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feat(#828): add authenticated lease broker

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Bind broker sessions to Linux SO_PEERCRED and /proc starttime ancestry, fence runtime generations, persist cryptographic single-use cycle tokens, and enforce protected Unix socket/state posture.\n\ncloses #828
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2026-07-17 20:45:00 -05:00
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docs/guides/lease-broker-operations.md Normal file
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# 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.
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 in WI-1. After a crash, preserve the protected state file and restart only after verifying that no broker owns the socket. 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 minimum same-principal hardening: 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. The stronger deployment runs the broker as a distinct principal behind a protected service boundary whose clients cannot unlink or rebind the socket; that is the T-C-closing option. Server-side branch protection remains the irreducible backstop.