feat(assistant): implement spec 021 chat assistant flow with semantic contracts

backend/src/models/assistant.py

@@ -0,0 +1,74 @@
+# [DEF:backend.src.models.assistant:Module]
+# @TIER: STANDARD
+# @SEMANTICS: assistant, audit, confirmation, chat
+# @PURPOSE: SQLAlchemy models for assistant audit trail and confirmation tokens.
+# @LAYER: Domain
+# @RELATION: DEPENDS_ON -> backend.src.models.mapping
+# @INVARIANT: Assistant records preserve immutable ids and creation timestamps.
+
+from datetime import datetime
+
+from sqlalchemy import Column, String, DateTime, JSON, Text
+
+from .mapping import Base
+
+
+# [DEF:AssistantAuditRecord:Class]
+# @TIER: STANDARD
+# @PURPOSE: Store audit decisions and outcomes produced by assistant command handling.
+# @PRE: user_id must identify the actor for every record.
+# @POST: Audit payload remains available for compliance and debugging.
+class AssistantAuditRecord(Base):
+    __tablename__ = "assistant_audit"
+
+    id = Column(String, primary_key=True)
+    user_id = Column(String, index=True, nullable=False)
+    conversation_id = Column(String, index=True, nullable=True)
+    decision = Column(String, nullable=True)
+    task_id = Column(String, nullable=True)
+    message = Column(Text, nullable=True)
+    payload = Column(JSON, nullable=True)
+    created_at = Column(DateTime, default=datetime.utcnow, nullable=False)
+# [/DEF:AssistantAuditRecord:Class]
+
+
+# [DEF:AssistantMessageRecord:Class]
+# @TIER: STANDARD
+# @PURPOSE: Persist chat history entries for assistant conversations.
+# @PRE: user_id, conversation_id, role and text must be present.
+# @POST: Message row can be queried in chronological order.
+class AssistantMessageRecord(Base):
+    __tablename__ = "assistant_messages"
+
+    id = Column(String, primary_key=True)
+    user_id = Column(String, index=True, nullable=False)
+    conversation_id = Column(String, index=True, nullable=False)
+    role = Column(String, nullable=False)  # user | assistant
+    text = Column(Text, nullable=False)
+    state = Column(String, nullable=True)
+    task_id = Column(String, nullable=True)
+    confirmation_id = Column(String, nullable=True)
+    payload = Column(JSON, nullable=True)
+    created_at = Column(DateTime, default=datetime.utcnow, nullable=False)
+# [/DEF:AssistantMessageRecord:Class]
+
+
+# [DEF:AssistantConfirmationRecord:Class]
+# @TIER: STANDARD
+# @PURPOSE: Persist risky operation confirmation tokens with lifecycle state.
+# @PRE: intent/dispatch and expiry timestamp must be provided.
+# @POST: State transitions can be tracked and audited.
+class AssistantConfirmationRecord(Base):
+    __tablename__ = "assistant_confirmations"
+
+    id = Column(String, primary_key=True)
+    user_id = Column(String, index=True, nullable=False)
+    conversation_id = Column(String, index=True, nullable=False)
+    state = Column(String, index=True, nullable=False, default="pending")
+    intent = Column(JSON, nullable=False)
+    dispatch = Column(JSON, nullable=False)
+    expires_at = Column(DateTime, nullable=False)
+    created_at = Column(DateTime, default=datetime.utcnow, nullable=False)
+    consumed_at = Column(DateTime, nullable=True)
+# [/DEF:AssistantConfirmationRecord:Class]
+# [/DEF:backend.src.models.assistant:Module]