Release 0.16.0: owner-only invite for per-RFC contribution + discussion (+ #21 Part C Amplitude wiring)

Wave 5 / Track B. Roadmap item #12. Folds in #21 Part C Amplitude
wiring inline (operator ask: "best practices from the very get-go").

RFC owners can invite specific users to one of two per-RFC roles:
contributor (open PRs + join discussion) or discussant (discussion
only). Non-invited users keep the v0.6.0 anonymous-read contract.
The per-RFC write gate layers on top of the existing
require_contributor gate; a super-draft with no owners yet falls
through to the platform-granted contract, preserving the
v0.6.0/v0.7.0/v0.8.0 contracts in their domains.

Backend: migration 018_rfc_invitations.sql (auto-applied — two
tables: rfc_invitations + rfc_collaborators); api_invitations.py
with five endpoints + transactional email; auth.py helpers
(is_rfc_owner / is_rfc_collaborator / can_discuss_rfc /
can_contribute_to_rfc / can_invite_to_rfc); api_discussion +
api_branches + api_prs gate composition; api_admin.py additive
rfc_invitations[] per user. 237 backend tests pass (18 new in
test_rfc_invitations_vertical.py).

Frontend: InvitationsModal.jsx (owner surface), AcceptInvitation.jsx
(/invitations/accept route), api.js helpers, RFCView.jsx
Invitations button, App.jsx route registration.

Amplitude wiring (inline, #21 Part C):
  - INVITATION_SENT from InvitationsModal { rfc_slug, role_in_rfc }
  - INVITATION_ACCEPTED from AcceptInvitation { rfc_slug, role_in_rfc }
  - identify() BEFORE the accept event with properties: invited_at
    (setOnce), last_invited_to_rfc, last_invite_role_in_rfc,
    claim_method: 'rfc-invite'
  - EVENTS taxonomy extended with INVITATION_SENT + INVITATION_ACCEPTED

No new secrets, no new overlay keys, no operator gesture beyond the
v0.15.0 overlay-set + restart. Frontend build verified green.

Subagent ν shipped the feature on feature/v0.16.0-owner-invite
(a51beec). Driver-side integration squash-merged into main,
hand-resolved VERSION + package.json + CHANGELOG (strict-descending
0.16.0 → 0.15.0), and added the inline Amplitude wiring.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/components/AcceptInvitation.jsx

@@ -0,0 +1,207 @@
+// AcceptInvitation.jsx — v0.16.0 / roadmap item #12.
+//
+// The /invitations/accept?token=... landing page the invitation email
+// links to. The page:
+//
+//   1. Reads `?token=...` from the URL.
+//   2. Calls GET /api/invitations/accept?token=... to preview what the
+//      invitation grants (RFC title, role-in-RFC, expiry, whether the
+//      currently-signed-in user's email matches the invitee's).
+//   3. Renders a confirmation surface — name the RFC, name the role,
+//      and either show "Accept" (when the email matches and the
+//      invitation is still pending) or a refusal message (expired,
+//      revoked, email mismatch).
+//   4. On accept, POST /api/invitations/accept lands the
+//      rfc_collaborators row and the page redirects to the RFC's view.
+//
+// For an anonymous viewer who lands here without signing in, the
+// preview call 401s and the page tells them to sign in. After
+// signing in (via the existing OTC/passcode surface at /login) they
+// can return to the same URL — the token is stable.
+
+import { useEffect, useState } from 'react'
+import { Link, useNavigate, useSearchParams } from 'react-router-dom'
+import { acceptInvitation, previewInvitation } from '../api'
+import { EVENTS, identify, track } from '../lib/analytics'
+
+export default function AcceptInvitation({ viewer }) {
+  const [searchParams] = useSearchParams()
+  const navigate = useNavigate()
+  const token = searchParams.get('token') || ''
+
+  const [preview, setPreview] = useState(null)
+  const [previewError, setPreviewError] = useState(null)
+  const [accepting, setAccepting] = useState(false)
+  const [acceptError, setAcceptError] = useState(null)
+
+  useEffect(() => {
+    if (!token) {
+      setPreviewError('No invitation token in the URL.')
+      return
+    }
+    if (!viewer) {
+      // Not signed in — the preview endpoint will 401. We surface a
+      // sign-in prompt without making the request.
+      return
+    }
+    previewInvitation(token)
+      .then(setPreview)
+      .catch(err => setPreviewError(err.message || 'Could not load invitation.'))
+  }, [token, viewer])
+
+  async function handleAccept() {
+    setAccepting(true)
+    setAcceptError(null)
+    try {
+      const result = await acceptInvitation(token)
+      // v0.16.0 + #21 Part C — re-identify with per-RFC invite
+      // properties on accept, BEFORE the track event fires, so the
+      // Amplitude user record carries the invite context from the
+      // moment of acceptance. setOnce on invited_at preserves the
+      // first-accepted timestamp if the same user accepts multiple
+      // RFC invitations.
+      if (viewer?.id != null) {
+        identify({
+          user_id: String(viewer.id),
+          properties: {
+            invited_at: ['__setOnce__', new Date().toISOString()],
+            last_invited_to_rfc: result.rfc_slug,
+            last_invite_role_in_rfc: result.role_in_rfc || preview?.role_in_rfc,
+            claim_method: 'rfc-invite',
+          },
+        })
+      }
+      track(EVENTS.INVITATION_ACCEPTED, {
+        rfc_slug: result.rfc_slug,
+        role_in_rfc: result.role_in_rfc || preview?.role_in_rfc,
+      })
+      navigate(`/rfc/${result.rfc_slug}`)
+    } catch (err) {
+      setAcceptError(err.message || 'Could not accept invitation.')
+    } finally {
+      setAccepting(false)
+    }
+  }
+
+  if (!token) {
+    return (
+      <div className="accept-invitation">
+        <h1>Invitation link is malformed</h1>
+        <p>No <code>token</code> parameter was found. Ask the person who
+          invited you to re-send the link.</p>
+        <p><Link to="/">Return to the catalog</Link></p>
+      </div>
+    )
+  }
+
+  if (!viewer) {
+    return (
+      <div className="accept-invitation">
+        <h1>Sign in to accept your invitation</h1>
+        <p>
+          You've been invited to collaborate on an RFC. Sign in first so we
+          can attach the membership to your account, then return to this
+          link.
+        </p>
+        <p>
+          <Link to="/login" className="btn-primary">Sign in</Link>
+        </p>
+      </div>
+    )
+  }
+
+  if (previewError) {
+    return (
+      <div className="accept-invitation">
+        <h1>Invitation unavailable</h1>
+        <p>{previewError}</p>
+        <p><Link to="/">Return to the catalog</Link></p>
+      </div>
+    )
+  }
+
+  if (!preview) {
+    return <div className="accept-invitation">Loading invitation…</div>
+  }
+
+  const { rfc_title, rfc_slug, role_in_rfc, status, invitee_email, email_matches_you } = preview
+
+  if (status === 'revoked') {
+    return (
+      <div className="accept-invitation">
+        <h1>Invitation revoked</h1>
+        <p>
+          The owner of <strong>{rfc_title}</strong> revoked this invitation.
+          Ask them to re-issue it if you should still have access.
+        </p>
+        <p><Link to={`/rfc/${rfc_slug}`}>Read the RFC anyway</Link></p>
+      </div>
+    )
+  }
+  if (status === 'expired') {
+    return (
+      <div className="accept-invitation">
+        <h1>Invitation expired</h1>
+        <p>
+          This invitation to <strong>{rfc_title}</strong> has expired. Ask
+          the RFC's owner to issue a fresh one.
+        </p>
+        <p><Link to={`/rfc/${rfc_slug}`}>Read the RFC anyway</Link></p>
+      </div>
+    )
+  }
+  if (status === 'accepted') {
+    return (
+      <div className="accept-invitation">
+        <h1>Already accepted</h1>
+        <p>
+          You've already accepted this invitation. You can{' '}
+          <Link to={`/rfc/${rfc_slug}`}>open {rfc_title}</Link> now.
+        </p>
+      </div>
+    )
+  }
+
+  if (!email_matches_you) {
+    return (
+      <div className="accept-invitation">
+        <h1>This invitation is for a different account</h1>
+        <p>
+          This invitation was sent to <strong>{invitee_email}</strong>. You're
+          currently signed in as <strong>{viewer.email || viewer.gitea_login}</strong>.
+          Sign out and sign back in with the invited address to accept.
+        </p>
+        <p><a className="btn-link" href="/auth/logout">Sign out</a></p>
+      </div>
+    )
+  }
+
+  return (
+    <div className="accept-invitation">
+      <h1>Join {rfc_title}</h1>
+      <p>
+        You've been invited to <strong>{rfc_title}</strong> as a{' '}
+        <strong>{role_in_rfc}</strong>.
+      </p>
+      <p style={{ color: '#666' }}>
+        {role_in_rfc === 'contributor'
+          ? 'Contributors can open PRs against this RFC and join its discussion.'
+          : 'Discussants can post in this RFC\'s discussion.'}
+      </p>
+      {acceptError && <div className="error-banner">{acceptError}</div>}
+      <p>
+        <button
+          type="button"
+          className="btn-primary"
+          onClick={handleAccept}
+          disabled={accepting}
+        >
+          {accepting ? 'Accepting…' : `Accept and open ${rfc_title}`}
+        </button>
+      </p>
+      <p>
+        <Link to={`/rfc/${rfc_slug}`}>or just read the RFC without accepting</Link>
+      </p>
+    </div>
+  )
+}