deepseek-harness/.agents/notes/implemented/feature/2026-07-28-tool-call-file-open-in-os.md

Agent Note: Tool-call file open in OS

Status: implemented

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Problem

Chat tool rows treated the whole summary line as a click target that opened the right-hand details panel, with a hover background on the row. For filesystem tools the useful action is opening the mentioned file in the operating system's default application, not inspecting the raw tool payload in a sidebar.

Decision

File-tool path summaries (read / write / edit args carrying path or file_path) render as links underlined at rest with a pointer cursor. Clicking the path calls host.openPath through WorkspacesService.openPath, resolving relative paths against the session cwd. File-link rows disable args expand (leading icon is inert); whole-row click, row hover fill, and the click-to-open-details gesture are removed from tool rows (including bash and todo registrations). The details panel and its inject surface remain for programmatic selection; rows no longer drive them.

host.openPath is a privileged unary RPC accepted only from loopback, same-origin browser requests (same carrier guard as host.pickDirectory). Platform adapters open without a shell: open on macOS, PowerShell Invoke-Item on Windows, and xdg-open on desktop Linux; browser-renderable documents prefer the named default browser on macOS and desktop Linux. WSL is a separate host shape despite Node reporting linux: the adapter recognizes its environment or Microsoft kernel release, translates the Linux path with wslpath -w, and passes the resulting Windows/UNC path to the same PowerShell handoff. The opener's platform facts and command runner are injectable for tests. URL-only read args (web_fetch) are not file links.

Alternatives considered

• Keep row-click details and add a separate file affordance — rejected; the product ask replaces the row gesture with the file link.
• Open files inside an in-app preview — rejected; the ask is the OS default application.
• Treat WSL as desktop Linux — rejected; a WSL process reports linux, but a Linux desktop association is optional while its ordinary operator desktop and browser live on Windows.
• Reuse host.pickDirectory's timeout exemption — unnecessary; path open hand-off completes quickly under the normal unary deadline.

Consequences

Clicking a file path in a tool row opens that path on the host. Non-file tool rows are inert summaries (expand toggles remain where the row already supported them). Remote or non-loopback clients cannot invoke host.openPath.

Risks

• Desktop Linux hosts without xdg-open, and WSL hosts without working Windows interop (wslpath plus powershell.exe), fail the RPC; the chat row stays silent while the host returns an internal error.
• Relative paths without a session cwd are forwarded verbatim and may fail on the host.