fix: enable batch operations in alembic for sqlite unique constraints

docs/superpowers/plans/2026-05-06-server-port-constraint.md

@@ -0,0 +1,147 @@
+# Server Port Constraint Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Ensure servers cannot share the same port by enforcing uniqueness at the database level and handling the constraint violation in the web UI.
+
+**Architecture:** We will add a unique constraint to the `Server.port` column, generate an Alembic migration, and update the `/servers` POST route to catch `IntegrityError` when a port conflict occurs, returning a 409 status code.
+
+**Tech Stack:** Python, Flask, SQLAlchemy, Alembic, Pytest
+
+---
+
+### Task 1: Add Unique Constraint to Server Port
+
+**Files:**
+- Modify: `l4d2web/models.py`
+- Modify: `l4d2web/routes/server_routes.py`
+- Create: `l4d2web/alembic/versions/XXXX_make_server_port_unique.py` (via alembic)
+
+- [ ] **Step 1: Update the database model**
+
+Update `l4d2web/models.py` to add `unique=True` to the `port` column on the `Server` model.
+
+```python
+class Server(Base):
+    __tablename__ = "servers"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True)
+    user_id: Mapped[int] = mapped_column(ForeignKey("users.id"), nullable=False)
+    blueprint_id: Mapped[int] = mapped_column(ForeignKey("blueprints.id"), nullable=False)
+    name: Mapped[str] = mapped_column(String(128), unique=True, nullable=False)
+    port: Mapped[int] = mapped_column(Integer, unique=True, nullable=False)
+    # ... rest of the columns
+```
+
+- [ ] **Step 2: Generate the Alembic migration**
+
+Run: `PYTHONPATH=. alembic -c l4d2web/alembic.ini revision --autogenerate -m "make server port unique"`
+Expected: Creates a new migration file in `l4d2web/alembic/versions/`
+
+- [ ] **Step 3: Update application logic**
+
+Update `l4d2web/routes/server_routes.py` to catch the `IntegrityError` when creating a server.
+
+```python
+from sqlalchemy.exc import IntegrityError
+# ... other imports
+
+@bp.post("/servers")
+@require_login
+def create_server() -> Response:
+    # ... existing user check and payload extraction
+
+    with session_scope() as db:
+        blueprint = db.scalar(
+            select(BlueprintModel).where(
+                BlueprintModel.id == int(payload["blueprint_id"]),
+                BlueprintModel.user_id == user.id,
+            )
+        )
+        if blueprint is None:
+            return Response("blueprint not found", status=404)
+
+        server = Server(
+            user_id=user.id,
+            blueprint_id=blueprint.id,
+            name=str(payload["name"]),
+            port=int(payload["port"]),
+            desired_state="stopped",
+            actual_state="unknown",
+            last_error="",
+        )
+        db.add(server)
+        
+        try:
+            db.flush()
+        except IntegrityError:
+            db.rollback()
+            return Response("port already in use", status=409)
+            
+        server_id = server.id
+
+    if json_response:
+        return jsonify({"id": server_id}), 201
+    return redirect(f"/servers/{server_id}")
+```
+
+- [ ] **Step 4: Commit**
+
+```bash
+git add l4d2web/models.py l4d2web/routes/server_routes.py l4d2web/alembic/versions/
+git commit -m "feat: enforce unique port constraint on servers"
+```
+
+### Task 2: Write Verification Tests
+
+**Files:**
+- Modify: `l4d2web/tests/test_servers.py`
+
+- [ ] **Step 1: Write the failing test**
+
+Add a test case to `l4d2web/tests/test_servers.py` that verifies the unique port constraint.
+
+```python
+def test_create_server_duplicate_port(client, auth, db_session):
+    auth.login()
+    
+    # First, create a blueprint
+    response = client.post(
+        "/blueprints",
+        data={"name": "my-blueprint", "arguments": "[]", "config": "[]"},
+    )
+    assert response.status_code == 302
+    
+    # Then create the first server
+    response = client.post(
+        "/servers",
+        data={"name": "server-1", "port": "27015", "blueprint_id": "1"},
+    )
+    assert response.status_code == 302
+    
+    # Try to create a second server with the same port
+    response = client.post(
+        "/servers",
+        data={"name": "server-2", "port": "27015", "blueprint_id": "1"},
+    )
+    assert response.status_code == 409
+    assert b"port already in use" in response.data
+    
+    # Verify the second server was not created
+    from l4d2web.models import Server
+    servers = db_session.query(Server).all()
+    assert len(servers) == 1
+    assert servers[0].name == "server-1"
+```
+
+- [ ] **Step 2: Run test to verify it passes**
+
+Run: `pytest l4d2web/tests/test_servers.py -v`
+Expected: PASS (It passes because we implemented the code in Task 1. We're doing this slightly out of TDD order to group the DB/Route changes together).
+
+- [ ] **Step 3: Commit**
+
+```bash
+git add l4d2web/tests/test_servers.py
+git commit -m "test: add test for duplicate port constraint"
+```

l4d2web/alembic/env.py

@@ -25,6 +25,7 @@ def run_migrations_offline() -> None:
         target_metadata=target_metadata,
         literal_binds=True,
         dialect_opts={"paramstyle": "named"},
+        render_as_batch=True
     )
 
     with context.begin_transaction():
@@ -41,7 +42,11 @@ def run_migrations_online() -> None:
     )
 
     with connectable.connect() as connection:
-        context.configure(connection=connection, target_metadata=target_metadata)
+        context.configure(
+            connection=connection, 
+            target_metadata=target_metadata,
+            render_as_batch=True
+        )
 
         with context.begin_transaction():
             context.run_migrations()

l4d2web/alembic/script.py.mako

@@ -0,0 +1,28 @@
+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+${imports if imports else ""}
+
+# revision identifiers, used by Alembic.
+revision: str = ${repr(up_revision)}
+down_revision: Union[str, Sequence[str], None] = ${repr(down_revision)}
+branch_labels: Union[str, Sequence[str], None] = ${repr(branch_labels)}
+depends_on: Union[str, Sequence[str], None] = ${repr(depends_on)}
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    ${downgrades if downgrades else "pass"}

l4d2web/alembic/versions/b2c684fddbd3_make_server_port_unique.py

@@ -0,0 +1,34 @@
+"""make server port unique
+
+Revision ID: b2c684fddbd3
+Revises: 0001_initial
+Create Date: 2026-05-06 20:52:35.109176
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = 'b2c684fddbd3'
+down_revision: Union[str, Sequence[str], None] = '0001_initial'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    with op.batch_alter_table('servers', schema=None) as batch_op:
+        batch_op.create_unique_constraint(batch_op.f('uq_servers_port'), ['port'])
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    with op.batch_alter_table('servers', schema=None) as batch_op:
+        batch_op.drop_constraint(batch_op.f('uq_servers_port'), type_='unique')
+    # ### end Alembic commands ###

l4d2web/models.py

@@ -63,7 +63,7 @@ class Server(Base):
     user_id: Mapped[int] = mapped_column(ForeignKey("users.id"), nullable=False)
     blueprint_id: Mapped[int] = mapped_column(ForeignKey("blueprints.id"), nullable=False)
     name: Mapped[str] = mapped_column(String(128), unique=True, nullable=False)
-    port: Mapped[int] = mapped_column(Integer, nullable=False)
+    port: Mapped[int] = mapped_column(Integer, unique=True, nullable=False)
     desired_state: Mapped[str] = mapped_column(String(16), default="stopped", nullable=False)
     actual_state: Mapped[str] = mapped_column(String(16), default="unknown", nullable=False)
     actual_state_updated_at: Mapped[datetime | None] = mapped_column(DateTime, nullable=True)

l4d2web/routes/server_routes.py

@@ -1,5 +1,6 @@
 from flask import Blueprint, Response, jsonify, redirect, request
 from sqlalchemy import select
+from sqlalchemy.exc import IntegrityError
 
 from l4d2web.auth import current_user, require_login
 from l4d2web.db import session_scope
@@ -38,7 +39,13 @@ def create_server() -> Response:
             last_error="",
         )
         db.add(server)
+        
+        try:
             db.flush()
+        except IntegrityError:
+            db.rollback()
+            return Response("port already in use", status=409)
+            
         server_id = server.id
 
     if json_response:

l4d2web/tests/test_servers.py

@@ -83,6 +83,37 @@ def test_reassign_blueprint_anytime(user_client_with_blueprints) -> None:
     assert response.status_code == 200
 
 
+def test_create_server_duplicate_port(user_client_with_blueprints) -> None:
+    client, data = user_client_with_blueprints
+    
+    # Create the first server
+    response = client.post(
+        "/servers",
+        data={"name": "server-1", "port": "27015", "blueprint_id": str(data["blueprint_id"])},
+        headers={"X-CSRF-Token": "test-token"},
+    )
+    assert response.status_code == 302
+    
+    # Try to create a second server with the same port
+    response = client.post(
+        "/servers",
+        data={"name": "server-2", "port": "27015", "blueprint_id": str(data["blueprint_id"])},
+        headers={"X-CSRF-Token": "test-token"},
+    )
+    assert response.status_code == 409
+    assert b"port already in use" in response.data
+    
+    # Verify the second server was not created by checking how many servers exist
+    from sqlalchemy import select
+    from l4d2web.db import session_scope
+    from l4d2web.models import Server
+    
+    with session_scope() as session:
+        servers = session.scalars(select(Server)).all()
+        assert len(servers) == 1
+        assert servers[0].name == "server-1"
+
+
 def test_lifecycle_form_creates_queued_job(user_client_with_blueprints) -> None:
     client, data = user_client_with_blueprints
     create_response = client.post(