Event-sourced management of MCP servers for qwen sessions: a catalog of
server templates (command/args/headers with ${VAR} holes) bound per
project, projected to SQLite, and handed to qwen via a per-project
settings overlay.

Core
- packages/mcp-core: config resolver, connectivity probe, structural
  config identity + overlay fingerprint, tool-policy model.

Server
- Catalog/bindings as event-sourced commands + projections; config-
  uniqueness guard, required-var validation, built-in template sync.
- Overlay engine: writes the per-project qwen settings overlay
  (QWEN_CODE_SYSTEM_SETTINGS_PATH) + server allowlist at turn-start; the
  provider reactor respawns the session only when the overlay fingerprint
  changes. Whole engine gated by MCP_ENGINE_USE_OVERLAY.
- Secrets live server-side only (scrypt + AES-GCM at rest), never in
  events, projections, or the client.
- Ephemeral overlay: the resolved overlay (plaintext secrets) is deleted
  on every spawn settle and swept on app start/shutdown; a new ACP start
  timeout (ACP_SESSION_START_TIMEOUT_MS) turns a wedged `qwen --acp` boot
  into an error so the cleanup reliably fires.
- Per-server trust flag, 64-bit dedup hash, readable error toasts.

Web
- MCP management UI: catalog list + detail, per-project config dialog,
  shared item card / control cluster.

Tests
- mcp-core unit tests + server integration (overlay apply & fingerprint,
  reactor respawn, secret-at-rest, ephemeral deletion, start timeout)
  plus the mcp-probe harness against real qwen.