Brokkr/docs/msgpack-payloads-cut.md

Brokkr stores on MessagePack payloads: target

This is campaign brokkr-msgpack. The mind holds its rulings, its spec and its verdicts. This page holds only the rationale and the shape the cut must produce.

Why

cultcache-py's payload default moves from JSON to MessagePack. The change is in CultLib branch hands/py-msgpack-default, which Soul held at d9f73281. Under the operator's ruling cultlib-gaps:ruling:py-migration-shape-ruled, convert writes a new MessagePack store and never writes its source.

Brokkr loads cultcache-py from the CultLib checkout its settings name (blender_target.py). It does not install a pinned package. So the moment CultLib's main takes that branch, the Blender bridge starts writing MessagePack payloads, and Brokkr's daemon must read them. The two changes therefore land together.

Design truths the cut must produce

• One payload format. Every store the daemon and the Blender bridge write carries MessagePack payloads. The daemon reads exactly one MessagePack value per payload and refuses trailing bytes.

• Conversion never writes a source. An existing JSON bridge store is converted into a new file with cultcache_py.convert, and the JSON original is kept for as long as the operator wants it. No daemon-written single-file store existed on 2026-10-14, so the cut ships no receipt converter. If one turns up at window time, stop and report it to the operator.

• The bridge refuses a cultcache-py without convert. A checkout older than the branch is refused at load, so it can never write a format the daemon cannot read.

• One operator window.

  1. Close Blender and stop sync.
  2. Merge CultLib's branch to main and move the checkout to it.
  3. Merge Brokkr.
  4. Build the daemon.
  5. Convert, open and swap in any stores that exist.
  6. Restart.

  None existed on 2026-10-14.

Not in scope

• The Unity mirror's directory store, against the daemon's single-file open (X1 in docs/brokkr-adoption-cut.md).
• The Blender bridge's move to a directory store, under ruling brush-tree:ruling:blender-transport-ruled. That move belongs to campaign brush-tree, and it lands after this cut.
• Bumping the daemon's cultcache-rs pin.

Evidence

Imagination's probes are recorded in the cut spec and its report. They show that converting a bridge store with the eight definitions preserves every record and leaves the source untouched. The daemon baseline is 20 of 20 tests passing at f97d4dc.