feat(memory): export REFLECTOR_PROMPT_HASH for content-addressed cache keys

Computed at module load time from the prompt rendered with neutral HEXACO
traits. Consumers (bench cache-key fingerprinting, observability) use this
to auto-invalidate caches on prompt changes — no manual fingerprint bump
needed. Follow-up to the Step 11 prompt tuning.

Author: jddunn

src/memory/index.ts

@@ -231,7 +231,10 @@ export { ObservationBuffer } from './pipeline/observation/ObservationBuffer.js';
 export type { BufferedMessage, ObservationBufferConfig } from './pipeline/observation/ObservationBuffer.js';
 export { MemoryObserver } from './pipeline/observation/MemoryObserver.js';
 export type { ObservationNote } from './pipeline/observation/MemoryObserver.js';
-export { MemoryReflector } from './pipeline/observation/MemoryReflector.js';
+export {
+  MemoryReflector,
+  REFLECTOR_PROMPT_HASH,
+} from './pipeline/observation/MemoryReflector.js';
 export type { MemoryReflectionResult } from './pipeline/observation/MemoryReflector.js';
 
 // --- Observation Compression & Reflection ---

src/memory/pipeline/observation/MemoryReflector.ts

@@ -13,6 +13,7 @@
  * @module agentos/memory/observation/MemoryReflector
  */
 
+import { createHash } from 'node:crypto';
 import type { MemoryTrace, MemoryType, MemoryScope } from '../../core/types.js';
 import type { HexacoTraits, PADState, ReflectorConfig } from '../../core/config.js';
 import type { ObservationNote } from './MemoryObserver.js';
@@ -145,6 +146,26 @@ After your <thinking> block, output JSON objects, one per line:
 Output your <thinking> block first, then ONLY valid JSON objects, one per line.`;
 }
 
+/**
+ * Content-addressed hash of the reflector system prompt, computed at
+ * module load time from the prompt rendered with neutral HEXACO traits.
+ * Exported so consumers (bench cache-key fingerprinting, observability)
+ * can auto-invalidate caches whenever the prompt text changes — no
+ * manual version bumping needed.
+ */
+const NEUTRAL_HEXACO_TRAITS: HexacoTraits = {
+  honesty: 0.5,
+  emotionality: 0.5,
+  extraversion: 0.5,
+  agreeableness: 0.5,
+  conscientiousness: 0.5,
+  openness: 0.5,
+} as HexacoTraits;
+
+export const REFLECTOR_PROMPT_HASH: string = createHash('sha256')
+  .update(buildReflectorSystemPrompt(NEUTRAL_HEXACO_TRAITS))
+  .digest('hex');
+
 // ---------------------------------------------------------------------------
 // MemoryReflector
 // ---------------------------------------------------------------------------