fix(runner): unblock session send on cancellation

[linkdata]

Summary

• make runMinimiser session sends respect context cancellation
• prevent shutdown from hanging when sessionCollectorCh is full
• add a blocked-send cancellation regression test

Tests

• go test ./pkg/runner ./...

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Reviewing files that changed from the base of the PR and between b615285 and 04a2a16.

📒 Files selected for processing (2)

• pkg/runner/run_minimiser_test.go
• pkg/runner/runner.go

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[linkdata]

Additional context from comment files

These notes were split from the local markdown comment files and attached here because they describe this PR's change.

Minimiser Session Send Backpressure

• Bug: In runMinimiser(), the send to sessionCollectorCh at line 2121 was a plain blocking send. If the channel filled up (capacity 100), the minimiser goroutine would block inside the inputFrame processing case and could never reach the outer case <-edm.ctx.Done() to exit.
• Impact: A slow or stalled dataCollector could prevent minimiser workers from shutting down gracefully, blocking minimiserWg.Wait() and stalling the entire shutdown sequence including the histogram flush.
• Fix: Wrapped the channel send with a select that includes case <-edm.ctx.Done(), allowing the minimiser to exit when context is cancelled even if the channel is full.
• Reasoning: All sends inside the main minimiser select must have a context escape hatch to honour graceful shutdown.
• Tests: Added TestRunMinimiserSessionSendUnblocksOnContextCancel which fills sessionCollectorCh to capacity and verifies the minimiser exits promptly (within 2 seconds) when context is cancelled.