Load order matters
For WebUI, backend/context/engine.py assembles the vault in seven layers: the soul's identity file first, then the shared instructions.md, the shared core/, the shared core catalog, the soul's own instructions.md, the soul's own core/, and finally the soul's index/. Shared loads before soul on purpose, so a soul-specific note overrides shared material on the same topic.
Not every layer loads the same way. A soul's own core/ loads whole. The shared core/ does not: a shared note loads whole only when its frontmatter declares it should, and every other shared note is a pointer — listed in the catalog the soul carries, retrievable by search, and one read away. The index/ layer has its own gate: a file that declares itself on-demand in its frontmatter is represented by its path instead of being inlined. Size alone never decides that; a file past 50 KB still loads whole and only logs a warning.
Identity is layered, not a single file
The order also shows that identity does not live in one place. The soul's entry file sets the face. The shared layer gives the family's common rules. The soul's own instructions and core overwrite whatever makes that soul different. The index is the map of memory, and a note that declares itself on-demand stays a pointer so the original can be read when it is actually needed. That is the note's own choice, never its size's.
What rides the turn, not the prompt
The retrieved RAG chunks (next lesson) are not part of the system prompt. Neither is the clock. Both change every turn, so both ride the current turn instead — prepended to the message the model reads, sent every time, and never written into the stored conversation. They are framed as reference material, not as a continuation of the current task. The system prompt holds only bytes that stay the same for the whole conversation.
Cache hint
The vault content is huge, and providers cache the leading bytes of a prompt. Same vault, same prefix, billed once and reused. The cache hint is implicit — the structure is what makes it work, and the structure only works if nothing inside the stable part moves. Lesson 8 tells how that was learned.