fix: show warning when live usage crosses threshold (first response case)

Previously shouldShowWarning only used lastUsagePercentage, so the warning
never appeared during the first streaming response. Now uses max of last
and live usage, ensuring the countdown renders when it should.

Author: ethanndickson

src/browser/utils/compaction/autoCompactionCheck.test.ts

@@ -369,6 +369,30 @@ describe("checkAutoCompaction", () => {
       expect(result.usagePercentage).toBe(75); // usagePercentage reflects live even with empty history
     });
 
+    test("shouldShowWarning uses live usage when no history exists", () => {
+      // No lastUsage, liveUsage at 65% - should show warning (65% >= 60%)
+      const liveUsage = createUsageEntry(130_000); // 65%
+      const usage: WorkspaceUsageState = {
+        usageHistory: [],
+        totalTokens: 0,
+        liveUsage,
+      };
+      const result = checkAutoCompaction(usage, KNOWN_MODELS.SONNET.id, false);
+
+      expect(result.shouldShowWarning).toBe(true);
+      expect(result.shouldForceCompact).toBe(false); // 65% < 75%
+    });
+
+    test("shouldShowWarning uses max of last and live usage", () => {
+      // lastUsage at 50% (below warning), liveUsage at 72% (above warning)
+      const liveUsage = createUsageEntry(144_000); // 72%
+      const usage = createMockUsage(100_000, undefined, KNOWN_MODELS.SONNET.id, liveUsage);
+      const result = checkAutoCompaction(usage, KNOWN_MODELS.SONNET.id, false);
+
+      expect(result.shouldShowWarning).toBe(true); // 72% >= 60%
+      expect(result.shouldForceCompact).toBe(false); // 72% < 75%
+    });
+
     test("shouldForceCompact is false when auto-compaction disabled", () => {
       const usage = createMockUsage(190_000); // 95% - would trigger if enabled
       const result = checkAutoCompaction(usage, KNOWN_MODELS.SONNET.id, false, 1.0); // disabled

src/browser/utils/compaction/autoCompactionCheck.ts

@@ -106,9 +106,11 @@ export function checkAutoCompaction(
   const forceCompactThreshold = thresholdPercentage + FORCE_COMPACTION_BUFFER_PERCENT;
   const shouldForceCompact = usagePercentage >= forceCompactThreshold;
 
-  // Warning based on last completed usage (not live) to avoid flickering
+  // Warning uses max of last completed and current (live when streaming)
+  // This ensures warning shows when live usage spikes above threshold mid-stream
   const lastUsagePercentage = lastUsage ? (getTotalTokens(lastUsage) / maxTokens) * 100 : 0;
-  const shouldShowWarning = lastUsagePercentage >= thresholdPercentage - warningAdvancePercent;
+  const shouldShowWarning =
+    Math.max(lastUsagePercentage, usagePercentage) >= thresholdPercentage - warningAdvancePercent;
 
   return {
     shouldShowWarning,