Test faithful on/off-task crediting through RecordWindow

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/session/session_test.go

@@ -1465,3 +1465,46 @@ func TestReflectionBlockOmitsEmptyOffTaskList(t *testing.T) {
 		t.Errorf("totals line missing or wrong, got:\n%s", got)
 	}
 }
+
+func TestRecordWindowCreditsSplitFaithfully(t *testing.T) {
+	c, _ := newTestController(t)
+	clk := &fakeClock{now: time.Unix(1000, 0)}
+	c.SetClock(clk.fn())
+	c.SetDriftJudge(&fakeJudge{verdict: ai.Verdict{OnTask: false, Reason: "off"}})
+
+	c.RecordWindow(snap("code", "main.go")) // latest window before start
+	startActive(t, c, []string{"code"})     // seeds code/main.go at t=1000, driftStatus idle
+
+	clk.advance(5 * time.Minute)
+	c.RecordWindow(snap("code", "main.go")) // credits 5m to code/main.go while idle -> unclassified; now on-task (local match)
+	clk.advance(10 * time.Minute)
+	c.RecordWindow(snap("code", "main.go")) // credits 10m on-task
+	clk.advance(10 * time.Minute)
+	c.RecordWindow(snap("firefox", "YouTube")) // credits 10m on-task (total 20m); firefox -> judge (pending)
+	waitDriftStatus(t, c, "drifting")          // wait for the async verdict before crediting the firefox segment
+
+	clk.advance(8 * time.Minute)
+	c.RecordWindow(snap("firefox", "Reddit")) // credits 8m to firefox/YouTube while drifting -> off-task; cache keeps drifting
+	clk.advance(4 * time.Minute)
+	if err := c.Complete(); err != nil { // flush: credits 4m to firefox/Reddit while drifting -> off-task
+		t.Fatalf("complete: %v", err)
+	}
+
+	c.mu.Lock()
+	got := c.buildReflectionFinishedLocked()
+	c.mu.Unlock()
+
+	want := "Next action: write report\n" +
+		"Success condition: report drafted\n" +
+		"Outcome: completed\n" +
+		"On-task 20m / Off-task 12m / Unclassified 5m\n" +
+		"Context switches: 2\n" +
+		"On-task:\n" +
+		"- code · main.go: 20m\n" +
+		"Off-task:\n" +
+		"- firefox · YouTube: 8m\n" +
+		"- firefox · Reddit: 4m"
+	if got != want {
+		t.Errorf("faithful split mismatch:\n--- got ---\n%s\n--- want ---\n%s", got, want)
+	}
+}