diff --git a/backend/alembic/versions/78fc200abac1_add_account_id_script_tables.py b/backend/alembic/versions/78fc200abac1_add_account_id_script_tables.py
new file mode 100644
index 00000000..21cf8f2b
--- /dev/null
+++ b/backend/alembic/versions/78fc200abac1_add_account_id_script_tables.py
@@ -0,0 +1,80 @@
+"""add account_id to script_builder_sessions, script_templates, script_generations
+
+Revision ID: 78fc200abac1
+Revises: 7f136778f5a8
+Create Date: 2026-04-09 00:00:00.000000
+"""
+from typing import Sequence, Union
+from alembic import op
+import sqlalchemy as sa
+
+revision: str = '78fc200abac1'
+down_revision: Union[str, None] = '7f136778f5a8'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    for table in ('script_builder_sessions', 'script_templates', 'script_generations'):
+        op.add_column(table, sa.Column('account_id', sa.UUID(), nullable=True))
+        op.create_foreign_key(
+            f'fk_{table}_account_id', table, 'accounts',
+            ['account_id'], ['id'], ondelete='CASCADE',
+        )
+
+    # script_builder_sessions: user_id → users.account_id
+    op.execute("""
+        UPDATE script_builder_sessions sbs
+        SET account_id = u.account_id
+        FROM users u
+        WHERE sbs.user_id = u.id
+          AND sbs.account_id IS NULL
+    """)
+
+    # script_templates: created_by → users.account_id (nullable created_by)
+    op.execute("""
+        UPDATE script_templates st
+        SET account_id = u.account_id
+        FROM users u
+        WHERE st.created_by = u.id
+          AND st.account_id IS NULL
+    """)
+    # Fallback for script_templates with NULL created_by: team_id → team admin user
+    op.execute("""
+        UPDATE script_templates st
+        SET account_id = u.account_id
+        FROM users u
+        WHERE u.team_id = st.team_id
+          AND u.is_team_admin = TRUE
+          AND u.account_id IS NOT NULL
+          AND st.account_id IS NULL
+    """)
+
+    # script_generations: user_id → users.account_id
+    op.execute("""
+        UPDATE script_generations sg
+        SET account_id = u.account_id
+        FROM users u
+        WHERE sg.user_id = u.id
+          AND sg.account_id IS NULL
+    """)
+
+    # VERIFY
+    for table in ('script_builder_sessions', 'script_templates', 'script_generations'):
+        result = op.get_bind().execute(
+            sa.text(f"SELECT COUNT(*) FROM {table} WHERE account_id IS NULL")
+        )
+        count = result.scalar()
+        if count > 0:
+            raise RuntimeError(f"ROLLBACK: {count} NULL account_id rows in {table}.")
+
+    for table in ('script_builder_sessions', 'script_templates', 'script_generations'):
+        op.alter_column(table, 'account_id', nullable=False)
+        op.create_index(f'ix_{table}_account_id', table, ['account_id'])
+
+
+def downgrade() -> None:
+    for table in ('script_builder_sessions', 'script_templates', 'script_generations'):
+        op.drop_index(f'ix_{table}_account_id', table_name=table)
+        op.drop_constraint(f'fk_{table}_account_id', table, type_='foreignkey')
+        op.drop_column(table, 'account_id')
diff --git a/backend/app/models/script_builder_session.py b/backend/app/models/script_builder_session.py
index f7075494..723a4cfb 100644
--- a/backend/app/models/script_builder_session.py
+++ b/backend/app/models/script_builder_session.py
@@ -29,6 +29,12 @@ class ScriptBuilderSession(Base):
         nullable=False,
         index=True,
     )
+    account_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("accounts.id", ondelete="CASCADE"),
+        nullable=False,
+        index=True,
+    )
     team_id: Mapped[Optional[uuid.UUID]] = mapped_column(
         UUID(as_uuid=True),
         ForeignKey("teams.id", ondelete="SET NULL"),
diff --git a/backend/app/models/script_template.py b/backend/app/models/script_template.py
index 838d2f3c..3624f031 100644
--- a/backend/app/models/script_template.py
+++ b/backend/app/models/script_template.py
@@ -44,6 +44,12 @@ class ScriptTemplate(Base):
     team_id: Mapped[Optional[uuid.UUID]] = mapped_column(
         UUID(as_uuid=True), ForeignKey("teams.id", ondelete="CASCADE"), nullable=True, index=True
     )
+    account_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("accounts.id", ondelete="CASCADE"),
+        nullable=False,
+        index=True,
+    )
     created_by: Mapped[Optional[uuid.UUID]] = mapped_column(
         UUID(as_uuid=True), ForeignKey("users.id", ondelete="SET NULL"), nullable=True
     )
@@ -97,6 +103,12 @@ class ScriptGeneration(Base):
     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,
+    )
     team_id: Mapped[Optional[uuid.UUID]] = mapped_column(
         UUID(as_uuid=True), ForeignKey("teams.id", ondelete="SET NULL"), nullable=True, index=True
     )
diff --git a/backend/tests/test_phase1_migrations.py b/backend/tests/test_phase1_migrations.py
index 32de973c..fe89c153 100644
--- a/backend/tests/test_phase1_migrations.py
+++ b/backend/tests/test_phase1_migrations.py
@@ -420,3 +420,26 @@ async def test_maintenance_schedule_account_id_matches_tree(test_db: AsyncSessio
     )
     row = result.scalar_one()
     assert row.account_id == account.id
+
+
+# ── Group 7: Legacy team_id tables ───────────────────────────────────────────
+
+@pytest.mark.asyncio
+async def test_script_builder_session_account_id(test_db: AsyncSession):
+    """script_builder_sessions.account_id must match user's account_id."""
+    from app.models.script_builder_session import ScriptBuilderSession
+
+    account, user = await _make_account_and_user(test_db, "sbs1")
+    sbs = ScriptBuilderSession(
+        user_id=user.id,
+        account_id=account.id,
+        language="powershell",
+    )
+    test_db.add(sbs)
+    await test_db.commit()
+
+    result = await test_db.execute(
+        select(ScriptBuilderSession).where(ScriptBuilderSession.id == sbs.id)
+    )
+    row = result.scalar_one()
+    assert row.account_id == account.id