feat: storage-time dedupe, stale pruning, and supersession (P0d)

- Project/reference entries dedupe by entity key (bilingual aware)
- Decision entries supersede by topic key (parser formats, template, etc)
- Feedback entries supersede by topic key (same issue, newer fix wins)
- Stale compaction/manual entries pruned after staleAfterDays + 30
- Explicit and feedback entries never age-pruned
- Freshness used as tie-breaker in priority-based trimming
- Adds 10 new tests covering dedup, supersession, staleness, and freshness

tests/workspace-memory.test.ts

@@ -17,6 +17,27 @@ function entry(id: string, text: string, type: LongTermMemoryEntry["type"] = "de
   };
 }
 
+/** Create an entry with a createdAt offset from now (negative = in the past) */
+function agedEntry(
+  id: string,
+  text: string,
+  type: LongTermMemoryEntry["type"] = "decision",
+  opts: { daysAgo: number; source?: "compaction" | "explicit" | "manual"; staleAfterDays?: number } = { daysAgo: 0, source: "compaction" },
+): LongTermMemoryEntry {
+  const createdAt = new Date(Date.now() - opts.daysAgo * 86400000).toISOString();
+  return {
+    id,
+    type,
+    text,
+    source: opts.source ?? "compaction",
+    confidence: 0.75,
+    status: "active",
+    createdAt,
+    updatedAt: createdAt,
+    staleAfterDays: opts.staleAfterDays,
+  };
+}
+
 // ============================================
 // Task 2: renderWorkspaceMemory tests
 // ============================================
@@ -207,4 +228,122 @@ test("enforceLongTermLimits respects maxEntries limit", () => {
 
   const kept = enforceLongTermLimits(entries);
   assert.ok(kept.length <= 28, `Should respect maxEntries. Got: ${kept.length}`);
+});
+
+// ============================================
+// P0d: identity-key dedup, supersession, staleness
+// ============================================
+
+test("enforceLongTermLimits project: bilingual variants collapse to one", () => {
+  // All three mention opencode-agenthub plugin system - should merge
+  const entries = [
+    agedEntry("p1", "此 repo 在開發時使用 opencode-agenthub 插件系統，目錄位於 /Users/sd_wo/work/opencode-working-memory/.opencode-agenthub/", "project", { daysAgo: 2 }),
+    agedEntry("p2", "此 repo 在開發時使用 opencode-agenthub 插件系統", "project", { daysAgo: 1 }),
+    agedEntry("p3", "This repo uses opencode-agenthub plugin system at /Users/sd_wo/work/opencode-working-memory/", "project", { daysAgo: 0 }),
+  ];
+
+  const kept = enforceLongTermLimits(entries);
+  const projectEntries = kept.filter(e => e.type === "project");
+  assert.equal(projectEntries.length, 1, "All three project variants should merge to one");
+});
+
+test("enforceLongTermLimits reference: same config path variants collapse to one", () => {
+  const entries = [
+    agedEntry("r1", "OpenCode plugin config location: .opencode-agenthub/current/xdg/opencode/opencode.json in workspace", "reference", { daysAgo: 1 }),
+    agedEntry("r2", "OpenCode plugin config: .opencode-agenthub/current/xdg/opencode/opencode.json in workspace", "reference", { daysAgo: 0 }),
+  ];
+
+  const kept = enforceLongTermLimits(entries);
+  const refEntries = kept.filter(e => e.type === "reference");
+  assert.equal(refEntries.length, 1, "Both reference variants should merge to one");
+});
+
+test("enforceLongTermLimits decision: newer supersedes older on same topic", () => {
+  // "4 formats" supersedes "3 formats" on the same parser topic
+  const entries = [
+    agedEntry("d1", "Parser supports 3 formats: HTML comment, Markdown section, legacy XML", "decision", { daysAgo: 2 }),
+    agedEntry("d2", "Parser supports 4 formats: plain text label, Markdown section, legacy section name, legacy XML", "decision", { daysAgo: 0 }),
+  ];
+
+  const kept = enforceLongTermLimits(entries);
+  const decisionEntries = kept.filter(e => e.text.includes("formats"));
+  assert.equal(decisionEntries.length, 1, "Newer 4-formats should supersede older 3-formats");
+  assert.ok(decisionEntries[0].text.includes("4 formats"), "Kept entry should be the 4-formats one");
+});
+
+test("enforceLongTermLimits feedback: newer supersedes older on same issue", () => {
+  const entries = [
+    agedEntry("f1", "Purple/italic text issue resolved by using plain text labels instead of any special markup syntax", "feedback", { daysAgo: 2 }),
+    agedEntry("f2", "Purple/italic text issue resolved by replacing default compaction template with ---free version using only Markdown headings", "feedback", { daysAgo: 0 }),
+  ];
+
+  const kept = enforceLongTermLimits(entries);
+  const feedbackEntries = kept.filter(e => e.type === "feedback");
+  assert.equal(feedbackEntries.length, 1, "Newer purple/italic fix should supersede older");
+  assert.ok(feedbackEntries[0].text.includes("replacing default compaction template"), "Kept entry should be the newer fix");
+});
+
+test("enforceLongTermLimits stale: compaction entry older than staleAfterDays+grace is pruned", () => {
+  // decision with staleAfterDays=45, 76 days old (> 45+30 grace=75)
+  const entries = [
+    agedEntry("stale", "Compaction output contract changed from XML to HTML comments to avoid Markdown rendering issues", "decision", { daysAgo: 76, staleAfterDays: 45 }),
+  ];
+
+  const kept = enforceLongTermLimits(entries);
+  assert.equal(kept.length, 0, "Stale compaction entry should be pruned");
+});
+
+test("enforceLongTermLimits stale: explicit entry is retained even if old", () => {
+  // explicit entry - never auto-pruned regardless of age
+  const entries = [
+    agedEntry("old_explicit", "User explicitly set Admin PIN 456123 for the system", "reference", { daysAgo: 500, source: "explicit", staleAfterDays: 90 }),
+  ];
+
+  const kept = enforceLongTermLimits(entries);
+  assert.equal(kept.length, 1, "Explicit entry should never be age-pruned");
+});
+
+test("enforceLongTermLimits stale: feedback entry is retained regardless of age", () => {
+  // feedback - never age-pruned (only superseded)
+  const entries = [
+    agedEntry("old_feedback", "Users prefer darker themes over light themes", "feedback", { daysAgo: 300, staleAfterDays: 30 }),
+  ];
+
+  const kept = enforceLongTermLimits(entries);
+  assert.equal(kept.length, 1, "Feedback entry should never be age-pruned");
+});
+
+test("enforceLongTermLimits stale: compaction entry within grace period is retained", () => {
+  // decision staleAfterDays=45, 60 days old (< 45+30=75 grace) - should keep
+  const entries = [
+    agedEntry("within_grace", "Some compaction decision made two months ago", "decision", { daysAgo: 60, staleAfterDays: 45 }),
+  ];
+
+  const kept = enforceLongTermLimits(entries);
+  assert.equal(kept.length, 1, "Entry within grace period should be retained");
+});
+
+test("enforceLongTermLimits dedup before trim: cleanup runs before maxEntries slice", () => {
+  // 30 entries that should dedupe to < 28, confirming trim doesn't run before dedupe
+  const entries = [
+    ...Array.from({ length: 15 }, (_, i) =>
+      agedEntry(`a${i}`, "opencode uses npm cache for plugin loading", "decision", { daysAgo: 0 })
+    ),
+    ...Array.from({ length: 15 }, (_, i) =>
+      agedEntry(`b${i}`, "opencode uses npm cache for plugin loading", "decision", { daysAgo: 0 })
+    ),
+  ];
+
+  const kept = enforceLongTermLimits(entries);
+  assert.equal(kept.length, 1, "All duplicates should merge to 1 entry, far below maxEntries");
+});
+
+test("enforceLongTermLimits priority: freshness used as tie-breaker among same priority entries", () => {
+  // Same type, same source, same confidence — newer should win
+  const older = agedEntry("older", "Some durable configuration fact about the workspace", "reference", { daysAgo: 30, source: "compaction", staleAfterDays: 90 });
+  const newer = agedEntry("newer", "Some durable configuration fact about the workspace", "reference", { daysAgo: 5, source: "compaction", staleAfterDays: 90 });
+
+  const kept = enforceLongTermLimits([older, newer]);
+  assert.equal(kept.length, 1);
+  assert.equal(kept[0].id, "newer", "Newer entry should win as tie-breaker");
 });