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# Desktop Agent Notes ## Frontend And Host Compatibility - The desktop frontend and host are versioned and shipped together. Do not support a current frontend talking to an older desktop host. - Evolve desktop protocol payloads, the frontend, and the host in lockstep. Do not make fields optional, hide controls, or add capability detection solely for compatibility with a pre-change host unless the user explicitly asks for it. ## Child Processes - For a one-shot command that collects stdout and stderr but must not read input, use `@processx.collect_output_no_stdin` from `desktop/internal/processx` instead of `@process.collect_output`. - `collect_output_no_stdin` gives the child a valid stdin handle that is already at EOF and always suppresses creation of a console window. Both are required for Windows GUI builds: inheriting a missing standard-input handle makes process creation fail, while launching a console application without suppression flashes a visible console window. - Do not use it for interactive commands, long-lived protocol processes, or commands that receive a real stdin pipe, file, or PTY. ## JSON Protocol Codecs - Never use `derive(FromJson)`, `derive(ToJson)`, or a combined `derive(FromJson, ToJson)` anywhere under `desktop/`. - Every type crossing a JSON boundary must provide explicit `FromJson` and `ToJson` implementations. The decoder must deliberately specify the behavior of required, missing, `null`, malformed, and unknown fields; the encoder must deliberately specify which optional fields are omitted. - When modifying an existing Desktop protocol type that still derives either JSON trait, replace that derived codec with explicit implementations in the same change. ## Desktop Trust And Security Model - A frontend connected and authenticated to a Desktop instance is trusted with the authority of the local user. This includes the Proton renderer, an authenticated relay frontend, and code the user runs in that frontend's DevTools. - The connected frontend can already invoke Desktop terminal and shell operations. Letting the same frontend select a working directory or send an app-server execution-policy field is therefore not, by itself, a privilege escalation or a Desktop security-boundary violation. - The security boundary is before a frontend obtains an authenticated Desktop command channel. Unauthenticated network peers, unrelated web origins, repository content, model output, and other displayed data are not trusted principals and must not acquire command authority merely by being processed or rendered. - Continue validating command payloads for type safety, protocol correctness, product invariants, and protection against accidental destructive actions. Workspace and path checks may enforce product scope, but they do not sandbox a trusted frontend that can already spawn a shell. - Prefer typed request and response models at Desktop command boundaries. They document the protocol, reject malformed data, and expose schema drift during development; do not justify them as a privilege boundary against the trusted frontend. - A security finding must name the less-trusted principal and the new capability it gains. Do not report a privilege escalation solely because a trusted frontend can craft fields that the normal UI does not expose.