perf(ai-vault): reduce scan-local occurrence metadata

src/main/ai-vault/codex-session-collection.test.ts

@@ -65,6 +65,31 @@ describe('CodexSessionCollection', () => {
     ).toEqual([first, first, first])
   })
 
+  it('preserves order as winning rows alternate between single and repeated occurrences', () => {
+    const other = session({ agent: 'claude' })
+    const custom = session({ codexHome: '/tmp/custom' })
+    const managed = session({ codexHome: '/tmp/codex-runtime-home/home' })
+    const newerManaged = session({ ...managed, updatedAt: '1970-01-01T00:00:03Z' })
+    const real = session()
+    const newerReal = session({ updatedAt: '1970-01-01T00:00:05Z' })
+    const tied = session({ ...newerReal })
+
+    expect(
+      checkBatches([
+        [custom, other],
+        [managed],
+        [managed, other, managed],
+        [newerManaged],
+        [real],
+        [real],
+        [real, other],
+        [newerReal],
+        [newerReal],
+        [tied]
+      ])
+    ).toEqual([other, other, other, newerReal, newerReal])
+  })
+
   it('retains non-Codex and non-rollout occurrences unchanged', () => {
     const claude = session({ agent: 'claude' })
     const otherFile = session({ filePath: '/tmp/session.jsonl' })

src/main/ai-vault/codex-session-root-dedup.ts

@@ -255,7 +255,10 @@ export function dedupeCodexSessionsBySessionId(
 /** Scan-local accumulation; parsed rows must not be mutated after admission. */
 export class CodexSessionCollection {
   private readonly sessions = new Map<number, AiVaultSession>()
-  private readonly bestByKey = new Map<string, { session: AiVaultSession; indices: number[] }>()
+  private readonly bestByKey = new Map<
+    string,
+    { session: AiVaultSession; indices: number | number[] }
+  >()
   private nextIndex = 0
 
   get size(): number {
@@ -273,17 +276,25 @@ export class CodexSessionCollection {
       const best = this.bestByKey.get(key)
       if (best?.session === session) {
         // The batch filter retains every occurrence of the winning object.
-        best.indices.push(index)
+        if (typeof best.indices === 'number') {
+          best.indices = [best.indices, index]
+        } else {
+          best.indices.push(index)
+        }
       } else {
         if (best) {
           if (!codexSessionAliasBeats(session, best.session)) {
             return
           }
-          for (const previousIndex of best.indices) {
-            this.sessions.delete(previousIndex)
+          if (typeof best.indices === 'number') {
+            this.sessions.delete(best.indices)
+          } else {
+            for (const previousIndex of best.indices) {
+              this.sessions.delete(previousIndex)
+            }
           }
         }
-        this.bestByKey.set(key, { session, indices: [index] })
+        this.bestByKey.set(key, { session, indices: index })
       }
     }
     this.sessions.set(index, session)