feat(memory): implement stability stage

Co-authored-by: multica-agent <github@multica.ai>

apps/worker/src/memory-regression.test.ts

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+import { describe, expect, it } from 'vitest'
+import type { Character, PlayerIntent } from '@dng/shared'
+import { buildRoundContext } from './orchestration'
+
+const hero: Character = {
+  id: 'aaaaaaaa-aaaa-4aaa-8aaa-aaaaaaaaaaaa',
+  name: 'Mara Venn',
+  concept: 'A careful investigator who remembers promises.',
+  controller: 'human',
+  userId: 'bbbbbbbb-bbbb-4bbb-8bbb-bbbbbbbbbbbb',
+  abilities: { str: 10, dex: 12, con: 10, int: 14, wis: 13, cha: 9 },
+  hp: 10,
+  maxHp: 10,
+  defense: 12,
+  proficiency: 2,
+  inventory: [],
+  statuses: [],
+}
+
+const scenarios = Array.from({ length: 20 }, (_, index) => {
+  const number = index + 1
+  const tag = `clue-${number.toString().padStart(2, '0')}`
+  return {
+    name: `memory regression ${number.toString().padStart(2, '0')}`,
+    tag,
+    fact: `In the opening round, Mara promised the keeper to preserve ${tag}.`,
+    action: `Mara invokes ${tag} and asks the keeper to honor their opening-round agreement.`,
+  }
+})
+
+describe('20-scenario AI memory context regression suite', () => {
+  it.each(scenarios)('$name retrieves the expected early fact after twenty rounds', ({ tag, fact, action }) => {
+    const intent: PlayerIntent = {
+      id: 'cccccccc-cccc-4ccc-8ccc-cccccccccccc',
+      roundId: 'dddddddd-dddd-4ddd-8ddd-dddddddddddd',
+      memberId: 'eeeeeeee-eeee-4eee-8eee-eeeeeeeeeeee',
+      characterId: hero.id,
+      action,
+      ready: true,
+      createdAt: '2026-01-01T00:00:00.000Z',
+      updatedAt: '2026-01-01T00:00:00.000Z',
+    }
+    const context = buildRoundContext({
+      scene: `Round 21 returns to the keeper's chamber near ${tag}.`,
+      storySummary: 'The party survived twenty rounds without replaying the full transcript.',
+      recentRounds: Array.from({ length: 20 }, (_, round) => ({ number: round + 1, narration: `Resolved round ${round + 1}.` })),
+      intents: [intent],
+      characters: [hero],
+      memories: [
+        { summary: fact, importance: 5, tags: [tag], entityIds: [] },
+        ...Array.from({ length: 24 }, (_, decoy) => ({
+          summary: `Unrelated later observation ${decoy + 1}.`,
+          importance: (decoy % 4) + 1,
+          tags: [`decoy-${decoy + 1}`],
+          entityIds: [],
+        })),
+      ],
+    })
+
+    expect(context.recentRounds.map(round => round.number)).toEqual([19, 20])
+    expect(context.memories.map(memory => memory.summary)).toContain(fact)
+    expect(context.memories).toHaveLength(8)
+  })
+})