diff --git a/src/features/inbox/components/chat/__tests__/useChatFilters.identity.test.ts b/src/features/inbox/components/chat/__tests__/useChatFilters.identity.test.ts
new file mode 100644
index 0000000000..64222419c2
--- /dev/null
+++ b/src/features/inbox/components/chat/__tests__/useChatFilters.identity.test.ts
@@ -0,0 +1,152 @@
+/**
+ * Tests for useChatFilters — referential identity (memoization).
+ *
+ * Guard against regressions where derived arrays lose referential stability,
+ * causing unnecessary re-renders in virtualised message lists. Each useMemo
+ * derivation must return the same array reference when its inputs haven't changed.
+ */
+
+import { describe, it, expect } from 'vitest';
+import { renderHook, act } from '@testing-library/react';
+import { MemoryRouter } from 'react-router-dom';
+import React from 'react';
+import { useChatFilters } from '../hooks/useChatFilters';
+import type { Message } from '@/types/chat';
+
+// ── Helpers ───────────────────────────────────────────────────────────────────
+
+function makeMessage(overrides: Partial<Message> = {}): Message {
+  return {
+    id: 'msg-1',
+    content: 'hello',
+    status: 'sent',
+    timestamp: new Date().toISOString(),
+    type: 'text',
+    fromMe: true,
+    conversationId: 'conv-1',
+    ...overrides,
+  } as Message;
+}
+
+function makeWrapper() {
+  const Wrapper: React.FC<{ children: React.ReactNode }> = ({ children }) =>
+    React.createElement(MemoryRouter, null, children);
+  return Wrapper;
+}
+
+const SENT = makeMessage({ id: 'ok-1', status: 'sent' });
+const FAILED = makeMessage({ id: 'fail-1', status: 'failed' });
+const FAILED_AUTH = makeMessage({ id: 'fail-2', status: 'failed_auth' });
+const FAILED_RETRIES = makeMessage({ id: 'fail-3', status: 'failed_retries' });
+
+const ALL_MESSAGES = [SENT, FAILED, FAILED_AUTH, FAILED_RETRIES];
+
+// ── Tests ─────────────────────────────────────────────────────────────────────
+
+describe('useChatFilters — referential identity', () => {
+  it('failedMessages reference is stable across renders with same input', () => {
+    const { result, rerender } = renderHook(() => useChatFilters(ALL_MESSAGES), {
+      wrapper: makeWrapper(),
+    });
+
+    const ref1 = result.current.failedMessages;
+    rerender();
+    const ref2 = result.current.failedMessages;
+
+    expect(ref1).toBe(ref2);
+  });
+
+  it('visibleMessages reference is stable across renders with same input', () => {
+    const { result, rerender } = renderHook(() => useChatFilters(ALL_MESSAGES), {
+      wrapper: makeWrapper(),
+    });
+
+    const ref1 = result.current.visibleMessages;
+    rerender();
+    const ref2 = result.current.visibleMessages;
+
+    expect(ref1).toBe(ref2);
+  });
+
+  it('categoryCounts reference is stable across renders with same input', () => {
+    const { result, rerender } = renderHook(() => useChatFilters(ALL_MESSAGES), {
+      wrapper: makeWrapper(),
+    });
+
+    const ref1 = result.current.categoryCounts;
+    rerender();
+    const ref2 = result.current.categoryCounts;
+
+    expect(ref1).toBe(ref2);
+  });
+
+  it('categoryFilteredMessages reference is stable across renders with same input', () => {
+    const { result, rerender } = renderHook(() => useChatFilters(ALL_MESSAGES), {
+      wrapper: makeWrapper(),
+    });
+
+    const ref1 = result.current.categoryFilteredMessages;
+    rerender();
+    const ref2 = result.current.categoryFilteredMessages;
+
+    expect(ref1).toBe(ref2);
+  });
+});
+
+describe('useChatFilters — correctness', () => {
+  it('failedMessages contains only failed-status messages', () => {
+    const { result } = renderHook(() => useChatFilters(ALL_MESSAGES), {
+      wrapper: makeWrapper(),
+    });
+
+    expect(result.current.failedMessages).toHaveLength(3);
+    expect(result.current.failedMessages.map((m) => m.id)).toEqual(['fail-1', 'fail-2', 'fail-3']);
+  });
+
+  it('categoryCounts matches actual failure distribution', () => {
+    const { result } = renderHook(() => useChatFilters(ALL_MESSAGES), {
+      wrapper: makeWrapper(),
+    });
+
+    expect(result.current.categoryCounts).toEqual({
+      failed: 1,
+      failed_auth: 1,
+      failed_retries: 1,
+    });
+  });
+
+  it('visibleMessages equals all messages when failuresOnly is false', () => {
+    const { result } = renderHook(() => useChatFilters(ALL_MESSAGES), {
+      wrapper: makeWrapper(),
+    });
+
+    expect(result.current.failuresOnly).toBe(false);
+    expect(result.current.visibleMessages).toHaveLength(ALL_MESSAGES.length);
+  });
+
+  it('setFailuresOnly callback is stable across renders', () => {
+    const { result, rerender } = renderHook(() => useChatFilters(ALL_MESSAGES), {
+      wrapper: makeWrapper(),
+    });
+
+    const cb1 = result.current.setFailuresOnly;
+    rerender();
+    expect(result.current.setFailuresOnly).toBe(cb1);
+  });
+
+  it('failedMessages updates when new failed message added', () => {
+    let messages = [SENT, FAILED];
+    const { result, rerender } = renderHook(() => useChatFilters(messages), {
+      wrapper: makeWrapper(),
+    });
+
+    expect(result.current.failedMessages).toHaveLength(1);
+
+    act(() => {
+      messages = [...messages, FAILED_AUTH];
+    });
+    rerender();
+
+    expect(result.current.failedMessages).toHaveLength(2);
+  });
+});
diff --git a/src/features/inbox/components/chat/__tests__/useChatPanelHandlers.edit.test.ts b/src/features/inbox/components/chat/__tests__/useChatPanelHandlers.edit.test.ts
new file mode 100644
index 0000000000..d038e0b06f
--- /dev/null
+++ b/src/features/inbox/components/chat/__tests__/useChatPanelHandlers.edit.test.ts
@@ -0,0 +1,219 @@
+/**
+ * Regression tests for the edit-message flow in useChatPanelHandlers.
+ *
+ * Critical invariant: editMessageApi MUST be awaited before any success toast.
+ * If the API call fails, no success toast should appear (no false-success).
+ * If preconditions are missing (no JID, no externalId, no instance), an error
+ * toast must appear instead of a success toast.
+ */
+
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { renderHook, act } from '@testing-library/react';
+import { useChatPanelHandlers } from '../useChatPanelHandlers';
+import type { Message } from '@/types/chat';
+
+// ── Mocks ─────────────────────────────────────────────────────────────────────
+
+const mockToast = vi.fn();
+vi.mock('@/hooks/use-toast', () => ({ toast: (p: unknown) => mockToast(p) }));
+
+const mockDbUpdate = vi.fn();
+const mockDbEq = vi.fn(() => ({
+  eq: vi.fn(() => ({
+    select: vi.fn(() => Promise.resolve({ data: [{ id: 'msg-1' }], error: null })),
+  })),
+}));
+const mockDbFrom = vi.fn(() => ({ update: mockDbUpdate }));
+mockDbUpdate.mockReturnValue({
+  eq: vi.fn(() => ({
+    select: vi.fn(() => Promise.resolve({ data: [{ id: 'msg-1' }], error: null })),
+  })),
+});
+
+vi.mock('@/integrations/datasource/db', () => ({
+  dbFrom: (...args: unknown[]) => mockDbFrom(...args),
+}));
+vi.mock('@/features/auth', () => ({ useAuth: () => ({ user: { id: 'user-1' } }) }));
+vi.mock('@/lib/logger', () => ({
+  getLogger: () => ({ warn: vi.fn(), error: vi.fn(), info: vi.fn() }),
+}));
+vi.mock('@/lib/undoToast', () => ({ undoToast: vi.fn() }));
+vi.mock('../../hooks/useWhisperMessagesMutation', () => ({ insertWhisperMessage: vi.fn() }));
+vi.mock('../useInputHandlers', async () => {
+  const { useState } = await import('react');
+  return {
+    useInputHandlers: () => {
+      const [inputValue, setInputValue] = useState('');
+      return {
+        inputValue,
+        setInputValue,
+        handleInputChange: vi.fn(),
+        applyTemplate: vi.fn(),
+        clearInput: vi.fn(),
+      };
+    },
+  };
+});
+vi.mock('../useProductHandlers', () => ({
+  useProductHandlers: () => ({ handleSendProduct: vi.fn() }),
+}));
+vi.mock('../useAudioVoiceChange', () => ({
+  useAudioVoiceChange: () => ({ handleAudioVoiceChange: vi.fn() }),
+}));
+vi.mock('../useMessageReactionHandlers', () => ({
+  useMessageReactionHandlers: () => ({ handleReaction: vi.fn() }),
+}));
+
+// ── Test helpers ──────────────────────────────────────────────────────────────
+
+const EDIT_JID = '5511999887766@s.whatsapp.net';
+const EDIT_MSG: Message = {
+  id: 'msg-1',
+  external_id: 'ext-abc123',
+  content: 'old text',
+  status: 'sent',
+  timestamp: new Date().toISOString(),
+  type: 'text',
+  fromMe: true,
+  conversationId: 'conv-1',
+} as unknown as Message;
+
+function makeHandlers(editMessageApi: ReturnType<typeof vi.fn>) {
+  return renderHook(() =>
+    useChatPanelHandlers({
+      conversationId: 'conv-1',
+      contactId: EDIT_JID,
+      contactPhone: '5511999887766',
+      instanceName: 'wpp2',
+      onSendMessage: vi.fn(),
+      editMessageApi,
+      applySignature: (t: string) => t,
+      handleTypingStart: vi.fn(),
+      handleTypingStop: vi.fn(),
+      openDialog: vi.fn(),
+      closeDialog: vi.fn(),
+      handleSetActiveTool: vi.fn(),
+    })
+  );
+}
+
+beforeEach(() => {
+  vi.clearAllMocks();
+  mockDbFrom.mockReturnValue({
+    update: () => ({
+      eq: () => ({
+        select: () => Promise.resolve({ data: [{ id: 'msg-1' }], error: null }),
+      }),
+    }),
+  });
+});
+
+// ── Tests ─────────────────────────────────────────────────────────────────────
+
+describe('edit message — API called before success toast', () => {
+  it('calls editMessageApi before showing success toast on happy path', async () => {
+    const callOrder: string[] = [];
+    const editMessageApi = vi.fn(async () => {
+      callOrder.push('api');
+    });
+    mockToast.mockImplementation(() => {
+      callOrder.push('toast');
+    });
+
+    const { result } = makeHandlers(editMessageApi);
+
+    act(() => {
+      result.current.handleEditStart(EDIT_MSG);
+    });
+    act(() => {
+      result.current.setInputValue('new text');
+    });
+
+    await act(async () => {
+      await result.current.handleSend();
+    });
+
+    expect(editMessageApi).toHaveBeenCalledTimes(1);
+    const apiIdx = callOrder.indexOf('api');
+    const toastIdx = callOrder.indexOf('toast');
+    expect(apiIdx).toBeGreaterThanOrEqual(0);
+    expect(toastIdx).toBeGreaterThan(apiIdx);
+  });
+
+  it('does NOT show success toast when editMessageApi throws', async () => {
+    const editMessageApi = vi.fn().mockRejectedValue(new Error('Network error'));
+
+    const { result } = makeHandlers(editMessageApi);
+
+    act(() => {
+      result.current.handleEditStart(EDIT_MSG);
+    });
+    act(() => {
+      result.current.setInputValue('new text');
+    });
+
+    await act(async () => {
+      await result.current.handleSend();
+    });
+
+    const successToasts = mockToast.mock.calls.filter(([p]) =>
+      typeof p === 'object' && p !== null && 'variant' in p
+        ? (p as { variant: string }).variant !== 'destructive'
+        : true
+    );
+    // Only destructive toasts (errors) should appear when API throws
+    const destructiveToasts = mockToast.mock.calls.filter(
+      ([p]) =>
+        typeof p === 'object' && p !== null && (p as { variant?: string }).variant === 'destructive'
+    );
+    expect(successToasts.length).toBe(0);
+    expect(destructiveToasts.length).toBeGreaterThan(0);
+  });
+});
+
+describe('edit message — precondition guard', () => {
+  it('shows error toast and does not call API when message has no external_id', async () => {
+    const editMessageApi = vi.fn();
+    const { result } = makeHandlers(editMessageApi);
+
+    const msgWithoutExternalId: Message = {
+      ...EDIT_MSG,
+      external_id: undefined,
+    } as unknown as Message;
+    act(() => {
+      result.current.handleEditStart(msgWithoutExternalId);
+    });
+    act(() => {
+      result.current.setInputValue('new text');
+    });
+
+    await act(async () => {
+      await result.current.handleSend();
+    });
+
+    expect(editMessageApi).not.toHaveBeenCalled();
+    expect(mockToast).toHaveBeenCalledWith(expect.objectContaining({ variant: 'destructive' }));
+  });
+
+  it('calls editMessageApi with correct params when all preconditions are met', async () => {
+    const editMessageApi = vi.fn().mockResolvedValue(undefined);
+    const { result } = makeHandlers(editMessageApi);
+
+    act(() => {
+      result.current.handleEditStart(EDIT_MSG);
+    });
+    act(() => {
+      result.current.setInputValue('updated text');
+    });
+
+    await act(async () => {
+      await result.current.handleSend();
+    });
+
+    expect(editMessageApi).toHaveBeenCalledWith('wpp2', {
+      number: EDIT_JID,
+      messageId: 'ext-abc123',
+      text: 'updated text',
+    });
+  });
+});
diff --git a/src/features/inbox/hooks/__tests__/useFallbackContact.test.ts b/src/features/inbox/hooks/__tests__/useFallbackContact.test.ts
new file mode 100644
index 0000000000..f4da662a31
--- /dev/null
+++ b/src/features/inbox/hooks/__tests__/useFallbackContact.test.ts
@@ -0,0 +1,119 @@
+/**
+ * Tests for useFallbackContact — verifies JID vs UUID routing to correct DB column.
+ *
+ * Critical regression guard: passing a JID into the `id` (UUID) column causes
+ * PostgREST 400 "invalid input syntax for type uuid". This hook must detect
+ * the format and route to the correct filter column.
+ */
+
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { renderHook, waitFor } from '@testing-library/react';
+import { useFallbackContact } from '../useFallbackContact';
+
+// ── Mock supabase client ──────────────────────────────────────────────────────
+
+const mockMaybeSingle = vi.fn();
+const mockEq = vi.fn(() => ({ maybeSingle: mockMaybeSingle }));
+const mockSelect = vi.fn(() => ({ eq: mockEq }));
+const mockFrom = vi.fn(() => ({ select: mockSelect }));
+
+vi.mock('@/integrations/supabase/client', () => ({
+  supabase: {
+    from: (...args: unknown[]) => mockFrom(...args),
+  },
+}));
+
+// ── Helpers ───────────────────────────────────────────────────────────────────
+
+const MOCK_UUID = '550e8400-e29b-41d4-a716-446655440000';
+const MOCK_JID = '5511999887766@s.whatsapp.net';
+const MOCK_PHONE = '5511999887766';
+
+const mockContact = { id: MOCK_UUID, phone: MOCK_PHONE, name: 'Test Contact' };
+
+beforeEach(() => {
+  vi.clearAllMocks();
+  mockMaybeSingle.mockResolvedValue({ data: mockContact, error: null });
+});
+
+// ── Tests ─────────────────────────────────────────────────────────────────────
+
+describe('useFallbackContact — UUID input', () => {
+  it('routes to id column when contactId is a UUID', async () => {
+    renderHook(() => useFallbackContact(MOCK_UUID, null));
+
+    await waitFor(() => {
+      expect(mockFrom).toHaveBeenCalledWith('contacts');
+      expect(mockEq).toHaveBeenCalledWith('id', MOCK_UUID);
+    });
+  });
+
+  it('does NOT use phone column for UUID input', async () => {
+    renderHook(() => useFallbackContact(MOCK_UUID, null));
+
+    await waitFor(() => {
+      expect(mockEq).not.toHaveBeenCalledWith('phone', expect.anything());
+    });
+  });
+});
+
+describe('useFallbackContact — JID input', () => {
+  it('routes to phone column when contactId is a JID', async () => {
+    renderHook(() => useFallbackContact(MOCK_JID, null));
+
+    await waitFor(() => {
+      expect(mockFrom).toHaveBeenCalledWith('contacts');
+      expect(mockEq).toHaveBeenCalledWith('phone', MOCK_PHONE);
+    });
+  });
+
+  it('does NOT route JID to id column (would cause PostgREST 400)', async () => {
+    renderHook(() => useFallbackContact(MOCK_JID, null));
+
+    await waitFor(() => {
+      expect(mockEq).not.toHaveBeenCalledWith('id', MOCK_JID);
+    });
+  });
+});
+
+describe('useFallbackContact — bare phone input', () => {
+  it('routes to phone column when contactId is a bare phone number', async () => {
+    renderHook(() => useFallbackContact(MOCK_PHONE, null));
+
+    await waitFor(() => {
+      expect(mockEq).toHaveBeenCalledWith('phone', MOCK_PHONE);
+    });
+  });
+});
+
+describe('useFallbackContact — early returns', () => {
+  it('skips DB call when selectedConversation is already available', () => {
+    const existing = {
+      contact: mockContact as never,
+      messages: [],
+      unreadCount: 0,
+      lastMessage: null,
+    };
+    renderHook(() => useFallbackContact(MOCK_UUID, existing));
+
+    expect(mockFrom).not.toHaveBeenCalled();
+  });
+
+  it('skips DB call when contactId is null', () => {
+    renderHook(() => useFallbackContact(null, null));
+
+    expect(mockFrom).not.toHaveBeenCalled();
+  });
+
+  it('returns selectedConversation directly when provided', () => {
+    const existing = {
+      contact: mockContact as never,
+      messages: [],
+      unreadCount: 0,
+      lastMessage: null,
+    };
+    const { result } = renderHook(() => useFallbackContact(MOCK_UUID, existing));
+
+    expect(result.current).toBe(existing);
+  });
+});