diff --git a/backend/app/api/endpoints/script_builder.py b/backend/app/api/endpoints/script_builder.py
index 1cb849f8..f028ae28 100644
--- a/backend/app/api/endpoints/script_builder.py
+++ b/backend/app/api/endpoints/script_builder.py
@@ -3,12 +3,14 @@ from typing import Annotated
 from uuid import UUID
 
 from fastapi import APIRouter, Depends, HTTPException, Request
-from sqlalchemy import text
+from sqlalchemy import select, text
+from sqlalchemy.exc import IntegrityError
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.core.database import get_db
 from app.core.rate_limit import limiter
 from app.api.deps import get_current_active_user
+from app.models.ai_session import AISession
 from app.models.user import User
 from app.models.script_builder_session import ScriptBuilderSession
 from app.schemas.script_builder import (
@@ -67,15 +69,85 @@ async def create_session(
     db: Annotated[AsyncSession, Depends(get_db)],
     current_user: Annotated[User, Depends(get_current_active_user)],
 ) -> ScriptBuilderSessionDetail:
-    """Start a new Script Builder session."""
+    """Start a new Script Builder session.
+
+    When origin='pilot_inline', behaves as get-or-create: the same row is
+    returned on repeated calls with the same (user, ai_session_id) pair.
+    Inline sessions are excluded from the session cap and the list endpoint.
+    """
+    # Phase 9: inline origin validation + authorization
+    if data.origin == "pilot_inline":
+        if data.ai_session_id is None:
+            raise HTTPException(
+                status_code=400,
+                detail="ai_session_id is required when origin='pilot_inline'",
+            )
+        # Ownership check: the pilot session must belong to the current user.
+        ai_session = await db.scalar(
+            select(AISession).where(
+                AISession.id == data.ai_session_id,
+                AISession.user_id == current_user.id,
+            )
+        )
+        if ai_session is None:
+            raise HTTPException(
+                status_code=404,
+                detail="Session not found",
+            )
+
+        # Idempotent get-or-create: if a pilot_inline row already exists for
+        # this (user, ai_session_id) pair, return it without creating a duplicate.
+        existing = await db.scalar(
+            select(ScriptBuilderSession).where(
+                ScriptBuilderSession.user_id == current_user.id,
+                ScriptBuilderSession.ai_session_id == data.ai_session_id,
+                ScriptBuilderSession.origin == "pilot_inline",
+            )
+        )
+        if existing is not None:
+            # Re-fetch with message_records loaded
+            session = await script_builder_service.get_session(db, existing.id, current_user.id)
+            return _session_to_detail(session)
+
+        # Create the inline session — wrap in IntegrityError catch for races.
+        try:
+            session = await script_builder_service.create_session(
+                db=db,
+                user_id=current_user.id,
+                account_id=current_user.account_id,
+                team_id=current_user.team_id,
+                language=data.language,
+                origin=data.origin,
+                ai_session_id=data.ai_session_id,
+            )
+            await db.commit()
+        except IntegrityError:
+            await db.rollback()
+            # Race: another request won the unique index — re-read the winner row.
+            existing = await db.scalar(
+                select(ScriptBuilderSession).where(
+                    ScriptBuilderSession.user_id == current_user.id,
+                    ScriptBuilderSession.ai_session_id == data.ai_session_id,
+                    ScriptBuilderSession.origin == "pilot_inline",
+                )
+            )
+            if existing is None:
+                raise
+            session = existing
+
+        # Re-fetch with message_records loaded
+        session = await script_builder_service.get_session(db, session.id, current_user.id)
+        return _session_to_detail(session)
+
+    # ── Standalone session ──────────────────────────────────────────────────
     # Acquire per-user advisory lock so concurrent create requests are serialized.
     # Without this, two simultaneous requests both read count < limit and both
     # insert, exceeding MAX_SESSIONS_PER_USER.
     user_lock_key = hash(str(current_user.id)) % (2**62)
     await db.execute(text("SELECT pg_advisory_xact_lock(:key)"), {"key": user_lock_key})
 
-    # Enforce max concurrent sessions
-    count = await script_builder_service.count_user_sessions(db, current_user.id)
+    # Enforce max concurrent sessions (inline sessions excluded from cap)
+    count = await script_builder_service.count_user_sessions(db, current_user.id, include_inline=False)
     if count >= MAX_SESSIONS_PER_USER:
         raise HTTPException(
             status_code=400,
@@ -88,6 +160,8 @@ async def create_session(
         account_id=current_user.account_id,
         team_id=current_user.team_id,
         language=data.language,
+        origin=data.origin,
+        ai_session_id=data.ai_session_id,
     )
     await db.commit()
     # Re-fetch with message_records loaded
diff --git a/backend/app/services/script_builder_service.py b/backend/app/services/script_builder_service.py
index aec7e87a..2422c437 100644
--- a/backend/app/services/script_builder_service.py
+++ b/backend/app/services/script_builder_service.py
@@ -148,6 +148,8 @@ async def create_session(
     team_id: UUID | None,
     language: str,
     initial_prompt: str | None = None,
+    origin: str = "standalone",
+    ai_session_id: UUID | None = None,
 ) -> ScriptBuilderSession:
     """Create a new Script Builder session."""
     session = ScriptBuilderSession(
@@ -155,6 +157,8 @@ async def create_session(
         account_id=account_id,
         team_id=team_id,
         language=language,
+        origin=origin,
+        ai_session_id=ai_session_id,
     )
     db.add(session)
     await db.flush()
@@ -295,15 +299,22 @@ async def list_sessions(
     user_id: UUID,
     limit: int = 20,
     offset: int = 0,
+    *,
+    include_inline: bool = False,
 ) -> list[ScriptBuilderSession]:
-    """List user's builder sessions ordered by updated_at desc."""
-    result = await db.execute(
+    """List user's builder sessions ordered by updated_at desc.
+
+    By default (include_inline=False) excludes pilot_inline sessions so the
+    /script-builder dashboard only shows standalone sessions.
+    """
+    stmt = (
         select(ScriptBuilderSession)
         .where(ScriptBuilderSession.user_id == user_id)
-        .order_by(ScriptBuilderSession.updated_at.desc())
-        .limit(limit)
-        .offset(offset)
     )
+    if not include_inline:
+        stmt = stmt.where(ScriptBuilderSession.origin == "standalone")
+    stmt = stmt.order_by(ScriptBuilderSession.updated_at.desc()).limit(limit).offset(offset)
+    result = await db.execute(stmt)
     return list(result.scalars().all())
 
 
@@ -321,13 +332,23 @@ async def delete_session(
     return True
 
 
-async def count_user_sessions(db: AsyncSession, user_id: UUID) -> int:
-    """Count active builder sessions for a user."""
-    result = await db.execute(
-        select(func.count(ScriptBuilderSession.id)).where(
-            ScriptBuilderSession.user_id == user_id
-        )
+async def count_user_sessions(
+    db: AsyncSession,
+    user_id: UUID,
+    *,
+    include_inline: bool = False,
+) -> int:
+    """Count active builder sessions for a user.
+
+    By default (include_inline=False) excludes pilot_inline sessions so they
+    don't consume slots against the MAX_SESSIONS_PER_USER cap.
+    """
+    stmt = select(func.count(ScriptBuilderSession.id)).where(
+        ScriptBuilderSession.user_id == user_id
     )
+    if not include_inline:
+        stmt = stmt.where(ScriptBuilderSession.origin == "standalone")
+    result = await db.execute(stmt)
     return result.scalar_one()
 
 
diff --git a/backend/tests/test_script_builder_inline.py b/backend/tests/test_script_builder_inline.py
new file mode 100644
index 00000000..2db04e2c
--- /dev/null
+++ b/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