docs(memory): document session-start memory and config defaults

docs/architecture/AGENT_DIAGRAM.md

@@ -31,13 +31,13 @@ flowchart LR
     RT[Routing\ncreateMessageRouter()]
     PF[Preferences\n~/.local/share/flynn/preferences.json\nmodelTier + backendMode]
     SM[SessionManager\nSQLite]
-    OR[AgentOrchestrator]
-    NA[NativeAgent\n(tool loop)]
-    EB[Optional External Backends\nclaude_code/opencode/codex/gemini/pi_embedded]
-    MR[ModelRouter]
-    TP[ToolPolicy + ToolRegistry]
-    TE[ToolExecutor\nhooks + enforcement + audit]
-    MEM[Memory Store\nfiles + vector/keyword]
+  OR[AgentOrchestrator]
+  NA[NativeAgent\n(tool loop)]
+  EB[Optional External Backends\nclaude_code/opencode/codex/gemini/pi_embedded]
+  MR[ModelRouter]
+  TP[ToolPolicy + ToolRegistry]
+  TE[ToolExecutor\nhooks + enforcement + audit]
+  MEM[Memory Store\nfiles + vector/keyword\nuser/profile + user/working]
     AU[Audit Logger\nredacted]
     HS[Hooks/Autonomy\nconfirm/log/silent]
     GA[Google OAuth Runtime\nsrc/google/oauth.ts]
@@ -67,6 +67,7 @@ flowchart LR
   RT --> OR
   RT --> EB
   OR --> NA
+  OR -->|session-start memory| MEM
   EB --> MP
   NA --> MR
   MR --> MP
@@ -135,6 +136,10 @@ Tool Calls (inside NativeAgent loop)
                  |                                 v
                  +---------------------------> AuditLogger (redacted)
 
+Session start (when `memory.user_namespace` is set)
+  AgentOrchestrator -> MemoryStore (user/profile + user/working)
+  AgentOrchestrator -> System prompt (session context injection)
+
 Outbound Reply
   -> ChannelAdapter.send()  (text + optional attachments)
 ```