Open a page in the container's browser, at a viewport you choose

The pane could only ever watch a browser something else had published.
This opens one: a URL and a viewport, launched inside the container and
bound so the pane picks it up. Two uses, one action — a sign-in page,
where the callback listener is *in* the container and the loop closes
with no host round trip and no auth bridge, and a dev server on container
loopback, which is how you watch a UI Claude is building.

Reachable from both places the question comes up: "Open a page…" in the
Browser tab, and an "In container" button on the terminal's URL prompt.

Verified first, because it decided the design: a second client cannot
join a bound browser. `chromium.connect()` against the published endpoint
times out in every URL form (`ws+unix://…`, with and without the trailing
path) — that socket speaks the dashboard's own transport, not the public
connect protocol. Whoever launches is therefore the only process that can
drive, so the helper is resident and holds the handle, and live resize
applies to pages we opened and never to `@playwright/mcp`'s. Those take
`--viewport-size` / `PLAYWRIGHT_MCP_VIEWPORT_SIZE` at launch, which the
docs now say.

The viewport is the interesting half. Resizing the *window* does nothing
to the page — the viewer is a CDP screencast, so a bigger window is the
same pixels drawn larger, which is why pages have been looking like they
were rendered small. `page.setViewportSize()` genuinely reflows: measured
against a `@media (max-width: 900px)` rule, it fires at 800×600 and
clears at 1440×900. Match-window mode pushes the pop-out's settled size
into it, debounced by generation counter because a drag emits `Resized`
continuously and each one costs a container exec.

Control is a polled JSON file in /tmp: no port, no second listener,
nothing added to the proxy's surface, and URLs travel as argv to `node`
so no shell ever parses one. A re-open with a helper already up
navigates instead of relaunching — otherwise the second page would throw
away the session the first one just signed into.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

app/src/components/projects/home/OpenPageDialog.tsx

@@ -0,0 +1,148 @@
+import { useState } from "react";
+import Modal from "../../ui/Modal";
+import Button from "../../ui/Button";
+
+/**
+ * Viewport presets. These are the *page's* resolution, not the window's — the
+ * pane is a screencast, so a bigger window shows the same pixels drawn larger
+ * while this is what actually reflows the layout.
+ */
+const PRESETS: { label: string; width: number; height: number }[] = [
+  { label: "1280 × 720", width: 1280, height: 720 },
+  { label: "1920 × 1080", width: 1920, height: 1080 },
+  { label: "1440 × 900", width: 1440, height: 900 },
+  { label: "390 × 844 (phone)", width: 390, height: 844 },
+];
+
+interface Props {
+  /** Prefilled URL — an auth URL from the terminal, or the last one used. */
+  initialUrl?: string;
+  initialWidth?: number;
+  initialHeight?: number;
+  busy?: boolean;
+  onOpen: (url: string, width: number, height: number) => void;
+  onClose: () => void;
+}
+
+/**
+ * Ask for a URL and a viewport, then open it in the container's browser.
+ *
+ * Deliberately modal and short-lived — the convention for a task with one
+ * question and one button. The URL is not opened here; the caller runs the
+ * command so failures land in its toast.
+ */
+export default function OpenPageDialog({
+  initialUrl = "",
+  initialWidth = 1280,
+  initialHeight = 720,
+  busy = false,
+  onOpen,
+  onClose,
+}: Props) {
+  const [url, setUrl] = useState(initialUrl);
+  const [width, setWidth] = useState(initialWidth);
+  const [height, setHeight] = useState(initialHeight);
+
+  const trimmed = url.trim();
+  // Mirrors the backend's allow-list, so the error arrives before the click
+  // rather than after a round trip.
+  const valid = /^https?:\/\/\S+$/i.test(trimmed);
+
+  return (
+    <Modal
+      title="Open a page in the container's browser"
+      onClose={onClose}
+      footer={
+        <>
+          <Button size="md" onClick={onClose} disabled={busy}>
+            Cancel
+          </Button>
+          <Button
+            size="md"
+            variant="primary"
+            disabled={!valid || busy}
+            onClick={() => onOpen(trimmed, width, height)}
+          >
+            {busy ? "Opening…" : "Open page"}
+          </Button>
+        </>
+      }
+    >
+      <div className="space-y-4">
+        <p className="text-[13px] text-[var(--text-secondary)] leading-relaxed">
+          Launches a browser <em>inside</em> this container and publishes it to the
+          Browser tab. Use it for a sign-in page — the callback listener is in the
+          container too, so the login completes without involving your host browser —
+          or for a dev server on container loopback.
+        </p>
+
+        <label className="block">
+          <span className="text-xs text-[var(--text-secondary)]">URL</span>
+          <input
+            autoFocus
+            value={url}
+            onChange={(e) => setUrl(e.target.value)}
+            onKeyDown={(e) => {
+              if (e.key === "Enter" && valid && !busy) onOpen(trimmed, width, height);
+            }}
+            placeholder="http://localhost:5173"
+            spellCheck={false}
+            className="mt-1 w-full px-2 py-1.5 bg-[var(--bg-primary)] border border-[var(--border-color)] rounded-[var(--radius-control)] text-[13px] font-mono text-[var(--text-primary)]"
+          />
+          {trimmed !== "" && !valid && (
+            <span className="mt-1 block text-xs text-[var(--error)]">
+              Only http:// and https:// URLs can be opened.
+            </span>
+          )}
+        </label>
+
+        <div>
+          <span className="text-xs text-[var(--text-secondary)]">Viewport</span>
+          <div className="mt-1 flex flex-wrap gap-1.5">
+            {PRESETS.map((p) => {
+              const active = p.width === width && p.height === height;
+              return (
+                <button
+                  key={p.label}
+                  type="button"
+                  aria-pressed={active}
+                  onClick={() => {
+                    setWidth(p.width);
+                    setHeight(p.height);
+                  }}
+                  className={`px-2 py-1 text-xs rounded-[var(--radius-control)] border transition-colors ${
+                    active
+                      ? "border-[var(--accent)] bg-[var(--accent-muted)] text-[var(--accent)]"
+                      : "border-[var(--border-color)] text-[var(--text-secondary)] hover:text-[var(--text-primary)]"
+                  }`}
+                >
+                  {p.label}
+                </button>
+              );
+            })}
+          </div>
+          <div className="mt-2 flex items-center gap-2">
+            <input
+              type="number"
+              aria-label="Viewport width"
+              value={width}
+              min={200}
+              onChange={(e) => setWidth(Number(e.target.value))}
+              className="w-24 px-2 py-1 bg-[var(--bg-primary)] border border-[var(--border-color)] rounded-[var(--radius-control)] text-xs text-[var(--text-primary)]"
+            />
+            <span aria-hidden="true" className="text-xs text-[var(--text-secondary)]">×</span>
+            <input
+              type="number"
+              aria-label="Viewport height"
+              value={height}
+              min={200}
+              onChange={(e) => setHeight(Number(e.target.value))}
+              className="w-24 px-2 py-1 bg-[var(--bg-primary)] border border-[var(--border-color)] rounded-[var(--radius-control)] text-xs text-[var(--text-primary)]"
+            />
+            <span className="text-xs text-[var(--text-secondary)]">CSS pixels</span>
+          </div>
+        </div>
+      </div>
+    </Modal>
+  );
+}