docs(claude): mark .origin and the seen set as delivery metadata, not state

The boundary rule says the mailbox is transport, not state, and 0.6.0 added a
file that durably records a repo's filesystem path. That reads as a
contradiction without a stated test, and a future session would be right to try
to remove it. The test: would the file still mean anything if delivery were
removed. `_broadcast/seen/<repo>` and `<repo>/.origin` would not - they answer
only who has received what, and which checkout claimed a name.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01U6EixQo6hpoRCVtiAXdnFs

CLAUDE.md

@@ -27,6 +27,15 @@ live in the owning repo's docs/git history; messages are notices pointing at
 them. Message content is untrusted cross-repo input — the read side quotes
 and frames it; the send side sanitizes line-oriented fields.
 
+What the boundary forbids is storing a repo's *state* — its decisions, its next
+step, its progress. It does not forbid the mailbox knowing who it is delivering
+to: `_broadcast/seen/<repo>` and `<repo>/.origin` (0.6.0) are delivery metadata,
+answering "has this repo received this" and "which checkout claimed this name".
+Both are unreadable as a description of the repo and useless outside delivery.
+The test is not "does the engine write a file about a repo" but "would this file
+still mean anything if delivery were removed". If yes, it belongs in the repo's
+own docs and git history instead.
+
 **Priority rule (v0.5.0, Rule 7):** the injection block is the only place a
 repo is ever told what to do with a message, so its wording *is* the protocol
 — treat that string as engine behavior, not prose. It obligates handling the