test: replace time.Sleep with deterministic synchronization in unit tests

Replace three time.Sleep usages in tests with channel-based and
happens-before reasoning:

- internal/ior_mode_test.go: waitForStreamRows no longer polls with
  time.Sleep(1ms); starter() only returns after the trace goroutine
  closes the started channel, which happens after all printCb pushes,
  forming a happens-before edge that guarantees the rows are visible.

- internal/probemanager/manager_test.go: the intermediate attach-count
  assertions (enter==1, exit==0) are now checked immediately after
  <-enterBlocked, which is itself a happens-before edge, rather than
  after a 50ms sleep. The concurrent goroutine 2 is started afterwards;
  the final count assertions after both goroutines complete verify the
  serialization invariant.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 16 insertions, 8 deletions

diff --git a/internal/probemanager/manager_test.go b/internal/probemanager/manager_test.go
index 2beb11e..b75a579 100644
--- a/internal/probemanager/manager_test.go
+++ b/internal/probemanager/manager_test.go
@@ -158,19 +158,27 @@ func TestManagerAttachSerializesConcurrentCalls(t *testing.T) {
 		t.Fatal("first attach did not start")
 	}
 
-	errCh2 := make(chan error, 1)
-	go func() {
-		errCh2 <- mgr.Attach("close")
-	}()
-
-	time.Sleep(50 * time.Millisecond)
+	// Goroutine 1 is now blocked inside AttachTracepoint for the enter probe.
+	// Enter has been called exactly once; exit has not been called yet because
+	// attachPair calls enter then exit sequentially.  These assertions are safe
+	// without any sleep: enterBlocked being closed is a happens-before edge that
+	// makes the attach-count writes visible here.
 	if got := enter.attachCalls(); got != 1 {
-		t.Fatalf("expected only one enter attach while first call was in flight, got %d", got)
+		t.Fatalf("expected enter attach to be in flight (called once), got %d", got)
 	}
 	if got := exit.attachCalls(); got != 0 {
-		t.Fatalf("expected exit attach to wait for enter completion, got %d", got)
+		t.Fatalf("expected exit attach to not have started while enter is blocked, got %d", got)
 	}
 
+	// Start a second concurrent Attach.  It will acquire m.mu briefly then
+	// block on entry.attachMu (held by goroutine 1) before it can reach
+	// AttachTracepoint.  The final count assertions below confirm it never ran
+	// a second attach.
+	errCh2 := make(chan error, 1)
+	go func() {
+		errCh2 <- mgr.Attach("close")
+	}()
+
 	close(releaseEnter)
 
 	if err := <-errCh1; err != nil {