feat(web): make produced-file overflow discoverable

.agents/notes/implemented/feature/2026-07-31-web-workspace-file-links.md

@@ -14,11 +14,11 @@ Two distinct defects sat behind that. The transcript never said what a turn had
 
 ## 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.
+**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. The file lane stays on one line and measures the exact chip and localized remainder widths with `ResizeObserver`; it renders the largest fitting first-seen prefix, bounded at six, plus `+ N files`. 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 `$BROWSER`; either falls back to the default application when no browser can be named. Windows uses its registered association, and WSL first translates the path before using that same Windows handoff.
+**Opening stays the Host's job, and prefers the default browser.** `host.openPath` hands the path to the operating system, which yields a `file://` document in a real browser: full page capabilities, and no reachability into `/api`, because a `file://` document is not same-origin with it. Measured on the reported artifact: `localStorage` works, the theme toggle flips, the tabs switch, and `fetch` to the API fails. For documents a browser renders — `.html`, `.htm`, `.xhtml`, `.svg` — the opener resolves the default *browser* rather than the type's default application when the platform can name one, because a developer who binds `.html` to an editor would otherwise click a produced page and get source code. macOS reads the LaunchServices `https` handler and desktop Linux reads `$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. `host.describe.canOpenPath` reports the configured or best-effort detected native-desktop capability, and the connection publishes that fact per successful generation. When the lane hides files, **Show in folder** opens the session workspace by passing `.` through the same owner `openFile`; it appears only when the page is loopback and the current description permits native opening, so direct remote Web and headless/container Linux Hosts omit the action by default. Deployments where platform detection cannot identify the operator-visible desktop — including SSH tunnels, headless macOS/Windows Hosts, and WSL without working Windows interop — must set gateway `nativeOpen: false`.
 
 **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.
 
@@ -28,8 +28,9 @@ Two distinct defects sat behind that. The transcript never said what a turn had
 - **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.
+- **Horizontal chip scrolling** — keeps every file in the DOM but makes the hidden tail undiscoverable, adds a nested horizontal gesture to the transcript, and provides no exact account of what is out of view. One measured line with a stable remainder preserves the answer's vertical rhythm and keeps the omission explicit.
 - **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.
+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 ten successful writes and pins two leading chips, the exact `+ 8 files` remainder, one-line geometry, and the capability-present folder action 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 still sees the file chips but sees no folder action; clicking a chip cannot open anything because `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. A local SSH port forward can make a remote Host look loopback-local, so such deployments must set `nativeOpen: false`; the same override is required whenever the permissive macOS/Windows/WSL probe or a stale Linux display/opener signal would be a false positive. A future operator-visible capability can replace that deployment declaration. 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.