fix(chat): keep MCP server connections alive across their lifetime

[localai-bot]

Summary

• ReconcileMCPServers connected user-configured MCP servers with a 30s-timeout context and called cancel() immediately after Connect() returned.
• The go-sdk's mcp.Client.Connect stores the context it's given for the connection's entire lifetime, not just the initial handshake — StreamableClientTransport.Connect derives a cancellable context from it to drive the background "hanging GET" SSE listener and reconnect machinery.
• Cancelling that context right after connect tore down the background SSE listener, so a later tool call on an otherwise-connected, healthy server that needed to re-establish its SSE stream failed with the real, user-reported error chain:

  connection closed: calling "tools/call": client is closing:
  hanging GET: failed to reconnect (session ID: ...):
  connection failed after 5 attempts: Get "https://<server>":
  context canceled
  

• Fix: hand Connect the session's own long-lived context (s.ctx) directly, with no per-connect timeout — mirroring the built-in host-tool connect path in NewSession, which has never exhibited this bug. Deleting only the cancel() call would not have been sufficient: the WithTimeout wrapper itself would still auto-cancel the connection 30s after connecting.
• Found via live debugging of a real nib-desktop user report, after two earlier, legitimate fixes (transport selection, built-in-tools allowlist scoping — this repo's PR fix(chat): built-in tools allowlist no longer filters user-configured MCP servers #41) resolved the symptom of no tools showing up, but this context-lifetime bug is what actually broke tool calls on an already-connected server.

Testing

• Added TestReconcileMCPServersKeepsConnectionAliveForToolCalls (chat/session_reload_test.go): stands up a real streamable-HTTP MCP server and asserts the background hanging-GET SSE stream is not torn down once ReconcileMCPServers returns. Confirmed it fails on the pre-fix code and passes on the fix.
• go build ./..., go vet ./..., go test ./... — 100% green across all packages.

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