Document D&D prompt cache ordering

docs/internal/llm.md

@@ -76,19 +76,22 @@ contract. Durable formats and compatibility rules remain in the
 ## Prompt Maintenance And Backend Caching
 
 Prompt message order and shared asset bytes are runtime behavior. Backend cache
-reuse depends on the same preceding messages and content, not merely equivalent
-meaning. Keep reusable shared assets byte-identical and keep stable material
-before the inputs that vary per request wherever a prompt’s declared sequence
-supports caching. Preserve the existing manifest order and cache-control hints
-when editing a prompt.
+reuse depends on identical preceding roles, rendered bytes, and cache-control
+metadata—not merely equivalent meaning. Keep reusable shared assets
+byte-identical and preserve each prompt’s declared ordering and cache controls
+when editing it.
 
-D&D extraction manifests place the changing chunk transcript at the end of the
-prompt after their reusable context. Scene chunking and NPC normalization use
-their own declared message sequences because their inputs and work differ. The
-family-specific asset and ordering rules belong in [D&D Module Internals](dnd.md).
-Do not add tests that enforce a fixed message-prefix length; prompt-asset tests
-should instead verify the meaningful asset sequence, inputs, and cache controls
-of the prompt being changed.
+For sibling prompts that can reuse the same source material, order universal
+shared context first, request source material next, and module-specific
+suffixes last. Put a cache boundary at a reusable prefix that is useful to the
+backend. Redundant intermediate cache boundaries do not extend that reusable
+prefix and add no value.
+
+Prompt-family owners may choose a different sequence when their inputs and
+reuse pattern differ. The D&D family’s extraction, scene-chunking, and NPC
+normalization policies are maintained in [D&D Module Internals](dnd.md#prompt-construction).
+Do not add tests that enforce prompt prose; prompt tests should verify the
+meaningful input placement and cache controls of the prompt being changed.
 
 ## Validation, Repair, And Retries