US-2.1. — As a user who already has a Hypermedia identity, I want to join a site from the browser so that I can participate in it.

Acceptance Criteria

Entry & join trigger

A Join button is visible in the site top bar when the user is not yet a member
Tapping Join opens a modal within the site context.
When user tries to comment, follow or bookmark the same flow starts.
The modal shows the site name (Ethosfera), explains it is built with Seed Hypermedia, and offers two options: Create identity or Already have a Hypermedia identity
A third low-commitment option is visible: "I have a different identity domain"
Tapping "Already have a Hypermedia identity" takes the user to the sign-in flow

Sign in — email

Sign in — passkey

Join confirmation

The join confirmation screen shows the user's name and email so they can verify which identity they are joining with
Copy changes depending if it is one account or +1 account.
Primary CTA is "Continue as <account> which joins the site and returns the user to the site as a member

Joined state

The Join button disappears from the top bar
The user's avatar appears in the top bar
The comment and participation areas become active
A confirmation alert appears: "You've joined [site name] — you can now comment and participate" and auto-dismisses after ~3 seconds

Remove this step please if there is no more that one account!

User arrives at Ethosfera as a guest and sees the Join button
User taps Join — modal opens within the site
User taps "Already have a Hypermedia identity"
User enters email linked to their Seed identity
User taps Continue — advances to passkey screen
User confirms with passkey (Face ID, Touch ID, or PIN)
Join confirmation screen shows name and email
User taps "Start participating" — joined
Returns to site as member — Join button gone, avatar visible, comment area active
Confirmation alert appears and auto-dismisses

Email

⚠️ Invalid email format → inline error: "That doesn't look like a valid email. Check for typos and try again." Button disabled until fixed
⚠️ Email not linked to any Seed identity → error with option to create one instead: "No Seed identity found for this email. Want to create one?"
⚠️User enters email from a different domain/site → redirect to "I have an identity from another site" path

Passkey

⚠️ Passkey fails or is cancelled → returns to passkey screen with retry option and "Send a verification code instead" fallback
⚠️Device doesn't support passkey → verification code fallback offered automatically
⚠️User taps "Use another email" → returns to email screen, previous entry cleared

Navigation

⚠️User closes the modal mid-flow → returns to site as guest, no partial state created
⚠️User presses browser back mid-flow → returns to previous step without losing email entry

When user comes from commenting: