Migrate MCP from Instance.state() to Effect Service/Layer/InstanceState
pattern with makeRunPromise and async facades.

- InstanceState for per-directory lifecycle with ScopedCache
- Effect.fn tracing on all service methods
- Extract closeClient helper (was duplicated 3x)
- Extract collectFromConnected helper (prompts/resources were identical)
- Fix readResource log messages (said "prompt" instead of "resource")
- Fix finishAuthImpl not updating state after OAuth reconnect
- OAuth impl stays as plain async (inherently imperative)

- convertMcpTool is sync — drop async, use plain for loop
- Extract withClient helper for getPrompt/readResource (tryPromise)
- Extract createAndStore for add/connect/finishAuth shared pattern
- Break removeAuth into individual Effect steps
- tools() inner loop uses plain for (convertMcpTool is sync now)

Replace Filesystem.readJson/writeJson with AppFileSystem Effect service.
All auth persistence is now proper Effect with tracing. Async facades
preserved for McpOAuthProvider and CLI backward compat.

…promise wrappers

When tools() encounters a listTools() failure, fork a background
reconnection fiber via createAndStore() instead of permanently
removing the server. The current turn gets no tools from that server,
but the background fiber re-establishes the connection so tools are
available on the next turn.

Previously, a single transient error (network blip, server restart)
would permanently delete the MCP server from the session with no
recovery path.

- Push Effect.orDie into McpAuth.Service interface (no error channel)
  eliminates 11 .pipe(Effect.orDie) at call sites
- Return oauthState from startAuth, eliminate redundant read-back
- Use Option.isNone() instead of ._tag === "None"
- Reuse getMcpConfig in connect
- Unify fetchPromptsForClient/fetchResourcesForClient into fetchFromClient
- Use Effect.callback for browser subprocess detection (was Promise
  wrapping event listeners inside Effect.tryPromise)
- Simplify closeClient to Effect.promise with .catch
- Use plain try/catch for process.kill (was Effect.try with ignore)

- Remove redundant auth.clearOAuthState after auth.remove in removeAuth
- Remove dead status assignment in create() (assigned then immediately
  returned a new identical object)
- Fix mcpNameToState leak on successful/error OAuth callback completion
- Extract mcpConfig lookup once in tools() loop (was looked up twice)

…rocesses

…ecycle

…ation

tools() no longer calls listTools() on every server each turn.
Instead, tool definitions are fetched once at connect time and
cached in state. The ToolListChangedNotification handler refreshes
the cache when a server reports its tools have changed.

- Add defs to State, populated by create() and createAndStore()
- watch() registers per-client notification handler with staleness guards
- tools() reads from s.defs (zero network calls on hot path)
- closeClient() clears defs to keep cache and client lifecycle in sync
- Close old client on ALL failure paths, not just disabled
- Tests verify caching (listToolsCalls stays at 1) and notification refresh