# Lease broker operations

Place the socket and state file in a dedicated directory with mode `0700`. Start the packaged daemon with:

```bash
python3 "$MOSAIC_HOME/tools/lease-broker/daemon.py" \
  --socket /run/user/1000/mosaic-lease/broker.sock \
  --state /run/user/1000/mosaic-lease/state.json
```

The broker refuses an existing parent directory whose mode is not exactly `0700`, an existing state file not at `0600`, corrupt/incompatible state, or an already-existing socket path. After bind it sets the socket to `0600`. It never silently unlinks a pre-existing socket. On normal termination it unlinks only the socket inode it created, so it does not remove a replacement path.

Before launching Claude or Pi, export the socket path; `mosaic` then runs the runtime through the packaged register-and-exec wrapper:

```bash
export MOSAIC_LEASE_BROKER_SOCKET=/run/user/1000/mosaic-lease/broker.sock
mosaic claude # or: mosaic pi
```

The wrapper obtains a broker-minted session ID and `exec`s the runtime without changing its PID/starttime anchor. The all-tools Claude `PreToolUse` hook and Pi `tool_call` handler inherit that identity. Broker registration failure denies runtime launch; missing identity, broker timeout/unavailability, and malformed replies block tools fail-closed.

Clients must complete the request boundary before waiting for a reply. After sending the single JSON object and its terminating newline, the client **MUST half-close the socket's write side** (`shutdown(SHUT_WR)` in POSIX clients; `socket.end()` in Node) and only then await the response. Merely calling `write()` and waiting is invalid: the broker waits for EOF to enforce the exact-one-frame contract and fails closed at its one-second deadline. Do not replace `end()` with `write()` in client helpers. A delayed second frame remains malformed and is rejected.

There is no automated recovery workflow yet. `mosaic_context_recover` is reserved as the only unverified mutator class, but its fixed payload/receipt implementation lands in a later WI. After a crash, preserve the protected state file and restart only after verifying that no broker owns the socket. Restart intentionally clears all volatile VERIFIED leases. A leftover socket requires an operator to verify the owning service is stopped and remove that exact socket deliberately. Corrupt, oversized, symlinked, or non-regular state fails closed; do not overwrite it. Preserve it for incident review and establish new state only through an explicit operational decision, which invalidates prior sessions and tokens.

## Security posture

Directory `0700` plus socket/state `0600` is built-in same-principal hardening only: it excludes other UIDs but does **not** stop the same UID from unlinking and counterfeiting the socket. It therefore does not close T-C same-UID replacement. WI-1 does not provide a distinct-principal boundary. A stronger distinct-principal deployment requires an external protected proxy, ACL, or service boundary that clients cannot unlink or rebind and that preserves the authenticated client identity required by the broker's `SO_PEERCRED` and ancestry checks. Server-side branch protection remains the irreducible backstop.