codeSplitter team threads: notes in a chat modal (search, filter by agent, newest/oldest, uploads) #3723

The owner's ask (2026-11-05, while #3713 was being built): notes to agents should feel like a chat, in a modal that pops up over the repo, not a box on a run card.

What it should do

• A modal, like a chat. Opens from anywhere in the repo (a run card, the agents list, a key), with the conversation in it. It's the thread page from codeSplitter: agent threads, a room the crew shares with a running agent #3721 (AgentThread, #/t/owner/repo/<run>), shown as an overlay instead of its own page.
• Search. Type to find a message across the thread (people's notes, the agent's words, its run events).
• Filter by agent. Pick one agent (or one person) and see only what they said. Across threads too, if a repo has several runs going.
• Sort. Newest first or oldest first, one toggle.
• Upload anything into it. Drop a file, image or screenshot into the chat; it goes into the thread, and a running agent gets it with the note (claude takes images in a stream-json user message; other CLIs get the file beside the one they edit).

How notes reach an agent today (for whoever builds this)

• A person's note goes in by POST /api/repos/:o/:r/agents/:id/notes (the MCP tool tell_agent is the same route; the "tell it something" box and the thread page post there too).
• The run polls for new notes every 3 s and writes each to claude's stdin as a stream-json user message (@who: text). On the desktop that's execCommand; hosted runs stream them down the container's /run (codeSplitter: agent threads, a room the crew shares with a running agent #3721, turned on in codeSplitter team threads: hosted runs hear notes while they work #3713).
• Any other CLI (codex, pi, opencode) gets the notes in the prompt of its next round.
• So no tool call or MCP on the agent's side: it just reads the next user message.

Open questions for the owner

• Upload limits: size, which types, and whether uploads are kept with the thread after the run ends (R2 cost).
• Does the modal replace the thread page, or sit on top of it?

Part of #3423.