Fix 9-hole handicap calculation when back-nine holes are missing from DB

When only front-nine holes are entered in course_holes (common setup),
course_par_full summed to ~36 instead of ~72, inflating the 9-hole
playing handicap by roughly 2x before halving. Fix by using
course_par_played×2 as the 18-hole par estimate in both the backend
create_game and the new_game confirmation preview.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/routers/games.py

@@ -292,7 +292,6 @@ async def create_game(request: Request, holes_count: int = Form(...),
 
     # Pre-fetch course holes for handicap calculation
     course_par_played = 0   # par for the holes being played
-    course_par_full = 0     # par for all holes on the course (needed for 9-of-18 halving)
     course_total_holes = holes_count  # assume matches unless we find otherwise
     hole_stroke_indices: dict[int, int] = {}
     if course_id:
@@ -305,14 +304,14 @@ async def create_game(request: Request, holes_count: int = Form(...),
             (course_id,),
         ) as c:
             for row in await c.fetchall():
-                course_par_full += row["par"] or 0
                 if row["hole_number"] <= holes_count:
                     course_par_played += row["par"] or 0
                     if row["stroke_index"] is not None:
                         hole_stroke_indices[row["hole_number"]] = row["stroke_index"]
 
     # For a 9-hole game on an 18-hole course the tee ratings are 18-hole values.
-    # Per WHS: compute 18-hole course handicap, then halve it.
+    # Per WHS: compute 18-hole course handicap using played-par×2 as the 18-hole par, then halve.
+    # Using played-par×2 avoids relying on back-nine holes being present in course_holes.
     nine_of_eighteen = (holes_count == 9 and course_total_holes == 18)
 
     played_holes = list(range(1, holes_count + 1))
@@ -331,7 +330,7 @@ async def create_game(request: Request, holes_count: int = Form(...),
 
         playing_handicap = None
         strokes_allocation_json = None
-        par_for_formula = course_par_full if nine_of_eighteen else course_par_played
+        par_for_formula = course_par_played * 2 if nine_of_eighteen else course_par_played
         if hc is not None and tee_id and par_for_formula:
             async with db.execute("SELECT slope, rating FROM course_tees WHERE id = ?", (tee_id,)) as c:
                 tee_row = await c.fetchone()

app/templates/games/new_game.html

@@ -65,9 +65,12 @@
          const player = this.getPlayer(uid);
          const tee = this.getTee(uid);
          const course = COURSES_DATA.find(c => c.id === this.courseId);
-         if (!course || !tee || player.handicap == null || !course.par) return null;
+         if (!course || !tee || player.handicap == null) return null;
          const nineOfEighteen = parseInt(this.holesCount) === 9 && course.holes === 18;
-         const ph = Math.round(player.handicap * (tee.slope / 113) + (tee.rating - course.par));
+         // For 9-of-18, use par_9×2 as the 18-hole par so back-nine holes don't need to be in DB.
+         const par = nineOfEighteen ? course.par_9 * 2 : course.par;
+         if (!par) return null;
+         const ph = Math.round(player.handicap * (tee.slope / 113) + (tee.rating - par));
          return nineOfEighteen ? Math.round(ph / 2) : ph;
        },
        goToConfirm() { this.step = 3; },