fix(monitor): implement WaitGroup synchronization and context gates to prevent shutdown panic #324

[Shubham-Gotawade]

Contributed as part of GSSoC '26.

Problem Description

When a system shutdown or manual cancellation was triggered while background monitoring operations (checkCommits, checkIssues, etc.) were actively making GitHub API calls, the orchestration thread would close out the primary notification pipeline channel immediately. Concurrently active worker routines finishing their network tasks would then blindly attempt to push payloads into the defunct channel, causing an unrecoverable runtime crash: panic: send on closed channel. Fixes #324.

Solution Implemented

1. Synchronized Worker Lifecycle: Integrated a sync.WaitGroup (workerWg) to explicitly monitor the lifecycles of all four parallel analytics modules running inside checkForUpdates.
2. Deterministic Pipeline Drain: Re-engineered the core execution cycle to block channel teardown until the active worker threads have completely un-registered from the wait group, establishing a strict chronological ordering gate.
3. Non-Blocking Channel Multiplexing: Wrapped all internal payload pushes inside a safe, context-aware select block:

   select {
   case <-m.ctx.Done():
       return
   case m.notifications <- notification:
   }

This ensures that any routine waking up post-cancellation instantly aborts execution instead of attempting an illegal write to a closed channel.
4. Data Race Eradication: Added explicit read-write mutual exclusion locks (sync.RWMutex) across all background evaluation routines and data persistence hooks (saveState) to guarantee complete memory visibility safety during parallel sweeps.
5. Simulated Panic Regression Test: Authored a specialized verification harness simulating high-concurrency event drops during rapid shutdown cycles. The test confirms clean, zero-fault exits across all parallel tracks.

Verification & Test Logs

Verified successfully on the local testbed setup:

go test -v ./internal/monitor/...: PASSED (All graceful shutdown edge cases fully validated)

go build ./...: PASSED (Clean binary compilation metrics)

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Reviewing files that changed from the base of the PR and between 6d6fa89 and c7ab775.

📒 Files selected for processing (1)

• internal/monitor/monitor.go

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