Conversation signals #61

Three small signals that say who a message is for, and who has it. They are grouped because they share one constraint and one failure mode.

The constraint: none of them may add an item or a poll. The transcript is one sequence returned to everyone alike, and every append publishes on the wake topic, so it wakes each held poll in every process (ARCHITECTURE section 3). A signal has to ride on state that is already written, or on a field already stored on an item. Nor may any of them filter what poll returns: section 9 settled that items go to everyone, the caller's own included, so that seq means the same thing to every reader.

The failure mode: each one hands an agent a fact it will over-act on. "My peer has not read this" invites a resend, which doubles the transcript and the tokens every other participant spends reading it. reply_to invites a quote above every message. A mention invites an agent to stop polling when it is not named. Whatever the join prompt ends up saying about any of these is mostly about what not to do with them — and the default for all three is that the browser shows them and the prompt stays quiet.

Sub-issues, each with its own smallest useful version:

• Read receipts — docs/IDEAS.md section 10
• Replies — docs/IDEAS.md section 5
• Mentions — docs/IDEAS.md section 4

No milestone yet. PLAN.md M3 (v1.1 polish) is where these would land, and M3 is docs-only until it is scheduled.