diff --git a/CHANGELOG.md b/CHANGELOG.md
index 226e7e1..c10edc2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -56,6 +56,24 @@ as the sole owner of their own account and sees identical data.
     freshly-created personal account (mirror of the signup flow).
   - `POST /api/account/transfer-ownership` — owner only. Atomic
     swap with the named member.
+- **Invitation API + redeem flow** — the no-email, link-only
+  invite path. Backend is complete; the Members tab UI that
+  drives it lands in a follow-up.
+  - `GET /api/account/invitations` — list outstanding (admin+).
+  - `POST /api/account/invitations` — create an invite, returns
+    the plaintext token + share URL **exactly once** (we store
+    only the SHA-256 hash on the row). Body
+    `{ role, expiresInDays?, label? }`. Admin+.
+  - `DELETE /api/account/invitations/[id]` — revoke (admin+).
+  - `GET /api/invitations/[token]/peek` — public, per-IP
+    rate-limited. Returns `{ ok, account_name, role, expires_at }`
+    or `{ ok: false, reason }` so the join page can render
+    "You're being invited to <Account> as <Role>".
+  - `POST /api/invitations/[token]/redeem` — authenticated.
+    Atomically moves the caller's profile to the inviter's
+    account and cleans up the orphan personal account. Refuses
+    with 409 if the caller's current account already contains
+    domain data (no silent data loss).
 
 ### Migration required
 
@@ -76,6 +94,12 @@ Apply against your Supabase project before deploying this version:
   role and raise SQLSTATE `42501` / `22023` on forbidden / bad
   input so the API layer can map cleanly to 403 / 400.
   Idempotent.
+- `supabase/migrations/019_invitation_rpcs.sql` — adds two
+  `SECURITY DEFINER` RPCs: `peek_invitation` (anonymous read by
+  token hash, returns a fixed-shape JSON envelope) and
+  `redeem_invitation` (authenticated atomic move + orphan
+  cleanup, with a domain-data safety check). Both bypass the
+  RLS that would otherwise block their reads/writes. Idempotent.
 
 ## [0.2.2] — 2026-05-29
 
diff --git a/src/app/api/account/invitations/[id]/route.ts b/src/app/api/account/invitations/[id]/route.ts
new file mode 100644
index 0000000..7679b8a
--- /dev/null
+++ b/src/app/api/account/invitations/[id]/route.ts
@@ -0,0 +1,61 @@
+// ============================================================
+// DELETE /api/account/invitations/[id]
+//
+// Admin+. Revokes a pending invitation by id. RLS on
+// `account_invitations` already restricts the DELETE to admins
+// of the inviting account; we lean on it and skip the explicit
+// ownership check.
+//
+// We intentionally delete the row outright rather than soft-
+// deleting (a "revoked_at" flag). Once revoked, an invite is
+// dead forever — there's no UX where a former invite should be
+// listed; the plaintext token is gone too. Hard delete keeps
+// the table small.
+// ============================================================
+
+import { NextResponse } from "next/server";
+
+import { requireRole, toErrorResponse } from "@/lib/auth/account";
+
+export async function DELETE(
+  _request: Request,
+  { params }: { params: Promise<{ id: string }> },
+) {
+  try {
+    const ctx = await requireRole("admin");
+    const { id } = await params;
+
+    // No `eq('account_id', ctx.accountId)` — the RLS policy
+    // (`is_account_member(account_id, 'admin')`) already scopes
+    // the DELETE to invites in the caller's account. Adding the
+    // filter would be redundant; omitting it surfaces a
+    // cross-account attempt as a silent 0-row delete (which is
+    // exactly what we want for a revocation endpoint).
+    const { error, count } = await ctx.supabase
+      .from("account_invitations")
+      .delete({ count: "exact" })
+      .eq("id", id);
+
+    if (error) {
+      console.error("[DELETE /api/account/invitations/[id]] error:", error);
+      return NextResponse.json(
+        { error: "Failed to revoke invitation" },
+        { status: 500 },
+      );
+    }
+
+    if (count === 0) {
+      // Either the id doesn't exist or RLS hid it (different
+      // account). 404 either way — surfacing "exists but not
+      // yours" would leak existence.
+      return NextResponse.json(
+        { error: "Invitation not found" },
+        { status: 404 },
+      );
+    }
+
+    return NextResponse.json({ ok: true });
+  } catch (err) {
+    return toErrorResponse(err);
+  }
+}
diff --git a/src/app/api/account/invitations/route.ts b/src/app/api/account/invitations/route.ts
new file mode 100644
index 0000000..d7e901e
--- /dev/null
+++ b/src/app/api/account/invitations/route.ts
@@ -0,0 +1,144 @@
+// ============================================================
+// /api/account/invitations
+//
+//   GET  — list outstanding (un-redeemed, non-expired) invites.
+//   POST — create a new invite link.
+//
+// Both admin+. The list endpoint is what the Members tab uses to
+// populate the "Pending invitations" section; create is what the
+// "Invite member" dialog calls.
+//
+// IMPORTANT: the plaintext token is returned exactly ONCE — in
+// the POST response. We store only the SHA-256 hash on the row,
+// so neither GET nor a future PATCH can ever resurface the
+// link. The admin sees it in the creation modal, copies it, and
+// shares it via WhatsApp/Slack/whatever they like. If they
+// dismiss the modal without copying, the only recourse is to
+// revoke and re-issue.
+// ============================================================
+
+import { NextResponse } from "next/server";
+
+import { requireRole, toErrorResponse } from "@/lib/auth/account";
+import {
+  clampExpiryDays,
+  generateInviteToken,
+  inviteExpiresAt,
+  inviteUrl,
+} from "@/lib/auth/invitations";
+import { isAccountRole } from "@/lib/auth/roles";
+
+// Resolve the base URL we publish invite links under. Mirrors the
+// .env.local.example default so dev / preview / forks all behave
+// without explicit config.
+function getBaseUrl(): string {
+  return process.env.NEXT_PUBLIC_SITE_URL || "https://wacrm.tech";
+}
+
+const MAX_LABEL_LEN = 80;
+
+export async function GET() {
+  try {
+    const ctx = await requireRole("admin");
+
+    const { data, error } = await ctx.supabase
+      .from("account_invitations")
+      .select(
+        "id, role, label, created_by_user_id, created_at, expires_at, accepted_at, accepted_by_user_id",
+      )
+      .eq("account_id", ctx.accountId)
+      .is("accepted_at", null)
+      .gt("expires_at", new Date().toISOString())
+      .order("created_at", { ascending: false });
+
+    if (error) {
+      console.error("[GET /api/account/invitations] fetch error:", error);
+      return NextResponse.json(
+        { error: "Failed to load invitations" },
+        { status: 500 },
+      );
+    }
+
+    return NextResponse.json({ invitations: data ?? [] });
+  } catch (err) {
+    return toErrorResponse(err);
+  }
+}
+
+export async function POST(request: Request) {
+  try {
+    const ctx = await requireRole("admin");
+
+    const body = (await request.json().catch(() => null)) as
+      | { role?: unknown; expiresInDays?: unknown; label?: unknown }
+      | null;
+
+    const role = body?.role;
+    if (!isAccountRole(role) || role === "owner") {
+      // The DB CHECK already rejects 'owner', but failing fast
+      // here gives a clearer 400 than the eventual constraint
+      // violation surfaced as a 500.
+      return NextResponse.json(
+        { error: "'role' must be one of admin, agent, viewer" },
+        { status: 400 },
+      );
+    }
+
+    const expiresInDaysRaw = body?.expiresInDays;
+    // `clampExpiryDays` tolerates undefined / NaN / negatives by
+    // collapsing to the safe default, so we just pass the raw
+    // value through after a type narrow.
+    const expiresInDays =
+      typeof expiresInDaysRaw === "number" ? expiresInDaysRaw : undefined;
+    const expiryDays = clampExpiryDays(expiresInDays);
+    const expiresAt = inviteExpiresAt(expiryDays);
+
+    let label: string | null = null;
+    if (typeof body?.label === "string") {
+      const trimmed = body.label.trim();
+      if (trimmed.length > MAX_LABEL_LEN) {
+        return NextResponse.json(
+          { error: `Label must be ${MAX_LABEL_LEN} characters or fewer` },
+          { status: 400 },
+        );
+      }
+      label = trimmed === "" ? null : trimmed;
+    }
+
+    const { token, hash } = generateInviteToken();
+
+    const { data, error } = await ctx.supabase
+      .from("account_invitations")
+      .insert({
+        account_id: ctx.accountId,
+        token_hash: hash,
+        role,
+        created_by_user_id: ctx.userId,
+        label,
+        expires_at: expiresAt.toISOString(),
+      })
+      .select("id, role, label, expires_at, created_at")
+      .single();
+
+    if (error || !data) {
+      console.error("[POST /api/account/invitations] insert error:", error);
+      return NextResponse.json(
+        { error: "Failed to create invitation" },
+        { status: 500 },
+      );
+    }
+
+    return NextResponse.json(
+      {
+        invitation: data,
+        // Plaintext payload — visible to the admin exactly once.
+        token,
+        url: inviteUrl(token, getBaseUrl()),
+        expiresInDays: expiryDays,
+      },
+      { status: 201 },
+    );
+  } catch (err) {
+    return toErrorResponse(err);
+  }
+}
diff --git a/src/app/api/invitations/[token]/peek/route.ts b/src/app/api/invitations/[token]/peek/route.ts
new file mode 100644
index 0000000..ef25a4f
--- /dev/null
+++ b/src/app/api/invitations/[token]/peek/route.ts
@@ -0,0 +1,87 @@
+// ============================================================
+// GET /api/invitations/[token]/peek
+//
+// Public — no auth required. Lets the /join/<token> page render
+// "You're being invited to <Account> as <Role>" before the
+// visitor signs up or signs in.
+//
+// Security model
+//   - Token is in the URL path, not the query, so it doesn't
+//     show up in standard access-log "referer" fields the way a
+//     `?token=` would.
+//   - The plaintext token never crosses the DB boundary — we
+//     hash it in TS first and look up by `token_hash`.
+//   - The peek RPC is SECURITY DEFINER so it bypasses the RLS
+//     that would otherwise block an anonymous SELECT on
+//     `account_invitations`. It returns a fixed-shape JSON
+//     payload that never leaks columns beyond what the join
+//     page renders.
+//   - Per-IP rate limit pinches brute-force enumeration of
+//     tokens. With 256 bits of entropy the enumeration risk is
+//     theoretical, but rate limiting is cheap insurance.
+// ============================================================
+
+import { NextResponse } from "next/server";
+
+import { hashInviteToken } from "@/lib/auth/invitations";
+import {
+  checkRateLimit,
+  rateLimitResponse,
+  RATE_LIMITS,
+} from "@/lib/rate-limit";
+import { createClient } from "@/lib/supabase/server";
+
+/**
+ * Best-effort client IP. The `x-forwarded-for` header is what
+ * every reverse proxy (Vercel, Hostinger, Cloudflare) sets when
+ * forwarding a request; we take the leftmost entry, which is
+ * the original client.
+ *
+ * Falls back to a constant when no proxy is in front (e.g.
+ * `localhost` during development) so rate-limit keys still
+ * exist — the limit then effectively applies "globally," which
+ * is fine for dev.
+ */
+function getClientIp(request: Request): string {
+  const xff = request.headers.get("x-forwarded-for");
+  if (xff) return xff.split(",")[0].trim();
+  const xri = request.headers.get("x-real-ip");
+  if (xri) return xri.trim();
+  return "unknown";
+}
+
+export async function GET(
+  request: Request,
+  { params }: { params: Promise<{ token: string }> },
+) {
+  // Rate-limit by IP first. Returns 429 to a serial bruteforcer
+  // before we ever touch the DB.
+  const ip = getClientIp(request);
+  const limit = checkRateLimit(`peek:${ip}`, RATE_LIMITS.invitationPeek);
+  if (!limit.success) return rateLimitResponse(limit);
+
+  const { token } = await params;
+  if (!token || typeof token !== "string") {
+    return NextResponse.json(
+      { ok: false, reason: "not_found" },
+      { status: 404 },
+    );
+  }
+
+  const supabase = await createClient();
+  const { data, error } = await supabase.rpc("peek_invitation", {
+    p_token_hash: hashInviteToken(token),
+  });
+
+  if (error) {
+    console.error("[peek] rpc error:", error);
+    return NextResponse.json(
+      { ok: false, reason: "server_error" },
+      { status: 500 },
+    );
+  }
+
+  // The RPC always returns a json object — either ok:true with
+  // metadata or ok:false with a reason. Forward verbatim.
+  return NextResponse.json(data);
+}
diff --git a/src/app/api/invitations/[token]/redeem/route.ts b/src/app/api/invitations/[token]/redeem/route.ts
new file mode 100644
index 0000000..538e6fe
--- /dev/null
+++ b/src/app/api/invitations/[token]/redeem/route.ts
@@ -0,0 +1,91 @@
+// ============================================================
+// POST /api/invitations/[token]/redeem
+//
+// Authenticated. Caller atomically moves from their personal
+// account (created at signup) to the inviter's account with the
+// invite's role. Heavy lifting lives in the SECURITY DEFINER
+// `redeem_invitation` RPC from migration 019.
+//
+// Refusal contract (from the RPC)
+//   - SQLSTATE 42501 → 401 (caller not authenticated)
+//   - SQLSTATE 22023 → 400 (invitation not_found / used / expired)
+//   - SQLSTATE 23505 → 409 (caller's account already has data /
+//     they're already in this or another shared account)
+//
+// Rate limit (per IP) is the same shape as peek but tighter —
+// a successful redeem changes data, and the RPC's data-loss
+// guard makes brute-force retries pointless past a few attempts.
+// ============================================================
+
+import { NextResponse } from "next/server";
+import type { PostgrestError } from "@supabase/supabase-js";
+
+import { hashInviteToken } from "@/lib/auth/invitations";
+import {
+  checkRateLimit,
+  rateLimitResponse,
+  RATE_LIMITS,
+} from "@/lib/rate-limit";
+import { createClient } from "@/lib/supabase/server";
+
+function getClientIp(request: Request): string {
+  const xff = request.headers.get("x-forwarded-for");
+  if (xff) return xff.split(",")[0].trim();
+  const xri = request.headers.get("x-real-ip");
+  if (xri) return xri.trim();
+  return "unknown";
+}
+
+function rpcErrorToResponse(err: PostgrestError): NextResponse {
+  if (err.code === "42501") {
+    return NextResponse.json({ error: err.message }, { status: 401 });
+  }
+  if (err.code === "22023") {
+    return NextResponse.json({ error: err.message }, { status: 400 });
+  }
+  if (err.code === "23505") {
+    return NextResponse.json({ error: err.message }, { status: 409 });
+  }
+  console.error("[redeem] unexpected RPC error:", err);
+  return NextResponse.json(
+    { error: "Failed to redeem invitation" },
+    { status: 500 },
+  );
+}
+
+export async function POST(
+  request: Request,
+  { params }: { params: Promise<{ token: string }> },
+) {
+  const ip = getClientIp(request);
+  const limit = checkRateLimit(`redeem:${ip}`, RATE_LIMITS.invitationRedeem);
+  if (!limit.success) return rateLimitResponse(limit);
+
+  const { token } = await params;
+  if (!token || typeof token !== "string") {
+    return NextResponse.json(
+      { error: "Missing invitation token" },
+      { status: 400 },
+    );
+  }
+
+  const supabase = await createClient();
+
+  // The RPC checks `auth.uid()` itself, but failing fast here
+  // gives a cleaner 401 without a Supabase round trip on the
+  // common "user clicked the link before logging in" path.
+  const {
+    data: { user },
+  } = await supabase.auth.getUser();
+  if (!user) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+
+  const { data: accountId, error } = await supabase.rpc("redeem_invitation", {
+    p_token_hash: hashInviteToken(token),
+  });
+
+  if (error) return rpcErrorToResponse(error);
+
+  return NextResponse.json({ ok: true, accountId });
+}
diff --git a/src/lib/rate-limit.ts b/src/lib/rate-limit.ts
index a6f905a..90daecf 100644
--- a/src/lib/rate-limit.ts
+++ b/src/lib/rate-limit.ts
@@ -125,6 +125,15 @@ export const RATE_LIMITS = {
    *  fidget with reactions and a single "swap" is actually two calls
    *  (remove + add) under the hood. */
   react: { limit: 120, windowMs: 60_000 },
+  /** Invitation peek (public, per-IP). 30/min lets a forwarded link
+   *  retry a handful of times under flaky connectivity without
+   *  enabling brute-force token enumeration. With 256-bit tokens the
+   *  enumeration risk is theoretical; this is belt-and-braces. */
+  invitationPeek: { limit: 30, windowMs: 60_000 },
+  /** Invitation redeem (authed, per-IP+user). Tighter than peek —
+   *  successful redemption mutates two profiles and an invite row, so
+   *  the abuse surface is "spam join attempts." */
+  invitationRedeem: { limit: 10, windowMs: 60_000 },
 } as const;
 
 /** Test-only helper. Clears the in-memory state so unit tests don't
diff --git a/supabase/migrations/019_invitation_rpcs.sql b/supabase/migrations/019_invitation_rpcs.sql
new file mode 100644
index 0000000..9e093b6
--- /dev/null
+++ b/supabase/migrations/019_invitation_rpcs.sql
@@ -0,0 +1,237 @@
+-- ============================================================
+-- 019_invitation_rpcs.sql — peek + redeem invitation RPCs
+--
+-- The third and last server-side migration in the multi-user
+-- accounts series. Both functions are SECURITY DEFINER for the
+-- same reason as the member RPCs in 018: the writes they need to
+-- do (or, for peek, the reads) cross RLS boundaries that the
+-- regular client policies (correctly) deny.
+--
+-- peek_invitation   — anonymous read. The /join/<token> page
+--   calls this to render "You're being invited to <Account> as
+--   <Role>" before the visitor signs in. Returns a uniform
+--   `{ ok, reason?, account_name?, role?, expires_at? }` JSON
+--   so the API route doesn't have to interpret error rows.
+--
+-- redeem_invitation — authenticated. Atomically moves the caller
+--   from their just-created personal account to the inviter's
+--   account, cleans up the orphan personal account, and stamps
+--   the invitation accepted. Refuses if the caller's current
+--   account holds any domain data (to avoid silent data loss).
+--
+-- Idempotent — safe to run multiple times.
+-- ============================================================
+
+-- ============================================================
+-- peek_invitation(p_token_hash text)
+--
+-- Anonymous read by token hash. The plaintext token never
+-- reaches the DB; the route handler hashes it first.
+--
+-- Returns a JSON object with one of two shapes:
+--   { "ok": true,  "account_name": "...", "role": "...",
+--     "expires_at": "2026-..." }
+--   { "ok": false, "reason": "not_found" | "expired" | "used" }
+--
+-- We could collapse all three failure cases to "not_found" to
+-- harden against enumeration, but the join page needs the
+-- distinction for UX ("This invite has expired — ask <name>
+-- for a new one"). Tokens carry 256 bits of entropy, so the
+-- enumeration risk is theoretical; rate-limiting the route on
+-- the IP layer adds belt-and-braces.
+-- ============================================================
+CREATE OR REPLACE FUNCTION public.peek_invitation(
+  p_token_hash TEXT
+) RETURNS JSON
+LANGUAGE plpgsql
+STABLE
+SECURITY DEFINER
+SET search_path = public
+AS $$
+DECLARE
+  v_inv account_invitations%ROWTYPE;
+  v_account_name TEXT;
+BEGIN
+  SELECT * INTO v_inv
+  FROM account_invitations
+  WHERE token_hash = p_token_hash;
+
+  IF NOT FOUND THEN
+    RETURN json_build_object('ok', false, 'reason', 'not_found');
+  END IF;
+
+  IF v_inv.accepted_at IS NOT NULL THEN
+    RETURN json_build_object('ok', false, 'reason', 'used');
+  END IF;
+
+  IF v_inv.expires_at <= NOW() THEN
+    RETURN json_build_object('ok', false, 'reason', 'expired');
+  END IF;
+
+  SELECT name INTO v_account_name
+  FROM accounts
+  WHERE id = v_inv.account_id;
+
+  RETURN json_build_object(
+    'ok', true,
+    'account_name', v_account_name,
+    'role', v_inv.role,
+    'expires_at', v_inv.expires_at
+  );
+END;
+$$;
+
+ALTER FUNCTION public.peek_invitation(TEXT) OWNER TO postgres;
+REVOKE ALL ON FUNCTION public.peek_invitation(TEXT) FROM PUBLIC;
+-- `anon` so the /join/<token> page can call this before the user
+-- signs in; `authenticated` so the same page works when already
+-- signed in (e.g. existing user clicks a forwarded link).
+GRANT EXECUTE ON FUNCTION public.peek_invitation(TEXT) TO anon, authenticated;
+
+-- ============================================================
+-- redeem_invitation(p_token_hash text)
+--
+-- Authenticated. The caller's auth.uid() is used both to scope
+-- the move ("which profile am I editing?") and as the safety
+-- check ("do you have any data we'd lose?").
+--
+-- Refusal codes (SQLSTATE):
+--   22023 — invite invalid (not_found / used / expired)
+--   42501 — caller not authenticated
+--   23505 — caller's account has data (would be lost by joining)
+--           NOTE: we reuse Postgres's "unique_violation" code here
+--           rather than invent a custom SQLSTATE because there's
+--           no proper standard SQLSTATE for "conflict"; the route
+--           handler maps it to HTTP 409.
+--
+-- Order of operations
+--   1. Lock the invite row (FOR UPDATE) so two concurrent redeems
+--      of the same token can't both succeed.
+--   2. Read caller's current account_id.
+--   3. Verify caller is the sole owner of their current account
+--      AND that the account has zero domain rows. (If the caller
+--      already joined someone else's account once, their
+--      profile.account_id points there, not to a personal account
+--      they own — that case fails the "is owner" check and
+--      surfaces as 23505.)
+--   4. Move profile.account_id + account_role to invite's.
+--   5. Mark invitation accepted (token_hash stays, so the same
+--      token can't be re-used).
+--   6. Delete the old personal account. The ON DELETE CASCADE on
+--      `accounts(id) ← profiles.account_id` would normally try to
+--      delete the caller's profile too, but step 4 already moved
+--      them to the new account, so the cascade is a no-op.
+-- ============================================================
+CREATE OR REPLACE FUNCTION public.redeem_invitation(
+  p_token_hash TEXT
+) RETURNS UUID  -- the joined account_id
+LANGUAGE plpgsql
+SECURITY DEFINER
+SET search_path = public
+AS $$
+DECLARE
+  v_caller_id UUID := auth.uid();
+  v_inv account_invitations%ROWTYPE;
+  v_old_account_id UUID;
+  v_old_account_owner UUID;
+  v_has_data BOOLEAN;
+BEGIN
+  IF v_caller_id IS NULL THEN
+    RAISE EXCEPTION 'Unauthorized' USING ERRCODE = '42501';
+  END IF;
+
+  SELECT * INTO v_inv
+  FROM account_invitations
+  WHERE token_hash = p_token_hash
+  FOR UPDATE;
+
+  IF NOT FOUND THEN
+    RAISE EXCEPTION 'Invitation not found' USING ERRCODE = '22023';
+  END IF;
+  IF v_inv.accepted_at IS NOT NULL THEN
+    RAISE EXCEPTION 'Invitation has already been redeemed'
+      USING ERRCODE = '22023';
+  END IF;
+  IF v_inv.expires_at <= NOW() THEN
+    RAISE EXCEPTION 'Invitation has expired' USING ERRCODE = '22023';
+  END IF;
+
+  -- Caller's current account + its owner.
+  SELECT p.account_id, a.owner_user_id
+  INTO v_old_account_id, v_old_account_owner
+  FROM profiles p
+  JOIN accounts a ON a.id = p.account_id
+  WHERE p.user_id = v_caller_id;
+
+  IF v_old_account_id IS NULL THEN
+    -- Defensive — every authenticated user has a profile post-017.
+    RAISE EXCEPTION 'Caller has no profile' USING ERRCODE = '42501';
+  END IF;
+
+  -- Edge case: the inviter sent themselves a link, or the
+  -- caller is somehow already in the inviter's account.
+  IF v_old_account_id = v_inv.account_id THEN
+    RAISE EXCEPTION 'You are already a member of this account'
+      USING ERRCODE = '23505';
+  END IF;
+
+  -- Safety: the caller must be the SOLE OWNER of their current
+  -- account (i.e. their fresh personal account from signup or a
+  -- prior removal). Any other state means they're either:
+  --   - a member of another shared account (joining a second
+  --     would silently orphan their access to the first), or
+  --   - the owner of an account with teammates (they'd abandon
+  --     their team to join the inviter's).
+  -- Either way, the safe answer is "make a different login".
+  IF v_old_account_owner <> v_caller_id THEN
+    RAISE EXCEPTION 'You are already in a shared account; sign up with a different email to join this one'
+      USING ERRCODE = '23505';
+  END IF;
+
+  -- Belt: even if they own their account, refuse if it has any
+  -- domain data — joining would orphan their contacts, deals,
+  -- broadcasts, automations, flows, templates, etc.
+  SELECT EXISTS (
+    SELECT 1 FROM contacts WHERE account_id = v_old_account_id
+    UNION ALL SELECT 1 FROM conversations WHERE account_id = v_old_account_id
+    UNION ALL SELECT 1 FROM broadcasts WHERE account_id = v_old_account_id
+    UNION ALL SELECT 1 FROM automations WHERE account_id = v_old_account_id
+    UNION ALL SELECT 1 FROM flows WHERE account_id = v_old_account_id
+    UNION ALL SELECT 1 FROM pipelines WHERE account_id = v_old_account_id
+    UNION ALL SELECT 1 FROM message_templates WHERE account_id = v_old_account_id
+    UNION ALL SELECT 1 FROM tags WHERE account_id = v_old_account_id
+    UNION ALL SELECT 1 FROM custom_fields WHERE account_id = v_old_account_id
+    UNION ALL SELECT 1 FROM contact_notes WHERE account_id = v_old_account_id
+    UNION ALL SELECT 1 FROM whatsapp_config WHERE account_id = v_old_account_id
+    LIMIT 1
+  ) INTO v_has_data;
+
+  IF v_has_data THEN
+    RAISE EXCEPTION 'Your account already contains data; sign up with a different email to join this one'
+      USING ERRCODE = '23505';
+  END IF;
+
+  -- Move the profile first so the cascade-on-delete of the old
+  -- account doesn't try to nuke this user's profile too.
+  UPDATE profiles
+  SET account_id = v_inv.account_id,
+      account_role = v_inv.role
+  WHERE user_id = v_caller_id;
+
+  UPDATE account_invitations
+  SET accepted_at = NOW(),
+      accepted_by_user_id = v_caller_id
+  WHERE id = v_inv.id;
+
+  -- Clean up the orphan personal account. Empty by the checks
+  -- above, so this is purely housekeeping — no cascades fire
+  -- because no other rows reference it.
+  DELETE FROM accounts WHERE id = v_old_account_id;
+
+  RETURN v_inv.account_id;
+END;
+$$;
+
+ALTER FUNCTION public.redeem_invitation(TEXT) OWNER TO postgres;
+REVOKE ALL ON FUNCTION public.redeem_invitation(TEXT) FROM PUBLIC;
+GRANT EXECUTE ON FUNCTION public.redeem_invitation(TEXT) TO authenticated;