Two security fixes bundled together because they all live on the
icon-click/fill path:
1. Icon + picker + TOFU hint now render inside closed-mode Shadow DOM
(via shadow.createShadowHost). Page scripts can no longer find our
overlay via document.querySelector or rewrite buttons.
2. Icon's get_autofill_candidates call drops the `url` field — router
derives origin from sender.tab.url. Similarly get_credentials.
3. Icon's get_credentials response handling was buggy: the response is a
discriminated union { requires_ack, hostname } | { username, password }
and the old code always read .username (→ undefined when requires_ack).
New code dispatches on the `requires_ack` marker and either shows an
in-page TOFU hint or fills directly.
4. fill_credentials is popup-only in the router — the icon click cannot
(and MUST NOT) issue it from content. The new flow calls fillFields()
directly after get_credentials returns the plaintext: the content
script IS the origin, so no SW round-trip is needed for the typing.
5. TOCTOU on the popup → SW → content fill path: the SW verified the
captured tab's hostname matched capturedUrl, then forwarded blindly.
Between that check and chrome.tabs.sendMessage delivery, the tab can
navigate; chrome.tabs.sendMessage delivers to whatever content-script
principal is loaded at send-time. Closed by:
- Router forwards { expectedHost: currentHost } in the payload.
- fill.ts re-checks location.href.hostname === expectedHost before
typing anything; on mismatch replies { ok: false, error: 'origin_changed' }
and types nothing.
6. Remove @ts-nocheck from icon.ts, fill.ts, and detector.ts — all three
now type-check clean.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
14397b33f0