feat(pilot): inline Script Builder session — idempotent create + auth + filtered list

POST /script-builder/sessions now supports origin='pilot_inline':
- Requires ai_session_id; validates it against current user ownership.
- Get-or-create: returns existing row for (user, ai_session_id) pair.
- Partial unique index on the DB backs the invariant; races resolve to
  the single winner row.

list_sessions + count_user_sessions default-scope to origin='standalone'
so inline scratch sessions don't pollute the /script-builder dashboard
or count against the 5-session cap.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/tests/test_script_builder_inline.py

@@ -0,0 +1,176 @@
+"""Integration tests for inline pilot_inline script_builder_session behavior.
+
+Covers:
+- Idempotent get-or-create for (user, ai_session_id) on origin='pilot_inline'
+- Authorization: ai_session_id must belong to current user
+- list_sessions + count_user_sessions default-scope to 'standalone'
+"""
+from __future__ import annotations
+
+import pytest
+from httpx import AsyncClient
+from sqlalchemy import select, func
+from uuid import uuid4
+
+from app.models.ai_session import AISession
+from app.models.script_builder_session import ScriptBuilderSession
+
+
+async def _make_pilot_session(test_db, user) -> str:
+    """Helper: create a minimal pilot session owned by `user`.
+
+    Matches the existing pattern used by test_fix_outcome_endpoint.py.
+    `user` is the dict returned by the test_user fixture:
+        {"email": ..., "password": ..., "user_data": {"id": ..., "account_id": ..., ...}}
+    """
+    user_id = user["user_data"]["id"]
+    account_id = user["user_data"]["account_id"]
+    session = AISession(
+        id=uuid4(), user_id=user_id, account_id=account_id,
+        session_type="tshoot", intake_type="psa_ticket",
+        intake_content={}, title="QA",
+        status="active", confidence_tier="exploring", confidence_score=0.0,
+    )
+    test_db.add(session)
+    await test_db.commit()
+    return str(session.id)
+
+
+@pytest.mark.asyncio
+async def test_inline_create_is_idempotent(
+    client: AsyncClient, test_user, auth_headers, test_db
+):
+    """Second create with same (user, ai_session_id) returns the existing row."""
+    ai_session_id = await _make_pilot_session(test_db, test_user)
+
+    r1 = await client.post(
+        "/api/v1/scripts/builder/sessions",
+        json={"language": "powershell", "origin": "pilot_inline",
+              "ai_session_id": ai_session_id},
+        headers=auth_headers,
+    )
+    assert r1.status_code in (200, 201), r1.text
+    first_id = r1.json()["id"]
+
+    r2 = await client.post(
+        "/api/v1/scripts/builder/sessions",
+        json={"language": "powershell", "origin": "pilot_inline",
+              "ai_session_id": ai_session_id},
+        headers=auth_headers,
+    )
+    assert r2.status_code in (200, 201)
+    assert r2.json()["id"] == first_id
+
+    # DB confirms only one row
+    row_count = await test_db.scalar(
+        select(func.count()).select_from(ScriptBuilderSession).where(
+            ScriptBuilderSession.user_id == test_user["user_data"]["id"],
+            ScriptBuilderSession.origin == "pilot_inline",
+        )
+    )
+    assert row_count == 1
+
+
+@pytest.mark.asyncio
+async def test_inline_requires_ai_session_id(
+    client: AsyncClient, auth_headers
+):
+    """origin='pilot_inline' without ai_session_id is rejected."""
+    r = await client.post(
+        "/api/v1/scripts/builder/sessions",
+        json={"language": "powershell", "origin": "pilot_inline"},
+        headers=auth_headers,
+    )
+    assert r.status_code == 400
+    assert "ai_session_id" in r.text.lower()
+
+
+@pytest.mark.asyncio
+async def test_inline_ai_session_must_belong_to_caller(
+    client: AsyncClient, test_user, auth_headers, test_db
+):
+    """ai_session_id pointing at another user's session is rejected."""
+    # Create pilot session owned by a DIFFERENT user
+    from app.models.user import User
+    from app.models.account import Account
+    other_account = Account(id=uuid4(), name="other", display_code="OTH-0001")
+    test_db.add(other_account)
+    await test_db.flush()
+    other_user = User(
+        id=uuid4(), email="other@example.com",
+        password_hash="x", name="Other", role="engineer",
+        is_super_admin=False, is_team_admin=False, is_active=True,
+        is_service_account=False, must_change_password=False,
+        account_id=other_account.id, account_role="engineer",
+    )
+    test_db.add(other_user)
+    await test_db.flush()
+    # Build user dict in the same shape as the test_user fixture
+    other_user_dict = {
+        "user_data": {"id": str(other_user.id), "account_id": str(other_account.id)}
+    }
+    other_session_id = await _make_pilot_session(test_db, other_user_dict)
+
+    r = await client.post(
+        "/api/v1/scripts/builder/sessions",
+        json={"language": "powershell", "origin": "pilot_inline",
+              "ai_session_id": other_session_id},
+        headers=auth_headers,
+    )
+    assert r.status_code in (403, 404), r.text
+
+
+@pytest.mark.asyncio
+async def test_list_sessions_excludes_inline(
+    client: AsyncClient, test_user, auth_headers, test_db
+):
+    """GET /scripts/builder/sessions returns only standalone rows."""
+    ai_session_id = await _make_pilot_session(test_db, test_user)
+
+    # Create one inline session
+    await client.post(
+        "/api/v1/scripts/builder/sessions",
+        json={"language": "powershell", "origin": "pilot_inline",
+              "ai_session_id": ai_session_id},
+        headers=auth_headers,
+    )
+    # Create one standalone session
+    await client.post(
+        "/api/v1/scripts/builder/sessions",
+        json={"language": "powershell"},
+        headers=auth_headers,
+    )
+
+    r = await client.get("/api/v1/scripts/builder/sessions", headers=auth_headers)
+    assert r.status_code == 200
+    body = r.json()
+    # Depending on response shape, this may be a list or {"sessions": [...]}.
+    items = body if isinstance(body, list) else body.get("sessions", body.get("items", []))
+    # Response schema does not surface `origin`; len==1 is the only meaningful guard:
+    # inline row would push this to 2.
+    assert len(items) == 1
+
+
+@pytest.mark.asyncio
+async def test_inline_sessions_do_not_count_against_cap(
+    client: AsyncClient, test_user, auth_headers, test_db
+):
+    """Creating 5 pilot_inline sessions does not block a subsequent standalone."""
+    # Create 5 distinct pilot sessions and attach inline builder sessions to each
+    for _ in range(5):
+        ai_session_id = await _make_pilot_session(test_db, test_user)
+        r = await client.post(
+            "/api/v1/scripts/builder/sessions",
+            json={"language": "powershell", "origin": "pilot_inline",
+                  "ai_session_id": ai_session_id},
+            headers=auth_headers,
+        )
+        assert r.status_code in (200, 201), r.text
+
+    # A standalone create should still succeed — inline sessions don't count
+    r = await client.post(
+        "/api/v1/scripts/builder/sessions",
+        json={"language": "powershell"},
+        headers=auth_headers,
+    )
+    assert r.status_code in (200, 201), r.text