Require sender to sign with the email address used to send

[rubenhensen]

Problem

Currently, the sender can sign an encrypted email with any identity in their Yivi app, which may not match the email address they are sending from. This allows a mismatch between the sender's signing identity and the actual From address.

Expected behavior

The addon should enforce that the sender signs the email using the same email address that the email is being sent from. If the sender's Yivi disclosure does not include the matching email address, the send should be blocked with an appropriate error message.

Why

Recipients rely on the sender verification badges to confirm the identity of the person who sent the encrypted email. If the signing identity doesn't match the From address, this undermines the trust model.

[dobby-coder]

/dobby fix — require the sender's Yivi signing identity to match the From address of the outgoing message.

Today the sender can sign with any email attribute in their wallet, so the verification badge the recipient sees can name an address the mail was not sent from. Compare the disclosed signing email against the compose window's From address (case-insensitively — see #75 for the casing mismatch) and block the send with a clear error when they differ.

Scope it to src/background/encryption-flow.ts and src/pages/policy-editor/ (validate.ts, collect.ts), plus the compose-action status surface if that is where the error belongs. Do not touch src/pages/yivi-popup/init-flow.ts or the other yivi-popup/ files — a sibling worker is on #46 there.

Add vitest coverage for the match and mismatch cases, and run npm test before opening the PR.

[dobby-coder]

Got it — I'm on this now. I'll update the send flow so it checks the disclosed Yivi signing email against the compose window's From address (case-insensitively) and blocks the send with a clear error on a mismatch, scoped to encryption-flow.ts and the policy-editor validate/collect files (and the compose-action status surface if that's the right home for the error). I'll leave yivi-popup/ untouched and add vitest cases for both the match and mismatch paths before running the test suite.

[dobby-coder]

Parked: this is dobby-initiated work coupled to @rubenhensen, who already has 4 dobby PRs waiting for review (budget: 3). I'm not opening another one until some of those merge or close — comment here to re-trigger dobby once there's room.