A Join button is visible in the site top bar.Tapping Join opens a modal within the app showing the site name and two options: Create identity in Hypermedia and Already have a Hypermedia identity, plus a quiet link "I have an identity from another site?"
The modal copy explains the site is built with Hypermedia and that creating an identity takes two minutes — no technical language
Tapping "Already have a Hypermedia identity" takes the user to the email screen inside the Hypermedia sign-in flow
Valid email advances to the passkey screen showing "Good to see you again" and the email address to remind
Passkey confirmation uses device biometrics or PIN
On successful passkey confirmation the user sees a "Join [site name]" screen showing all their available identities, the currently active identity is pre-selected with a checkmark
Primary CTA is "Start participating" — one tap, no further steps
On joining, the site is added to Joined Sites in the sidebar immediately and the Join button disappears from the site top bar
A toast alert appears: "You've joined [site name] — you can now comment and participate" and auto-dismisses after ~3 seconds
No new identity is created — the user's existing remote identity is used throughout and user is as a full member with participation features

User is viewing a site in the app — Join button visible in top bar
Taps Join — modal opens showing "Join [site name]"
Taps "Already have a Hypermedia identity"
Enters email linked to their Hypermedia identity
Taps Continue — passkey screen appears
Confirms with passkey
"Join [site name]" screen shows available identities — primary identity pre-selected
Taps "Start participating"
Returns to site as member — Join button gone, site added to sidebar, toast appears

⚠️ 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 Hypermedia identity → "No Hypermedia identity found for this email." with option to create one instead
Passkey
- ⚠️ Device does not support passkeys → fallback method offered, user not blocked (password needs to be developed later)
- ⚠️User cancels the biometric prompt → returns to passkey screen, can retry
- ⚠️ Passkey creation fails due to device error → retry option shown
- Clear error messages: avoid: "Failed to fletched" "Invalid Handoff token" _ review this one by one
⚠️ User taps "Use another email" → returns to email screen, previous entry cleared
⚠️ User is already a member of this site → join confirmation is skipped, user lands directly as a member with no duplicate entry created
⚠️ User taps "I have an identity from another site?" → path TBD
⚠️ User closes the modal mid-flow → returns to site as guest, no partial state created, Join button remains visible