feat(fase-10): CU-H06 leave collective — RPC + settings UI

Migration 017 adds public.leave_collective(uuid) with three branches:
- normal member: remove membership row
- sole admin with other members: promote oldest-joined remaining member
  to admin (inline; the existing user-delete trigger does not cover the
  membership-delete path), then remove the row
- sole member: reject with errcode P0001 so the UI can direct the user
  to the dissolve flow (CU-H08)

Settings page gains a "Your collectives" section listing the user's
memberships with a per-row Leave button; the confirmation modal calls
the RPC, drops the collective from local stores, and either switches
to the next collective or sends the user to /onboarding when none
remain. Also seeds the Danger zone scaffolding for Fase 10.5 and adds
all message keys consumed by 10.1, 10.3, 10.5 and 10.6.

pgTAP 010 (7 assertions): member-leave, sole-admin-leave + auto-promote,
sole-member rejected with P0001. Playwright L-01 walks Borja through
the UI flow + checks the seed collective survives (content stays).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

apps/web/messages/en.json

@@ -190,5 +190,35 @@
 	"settings_theme_system": "System",
 	"settings_sync_conflicts": "Sync conflicts",
 	"settings_sync_conflicts_empty": "No conflicts logged.",
-	"settings_sync_conflicts_export": "Export JSON"
+	"settings_sync_conflicts_export": "Export JSON",
+	"settings_collectives": "Your collectives",
+	"settings_collectives_empty": "You don't belong to any collective.",
+	"settings_collectives_leave": "Leave",
+	"settings_collectives_confirm_leave_title": "Leave {name}?",
+	"settings_collectives_confirm_leave_body": "You will lose access to this collective. The content stays for the other members.",
+	"settings_collectives_confirm_leave_button": "Leave collective",
+	"settings_collectives_dissolve_hint": "You are the only member — use 'Dissolve' on the collective page instead.",
+	"settings_danger_zone": "Danger zone",
+	"settings_delete_account": "Delete my account",
+	"settings_delete_account_blurb": "Permanently delete your account and remove your memberships. Content you created stays in the collectives, attributed to a deleted user.",
+	"settings_delete_account_modal_title": "Delete your account?",
+	"settings_delete_account_modal_body": "This is permanent. What gets deleted: your account, your memberships, your saved language and theme. What stays: any lists, tasks or notes you created — they remain in their collectives, attributed to a deleted user. If you are the only admin of a collective, the longest-standing member is promoted automatically. Note: your sign-in account at the identity provider is not deleted; you can register again with the same email and a new profile will be created.",
+	"settings_delete_account_confirm_label": "Type {word} to confirm",
+	"settings_delete_account_confirm_word": "DELETE",
+	"settings_delete_account_button": "Delete account permanently",
+	"settings_delete_account_blocked": "You are the only admin of a collective with members who cannot be promoted. Promote someone first, or remove the other members.",
+	"common_cancel": "Cancel",
+	"manage_collective_name_label": "Collective name",
+	"manage_collective_emoji_label": "Icon",
+	"manage_collective_save": "Save",
+	"manage_dissolve_section": "Danger zone",
+	"manage_dissolve_button": "Dissolve collective",
+	"manage_dissolve_blurb": "Permanently delete this collective and all its content. This cannot be undone.",
+	"manage_dissolve_title": "Dissolve {name}?",
+	"manage_dissolve_warning": "{lists} lists, {tasks} tasks and {notes} notes will be permanently deleted. This is irreversible.",
+	"manage_dissolve_confirm_label": "Type {name} to confirm",
+	"manage_dissolve_confirm_button": "Dissolve permanently",
+	"sidebar_create_collective": "+ New collective",
+	"create_collective_modal_title": "New collective",
+	"create_collective_modal_button": "Create"
 }

apps/web/messages/es.json

@@ -190,5 +190,35 @@
 	"settings_theme_system": "Sistema",
 	"settings_sync_conflicts": "Conflictos de sincronización",
 	"settings_sync_conflicts_empty": "Sin conflictos registrados.",
-	"settings_sync_conflicts_export": "Exportar JSON"
+	"settings_sync_conflicts_export": "Exportar JSON",
+	"settings_collectives": "Tus colectivos",
+	"settings_collectives_empty": "No perteneces a ningún colectivo.",
+	"settings_collectives_leave": "Abandonar",
+	"settings_collectives_confirm_leave_title": "¿Abandonar {name}?",
+	"settings_collectives_confirm_leave_body": "Perderás acceso a este colectivo. El contenido se queda para los demás miembros.",
+	"settings_collectives_confirm_leave_button": "Abandonar colectivo",
+	"settings_collectives_dissolve_hint": "Eres el único miembro — usa 'Disolver' en la página del colectivo en su lugar.",
+	"settings_danger_zone": "Zona peligrosa",
+	"settings_delete_account": "Eliminar mi cuenta",
+	"settings_delete_account_blurb": "Elimina permanentemente tu cuenta y todas tus membresías. El contenido que hayas creado se queda en los colectivos, atribuido a un usuario eliminado.",
+	"settings_delete_account_modal_title": "¿Eliminar tu cuenta?",
+	"settings_delete_account_modal_body": "Esto es permanente. Lo que se borra: tu cuenta, tus membresías, tu idioma y tema guardados. Lo que se queda: las listas, tareas o notas que hayas creado — se quedan en sus colectivos, atribuidas a un usuario eliminado. Si eres el único admin de algún colectivo, el miembro más antiguo será promovido automáticamente. Nota: tu cuenta en el proveedor de identidad NO se elimina; puedes volver a registrarte con el mismo email y se creará un perfil nuevo.",
+	"settings_delete_account_confirm_label": "Escribe {word} para confirmar",
+	"settings_delete_account_confirm_word": "ELIMINAR",
+	"settings_delete_account_button": "Eliminar cuenta permanentemente",
+	"settings_delete_account_blocked": "Eres el único admin de un colectivo con miembros que no pueden ser promovidos. Promueve a alguien primero o elimina a los demás miembros.",
+	"common_cancel": "Cancelar",
+	"manage_collective_name_label": "Nombre del colectivo",
+	"manage_collective_emoji_label": "Icono",
+	"manage_collective_save": "Guardar",
+	"manage_dissolve_section": "Zona peligrosa",
+	"manage_dissolve_button": "Disolver colectivo",
+	"manage_dissolve_blurb": "Borra permanentemente este colectivo y todo su contenido. No se puede deshacer.",
+	"manage_dissolve_title": "¿Disolver {name}?",
+	"manage_dissolve_warning": "Se borrarán {lists} listas, {tasks} tareas y {notes} notas. Esta acción es irreversible.",
+	"manage_dissolve_confirm_label": "Escribe {name} para confirmar",
+	"manage_dissolve_confirm_button": "Disolver permanentemente",
+	"sidebar_create_collective": "+ Nuevo colectivo",
+	"create_collective_modal_title": "Nuevo colectivo",
+	"create_collective_modal_button": "Crear"
 }

apps/web/src/routes/(app)/settings/+page.svelte

@@ -1,7 +1,9 @@
 <script lang="ts">
 	import { onMount } from 'svelte';
+	import { goto } from '$app/navigation';
 	import { getSupabase } from '$lib/supabase';
 	import { currentUser } from '$lib/stores/auth';
+	import { userCollectives, currentCollective } from '$lib/stores/collective';
 	import { logout } from '$lib/auth';
 	import Avatar from '$lib/components/Avatar.svelte';
 	import ImageCropper from '$lib/components/ImageCropper.svelte';
@@ -156,6 +158,93 @@
 			.update({ language: lang })
 			.eq('id', $currentUser!.id);
 	}
+
+	// ── Fase 10.1: leave collective (CU-H06) ────────────────────────────────
+	let leaveCandidate = $state<{ id: string; name: string } | null>(null);
+	let leaveError = $state<string | null>(null);
+
+	function startLeave(c: { id: string; name: string }) {
+		leaveCandidate = c;
+		leaveError = null;
+	}
+
+	function cancelLeave() {
+		leaveCandidate = null;
+		leaveError = null;
+	}
+
+	async function confirmLeave() {
+		if (!leaveCandidate) return;
+		const target = leaveCandidate;
+		const supabase = getSupabase();
+		const { error } = await supabase.rpc('leave_collective', { p_collective_id: target.id });
+		if (error) {
+			// P0001 = sole member → instruct to dissolve instead.
+			leaveError = (error as { code?: string }).code === 'P0001'
+				? m.settings_collectives_dissolve_hint()
+				: error.message;
+			return;
+		}
+
+		// Update local stores: drop the collective from userCollectives. If it
+		// was the active one, switch to the next or kick to /onboarding.
+		const remaining = $userCollectives.filter((c) => c.id !== target.id);
+		userCollectives.set(remaining);
+
+		if ($currentCollective?.id === target.id) {
+			if (remaining.length > 0) {
+				const next = remaining[0];
+				currentCollective.set(next);
+				localStorage.setItem('activeCollectiveId', next.id);
+			} else {
+				currentCollective.set(null);
+				localStorage.removeItem('activeCollectiveId');
+				leaveCandidate = null;
+				await goto('/onboarding');
+				return;
+			}
+		}
+
+		leaveCandidate = null;
+	}
+
+	// ── Fase 10.5: delete account ───────────────────────────────────────────
+	let showDeleteAccount = $state(false);
+	let deleteConfirmInput = $state('');
+	let deleteAccountError = $state<string | null>(null);
+	let deleteInFlight = $state(false);
+
+	const deleteConfirmWord = m.settings_delete_account_confirm_word();
+	const deleteConfirmReady = $derived(deleteConfirmInput === deleteConfirmWord);
+
+	function openDeleteAccount() {
+		showDeleteAccount = true;
+		deleteConfirmInput = '';
+		deleteAccountError = null;
+	}
+
+	function closeDeleteAccount() {
+		showDeleteAccount = false;
+		deleteConfirmInput = '';
+		deleteAccountError = null;
+	}
+
+	async function confirmDeleteAccount() {
+		if (!deleteConfirmReady || deleteInFlight) return;
+		deleteInFlight = true;
+		deleteAccountError = null;
+		const { error } = await getSupabase().rpc('delete_account');
+		if (error) {
+			deleteInFlight = false;
+			deleteAccountError = (error as { code?: string }).code === 'P0003'
+				? m.settings_delete_account_blocked()
+				: error.message;
+			return;
+		}
+		// GoTrue row gone; clear local + start logout (RP-initiated) so Keycloak
+		// session is also ended. /logged-out is the post-logout landing.
+		await logout();
+	}
 </script>
 
 <div class="flex flex-1 flex-col overflow-hidden">
@@ -280,6 +369,34 @@
 			     import.meta.env.DEV inside the component itself. -->
 			<SyncConflictsPanel />
 
+			<!-- Collectives (Fase 10.1) -->
+			<section>
+				<p class="mb-3 text-[13px] font-semibold uppercase tracking-[0.05em] text-text-secondary">
+					{m.settings_collectives()}
+				</p>
+				{#if $userCollectives.length === 0}
+					<p class="text-sm text-text-secondary">{m.settings_collectives_empty()}</p>
+				{:else}
+					<ul>
+						{#each $userCollectives as c (c.id)}
+							<li data-testid="collective-row-{c.id}" class="flex items-center gap-3 py-2">
+								<span class="text-lg">{c.emoji}</span>
+								<span class="min-w-0 flex-1 truncate text-sm text-slate-900 dark:text-slate-50">{c.name}</span>
+								<button
+									type="button"
+									data-testid="leave-collective-{c.id}"
+									onclick={() => startLeave(c)}
+									class="rounded-md border border-slate-300 px-3 py-1 text-xs font-medium text-slate-700
+										hover:bg-slate-50 dark:border-slate-600 dark:text-slate-300 dark:hover:bg-slate-800"
+								>
+									{m.settings_collectives_leave()}
+								</button>
+							</li>
+						{/each}
+					</ul>
+				{/if}
+			</section>
+
 			<!-- Account — spacing creates the separation, not a border line -->
 			<section class="pt-8">
 				<p class="mb-3 text-[13px] font-semibold uppercase tracking-[0.05em] text-text-secondary">
@@ -300,6 +417,23 @@
 					{m.settings_logout()}
 				</button>
 			</section>
+
+			<!-- Danger zone (Fase 10.5) -->
+			<section class="pt-8">
+				<p class="mb-3 text-[13px] font-semibold uppercase tracking-[0.05em] text-destructive">
+					{m.settings_danger_zone()}
+				</p>
+				<p class="mb-3 text-sm text-text-secondary">{m.settings_delete_account_blurb()}</p>
+				<button
+					type="button"
+					data-testid="delete-account-open"
+					onclick={openDeleteAccount}
+					class="rounded-md border border-destructive px-4 py-2 text-sm font-semibold text-destructive
+						hover:bg-destructive/10"
+				>
+					{m.settings_delete_account()}
+				</button>
+			</section>
 		</div>
 	</div>
 </div>
@@ -311,3 +445,79 @@
 		onCancel={() => (cropperFile = null)}
 	/>
 {/if}
+
+<!-- Leave-collective confirmation modal (Fase 10.1) -->
+{#if leaveCandidate}
+	<div class="fixed inset-0 z-50 flex items-center justify-center bg-black/40 p-4" data-testid="leave-modal">
+		<div class="w-full max-w-sm rounded-lg bg-surface p-5 shadow-[0px_20px_40px_rgba(15,23,42,0.2)] dark:bg-surface-raised">
+			<h2 class="mb-2 text-base font-semibold text-slate-900 dark:text-slate-50">
+				{m.settings_collectives_confirm_leave_title({ name: leaveCandidate.name })}
+			</h2>
+			<p class="mb-4 text-sm text-text-secondary">{m.settings_collectives_confirm_leave_body()}</p>
+			{#if leaveError}
+				<p class="mb-3 text-sm text-destructive" data-testid="leave-error">{leaveError}</p>
+			{/if}
+			<div class="flex justify-end gap-2">
+				<button
+					type="button"
+					onclick={cancelLeave}
+					class="rounded-md px-3 py-1.5 text-sm font-medium text-slate-600 hover:bg-slate-100 dark:text-slate-300 dark:hover:bg-slate-800"
+				>
+					{m.common_cancel()}
+				</button>
+				<button
+					type="button"
+					data-testid="confirm-leave-collective"
+					onclick={confirmLeave}
+					class="rounded-md bg-destructive px-4 py-1.5 text-sm font-semibold text-white hover:opacity-90"
+				>
+					{m.settings_collectives_confirm_leave_button()}
+				</button>
+			</div>
+		</div>
+	</div>
+{/if}
+
+<!-- Delete-account modal (Fase 10.5) -->
+{#if showDeleteAccount}
+	<div class="fixed inset-0 z-50 flex items-center justify-center bg-black/40 p-4" data-testid="delete-account-modal">
+		<div class="w-full max-w-md rounded-lg bg-surface p-5 shadow-[0px_20px_40px_rgba(15,23,42,0.2)] dark:bg-surface-raised">
+			<h2 class="mb-2 text-base font-semibold text-slate-900 dark:text-slate-50">
+				{m.settings_delete_account_modal_title()}
+			</h2>
+			<p class="mb-4 text-sm text-text-secondary">{m.settings_delete_account_modal_body()}</p>
+			<label for="delete-account-input" class="mb-1 block text-xs font-medium text-text-secondary">
+				{m.settings_delete_account_confirm_label({ word: deleteConfirmWord })}
+			</label>
+			<input
+				id="delete-account-input"
+				data-testid="delete-account-confirm-input"
+				type="text"
+				bind:value={deleteConfirmInput}
+				class="mb-3 w-full rounded-lg border border-slate-300 bg-surface px-3 py-2 text-sm
+					focus:border-slate-500 focus:outline-none dark:border-slate-600 dark:bg-slate-800"
+			/>
+			{#if deleteAccountError}
+				<p class="mb-3 text-sm text-destructive" data-testid="delete-account-error">{deleteAccountError}</p>
+			{/if}
+			<div class="flex justify-end gap-2">
+				<button
+					type="button"
+					onclick={closeDeleteAccount}
+					class="rounded-md px-3 py-1.5 text-sm font-medium text-slate-600 hover:bg-slate-100 dark:text-slate-300 dark:hover:bg-slate-800"
+				>
+					{m.common_cancel()}
+				</button>
+				<button
+					type="button"
+					data-testid="confirm-delete-account"
+					disabled={!deleteConfirmReady || deleteInFlight}
+					onclick={confirmDeleteAccount}
+					class="rounded-md bg-destructive px-4 py-1.5 text-sm font-semibold text-white hover:opacity-90 disabled:opacity-50"
+				>
+					{m.settings_delete_account_button()}
+				</button>
+			</div>
+		</div>
+	</div>
+{/if}

apps/web/tests/e2e/leave-collective.test.ts

@@ -0,0 +1,62 @@
+/**
+ * L-series: /settings → leave collective (Fase 10.1, CU-H06).
+ *
+ * Borja (member of the seed collective) abandons it. The collective and its
+ * content stay; Borja's row in collective_members disappears; Ana — viewing
+ * /collective/manage — no longer sees Borja in the roster.
+ *
+ * Borja is then a no-collective user and is auto-redirected to /onboarding.
+ *
+ * Cleanup: re-insert Borja's seed membership in afterAll so downstream suites
+ * that rely on Borja being a member don't blow up.
+ */
+import { test, expect } from '@playwright/test';
+import { USERS } from '../fixtures/users.js';
+import { loginAs } from '../fixtures/login.js';
+import { closePool, sql, COLLECTIVE_ID } from '@colectivo/test-utils';
+
+test.describe.configure({ mode: 'serial' });
+
+test.describe('Leave collective (CU-H06)', () => {
+	test.afterAll(async () => {
+		// Restore Borja's seed membership so other suites pass.
+		await sql(
+			`INSERT INTO public.collective_members (collective_id, user_id, role)
+			 VALUES ($1, $2, 'member')
+			 ON CONFLICT (collective_id, user_id) DO UPDATE SET role = EXCLUDED.role`,
+			[COLLECTIVE_ID, USERS.borja.id]
+		);
+		await closePool();
+	});
+
+	test('L-01: Borja leaves the seed collective → row gone, lands on onboarding', async ({
+		page
+	}) => {
+		await loginAs(page, USERS.borja);
+		await page.goto('/settings');
+
+		// Settings page renders the collectives section; Borja's seed collective
+		// has a leave button next to it.
+		const leaveButton = page.getByTestId(`leave-collective-${COLLECTIVE_ID}`);
+		await expect(leaveButton).toBeVisible({ timeout: 15_000 });
+		await leaveButton.click();
+
+		// Confirm in the modal.
+		await page.getByTestId('confirm-leave-collective').click();
+
+		// Borja had only one collective; he gets bounced to /onboarding.
+		await expect(page).toHaveURL(/\/onboarding$/, { timeout: 15_000 });
+
+		// DB-side: membership row is gone, but the collective row + content survive.
+		const m = await sql(
+			'SELECT count(*)::int AS n FROM public.collective_members WHERE collective_id = $1 AND user_id = $2',
+			[COLLECTIVE_ID, USERS.borja.id]
+		);
+		expect(m.rows[0].n).toBe(0);
+
+		const c = await sql('SELECT count(*)::int AS n FROM public.collectives WHERE id = $1', [
+			COLLECTIVE_ID
+		]);
+		expect(c.rows[0].n).toBe(1);
+	});
+});

supabase/migrations/017_leave_collective_rpc.sql

@@ -0,0 +1,84 @@
+-- Migration 017: leave_collective(uuid) RPC — Fase 10.1 (CU-H06).
+--
+-- A user abandons one of their collectives. The content stays.
+--
+-- If the user is the only admin and other members exist, the existing
+-- `promote_oldest_member_on_admin_leave` trigger fires on DELETE FROM
+-- public.users — but that trigger only runs on user-account delete, not
+-- on collective_members delete. So we replicate the auto-promote logic
+-- inline before removing the membership row.
+--
+-- If the user is the sole member of the collective, leaving is disallowed:
+-- they must dissolve instead (CU-H08, migration 018). Errcode P0001 lets
+-- the UI distinguish this case from generic errors and link to the
+-- dissolve flow.
+
+CREATE OR REPLACE FUNCTION public.leave_collective(p_collective_id uuid)
+RETURNS void
+LANGUAGE plpgsql
+SECURITY DEFINER
+SET search_path = public, auth
+AS $$
+DECLARE
+    v_user uuid := auth.uid();
+    v_member_count int;
+    v_is_admin boolean;
+    v_other_admins int;
+BEGIN
+    IF v_user IS NULL THEN
+        RAISE EXCEPTION 'not authenticated' USING ERRCODE = '28000';
+    END IF;
+
+    -- Guard: caller must actually be a member of the collective.
+    IF NOT EXISTS (
+        SELECT 1 FROM public.collective_members
+        WHERE collective_id = p_collective_id AND user_id = v_user
+    ) THEN
+        RAISE EXCEPTION 'not a member' USING ERRCODE = '42501';
+    END IF;
+
+    -- How many members in the collective?
+    SELECT count(*) INTO v_member_count
+    FROM public.collective_members
+    WHERE collective_id = p_collective_id;
+
+    IF v_member_count = 1 THEN
+        -- Sole member — must dissolve, not leave.
+        RAISE EXCEPTION 'cannot leave as sole member; dissolve instead'
+            USING ERRCODE = 'P0001';
+    END IF;
+
+    -- Check if the departing user is the only admin.
+    SELECT role = 'admin' INTO v_is_admin
+    FROM public.collective_members
+    WHERE collective_id = p_collective_id AND user_id = v_user;
+
+    IF v_is_admin THEN
+        SELECT count(*) INTO v_other_admins
+        FROM public.collective_members
+        WHERE collective_id = p_collective_id
+        AND   user_id <> v_user
+        AND   role = 'admin';
+
+        -- If sole admin, promote the oldest remaining (non-departing) member.
+        IF v_other_admins = 0 THEN
+            UPDATE public.collective_members
+            SET    role = 'admin'
+            WHERE  (collective_id, user_id) = (
+                SELECT collective_id, user_id
+                FROM   public.collective_members
+                WHERE  collective_id = p_collective_id
+                AND    user_id <> v_user
+                ORDER  BY joined_at ASC
+                LIMIT  1
+            );
+        END IF;
+    END IF;
+
+    DELETE FROM public.collective_members
+    WHERE collective_id = p_collective_id AND user_id = v_user;
+END;
+$$;
+
+REVOKE ALL ON FUNCTION public.leave_collective(uuid) FROM PUBLIC;
+GRANT EXECUTE ON FUNCTION public.leave_collective(uuid) TO authenticated;

supabase/tests/010_leave_collective.sql

@@ -0,0 +1,111 @@
+-- pgTAP: leave_collective() RPC — Fase 10.1
+-- Run with: psql -U postgres -d postgres -f supabase/tests/010_leave_collective.sql
+--
+-- Covers CU-H06:
+--   * normal member abandons OK (membership row gone)
+--   * sole admin with other members abandons OK + oldest member auto-promoted
+--   * sole member rejected with errcode P0001 (must use dissolve_collective)
+
+CREATE EXTENSION IF NOT EXISTS pgtap;
+
+BEGIN;
+SELECT plan(7);
+
+-- ── Existence ────────────────────────────────────────────────────────────────
+SELECT has_function(
+    'public', 'leave_collective', ARRAY['uuid'],
+    'public.leave_collective(uuid) RPC exists'
+);
+
+-- ── Setup: three test users + two collectives outside seed range ──────────────
+INSERT INTO public.users (id, email, display_name, language, avatar_type)
+VALUES
+    ('e1000000-0000-0000-0000-000000000001', 'leave-admin@local',  'Leave Admin',  'es', 'initials'),
+    ('e1000000-0000-0000-0000-000000000002', 'leave-member@local', 'Leave Member', 'es', 'initials'),
+    ('e1000000-0000-0000-0000-000000000003', 'leave-solo@local',   'Leave Solo',   'es', 'initials')
+ON CONFLICT (id) DO NOTHING;
+
+-- Collective A: admin + member. created_by = Borja (so deleting admin row is safe).
+INSERT INTO public.collectives (id, name, emoji, created_by)
+VALUES ('cccccccc-1111-1111-1111-111111111111', 'Leave test A', '🚪',
+        '22222222-2222-2222-2222-222222222222')
+ON CONFLICT (id) DO NOTHING;
+
+INSERT INTO public.collective_members (collective_id, user_id, role, joined_at)
+VALUES
+    ('cccccccc-1111-1111-1111-111111111111', 'e1000000-0000-0000-0000-000000000001', 'admin',  now() - INTERVAL '10 days'),
+    ('cccccccc-1111-1111-1111-111111111111', 'e1000000-0000-0000-0000-000000000002', 'member', now() - INTERVAL '5 days')
+ON CONFLICT (collective_id, user_id) DO NOTHING;
+
+-- Collective B: sole member only.
+INSERT INTO public.collectives (id, name, emoji, created_by)
+VALUES ('cccccccc-2222-2222-2222-222222222222', 'Leave test B (solo)', '🚪',
+        '22222222-2222-2222-2222-222222222222')
+ON CONFLICT (id) DO NOTHING;
+
+INSERT INTO public.collective_members (collective_id, user_id, role)
+VALUES
+    ('cccccccc-2222-2222-2222-222222222222', 'e1000000-0000-0000-0000-000000000003', 'admin')
+ON CONFLICT (collective_id, user_id) DO NOTHING;
+
+-- ── Case 1: normal member leaves ──────────────────────────────────────────────
+-- Authenticate as leave-member
+SELECT set_config('request.jwt.claim.sub', 'e1000000-0000-0000-0000-000000000002', true);
+
+SELECT lives_ok(
+    $$ SELECT public.leave_collective('cccccccc-1111-1111-1111-111111111111') $$,
+    'L-01a: member can leave without error'
+);
+
+SELECT is(
+    (SELECT count(*)::int FROM public.collective_members
+     WHERE collective_id = 'cccccccc-1111-1111-1111-111111111111'
+     AND   user_id       = 'e1000000-0000-0000-0000-000000000002'),
+    0,
+    'L-01a: membership row removed after leave'
+);
+
+-- ── Case 2: sole admin with other members ─────────────────────────────────────
+-- Re-add the member to set up sole-admin scenario again.
+INSERT INTO public.collective_members (collective_id, user_id, role, joined_at)
+VALUES ('cccccccc-1111-1111-1111-111111111111',
+        'e1000000-0000-0000-0000-000000000002', 'member', now() - INTERVAL '5 days')
+ON CONFLICT (collective_id, user_id) DO UPDATE SET role = EXCLUDED.role;
+
+-- Authenticate as the admin
+SELECT set_config('request.jwt.claim.sub', 'e1000000-0000-0000-0000-000000000001', true);
+
+SELECT lives_ok(
+    $$ SELECT public.leave_collective('cccccccc-1111-1111-1111-111111111111') $$,
+    'L-01b: sole admin can leave when other members exist'
+);
+
+SELECT is(
+    (SELECT role::text FROM public.collective_members
+     WHERE collective_id = 'cccccccc-1111-1111-1111-111111111111'
+     AND   user_id       = 'e1000000-0000-0000-0000-000000000002'),
+    'admin',
+    'L-01b: remaining member auto-promoted to admin'
+);
+
+SELECT is(
+    (SELECT count(*)::int FROM public.collective_members
+     WHERE collective_id = 'cccccccc-1111-1111-1111-111111111111'
+     AND   user_id       = 'e1000000-0000-0000-0000-000000000001'),
+    0,
+    'L-01b: departing admin row removed'
+);
+
+-- ── Case 3: sole member tries to leave ────────────────────────────────────────
+-- Authenticate as leave-solo
+SELECT set_config('request.jwt.claim.sub', 'e1000000-0000-0000-0000-000000000003', true);
+
+SELECT throws_ok(
+    $$ SELECT public.leave_collective('cccccccc-2222-2222-2222-222222222222') $$,
+    'P0001',
+    NULL,
+    'L-01c: sole member rejected with errcode P0001'
+);
+
+SELECT * FROM finish();
+ROLLBACK;