fix(test): Stop TestServerHandlesLoadsOfPendingTasks deadlocking

[keelerm84]

Summary

TestServerHandlesLoadsOfPendingTasks deadlocks intermittently and fails the build with panic: test timed out. On main at 90772ec it reproduced at iteration 6 of 20 running the test alone, and at iteration 4 of 20 running the full suite.

The test opened a subscriber with http.Get, discarded the response, and never closed the body or the Server. The SSE handler kept that connection open indefinitely, so the deferred httptest.Server.Close() blocked in its wait-for-outstanding-requests loop. The goroutine dump puts the test at server_test.go:76 inside net/http/httptest.(*Server).Close. Whether it finished depended on whether the runtime had released the connection by then, which is what made it intermittent.

Closing the subscriber cancels the request context, so the handler returns and httptest can finish. TestServerHandlerReceivesPublishedEvents right below it already does exactly this.

The sync.WaitGroup goes away with it. http.Get returns once the handler flushes the SSE response headers, so nothing was needed to hold the connection open across the publish loop -- the WaitGroup only delayed the goroutine's exit, and the goroutine was not doing anything after the Get.

Defer order is load-bearing and called out in a comment: the subscriber disconnects, then the Server stops, then httptest waits for the handler. Each step is what lets the next one finish.

Verification

• The fixed test: 60 consecutive runs, no failures.
• The full suite: 12 consecutive runs, no failures, plus -race.
• Before the fix, the same loops failed within 20 runs.

Origin

Found while verifying #75. That change touches only the client's error-response path, and this flake reproduces on main without it, so the two are independent.

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Note

Overview
Fixes an intermittent test timeout in TestServerHandlesLoadsOfPendingTasks by tearing down the SSE subscriber and server in a defined order instead of leaving an open http.Get connection.

The test now keeps the subscriber connected during the 1000 PublishComment calls (response body held open until defer resp.Body.Close()), adds defer server.Close(), and drops the sync.WaitGroup + background goroutine pattern that did not actually coordinate shutdown. Comments document why defer order matters: close the body first so the handler exits, then stop the Server, then let httptest finish waiting.

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