fix(flowpilot): extract _build_session_detail helper, fix link_ticket 500

The same model_validate bug existed in link_ticket endpoint (line 467).
Extracted the manual AISessionDetail construction into a shared helper
_build_session_detail() used by both get_session and link_ticket.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/api/endpoints/ai_sessions.py

@@ -52,6 +52,64 @@ logger = logging.getLogger(__name__)
 router = APIRouter(prefix="/ai-sessions", tags=["ai-sessions"])
 
 
+def _build_session_detail(session: AISession) -> AISessionDetail:
+    """Build AISessionDetail from ORM session with properly mapped steps.
+
+    AISessionDetail.model_validate(session) fails because the ORM steps
+    relationship uses 'id' while AISessionStepResponse expects 'step_id'.
+    This helper manually maps all fields to avoid that validation error.
+    """
+    step_responses = []
+    for step in (session.steps or []):
+        options = []
+        if step.options_presented:
+            options = [
+                StepOptionSchema(
+                    label=opt.get("label", ""),
+                    value=opt.get("value", ""),
+                    followup_hint=opt.get("followup_hint"),
+                )
+                for opt in step.options_presented
+            ]
+        content = step.content or {}
+        step_responses.append(AISessionStepResponse(
+            step_id=step.id,
+            step_order=step.step_order,
+            step_type=step.step_type,
+            content=content,
+            context_message=step.context_message,
+            options=options,
+            allow_free_text=content.get("allow_free_text", True),
+            allow_skip=content.get("allow_skip", True),
+            confidence_tier=session.confidence_tier,
+            confidence_score=step.confidence_at_step,
+        ))
+
+    return AISessionDetail(
+        id=session.id,
+        status=session.status,
+        intake_type=session.intake_type,
+        intake_content=session.intake_content or {},
+        problem_summary=session.problem_summary,
+        problem_domain=session.problem_domain,
+        confidence_tier=session.confidence_tier,
+        step_count=session.step_count,
+        session_rating=session.session_rating,
+        psa_ticket_id=session.psa_ticket_id,
+        psa_connection_id=session.psa_connection_id,
+        escalation_reason=session.escalation_reason,
+        matched_flow_id=session.matched_flow_id,
+        match_score=getattr(session, 'match_score', None),
+        resolution_summary=session.resolution_summary,
+        resolution_action=getattr(session, 'resolution_action', None),
+        session_feedback=session.session_feedback,
+        ticket_data=session.ticket_data,
+        created_at=session.created_at,
+        resolved_at=session.resolved_at,
+        steps=step_responses,
+    )
+
+
 def _require_ai_enabled() -> None:
     if not settings.ai_enabled:
         raise HTTPException(
@@ -464,8 +522,7 @@ async def link_ticket_to_session(
     if not session:
         raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Session not found")
 
-    detail = AISessionDetail.model_validate(session)
-    return detail
+    return _build_session_detail(session)
 
 
 # ── Search sessions (Command Palette) ──
@@ -618,60 +675,7 @@ async def get_session(
     if session.user_id != current_user.id and session.escalated_to_id != current_user.id and not is_handler:
         raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail="Not authorized")
 
-    # Build step responses
-    step_responses = []
-    for step in session.steps:
-        options = []
-        if step.options_presented:
-            options = [
-                StepOptionSchema(
-                    label=opt.get("label", ""),
-                    value=opt.get("value", ""),
-                    followup_hint=opt.get("followup_hint"),
-                )
-                for opt in step.options_presented
-            ]
-        content = step.content or {}
-        step_responses.append(AISessionStepResponse(
-            step_id=step.id,
-            step_order=step.step_order,
-            step_type=step.step_type,
-            content=content,
-            context_message=step.context_message,
-            options=options,
-            allow_free_text=content.get("allow_free_text", True),
-            allow_skip=content.get("allow_skip", True),
-            confidence_tier=session.confidence_tier,
-            confidence_score=step.confidence_at_step,
-        ))
-
-    # Build detail manually — AISessionDetail.model_validate(session) fails because
-    # the ORM relationship 'steps' has 'id' not 'step_id', causing validation errors.
-    # Instead, extract non-step fields from ORM and set step_responses separately.
-    detail = AISessionDetail(
-        id=session.id,
-        status=session.status,
-        intake_type=session.intake_type,
-        intake_content=session.intake_content or {},
-        problem_summary=session.problem_summary,
-        problem_domain=session.problem_domain,
-        confidence_tier=session.confidence_tier,
-        step_count=session.step_count,
-        session_rating=session.session_rating,
-        psa_ticket_id=session.psa_ticket_id,
-        psa_connection_id=session.psa_connection_id,
-        escalation_reason=session.escalation_reason,
-        matched_flow_id=session.matched_flow_id,
-        match_score=getattr(session, 'match_score', None),
-        resolution_summary=session.resolution_summary,
-        resolution_action=getattr(session, 'resolution_action', None),
-        session_feedback=session.session_feedback,
-        ticket_data=session.ticket_data,
-        created_at=session.created_at,
-        resolved_at=session.resolved_at,
-        steps=step_responses,
-    )
-    return detail
+    return _build_session_detail(session)
 
 
 # ── Documentation ──