# Agent Note: opening a produced file from the web UI

Status: implemented

English | [中文](2026-07-31-web-workspace-file-links.zh.md)

> Scope: the produced-files row a finished turn ends with, the file-path link that reads as one, and the Host opener preferring the default browser for documents a browser renders. Not in scope, by decision: serving workspace files over HTTP, and previews for a client that is not on the Host machine.

## Problem

A web session that produced a file had no way to look at it. The agent wrote `deepseek-homepage.html`, said so, and the user's only recourse was to copy an absolute path like `/private/tmp/dsh-client-hotplug.ygPvsm/workspaces/plugin-hotplug/deepseek-homepage.html` into a terminal.

Two distinct defects sat behind that. The transcript never said what a turn had produced: `ToolCallView.locations` — the follow-along vocabulary the file tools already populate — had no consumer in the client, so a reader's only account of the output was whatever the closing message happened to spell. And the affordance that did exist was invisible: `ToolRow` already renders a mutation or read row's path as a real button wired to `host.openPath`, but styled exactly like the surrounding prose and underlined only on hover, so nobody found it. The reported "I can't open what it made" was a discoverability failure sitting on top of a working capability.

## Decision

**A finished turn ends with the files it produced.** The row is its own plugin, `@deepseek-ai/dsh-client-ui-deliverables`, registered into the `conversation.chat.turnTail` hole the chat view renders between a closing message's body and its IconActions — ui-conversation owns the hole and the owner currency (nodes, closing seq, `openFile`), the plugin owns every policy. `producedForClosing` reads the paths off the mutation tools' own follow-along `locations` — a diff card, or a generic card whose `kind` is `edit` (the shape `str_replace_editor`'s insert presents) — so a turn's output is listed whether or not the closing message named it, and a new mutation tool joins by declaring what it does rather than by being added to a list. Reads, deletes, and failed calls contribute nothing; a path appears once per turn in first-seen order; accumulation resets on the turn boundary, so a turn that mutates and then ends without content text cannot spill into the next turn's row. One cordis.yml line composes the surface in or out; the unregistered hole renders nothing.

**The path link reads as a link.** Underlined at rest, not only on hover. This is the smaller half of the diff and the larger half of the fix.

**Opening stays the Host's job, and prefers the default browser.** `host.openPath` hands the path to the operating system, which yields a `file://` document in a real browser: full page capabilities, and no reachability into `/api`, because a `file://` document is not same-origin with it. Measured on the reported artifact: `localStorage` works, the theme toggle flips, the tabs switch, and `fetch` to the API fails. For documents a browser renders — `.html`, `.htm`, `.xhtml`, `.svg` — the opener resolves the default *browser* rather than the type's default application when the platform can name one, because a developer who binds `.html` to an editor would otherwise click a produced page and get source code. macOS reads the LaunchServices `https` handler and desktop Linux reads `$BROWSER`; either falls back to the default application when no browser can be named. Windows uses its registered association, and WSL first translates the path before using that same Windows handoff.

**Serving workspace files over HTTP is out of scope, and so are non-local clients.** Serving files from the harness itself — same-origin with `/api`, behind `CSP: sandbox`, or from a second listener whose own port gives served documents their own origin — was rejected with the product scope: previews for a browser that is not on the Host machine are not supported, so the Host opener answers the supported case completely and the HTTP machinery would answer only the unsupported one.

## Alternatives considered

- **Serving `/f/<sessionId>/<segments…>` from the harness** — built and working, including confinement by dual `realpath`, the browser-trust fence, streamed reads, and a separate listener whose port gave served documents their own origin. It is the only design that shows a preview to a client on another machine, which is exactly the case ruled out of scope. Retired for that reason, not because it failed; its cost was a second socket with its own lifecycle, a port published into the page, and a URL-shape contract shared across two packages.
- **Same-origin HTTP serving without isolation** — measurably unsafe, and recorded so nobody retries it: a document served beside `/api` drove `settings.describe` to a `200` with full data and `session.list` to 35 KB of every session's transcript, from a page that need not be agent-authored at all (a read row makes every file in a cloned repository openable).
- **`Content-Security-Policy: sandbox` over that same-origin serving** — closes the hole by taking the document's origin away, which measurably breaks the pages this feature exists to show: the reported artifact throws `SecurityError` on load, and because an uncaught exception aborts the rest of its `<script>`, every listener declared after that line — theme toggle, mobile menu, model tabs — never binds. Two of the four artifacts in the reporting user's workspace were dead pages under it, and they still rendered perfectly, so the breakage was invisible.
- **Linkifying paths in the assistant's closing message** — the shape a user asks for ("put the link at the end"), but it makes rendering depend on the model spelling a path recognizably. The tool calls already carry `locations` as structured fact, so the produced-files row consumes that instead.
- **An embedded WebView in the desktop shell** — the strongest isolation available, since the preview then runs in a container the product owns rather than in the user's browser. It belongs to the desktop shell's own design, not to this surface, and is recorded here as the direction a future preview capability should take.

## Consequences

Every existing file affordance changed at once: write, edit, read, and the generic single-file card all reach `openFile`, so the link fix and the browser preference apply to all of them without a per-row change. The keyless web lane (`apps/web/tests/produced-files.e2e.ts`) cold-seeds a recorded write turn and pins the row in the assembled application; it deliberately does not click, because the click hands a path to the Host's opener and would launch a real application on the machine running the suite. A produced file opens as a `file://` document, which cannot `fetch` its own siblings (a multi-file artifact that loads `./data.json` breaks, while `<script src>`, `<img>`, and CSS `@import` are unaffected) — the one capability HTTP serving had that this does not. A client reached over the network sees nothing when it clicks: `host.openPath` runs on the Host and is loopback-pinned by the `/api` trust fence. That is the scope decision showing through, not a defect, and it is why the row keeps the full path in its `title` for a reader who can only copy it. Markdown opens in whatever the platform hands `.md`, usually an editor rather than a renderer; rendering it inside the product is a separate, deferred surface.
