fix(backend): add context cancellation to between-run listener goroutines

[Gkrumbach07]

Summary

• Prevents goroutine leaks when runner pods die without closing TCP connections
• Adds context.Context to between-run listener goroutines for clean cancellation

Changes

• Store context.CancelFunc in betweenRunListeners map (was struct{})
• Use http.NewRequestWithContext so context cancellation closes the HTTP response body and unblocks ReadString
• Replace time.Sleep with select{} on ctx.Done for interruptible backoff
• cleanupStaleSessions calls the CancelFunc to terminate the goroutine
• Check ctx.Err() at retry boundaries to exit promptly on cancellation

Why

Without context cancellation, if a runner pod dies (e.g., OOM kill) without sending EOF, the listener goroutine blocks forever on ReadString('\n'). Each leaked goroutine holds ~8KB stack + one open TCP connection. The sync.Map entry stays, preventing new listeners for that session.

Test plan

• go build ./... passes
• Deploy and verify goroutines exit when sessions are cleaned up

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: ab45a95f-5e5f-4d8d-826f-bb2bccf8d48b

📥 Commits

Reviewing files that changed from the base of the PR and between 03f9f1f and 2cc1f76.

📒 Files selected for processing (1)

• components/backend/websocket/agui_proxy.go

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Walkthrough

Refactors between-run listener lifecycle management in the websocket proxy by replacing sentinel values with context.CancelFunc storage. The listener now uses context-based cancellation for graceful shutdown and goroutine cleanup, replacing time-based backoffs with context-aware select blocks and applying context to SSE HTTP requests.

Changes

Cohort / File(s)

Summary

Between-run Listener Lifecycle components/backend/websocket/agui_proxy.go

Refactored listener lifecycle from sentinel-based to context-based cancellation. betweenRunListeners now stores context.CancelFunc instead of struct{}. ensureBetweenRunListener creates cancellable contexts and stores cancel functions; duplicate startups cancel the new context to prevent orphans. Stale session cleanup invokes LoadAndDelete on stored cancel functions. listenBetweenRunEvents accepts context.Context, creates SSE requests via http.NewRequestWithContext, replaces time.Sleep backoffs with context-aware select blocks, closes response bodies on context cancellation, and exits early when context is done.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: adding context cancellation to between-run listener goroutines to fix resource leaks.
Description check	✅ Passed	The description is directly related to the changeset, explaining the problem, solution, specific changes, rationale, and test plan.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/between-run-listener-context

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Review Queue Status

Check	Status	Detail
CI	FAIL	CodeQL check failed
Conflicts	pass	---
Reviews	pass	---

Action needed: Fix CodeQL failure

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