  "alias":"Coder 0",
  "className":"code",
  "runtime":"pi",
  "provider":"openai",
  "model":"gpt-5.6-sol",
  "reasoning":"high",
  "toolPolicy":"code",
  "workingDirectory":"/srv/mosaic",
  "persistentPersona":false,
  "resetBetweenTasks":true,
  "launch":{"yolo":true}
}'
```

Create defaults to enabled: true and desired_state: stopped. It does not start a process. Add `--persisted-start` only to persist desired_state: running; that still does not start a runtime in this M2 command. The JSON payload is an allowlist of the roster-v2 fields shown above plus `launch.yolo`; command, channel, secret-reference, and other unknown keys are rejected rather than ignored. The JSON error exposes only a stable code, never the rejected value.

## Update and delete safely

```fleet-synopsis
mosaic fleet update <name> --expected-generation <n> --agent '<complete JSON agent payload>'
mosaic fleet delete <name> --expected-generation <n>
```

Updates require a complete agent JSON payload and preserve the stable name. Delete removes only the exact roster-owned `coder0.env.generated` projection. It retains `coder0.env.local`, legacy `coder0.env`, `coder0.env.quarantine`, and every unrelated projection. A delete dry-run leaves all of those files byte-identical.

## Handle generation conflicts

Every mutation requires the current authoritative `--expected-generation`. A stale value returns JSON error.code: "stale-generation" with a non-zero exit. Reload with mosaic fleet get <name> or reread the roster, plan again using the returned generation, then retry. A concurrent mutation returns `concurrent-mutation`; do not force or bypass the lock.

## Interpret partial failures

The roster is authoritative and is written before derived projections. A late projection I/O failure returns non-zero with redacted, actionable JSON:

```json
{
  "applied": false,
  "authoritativeRoster": "committed",
  "projections": "incomplete",
  "recovery": {
    "code": "projection-apply-failed",
    "action": "regenerate-projections-from-roster"
  }
}
```

This is not a rollback and not a no-op: reload the roster because its generation and membership were committed, regenerate projections from that roster, then plan a new mutation. Recovery output never contains environment values, credentials, or command text.

## Exit and boundary behavior

Handled validation errors and partial projection failures exit non-zero. `plan`/`--dry-run` and normal mutation JSON make the state explicit; scripts should use both the exit code and `authoritativeRoster`/`projections`, not `applied` alone.

The commands operate only on <mosaic-home>/fleet/roster.yaml, the local roster desired-state authority. They do not accept arbitrary commands, channels, secrets, remote/connector actions, migration/canary actions, or runtime lifecycle operations.
