fix(core): ensure hard threshold always exceeds auto threshold

packages/core/src/services/chatCompressionService.test.ts

@@ -1883,14 +1883,23 @@ describe('ChatCompressionService.compress cheap-gate uses estimated tokens', ()
 });
 
 describe('computeThresholds', () => {
-  it('32K window — proportional fallback for all tiers, hard degrades to auto', () => {
+  it('32K window — proportional fallback for all tiers, hard = auto + HARD_BUFFER', () => {
     const t = computeThresholds(32_000);
     expect(t.warn).toBe(19_200); // 0.6 * 32K
     expect(t.auto).toBe(22_400); // 0.7 * 32K
-    expect(t.hard).toBe(22_400); // max(window-23K=9K, auto=22.4K) = auto
+    expect(t.hard).toBe(25_400); // auto + HARD_BUFFER = 22.4K + 3K
     expect(t.effectiveWindow).toBe(12_000);
   });
 
+  it('60K window — hard no longer equals auto (issue #4945)', () => {
+    const t = computeThresholds(60_000);
+    expect(t.warn).toBe(36_000); // 0.6 * 60K
+    expect(t.auto).toBe(42_000); // 0.7 * 60K (pct wins: 42K vs ew-13K=27K)
+    expect(t.hard).toBe(45_000); // auto + HARD_BUFFER = 42K + 3K
+    expect(t.hard).toBeGreaterThan(t.auto);
+    expect(t.effectiveWindow).toBe(40_000);
+  });
+
   it('128K window — mixed (warn=pct, auto/hard=abs)', () => {
     const t = computeThresholds(128_000);
     expect(t.warn).toBe(76_800); // 0.6 * 128K (pct wins: 76.8K vs auto-20K=75K)
@@ -1933,11 +1942,13 @@ describe('computeThresholds', () => {
     expect(t.hard).toBe(0);
   });
 
-  it('thresholds always satisfy warn <= auto <= hard', () => {
-    for (const w of [32_000, 64_000, 128_000, 200_000, 256_000, 1_000_000]) {
+  it('thresholds always satisfy warn <= auto < hard for non-zero windows', () => {
+    for (const w of [
+      10_000, 32_000, 60_000, 64_000, 128_000, 200_000, 256_000, 1_000_000,
+    ]) {
       const t = computeThresholds(w);
       expect(t.warn).toBeLessThanOrEqual(t.auto);
-      expect(t.auto).toBeLessThanOrEqual(t.hard);
+      expect(t.auto).toBeLessThan(t.hard);
     }
   });
 });

packages/core/src/services/chatCompressionService.ts

@@ -120,7 +120,7 @@ export interface CompactionThresholds {
  * Each tier is `max(proportional, absolute)`:
  *   auto = max(DEFAULT_PCT * window,                       effectiveWindow - AUTOCOMPACT_BUFFER)
  *   warn = max((DEFAULT_PCT - WARN_PCT_OFFSET) * window,   auto - WARN_BUFFER)
- *   hard = max(effectiveWindow - HARD_BUFFER,              auto)   // hard degrades to auto for tiny windows
+ *   hard = min(window, max(effectiveWindow - HARD_BUFFER,  auto + HARD_BUFFER))
  *
  * Small windows (where the absolute branch goes negative) automatically
  * fall back to the proportional branch. Large windows are dominated by
@@ -144,7 +144,10 @@ export function computeThresholds(window: number): CompactionThresholds {
   const warn = Math.max((DEFAULT_PCT - WARN_PCT_OFFSET) * window, absWarn);
 
   const rawHard = effectiveWindow - HARD_BUFFER;
-  const hard = Math.max(rawHard, auto);
+  // Guarantee hard > auto so compaction doesn't wait until the last moment.
+  // For tiny/zero windows where auto is already at the proportional floor,
+  // clamp hard to the window itself so it never exceeds the actual limit.
+  const hard = Math.min(window, Math.max(rawHard, auto + HARD_BUFFER));
 
   return { warn, auto, hard, effectiveWindow };
 }