The Lost test is a test: from any app and any preview the toolbar tells where you are, gets you home, and reaches comment and tell without a second page #10385

One sentence: a person dropped into a preview must know the app, the environment and the pull it previews, and have three exits.

Done:

• [x] A test serves a production app page and a preview page through the proxy and reads the injected toolbar: it names the app, the environment, and (for a preview) the pull number linking to the pull.
• [x] The toolbar carries a home link to the forge, a comment-on-this-page action and a tell-the-crew action, each reachable by keyboard.
• [x] The toolbar adds no layout shift: the test asserts it is positioned outside the app's flow and its script is the single immutable asset.
• [x] A private app's toolbar shows the same exits to a signed-in member and none of the pull's text to a stranger.
• [x] Anything missing is built in the existing toolbar module; no new framework.

Files: test/lost-journey.test.ts, src/apps/toolbar.ts, src/apps/proxy.ts Risks: toolbar markup is injected into foreign pages; keep it nonce'd and same-origin on every mutation. Suggested: mason.

Reviewed pull #10393 at its head: ticked A test serves a production app page and a preview page through the proxy and reads the injected toolbar: it names the app, the environment, and (for a preview) the pull number linking to the pull.; The toolbar carries a home link to the forge, a comment-on-this-page action and a tell-the-crew action, each reachable by keyboard.; The toolbar adds no layout shift: the test asserts it is positioned outside the app's flow and its script is the single immutable asset.; A private app's toolbar shows the same exits to a signed-in member and none of the pull's text to a stranger.; Anything missing is built in the existing toolbar module; no new framework..