Improve message schema, assign or create main agent chat automatically

backend/database.py

@@ -33,6 +33,7 @@ class Agent(Base):
     visibility: Mapped[int] = mapped_column(default=0)
     # Comma separated list of permission symbols
     permissions: Mapped[str] = mapped_column(default="")
+    main_chat_id: Mapped[int] = mapped_column(ForeignKey("chats.id"))
 
     name: Mapped[str]
     description: Mapped[Optional[str]]
@@ -77,19 +78,27 @@ class Message(Base):
 
     id: Mapped[int] = mapped_column(primary_key=True, autoincrement=True)
     chat_id: Mapped[int] = mapped_column(ForeignKey("chats.id"))
+    thread_id: Mapped[Optional[int]] = mapped_column(ForeignKey("threads.id"))
 
     # Timestamp of this message
     time: Mapped[int]
-    # Identifier of the sender: user / system / $AGENT_ID
+    # Identifier of the sender: user / system / user-$ID / agent-$ID
     sender: Mapped[str]
 
-    # Predefined set of message types, interpreted as 'text' when empty.
+    # Predefined set of message types:
+    # message, log, memory, file, note
     kind: Mapped[str]
+    # Each kind has a set of subkinds, and a default for empty values
+    # message: (empty)
+    # log: debug, info
+    # memory: (depends on the agent)
+    # file: (empty)
+    # note: public, private, pinned
+    subkind: Mapped[Optional[str]]
+    # For the kinds message, log and note, a format can be specified,
+    # empty defaults to 'text' and can also be 'markdown', 'csv'
+    format: Mapped[Optional[str]]
     content: Mapped[str]
-    # Tells whether this message continues in the chat after the session when it was sent.
-    persistent: Mapped[bool] = mapped_column(default=False)
-
-    thread_id: Mapped[Optional[int]] = mapped_column(ForeignKey("threads.id"))
 
 # Represents a temporary topic or stage in a conversation
 class Thread(Base):
@@ -118,16 +127,3 @@ class AgentResource(Base):
     key: Mapped[str]
     value = mapped_column(JSON, default=None)
 
-# A log entry of an agent, the use and meaning depends on the agent class
-class AgentLog(Base):
-    __modelname__ = 'agent_log'
-    __tablename__ = 'agent_logs'
-
-    id: Mapped[int] = mapped_column(primary_key=True, autoincrement=True)
-    agent_id: Mapped[int] = mapped_column(ForeignKey("agents.id"))
-
-    # Kind is the class of the resource
-    # Key is the specific identifier within the class
-    # Multiple resources can share key
-    value: Mapped[str]
-