feat: add episodic history recall

docs/memory-v2/README.md

@@ -378,6 +378,21 @@ Preferred backend name. The current default is `legacy`.
 
 Defaults to enabled. Backend failures return degraded empty payloads rather than blocking chat.
 
+`MEMORY_RETRIEVER_EPISODIC_ENABLED`
+
+Enables the historical-session recall capability, but does not by itself authorize retrieval.
+`MEMORY_RETRIEVER_ENABLED` must also be enabled and `MEMORY_RETRIEVER_EPISODIC_MODE` must be
+`canary` or `active`. Missing or invalid mode is treated as `off`.
+
+`MEMORY_RETRIEVER_EPISODIC_MODE`
+
+Historical recall rollout mode: `off`, `canary`, or `active`. In canary mode only users listed in
+`MEMORY_RETRIEVER_EPISODIC_CANARY_USER_IDS` may be indexed or queried.
+
+`MEMORY_RETRIEVER_EPISODIC_CANARY_USER_IDS`
+
+Comma- or whitespace-separated user IDs for historical recall canary testing.
+
 `MEMORY_PGVECTOR_DATABASE_URL`
 
 Dedicated PostgreSQL connection string for Memory V2 semantic memory. It must not point at the MySQL business database and is ignored unless `MEMORY_VECTOR_ENABLED=1`.
@@ -417,6 +432,15 @@ tkmind-proxy
   -> existing harness remember/bootstrap
 ```
 
+Explicit historical recall is a separate bounded read path layered beside personal memory:
+
+```text
+direct chat / Agent memory context
+  -> episodicMemory.resolve
+  -> h5_episodic_memory_items (same user, excluding current session)
+  -> bounded h5_session_snapshots fallback for pre-index history
+```
+
 Write path:
 
 ```text