Define subject content format

Docs/KnowledgeAndSkillFoundation.md

@@ -379,3 +379,35 @@ Non-punitive practice paths:
 
 Accessibility rule: learning should make players more capable without making
 them feel trapped, shamed, or forced into a classroom flow.
+
+## Subject Content Format
+
+Learning content should use a small structured format so topics can become data
+assets later without rewriting design intent.
+
+Required fields:
+
+- `topic`: stable identifier and display name, such as `fire.clearance`.
+- `concepts`: one or more concept tags the player may learn or demonstrate.
+- `difficulty_tier`: `elementary`, `practical`, `advanced`, or `expert`.
+- `prerequisite_concepts`: concept tags that should be known first, if any.
+- `in_game_effect`: the warning, modifier, feedback, unlock, or quality effect
+  this topic can influence.
+- `practice_action`: the action that can build practical experience for the
+  topic.
+- `source_note`: a short design/source note explaining why the topic matters.
+
+Example:
+
+```text
+topic: fire.clearance
+concepts: fire_safety, dry_fuel, wind_spread
+difficulty_tier: elementary
+prerequisite_concepts: none
+in_game_effect: clearer fire-risk warning and lower unsafe-placement mistakes
+practice_action: clear area, contain fire, maintain fire, extinguish fire
+source_note: Open flame near dry fuel and wind can spread beyond the campfire.
+```
+
+Format rule: content records should be small enough to review in source control
+and explicit enough to become data assets later.