fix: handle negative keepalive replies

[skevetter]

Summary

• require both ok == true and err == nil before resetting server keepalive state
• apply the check to channel-level and connection-level keepalive requests
• add regressions proving negative replies do not postpone transport teardown

Verification

• go test ./...
• git diff --check

Summary by CodeRabbit

• Bug Fixes

  • Improved SSH connection keep-alive handling so negative replies no longer incorrectly reset connection activity timers.
  • Stalled connections can now close as expected when keep-alive requests are rejected.

• Tests

  • Added coverage for rejected global and channel keep-alive replies.
  • Simplified test syntax without changing behavior.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Team

Run ID: d0e7ec51-ee15-48bf-8f58-e192a3ec54a6

📥 Commits

Reviewing files that changed from the base of the PR and between 9f0e347 and 0245983.

📒 Files selected for processing (3)

• options_test.go
• server.go
• server_test.go

Included review availability: Your plan provides up to 1 included review per hour; 0 remain after this review.

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📝 Walkthrough

Walkthrough

Changes

The server now resets keepalive liveness timers only after positive replies. New tests cover negative global and channel replies. Test code also removes redundant atomic-expression parentheses.

Keepalive validation

Layer / File(s)	Summary
Reply-aware keepalive handling server.go, server_test.go	connectionKeepAlive checks both the error and boolean reply. Tests verify that negative global and channel replies do not reset the liveness deadline.
Atomic expression cleanup options_test.go	Test code removes redundant parentheses from atomic field address expressions.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to 02459

The change prevents negative keepalive replies from postponing transport teardown while preserving successful keepalive behavior, with regressions covering both request levels. No actionable merge-blocking risk remains beyond normal checks and review.

Sequence Diagram(s)

sequenceDiagram
  participant connectionKeepAlive
  participant sshConn
  participant SSHPeer
  participant ConnectionClosingCallback
  connectionKeepAlive->>sshConn: SendRequest keepalive
  sshConn->>SSHPeer: Send keepalive
  SSHPeer-->>sshConn: Negative reply
  connectionKeepAlive->>connectionKeepAlive: Keep liveness deadline
  connectionKeepAlive->>ConnectionClosingCallback: Close after failure threshold

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🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 75.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
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.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: handling negative keepalive replies correctly.

• Fix all pre-merge checks with AI

✨ Finishing Touches

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch fix/keepalive-negative-replies

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