docs: define emergent world architecture

AGENTS.md

@@ -77,6 +77,47 @@ Preserve the simulation/presentation boundary.
 When adding a system, first prove the contract with one real gameplay use case.
 Do not extract generic frameworks before multiple real consumers justify them.
 
+## Emergent-world doctrine
+
+The game world is the source of narrative truth. Dialogue, tasks, quests, and
+visible happenings must arise from ordinary simulation state and events rather
+than maintaining parallel scripted copies.
+
+- Keep immutable definitions, authored instance placement, mutable state,
+  systems, and presentation as separate layers.
+- Persist stable IDs and primitive data only. Saved state must never contain
+  scripts, nodes, `NodePath`s, callables, or resource paths.
+- Mutate authoritative state before recording the fact that describes the
+  mutation. Facts may reference exact causes; they may not stand in for a
+  missing world change.
+- Treat dialogue prose as presentation. Semantic intents, selected response
+  IDs, action commands, commitments, and their causal world events are the
+  authoritative contract.
+- Treat quests as player-facing projections of real unresolved situations.
+  Never create quest-only enemies, items, damage, relationships, resources, or
+  completion facts.
+- Route player and NPC interactions through the same authoritative action and
+  capability contracts. Presentation can suggest or submit a command, but the
+  simulation must revalidate it.
+- Loaded visuals must not decide whether travel, work, growth, or distant
+  conflict completes. Presentation interpolates authoritative state and may
+  report local feasibility or obstruction.
+- Every generated action, situation, helper, dialogue intent, or consequence
+  must expose a concise reason trace with the definition and causal fact IDs
+  that justified it.
+- “Data-only content” means new combinations of existing typed predicates,
+  capabilities, effects, behavior profiles, and presentation cues. A genuinely
+  new mechanic adds one bounded reusable handler and tests; it does not add one
+  script per item, creature, quest, or conversation.
+- Prefer typed Godot resources, composition, deterministic registries, and
+  explicit strategy handlers. Do not introduce a universal reflection DSL or
+  rewrite the project as a full ECS.
+
+The intended extension path is therefore definition plus content pack, optional
+presentation cue, and authored placement or simulation spawn. A berry, bear,
+caravan, shortage, or conversation topic should reuse the same state, action,
+event, and presentation contracts that existing content uses.
+
 ## Resource and target rules
 
 Do not reintroduce abstract food/wood task-zone fallbacks.