docs(meta): capture debug decisions testing idea

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

docs/IDEAS.md

@@ -16,6 +16,16 @@ just captured so they don't get lost.
 
 ## Mechanics
 
+- **Testing decisions per milestone** — Create temporary debug decisions
+  gated behind a `debug_mode` game rule for each milestone. These let us
+  force specific game states for testing (e.g., "Set Lord Ruler Attention
+  to 80," "Trigger Snapping on Target," "Spawn Inquisitor," "Set Caste
+  Law to Relaxed," "Unlock Age of Liberation," "Kill Kelsier"). Ship
+  them in a separate `common/decisions/99_debug_decisions.txt` that gets
+  removed (or gated behind a hidden game rule) before Steam release.
+  Each milestone doc should specify which debug decisions are needed for
+  its testing checkpoints.
+
 ## Lore / Flavor
 
 ## Art / UI