Use native S-expression for recipe/plan display

- Display recipe's original S-expression when available (code is data)
- Fall back to generating S-expression from plan for legacy JSON
- Run service now prefers .sexp plan files over .json
- Add get_run_plan_sexp() for direct S-expression access

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/routers/runs.py

@@ -178,6 +178,7 @@ async def get_run(
 
         # Try to load the recipe to show the plan
         plan = None
+        plan_sexp = None  # Native S-expression if available
         recipe_id = run.get("recipe")
         if recipe_id and len(recipe_id) == 64:  # Looks like a hash
             try:
@@ -185,7 +186,11 @@ async def get_run(
                 recipe_service = RecipeService(get_redis_client(), get_cache_manager())
                 recipe = await recipe_service.get_recipe(recipe_id)
                 if recipe:
-                    # Use the new build_dag method if available
+                    # Use native S-expression if available (code is data!)
+                    if recipe.get("sexp"):
+                        plan_sexp = recipe["sexp"]
+
+                    # Build steps for DAG visualization
                     dag = recipe.get("dag", {})
                     nodes = dag.get("nodes", [])
 
@@ -311,8 +316,9 @@ async def get_run(
                             }
                         })
 
-        # Generate S-expression representation of the plan
-        plan_sexp = plan_to_sexp(plan, run.get("recipe_name"))
+        # Use native S-expression if available, otherwise generate from plan
+        if not plan_sexp and plan:
+            plan_sexp = plan_to_sexp(plan, run.get("recipe_name"))
 
         templates = get_templates(request)
         return render(templates, "runs/detail.html", request,