feat: Phase 1 Group 9 — enforce NOT NULL on all account_id columns

All previously-nullable account_id columns are now NOT NULL.
tree_embeddings and feedback backfilled before constraint applied.
Global content assigned to platform sentinel account (00000000-...-0001)
in preceding migration.

Tables updated: users, trees, tree_categories, tree_tags,
step_categories, step_library, tree_embeddings, feedback

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

backend/app/models/category.py

@@ -39,10 +39,10 @@ class TreeCategory(Base):
         nullable=True,
         index=True
     )
-    account_id: Mapped[Optional[uuid.UUID]] = mapped_column(
+    account_id: Mapped[uuid.UUID] = mapped_column(
         UUID(as_uuid=True),
         ForeignKey("accounts.id", ondelete="CASCADE"),
-        nullable=True,
+        nullable=False,
         index=True
     )
     display_order: Mapped[int] = mapped_column(Integer, nullable=False, default=0, index=True)

backend/app/models/feedback.py

@@ -1,6 +1,5 @@
 import uuid
 from datetime import datetime, timezone
-from typing import Optional
 from sqlalchemy import String, Text, DateTime, ForeignKey
 from sqlalchemy.orm import Mapped, mapped_column
 from sqlalchemy.dialects.postgresql import UUID
@@ -11,7 +10,7 @@ class Feedback(Base):
     __tablename__ = "feedback"
 
     id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
-    account_id: Mapped[Optional[uuid.UUID]] = mapped_column(UUID(as_uuid=True), ForeignKey("accounts.id", ondelete="SET NULL"), nullable=True)
+    account_id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), ForeignKey("accounts.id", ondelete="CASCADE"), nullable=False, index=True)
     user_id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), ForeignKey("users.id", ondelete="SET NULL"), nullable=False)
     email: Mapped[str] = mapped_column(String(255), nullable=False)
     feedback_type: Mapped[str] = mapped_column(String(50), nullable=False)

backend/app/models/step_category.py

@@ -38,10 +38,10 @@ class StepCategory(Base):
         nullable=True,
         index=True
     )
-    account_id: Mapped[Optional[uuid.UUID]] = mapped_column(
+    account_id: Mapped[uuid.UUID] = mapped_column(
         UUID(as_uuid=True),
         ForeignKey("accounts.id", ondelete="CASCADE"),
-        nullable=True,
+        nullable=False,
         index=True
     )
     display_order: Mapped[int] = mapped_column(Integer, nullable=False, default=0, index=True)

backend/app/models/step_library.py

@@ -46,10 +46,10 @@ class StepLibrary(Base):
         ForeignKey("teams.id", ondelete="CASCADE"),
         nullable=True
     )
-    account_id: Mapped[Optional[uuid.UUID]] = mapped_column(
+    account_id: Mapped[uuid.UUID] = mapped_column(
         UUID(as_uuid=True),
         ForeignKey("accounts.id", ondelete="CASCADE"),
-        nullable=True,
+        nullable=False,
         index=True
     )
 

backend/app/models/tag.py

@@ -51,10 +51,10 @@ class TreeTag(Base):
         nullable=True,
         index=True
     )
-    account_id: Mapped[Optional[uuid.UUID]] = mapped_column(
+    account_id: Mapped[uuid.UUID] = mapped_column(
         UUID(as_uuid=True),
         ForeignKey("accounts.id", ondelete="CASCADE"),
-        nullable=True,
+        nullable=False,
         index=True
     )
     usage_count: Mapped[int] = mapped_column(Integer, nullable=False, default=0, index=True)

backend/app/models/tree.py

@@ -76,10 +76,10 @@ class Tree(Base):
         nullable=True,
         index=True
     )
-    account_id: Mapped[Optional[uuid.UUID]] = mapped_column(
+    account_id: Mapped[uuid.UUID] = mapped_column(
         UUID(as_uuid=True),
         ForeignKey("accounts.id", ondelete="CASCADE"),
-        nullable=True,
+        nullable=False,
         index=True
     )
     is_active: Mapped[bool] = mapped_column(Boolean, default=True)

backend/app/models/tree_embedding.py

@@ -37,10 +37,10 @@ class TreeEmbedding(Base):
         ForeignKey("trees.id", ondelete="CASCADE"),
         nullable=False,
     )
-    account_id: Mapped[Optional[uuid.UUID]] = mapped_column(
+    account_id: Mapped[uuid.UUID] = mapped_column(
         UUID(as_uuid=True),
         ForeignKey("accounts.id", ondelete="CASCADE"),
-        nullable=True,
+        nullable=False,
     )
     chunk_type: Mapped[str] = mapped_column(
         String(30),

backend/app/models/user.py

@@ -43,10 +43,10 @@ class User(Base):
     must_change_password: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False, server_default="false")
 
     # Account-based multi-tenancy (new)
-    account_id: Mapped[Optional[uuid.UUID]] = mapped_column(
+    account_id: Mapped[uuid.UUID] = mapped_column(
         UUID(as_uuid=True),
         ForeignKey("accounts.id", ondelete="RESTRICT"),
-        nullable=True,
+        nullable=False,
         index=True
     )
     account_role: Mapped[str] = mapped_column(String(50), nullable=False, default="engineer")