feat: add ai_chat_sessions database model and migration

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/models/__init__.py

@@ -28,6 +28,7 @@ from .maintenance_schedule import MaintenanceSchedule
 from .feedback import Feedback
 from .ai_conversation import AIConversation
 from .ai_usage import AIUsage
+from .ai_chat_session import AIChatSession
 
 __all__ = [
     "User",
@@ -67,4 +68,5 @@ __all__ = [
     "Feedback",
     "AIConversation",
     "AIUsage",
+    "AIChatSession",
 ]

backend/app/models/ai_chat_session.py

@@ -0,0 +1,88 @@
+"""AI Chat Builder session tracking.
+
+Stores conversational flow builder state across the multi-phase interview.
+Sessions expire after 24 hours.
+"""
+import uuid
+from datetime import datetime, timezone
+from typing import Optional, Any
+
+from sqlalchemy import String, DateTime, ForeignKey, Integer
+from sqlalchemy.orm import Mapped, mapped_column
+from sqlalchemy.dialects.postgresql import UUID, JSONB
+
+from app.core.database import Base
+
+
+class AIChatSession(Base):
+    __tablename__ = "ai_chat_sessions"
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), primary_key=True, default=uuid.uuid4
+    )
+    user_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("users.id", ondelete="CASCADE"),
+        nullable=False,
+        index=True,
+    )
+    account_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("accounts.id", ondelete="CASCADE"),
+        nullable=False,
+        index=True,
+    )
+    status: Mapped[str] = mapped_column(
+        String(20),
+        nullable=False,
+        default="active",
+        comment="active | completed | abandoned",
+    )
+    current_phase: Mapped[str] = mapped_column(
+        String(20),
+        nullable=False,
+        default="scoping",
+        comment="scoping | discovery | enrichment | review | generation",
+    )
+    flow_type: Mapped[str] = mapped_column(
+        String(20),
+        nullable=False,
+        comment="troubleshooting | procedural",
+    )
+    conversation_history: Mapped[list[dict[str, Any]]] = mapped_column(
+        JSONB, nullable=False, default=list
+    )
+    working_tree: Mapped[Optional[dict[str, Any]]] = mapped_column(
+        JSONB, nullable=True
+    )
+    tree_metadata: Mapped[dict[str, Any]] = mapped_column(
+        JSONB, nullable=False, default=dict
+    )
+    provider_used: Mapped[Optional[str]] = mapped_column(
+        String(20), nullable=True
+    )
+    message_count: Mapped[int] = mapped_column(
+        Integer, nullable=False, default=0
+    )
+    total_input_tokens: Mapped[int] = mapped_column(
+        Integer, nullable=False, default=0
+    )
+    total_output_tokens: Mapped[int] = mapped_column(
+        Integer, nullable=False, default=0
+    )
+    generated_tree_id: Mapped[Optional[uuid.UUID]] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("trees.id", ondelete="SET NULL"),
+        nullable=True,
+    )
+    expires_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), nullable=False
+    )
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)
+    )
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True),
+        default=lambda: datetime.now(timezone.utc),
+        onupdate=lambda: datetime.now(timezone.utc),
+    )