D1110 — instructions.md is capped at 64 KiB where it is read, and artifact_write refuses more

Decision. The curated instructions.md is read through one bounded reader in internal/provisioning (KBCuratedInstructions, at most MaxInstructionsBytes = 64 KiB plus one byte of look-ahead). Past the cap the text is cut at the last line boundary within it and a marker line says the file was cut and how many bytes were left out. The initialize guide and the managed block share that reader, so they never disagree on what a KB's instructions are. artifact_write refuses an instructions.md body over the cap, naming the cap and the size.

Why. After D1097 every handshake read the whole file from disk and sent it to every generic client, so anyone able to write the file could make each session read and carry an arbitrarily large text. The marker tells the agent it is reading a partial text and the operator what to fix.

Alternatives rejected. Dropping the curated section past the cap: the agent loses rules it could still use. A cap on the guide only: a file one path accepts and the other refuses. Refusing only in artifact_write: a push into the KB's remote bypasses it, so the readers must bound the read anyway.

Consequences. A push can still bring in a larger file; it is served truncated. The raw listing of instructions.md in the artifact catalog (sync_pull) stays unbounded on purpose: it must carry the true content for the sha256 that artifact_write takes as if_match, like the templates and skills listed beside it, and it runs per call with read access, not per handshake. The reader refuses a symlinked instructions.md itself, so the guide and the managed block agree on it. A cut inside the frontmatter keeps the marker and no body; a cut with no line boundary backs off to a rune boundary.