feat: coordinate concurrent CBM sessions

[DeusData]

Summary

Adds one mandatory per-account coordination daemon for long-lived MCP and hook sessions.

• The first daemon-backed session starts the daemon; the final session shuts it down.
• Watchers, indexing jobs, resource state, and the optional UI are shared across Claude Code, Codex, OpenCode, and other clients.
• Work remains session-owned: disconnecting one session cancels its exclusive work while shared work continues.
• One-shot CLI commands stay local and leave no daemon behind. They use coordinated admission and per-project locks, and can be cancelled safely during maintenance.
• Interactive CLI commands show progress on stderr; stdout remains machine-safe.

Coordination and activation

All concurrent CBM processes must agree on the exact version, executable build, coordination ABI, and canonical CBM_CACHE_DIR. Conflicting processes fail before doing work, report the conflict to the launching session, and record it in daemon-conflicts.ndjson.

Native install, update, and uninstall commands:

1. download, verify, and stage the candidate;
2. publish account-wide maintenance intent;
3. cancel daemon sessions and temporary CLI operations;
4. wait for coordinated processes to exit;
5. activate atomically while holding exclusive admission barriers;
6. log the outcome and tell the user to restart open coding-agent sessions.

Windows uses a permanent launcher with an atomically replaceable payload, allowing the same lifecycle guarantees despite executable-file locking. npm, PyPI, and Go wrappers verify and publish their private cached binaries safely.

Security and observability

• Local IPC authenticates the connecting OS account using Unix peer credentials or Windows access-token checks.
• Coordination state, locks, logs, and activation files use private permissions and fail closed when ownership, ACLs, path identity, or namespace validation is unsafe.
• MCP stdout remains reserved for JSON-RPC; immediate session failures use stderr.
• Durable daemon, conflict, and activation logs are written beneath the canonical cache root.
• No third-party runtime dependency or external coordination service is introduced.

Verification

• Full C ASan/UBSan suite: 6,723 passed, 2 skipped
• Daemon frontend tests: 12/12 passed
• CLI tests: 255/255 passed
• Main-sync affected suites: 365/365 passed
• npm wrapper tests: 10/10 passed
• Python wrapper tests: 3/3 passed
• Go wrapper tests and Windows amd64 cross-compilation passed
• Windows launcher/bundle contracts passed
• Parent and worker watchdog tests passed
• Production smoke: all phases passed
• MCP robustness fuzzing: 23/23 passed, including harness anti-false-positive checks
• Static security audit, vendored integrity, formatting, cppcheck, and lint passed
• End-to-end daemon lifecycle smoke passed for shared startup/shutdown, bidirectional version conflicts, coordinated maintenance, CLI cancellation, and per-session cancellation