On an app's production page the forge pill's Home link returns to the exact forge page the visitor left, and is reachable by keyboard #11384

The pill's Home link now goes back to the forge page the visitor left, but the forge's own Referrer-Policy stops that from working for most visitors today. Only a referrer on the forge's own origin is used; anything else, or none, still gives the forge's /. I did not fix the policy, so this is not yet reachable end to end (details at the end).

What changed

• Pill code: src/apps/toolbar.ts reads document.referrer, parses it as a URL, and uses it only if its origin equals the forge origin the pill already knows and it is http or https. It uses origin, path and query, and drops the fragment. The Home link's href is set from that target. The pill adds no new inline script or style attribute.
• Keyboard: Home was already a normal link in the panel, so Tab reaches it and Enter follows it. Escape already closed the panel; I didn't change either.
• Tests: test/toolbar-back.test.ts runs the pill source against a fake document. A forge page referrer becomes the Home target. A foreign origin, javascript: and an empty referrer all give https://forge.test/. Without the change the first test fails.
• Docs: docs/APPS.md has a line on what Home does now.
• Checks: The new test, the existing toolbar tests and test/mcp-size.test.ts pass, and tsc and the gate are clean. The toolbar asset hash changes because the script changed. No MCP code changed.

What I left out

• Referrer policy: securityFloor sets Referrer-Policy: same-origin on forge pages. A browser therefore sends no referrer when a visitor clicks from a forge page into an app on another origin, and Home falls back to /.
• The follow-up: making this work end to end needs referrerpolicy="origin-when-cross-origin" on the forge's links into apps, which are spread across many pages, plus a decision that path-level referrers may leave the forge. I haven't touched either.
• Keyboard test: I added no Chromium keyboard test.

Closes #11295

The pill's Home link now goes back to the forge page the visitor left, but the forge's own Referrer-Policy stops that from working for most visitors today. Only a referrer on the forge's own origin is used; anything else, or none, still gives the forge's /. I did not fix the policy, so this is not yet reachable end to end (details at the end).

What changed

• Pill code: src/apps/toolbar.ts reads document.referrer, parses it as a URL, and uses it only if its origin equals the forge origin the pill already knows and it is http or https. It uses origin, path and query, and drops the fragment. The Home link's href is set from that target. The pill adds no new inline script or style attribute.
• Keyboard: Home was already a normal link in the panel, so Tab reaches it and Enter follows it. Escape already closed the panel; I didn't change either.
• Tests: test/toolbar-back.test.ts runs the pill source against a fake document. A forge page referrer becomes the Home target. A foreign origin, javascript: and an empty referrer all give https://forge.test/. Without the change the first test fails.
• Docs: docs/APPS.md has a line on what Home does now.
• Checks: The new test, the existing toolbar tests and test/mcp-size.test.ts pass, and tsc and the gate are clean. The toolbar asset hash changes because the script changed. No MCP code changed.

What I left out

• Referrer policy: securityFloor sets Referrer-Policy: same-origin on forge pages. A browser therefore sends no referrer when a visitor clicks from a forge page into an app on another origin, and Home falls back to /.
• The follow-up: making this work end to end needs referrerpolicy="origin-when-cross-origin" on the forge's links into apps, which are spread across many pages, plus a decision that path-level referrers may leave the forge. I haven't touched either.
• Keyboard test: I added no Chromium keyboard test.

The forge's Open the app redirect now lets the forge page's address through to the app, so the pill's Home link has a referrer to return to. I haven't seen it work in a browser. The new test only checks the redirect's header, and the sandbox can't open a browser or click through. tsc, the gate, the design lint and the toolbar and apps-api tests pass. The tests I ran don't cover the pill's Tab/Enter behaviour in a browser (Keyboard test below).

What changed

• Referrer fix. GET /:owner/:name/app/:env/open (appOpen) is the single redirect behind every "Open the app" link, and it now answers with Referrer-Policy: no-referrer-when-downgrade. I did not change securityFloor.
• Policy choice. I did not use origin-when-cross-origin as suggested. Across origins it sends only the origin, so the page's path would never reach the app and Home would still go to /. Because of that, the app now receives the forge page's full address, path and query, over https only. Any app the visitor opens through that redirect can read which forge page they came from, including private repo names in the path. The pill drops the fragment, but the app's server still sees it.
• Test for the fix. In test/apps-api.test.ts, the redirect test asserts a 302 with that policy, and it fails without the change.
• Test crash handling. In test/toolbar-back.test.ts, the client no longer swallows exceptions. The helper asserts the Home link was built and has an href.
• Keyboard test. I added only the source-level check you minimum-asked for: Home is an anchor, and the Escape handler is present. A real Tab/Enter/Escape test belongs in toolbar-keyboard.test.ts (headless Chromium), which I did not extend.
• Docs. The docs/APPS.md line is wrapped. It says Home only returns to the forge page when the redirect lets the referrer through, otherwise it goes to /.

Left out

• Other app links. Links that point straight at an app, bypassing the redirect, are unchanged and still send no referrer. These are talk_build's productionUrl/previewUrl links and the "Open on its own" link in talk_preview. Several of them also carry rel="noreferrer", so each needs its own look.

To try

1. On a repo's page, press Open the app.
2. On the app's page, open the pill's panel. Home should return to the repo page.