file-attach

Drop a file on the prompt — it rides to the worker's /tmp and the prompt keeps its path.

The agent and the dashboard rarely live on the same machine, so an image in your clipboard is bytes the agent can't see. This node closes that gap: a file attached to the prompt is carried to the machine the session runs on, and the prompt is left holding its path. An attachment becomes an ordinary local path the agent can just read — no bytes smuggled through the prompt, no out-of-band copy step the human has to narrate.

attach three ways, both input surfaces

The same gesture set works on both prompt boxes — the New Session prompt and a running session's ❯ inbox:

• Paste a file (a screenshot, a copied file). A paste that carries files attaches them; a plain text paste is untouched and types as before.
• Drop a file onto the box. The surface rings to signal it's droppable while a file hovers.
• Pick a file from the small attach affordance beside the box.

The offline ❯ box takes none of these — there is no live machine to carry a file to until it relaunches.

the path is the whole handoff

Each attached file is uploaded to the backend, which is by construction the machine every session and worker runs on — its temp dir is the same /tmp home the rendezvous sockets already use, so an upload shares the worker's filesystem for free. The file lands in one spexcode-uploads/ sink there under a collision-proof, path-safe name, and its absolute path is what gets spliced into the prompt at the caret, padded so it never glues to a neighbouring word. The human types around it; the agent reads it. That is the entire contract — "send the file over, hand me the path" — with no transport leaking into the prompt text.

fail loud, never silently drop

An upload is the one moment a file can vanish, so it is fail-loud on both ends. The server refuses an empty file, and a stray oversized one, rather than quietly filling the disk; a write that fails answers with its reason, never a false success. The client mirrors that: while bytes are in flight the attach control shows it's busy, and an upload that returns no path raises a visible error on that surface instead of swallowing the file. A crafted filename can't escape the upload dir — the name is reduced to a bare, sanitised basename first.

where it lives

The gestures, the path-splicing, and the attach affordance are the prompt boxes in SessionInterface.jsx (session-console, term-input); their styling rides styles.css. The upload endpoint and the /tmp sink are the backend's (api-endpoint, sessions) — a thin route over a small upload module, the same shape session-rename uses to span the UI and the server for one feature. This node's slices of those shared files are just the attach-control styling in styles.css and the /api/uploads route in index.ts; the yatsu eval tab's .eval-* classes and its eval-blob endpoint, reworked when yatsu was reframed to serve a verdict over transcript-or-image evidence, are spec-yatsu's churn, not file-attach's drift.