fix: trigger reconnect after failed live-connection check instead of re-probing the same dead session

[Pratham-Mishra04]

Summary

When a live connection check fails, the dead connection remains installed on the client entry. Without an explicit reconnect trigger at that point, every subsequent checker tick re-probes the same dead session indefinitely, and the Conn == nil branch that would normally initiate a reconnect is never reached while a connection is installed.

Changes

• Added reconnectAfterFailedCheck which fires a background ReconnectClient call immediately after a failed live connection check, so the dead connection is replaced rather than re-probed on every tick.
• The method includes a staleness guard: if the connection generation has advanced (a reconnect already replaced the dead session), or the client is in Disabled or NeedsReauth state, the reconnect is skipped. Disabled and NeedsReauth are checked independently of the generation because neither DisableClient nor CloseAndMarkNeedsReauth bumps ConnGeneration when clearing the connection.
• Concurrent reconnect attempts (e.g. from the reactive per-request path) are safe to ignore since ReconnectClient deduplicates attempts per client through its own exclusive-op guard.
• Added tests covering the staleness guard cases: a check that spanned a reconnect, a client disabled mid-check, a client in NeedsReauth, and a current-generation failure on a live client that should redial.

Type of change

• Bug fix

Affected areas

• Core (Go)

How to test

go test ./core/mcp/...

The new test TestReconnectAfterFailedCheck_StaleOrAuthoritativeState_DoesNotReconnect validates the guard logic across all four cases. The existing TestPerformCheck_LiveConn_FailedCheck_TriggersReconnect confirms the dead connection is replaced rather than re-probed.

Breaking changes

• No

Security considerations

None. This change only affects reconnect scheduling logic for MCP client connections and does not touch auth, secrets, or PII handling.

Checklist

• I read docs/contributing/README.md and followed the guidelines
• I added/updated tests where appropriate
• I updated documentation where needed
• I verified builds succeed (Go and UI)
• I verified the CI pipeline passes locally if applicable

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[Pratham-Mishra04]

• fix: widen OAuth2 client-controlled columns (state, scope, client_name) from varchar to text to stop Postgres rejecting long values with server_error #7405
• docs: add reregister endpoint and "Reauthorizing with a new client" section for invalid/dropped DCR client recovery #7230
• feat: add "Reauthorize with a new client" action to re-register OAuth client when provider rejects the existing client_id #7229
• feat: add ReregisterDynamicClient and POST /api/mcp/client/{id}/reregister to recover from evicted DCR registrations #7228
• fix: surface context-aware rejection message when inbound bearer token is rejected during delegated exchange #7051
• docs: add authenticated-user-without-access-profile breaking change and clarify allow_by_default scope in v2.1.0 changelog #7050
• feat: add flow_id to reauthorize status polling so stale "authorized" config status is not mistaken for a completed consent #7041
• docs: add refresh-tools endpoint and Manual Tool Refresh section across MCP connection docs #6929
• feat: add "Refresh tools" action to MCP client table for immediate tool re-discovery #6928
• feat: add RefreshMCPClientTools for on-demand tool rediscovery across all client types #6927
• docs: overhaul health monitoring docs to reflect adaptive cadence, automatic reconnect recovery, and simplified config knob #6931
• test: add STDIO respawn and SSE stream-drop checker reconnect tests #6930
• fix: preserve pending_verification state through EnableClient and connection checker #6926
• chore: clarify that connect-failure checker stops itself rather than retrying and rename test to match #6925
• fix: retry probe timeouts but treat dead sessions and auth failures as permanent in ProbeRetryConfig #6924
• feat: extend dead-session detection and recovery to executeToolInternal, renaming attemptAuthFailureRecovery to attemptCallFailureRecovery #6923
• fix: trigger reconnect after failed live-connection check instead of re-probing the same dead session #6922 👈 (View in Graphite)
• fix: preserve live connection on failed make-before-break re-dial instead of tearing it down #6921
• dev

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📝 Summary

Summary by CodeRabbit

• Bug Fixes

  • Improved connection recovery after failed live checks by preventing reconnect attempts for stale, disabled, or reauthentication-required connections.
  • Current unstable connections can still reconnect automatically when appropriate.

• Tests

  • Added coverage for reconnect behavior across stale, disabled, reauthentication-required, and recoverable connection states.

Walkthrough

Failed MCP connection checks now use a guarded asynchronous reconnect helper. The helper skips missing, stale, disabled, or reauthentication-required clients. A table-driven test verifies guarded states and the valid unstable state.

Changes

MCP reconnect guards

Layer / File(s)	Summary
Failed-check reconnect flow core/mcp/connectionchecker.go	Failed live checks now delegate reconnect initiation to reconnectAfterFailedCheck.
Reconnect state validation and tests core/mcp/connectionchecker.go, core/mcp/connectionchecker_reconnect_test.go	The helper validates client existence, connection generation, and reconnectable state before starting asynchronous reconnects. Tests cover stale, disabled, reauthentication-required, and current-generation unstable states.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: 🟡 Moderate · up to 768f6

Failed connection checks now initiate automatic reconnects, but a concurrent disablement, reauthentication requirement, or client replacement can still be bypassed by the delayed reconnect. Resolve this synchronization gap before merging to preserve intended client state behavior.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 2 files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly identifies the main change: triggering a reconnect after a failed live-connection check instead of repeatedly probing the dead session.
Description check	✅ Passed	The description explains the problem, implementation, guards, tests, affected area, change type, breaking-change status, and security impact. It omits the Screenshots/Recordings and Related issues sec…

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Actionable comments posted: 1

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Inline comments:
In `@core/mcp/connectionchecker.go`:
- Around line 325-329: Update the reconnect flow around ReconnectClient so
expected-generation and reconnectable-state validation occur under the exclusive
reconnect guard, immediately before snapshotting client configuration and
dialing. Revalidate against the captured generation and terminal states there,
preserving race-safe access to shared client state and preventing replaced,
disabled, or NeedsReauth clients from reconnecting.

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📥 Commits

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📒 Files selected for processing (2)

• core/mcp/connectionchecker.go
• core/mcp/connectionchecker_reconnect_test.go

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[Pratham-Mishra04]

Merge activity

• Sep 23, 6:50 AM UTC: A user started a stack merge that includes this pull request via Graphite.
• Sep 23, 6:54 AM UTC: Graphite rebased this pull request as part of a merge.
• Sep 23, 6:56 AM UTC: @Pratham-Mishra04 merged this pull request with Graphite.

The base branch was changed.