Redirect Get Feedback to the canonical subscript.to origin

[lsegal]

Get Feedback redirected users to write.subscript.to after uploading their draft, where SSO login fails. It now always lands on the canonical Subscript site (subscript.to).

Root cause

getFeedback in app/src/App.tsx POSTs to the relative path /write/feedback and then called window.location.assign(result.redirect_url) directly. When the editor is served from write.subscript.to, a relative redirect_url (or one the server built from the request host) resolves to write.subscript.to, not subscript.to.

Change

• New helper feedbackRedirectUrl (app/src/lib/feedback.ts) resolves the returned redirect against the configured Subscript homepage (config.homepage, default https://subscript.to):
  • relative URLs resolve against the homepage origin;
  • absolute URLs pointing at the editor's own host are moved onto the homepage origin (path, query, and hash preserved);
  • URLs on any other origin are left alone, and nothing changes when the editor is embedded on the homepage itself.
• getFeedback uses the helper before navigating.

User impact

After clicking Get Feedback on write.subscript.to, users land on subscript.to, where SSO login works.

Tests

• Added app/src/lib/feedback.test.ts covering relative, editor-host, foreign-origin, and embedded-on-homepage redirects.
• pnpm run lint and pnpm run test (13 files, 41 tests) pass locally.

Notes

• No changelog entry: the project has no changelog.
• No screenshots: the change only affects the navigation target, not any rendered UI.

Closes #2

Agents: claude-code (claude-opus-5-5)

[lsegal]

Manual verification

CI can't cover these because they need the deployed site and a real Subscript account.

• Once this is deployed, open https://write.subscript.to while signed out of Subscript, write a short draft, and click Get Feedback. The upload should finish and the browser should land on a https://subscript.to/... URL, not write.subscript.to.
• Sign in through SSO on that page. Login should succeed and you should reach the feedback flow for the uploaded draft.
• Repeat while already signed in to Subscript. The redirect should go straight to the subscript.to feedback page.