diff --git a/CLAUDE.md b/CLAUDE.md
index 831c47b..1ed90d9 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -87,6 +87,10 @@ These are absolute rules — never violate them:
 - **React SPA input masking**: For dialog inputs in React/Vue SPAs, do NOT set `visibility: visible` after masking — the framework overwrites `input.value` but keeps our inline styles, exposing plaintext. Instead, keep inputs hidden by manifest CSS.
 - **AWS dual-key capture**: AWS has Access Key ID (`AKIA...`, DOM scan) + Secret Access Key (no prefix, 40-char base64, clipboard-only capture via `isAwsConsolePage()` in `handleClipboardText()`).
 - **Toast stacking**: Multiple consecutive captures show stacked toasts (each calculates top offset from existing toasts) instead of replacing the previous one.
+- **NMH dual-path IPC**: NativeMessagingHost supports both `get_config` (direct ipc.json read) and WS relay (`get_state`, `submit_captured_key`, `toggle_demo_mode`). WS relay uses `URLSessionWebSocketTask` short-lived connection (~20-60ms). clientType `"nmh"` — Core skips NMH in broadcast. `sendRequest()` in service-worker.ts tries WS first, then NMH fallback.
+- **NMH no plaintext queue**: When both WS and NMH fail for `submit_captured_key`, the key is NOT queued to `chrome.storage.local`. Storing plaintext API keys in browser storage violates security red line #1. The key is lost and must be re-captured.
+- **NMH isConnected semantics**: NMH relay success does NOT set `state.isConnected = true` — NMH is a one-shot relay, not a persistent connection. Popup shows "Connected (NMH)" via `connectionPath` field only, while WS reconnect continues independently.
+- **NMHInstaller**: Core auto-installs NMH binary + Chrome manifest from app bundle Resources on startup. Uses binary file size comparison for version checking. `install.sh` retained as manual fallback.
 
 ## Documentation
 
diff --git a/docs/01-product-spec/implementation-status.md b/docs/01-product-spec/implementation-status.md
index 29d6238..a5dbc8b 100644
--- a/docs/01-product-spec/implementation-status.md
+++ b/docs/01-product-spec/implementation-status.md
@@ -1,6 +1,6 @@
 # 實作狀態追蹤
 
-> 最後更新：2026-03-17
+> 最後更新：2026-03-18
 
 ## 狀態圖例
 
@@ -19,7 +19,7 @@
 | KeychainService | ✅ | store / retrieve / delete 完成 |
 | ClipboardEngine | ✅ | copy + autoClear + detectKeys 完成 |
 | MaskingCoordinator | ✅ | isDemoMode / activeContext / pattern 匹配完成 |
-| IPCServer (WebSocket) | ✅ | handshake / state_changed / pattern_cache_sync / toggle_demo_mode |
+| IPCServer (WebSocket) | ✅ | handshake / state_changed / pattern_cache_sync / toggle_demo_mode / nmh clientType |
 | HotkeyManager | ✅ | `⌃⌥⌘D` toggle、`⌃⌥Space` hold 偵測、`⌃⌥[1-9]` paste、flagsChanged 監聽 |
 | Floating Toolbox (HUD) | ✅ | NSPanel 浮動視窗、hold-to-search、Scheme B 鎖定、↑↓ 導航 |
 | ToolboxState (ViewModel) | ✅ | 搜尋過濾、選取狀態、release/confirm/dismiss 邏輯 |
@@ -67,14 +67,16 @@
 
 | 功能 | 狀態 | 備註 |
 |------|------|------|
-| Background Service Worker | ✅ | WebSocket 連線、state 管理、reconnect |
-| Popup UI | ✅ | 連線狀態、Demo Mode、Context、Patterns |
+| Background Service Worker | ✅ | WebSocket 連線、NMH fallback 雙路分派、state 管理、reconnect |
+| Popup UI | ✅ | 連線狀態（WebSocket/NMH/Offline）、Demo Mode、Context、Patterns |
 | Toggle Demo Mode | ✅ | Popup → Background → Core → broadcast |
 | Content Script DOM masking | ✅ | TreeWalker + CSS overlay + MutationObserver |
 | Content Script unmask | ✅ | 退出 Demo Mode 恢復原始文字 |
 | Options 頁面 | ✅ | Pattern cache 管理 + Dev IPC Config |
 | Dev IPC Config (workaround) | ✅ | 替代 Native Messaging Host |
-| Native Messaging Host | ❌ | Swift binary 未編譯部署 |
+| Native Messaging Host | ✅ | get_config + WS relay（get_state / submit_captured_key / toggle_demo_mode） |
+| NMH 雙路 IPC | ✅ | WS primary + NMH fallback，popup 顯示連線路徑 |
+| NMHInstaller（Core 自動安裝） | ✅ | Core 啟動時從 bundle Resources 安裝 binary + manifest |
 | Active Key Capture | ✅ | 4 層偵測：DOM scan → attribute → clipboard → platform selectors |
 | capture-patterns.ts (SSoT) | ✅ | 11 平台 pattern 定義，單一檔案維護 |
 | Pre-hide anti-flash | ✅ | 三層：manifest CSS → pre-hide.ts → instant MutationObserver |
diff --git a/docs/02-technical-architecture/chrome-extension-architecture.md b/docs/02-technical-architecture/chrome-extension-architecture.md
index 29f8aa6..02823de 100644
--- a/docs/02-technical-architecture/chrome-extension-architecture.md
+++ b/docs/02-technical-architecture/chrome-extension-architecture.md
@@ -1,7 +1,7 @@
 # Chrome Extension 架構
 
-> 狀態：✅ 核心功能完成（WebSocket 連線、Content Script masking、Popup UI）
-> 尚未完成：Native Messaging Host 部署、Smart Extract
+> 狀態：✅ 核心功能完成（WebSocket 連線、NMH 雙路 IPC、Content Script masking、Popup UI）
+> 尚未完成：Smart Extract
 
 ---
 
@@ -43,6 +43,7 @@
 **職責**：
 - 維持與 Swift Core 的 WebSocket 連線（含指數退避重連）
 - 透過 Native Messaging Host 取得 IPC 連線資訊
+- **雙路分派**：WS primary → NMH fallback（get_state / submit_captured_key / toggle_demo_mode）
 - 接收 Core 事件並轉發至 Content Scripts
 - 回應 Popup 的狀態查詢
 - 持久化 pattern cache 至 `chrome.storage.local`
@@ -53,6 +54,12 @@
 3. 發送 handshake（clientType: 'chrome', token, version）
 4. 收到 success → 標記 connected，開始接收事件
 
+**雙路分派（Dual-path Dispatch）**：
+- `sendRequest(action, payload)` 統一入口
+- WS 連線中 → 透過 WS 發送（含 request-response correlation + 5s timeout）
+- WS 斷線且 action 為 relay 清單 → 透過 NMH fallback
+- 雙路皆失敗 → log warning（不將明文 key 存入 chrome.storage，遵守安全紅線）
+
 **Dev Fallback**：
 - Native Host 不可用時，從 `chrome.storage.local` 讀取手動設定的 port/token
 - Options 頁面提供 Dev IPC Config 輸入介面
@@ -108,11 +115,12 @@ chrome.runtime.sendMessage({ type: 'get_state' }, (response) => {
 ### Popup (`popup.ts` + `popup.html`)
 
 **顯示資訊**：
-- Connection 狀態（綠點 Connected / 紅點 Offline）
+- Connection 狀態與路徑（綠點 WebSocket / 藍點 NMH / 紅點 Offline）
 - Mode（Normal / Demo）
 - Active Context 名稱
 - Pattern 數量
 - Toggle Demo Mode 按鈕
+- Capture Mode 控制
 
 ### Options (`options.ts` + `options.html`)
 
@@ -126,31 +134,61 @@ chrome.runtime.sendMessage({ type: 'get_state' }, (response) => {
 
 ## Native Messaging Host
 
-### 架構
+### 架構（雙路 IPC）
+
+NMH 同時支援兩種模式：**config 查詢**和 **WS relay**。
 
 ```
 Chrome Extension → chrome.runtime.sendNativeMessage('com.demosafe.nmh', ...)
     ↓ stdin (4-byte length prefix + JSON)
 NativeMessagingHost (Swift binary)
-    ↓ 讀取 ~/.demosafe/ipc.json
+    ├─ action: get_config → 讀取 ~/.demosafe/ipc.json → 回傳 {port, token}
+    └─ action: get_state / submit_captured_key / toggle_demo_mode
+         → 讀取 ipc.json 取得 port/token
+         → 建立短暫 WS 連線至 Core（URLSessionWebSocketTask）
+         → handshake (clientType: "nmh") → 送 request → 收 response → 斷線
+         → stdout 回傳 Core 的 response
     ↓ stdout (4-byte length prefix + JSON)
-Chrome Extension ← { port: 55535, token: "..." }
+Chrome Extension ← response
 ```
 
+**WS Relay 特性**：
+- 短暫連線：connect → handshake → 1 request → 1 response → close（~20-60ms）
+- clientType `"nmh"`：Core 不會對 NMH 連線推送 events（broadcast 時跳過）
+- 5 秒 timeout，失敗回傳 `{"error": "core_unreachable" | "auth_failed" | "timeout"}`
+- 會自動跳過 handshake 後 Core 推送的 event messages（如 pattern_cache_sync）
+
+### 支援的 Actions
+
+| Action | 模式 | 說明 |
+|--------|------|------|
+| `get_config` | 直讀 ipc.json | 回傳 `{port, token}`，原有行為 |
+| `get_state` | WS relay | 回傳 isDemoMode、activeContext、patternCacheVersion |
+| `submit_captured_key` | WS relay | 提交截取到的 API key |
+| `toggle_demo_mode` | WS relay | 切換 Demo Mode |
+
 ### 安裝路徑
 
 | 檔案 | 路徑 |
 |------|------|
-| Swift binary | `/Applications/DemoSafe.app/Contents/Helpers/demosafe-nmh` |
+| Swift binary | `~/.demosafe/bin/demosafe-nmh` |
 | Host manifest | `~/Library/Application Support/Google/Chrome/NativeMessagingHosts/com.demosafe.nmh.json` |
 
+### 自動安裝（NMHInstaller）
+
+Core 啟動時自動檢查並安裝 NMH：
+1. 檢查 `~/.demosafe/bin/demosafe-nmh` 是否存在（比對 binary size）
+2. 檢查 Chrome NMH manifest 是否存在且 allowed_origins 正確
+3. 缺少或版本不符 → 從 app bundle Resources 複製 binary + 寫入 manifest
+4. `install.sh` 保留作為手動備援
+
 ### Host Manifest (`com.demosafe.nmh.json`)
 
 ```json
 {
     "name": "com.demosafe.nmh",
-    "description": "DemoSafe Native Messaging Host",
-    "path": "/Applications/DemoSafe.app/Contents/Helpers/demosafe-nmh",
+    "description": "DemoSafe Native Messaging Host — relay for Chrome Extension",
+    "path": "/Users/<user>/.demosafe/bin/demosafe-nmh",
     "type": "stdio",
     "allowed_origins": [
         "chrome-extension://ACTUAL_EXTENSION_ID/"
@@ -158,13 +196,6 @@ Chrome Extension ← { port: 55535, token: "..." }
 }
 ```
 
-### 部署步驟（尚未自動化）
-
-1. 編譯 `native-host/NativeMessagingHost.swift` 為 binary
-2. 放置至 `/Applications/DemoSafe.app/Contents/Helpers/demosafe-nmh`
-3. 將 `com.demosafe.nmh.json` 複製至 NativeMessagingHosts 目錄
-4. 替換 `EXTENSION_ID_HERE` 為實際 Chrome Extension ID
-
 ---
 
 ## Content Script 目標網站
diff --git a/docs/02-technical-architecture/extension-boundaries.md b/docs/02-technical-architecture/extension-boundaries.md
index 95d5f3a..7c5d800 100644
--- a/docs/02-technical-architecture/extension-boundaries.md
+++ b/docs/02-technical-architecture/extension-boundaries.md
@@ -60,20 +60,22 @@
 ### 連線架構
 
 - Background Service Worker 維護與 Core 的 WebSocket 連線
-- Native Messaging Host（Swift helper）讀取 `ipc.json` 以輔助探索
+- Native Messaging Host（Swift helper）提供 config 查詢 + WS relay 雙路備援
 
 ### Native Messaging Host 規格
 
-Chrome Extension 無法直接讀取檔案系統（`~/.demosafe/ipc.json`），因此需要 Native Messaging Host 作為橋接：
+Chrome Extension 無法直接讀取檔案系統（`~/.demosafe/ipc.json`），因此需要 Native Messaging Host 作為橋接。NMH 同時作為 WS 斷線時的 fallback relay。
 
 | 項目 | 說明 |
 |------|------|
-| 實作語言 | Swift（macOS helper binary） |
-| 安裝位置 | `~/Library/Application Support/Google/Chrome/NativeMessagingHosts/com.demosafe.nmh.json` |
-| 職責 | 讀取 `ipc.json` → 回傳 `{port, token}` 給 Background Service Worker |
+| 實作語言 | Swift（macOS helper binary，standalone swiftc 編譯，~93KB） |
+| 安裝位置 | binary: `~/.demosafe/bin/demosafe-nmh`，manifest: `~/Library/Application Support/Google/Chrome/NativeMessagingHosts/com.demosafe.nmh.json` |
+| 職責 | (1) 讀取 `ipc.json` → 回傳 `{port, token}`；(2) WS relay：get_state / submit_captured_key / toggle_demo_mode |
 | 通訊協定 | Chrome Native Messaging（stdin/stdout JSON） |
-| 觸發時機 | Extension 啟動時呼叫一次取得連線資訊；Core 重啟後重新呼叫 |
-| 安全性 | manifest 限定 `allowed_origins` 僅允許本 Extension ID |
+| WS Relay | 短暫連線（connect → handshake → 1 request → 1 response → close），clientType: `"nmh"`，5s timeout |
+| 觸發時機 | Extension 啟動時取連線資訊；WS 斷線時 fallback relay |
+| 安裝方式 | Core 啟動時 NMHInstaller 自動安裝；`install.sh` 手動備援 |
+| 安全性 | manifest 限定 `allowed_origins`；NMH 不儲存任何資料，僅轉發 |
 
 ---
 
diff --git a/docs/05-ipc-protocol/protocol-spec.md b/docs/05-ipc-protocol/protocol-spec.md
index 4daba39..3e34270 100644
--- a/docs/05-ipc-protocol/protocol-spec.md
+++ b/docs/05-ipc-protocol/protocol-spec.md
@@ -36,7 +36,7 @@
 
 | Action | Payload | Response |
 |--------|---------|----------|
-| `handshake` | `clientType`, `token`, `version` | port, pid, patternCache version, 連線狀態 |
+| `handshake` | `clientType`（`vscode` / `chrome` / `accessibility` / `nmh`）, `token`, `version` | port, pid, patternCache version, 連線狀態 |
 | `get_state` | (無) | isDemoMode, activeContext, patternCache, version |
 | `request_paste` | `keyId` | status (`success` \| `denied` \| `offline`) |
 | `request_paste_group` | `groupId`, `fieldIndex`（可選） | status, groupId |
@@ -159,6 +159,19 @@ Core 維護 `patternCacheVersion`，每次 pattern 變更時遞增。Extension 
 
 ---
 
+## NMH Relay（Native Messaging Host 短暫連線）
+
+clientType `"nmh"` 為 Chrome Native Messaging Host 透過短暫 WS 連線轉發請求。
+
+| 特性 | 說明 |
+|------|------|
+| 連線生命週期 | connect → handshake → 1 request → 1 response → close（~20-60ms） |
+| 支援的 action | `get_state`、`submit_captured_key`、`toggle_demo_mode` |
+| broadcast 排除 | Core broadcast events 時自動跳過 `.nmh` clients |
+| 使用場景 | Chrome Extension WS 斷線時的 fallback 路徑 |
+
+---
+
 ## 安全約束
 
 | 規則 | 說明 |
@@ -166,4 +179,5 @@ Core 維護 `patternCacheVersion`，每次 pattern 變更時遞增。Extension 
 | WebSocket 僅 127.0.0.1 | 禁止綁定外部介面 |
 | Handshake 認證 | 需要 `ipc.json` 中的 token |
 | **明文永不經過 IPC** | 僅遮蔽表示和參照流過網路 |
+| **明文不存入 chrome.storage** | submit_captured_key 失敗時不 queue，遵守安全紅線 |
 | `ipc.json` 權限 600 | 僅限使用者讀寫 |
diff --git a/docs/en/01-product-spec/implementation-status.md b/docs/en/01-product-spec/implementation-status.md
index da5d2d5..a38f7bf 100644
--- a/docs/en/01-product-spec/implementation-status.md
+++ b/docs/en/01-product-spec/implementation-status.md
@@ -1,6 +1,6 @@
 # Implementation Status Tracking
 
-> Last updated: 2026-03-17
+> Last updated: 2026-03-18
 
 ## Status Legend
 
@@ -19,7 +19,7 @@
 | KeychainService | ✅ | store / retrieve / delete completed |
 | ClipboardEngine | ✅ | copy + autoClear + detectKeys completed |
 | MaskingCoordinator | ✅ | isDemoMode / activeContext / pattern matching completed |
-| IPCServer (WebSocket) | ✅ | handshake / state_changed / pattern_cache_sync / toggle_demo_mode |
+| IPCServer (WebSocket) | ✅ | handshake / state_changed / pattern_cache_sync / toggle_demo_mode / nmh clientType |
 | HotkeyManager | ✅ | `⌃⌥⌘D` toggle, `⌃⌥Space` hold detection, `⌃⌥[1-9]` paste, flagsChanged listener |
 | Floating Toolbox (HUD) | ✅ | NSPanel floating window, hold-to-search, Scheme B lock, ↑↓ navigation |
 | ToolboxState (ViewModel) | ✅ | Search filtering, selection state, release/confirm/dismiss logic |
@@ -67,14 +67,16 @@
 
 | Feature | Status | Notes |
 |---------|--------|-------|
-| Background Service Worker | ✅ | WebSocket connection, state management, reconnect |
-| Popup UI | ✅ | Connection status, Demo Mode, Context, Patterns |
+| Background Service Worker | ✅ | WebSocket connection, NMH fallback dual-path dispatch, state management, reconnect |
+| Popup UI | ✅ | Connection status (WebSocket/NMH/Offline), Demo Mode, Context, Patterns |
 | Toggle Demo Mode | ✅ | Popup → Background → Core → broadcast |
 | Content Script DOM masking | ✅ | TreeWalker + CSS overlay + MutationObserver |
 | Content Script unmask | ✅ | Restore original text when exiting Demo Mode |
 | Options page | ✅ | Pattern cache management + Dev IPC Config |
 | Dev IPC Config (workaround) | ✅ | Alternative to Native Messaging Host |
-| Native Messaging Host | ❌ | Swift binary not compiled/deployed |
+| Native Messaging Host | ✅ | get_config + WS relay (get_state / submit_captured_key / toggle_demo_mode) |
+| Dual-path IPC (NMH fallback) | ✅ | WS primary + NMH fallback, popup shows connection path |
+| NMHInstaller (Core auto-install) | ✅ | Core installs binary + manifest from bundle Resources on startup |
 | Active Key Capture | ✅ | 4-layer detection: DOM scan → attribute → clipboard → platform selectors |
 | capture-patterns.ts (SSoT) | ✅ | 11 platform pattern definitions, single file maintenance |
 | Pre-hide anti-flash | ✅ | 3 layers: manifest CSS → pre-hide.ts → instant MutationObserver |
diff --git a/docs/en/02-technical-architecture/chrome-extension-architecture.md b/docs/en/02-technical-architecture/chrome-extension-architecture.md
index 6e5544a..84572e3 100644
--- a/docs/en/02-technical-architecture/chrome-extension-architecture.md
+++ b/docs/en/02-technical-architecture/chrome-extension-architecture.md
@@ -1,7 +1,7 @@
 # Chrome Extension Architecture
 
-> Status: ✅ Core features completed (WebSocket connection, Content Script masking, Popup UI)
-> Not yet completed: Native Messaging Host deployment, Smart Extract
+> Status: ✅ Core features completed (WebSocket connection, NMH dual-path IPC, Content Script masking, Popup UI)
+> Not yet completed: Smart Extract
 
 ---
 
@@ -43,6 +43,7 @@
 **Responsibilities**:
 - Maintain WebSocket connection to Swift Core (with exponential backoff reconnection)
 - Obtain IPC connection info via Native Messaging Host
+- **Dual-path dispatch**: WS primary → NMH fallback (get_state / submit_captured_key / toggle_demo_mode)
 - Receive Core events and forward to Content Scripts
 - Respond to Popup state queries
 - Persist pattern cache to `chrome.storage.local`
@@ -53,6 +54,12 @@
 3. Send handshake (clientType: 'chrome', token, version)
 4. Receive success → mark as connected, start receiving events
 
+**Dual-path Dispatch**:
+- `sendRequest(action, payload)` — unified entry point
+- WS connected → send via WS (with request-response correlation + 5s timeout)
+- WS disconnected + action in relay list → fallback via NMH
+- Both fail → log warning (plaintext keys are NOT queued to chrome.storage — security red line)
+
 **Dev Fallback**:
 - When Native Host is unavailable, read manually configured port/token from `chrome.storage.local`
 - Options page provides Dev IPC Config input interface
@@ -108,11 +115,12 @@ chrome.runtime.sendMessage({ type: 'get_state' }, (response) => {
 ### Popup (`popup.ts` + `popup.html`)
 
 **Displayed Information**:
-- Connection status (green dot Connected / red dot Offline)
+- Connection status and path (green dot WebSocket / blue dot NMH / red dot Offline)
 - Mode (Normal / Demo)
 - Active Context name
 - Pattern count
 - Toggle Demo Mode button
+- Capture Mode control
 
 ### Options (`options.ts` + `options.html`)
 
@@ -126,31 +134,61 @@ chrome.runtime.sendMessage({ type: 'get_state' }, (response) => {
 
 ## Native Messaging Host
 
-### Architecture
+### Architecture (Dual-path IPC)
+
+NMH supports two modes: **config query** and **WS relay**.
 
 ```
 Chrome Extension → chrome.runtime.sendNativeMessage('com.demosafe.nmh', ...)
     ↓ stdin (4-byte length prefix + JSON)
 NativeMessagingHost (Swift binary)
-    ↓ reads ~/.demosafe/ipc.json
+    ├─ action: get_config → read ~/.demosafe/ipc.json → return {port, token}
+    └─ action: get_state / submit_captured_key / toggle_demo_mode
+         → read ipc.json for port/token
+         → open short-lived WS to Core (URLSessionWebSocketTask)
+         → handshake (clientType: "nmh") → send request → receive response → close
+         → stdout returns Core's response
     ↓ stdout (4-byte length prefix + JSON)
-Chrome Extension ← { port: 55535, token: "..." }
+Chrome Extension ← response
 ```
 
+**WS Relay Characteristics**:
+- Short-lived connection: connect → handshake → 1 request → 1 response → close (~20-60ms)
+- clientType `"nmh"`: Core skips NMH connections when broadcasting events
+- 5 second timeout, failure returns `{"error": "core_unreachable" | "auth_failed" | "timeout"}`
+- Automatically skips event messages pushed by Core after handshake (e.g., pattern_cache_sync)
+
+### Supported Actions
+
+| Action | Mode | Description |
+|--------|------|-------------|
+| `get_config` | Direct ipc.json read | Returns `{port, token}`, original behavior |
+| `get_state` | WS relay | Returns isDemoMode, activeContext, patternCacheVersion |
+| `submit_captured_key` | WS relay | Submit captured API key |
+| `toggle_demo_mode` | WS relay | Toggle Demo Mode |
+
 ### Installation Paths
 
 | File | Path |
 |------|------|
-| Swift binary | `/Applications/DemoSafe.app/Contents/Helpers/demosafe-nmh` |
+| Swift binary | `~/.demosafe/bin/demosafe-nmh` |
 | Host manifest | `~/Library/Application Support/Google/Chrome/NativeMessagingHosts/com.demosafe.nmh.json` |
 
+### Auto-installation (NMHInstaller)
+
+Core automatically checks and installs NMH on startup:
+1. Check if `~/.demosafe/bin/demosafe-nmh` exists (compare binary size)
+2. Check if Chrome NMH manifest exists with correct allowed_origins
+3. Missing or version mismatch → copy binary from app bundle Resources + write manifest
+4. `install.sh` retained as manual fallback
+
 ### Host Manifest (`com.demosafe.nmh.json`)
 
 ```json
 {
     "name": "com.demosafe.nmh",
-    "description": "DemoSafe Native Messaging Host",
-    "path": "/Applications/DemoSafe.app/Contents/Helpers/demosafe-nmh",
+    "description": "DemoSafe Native Messaging Host — relay for Chrome Extension",
+    "path": "/Users/<user>/.demosafe/bin/demosafe-nmh",
     "type": "stdio",
     "allowed_origins": [
         "chrome-extension://ACTUAL_EXTENSION_ID/"
@@ -158,13 +196,6 @@ Chrome Extension ← { port: 55535, token: "..." }
 }
 ```
 
-### Deployment Steps (not yet automated)
-
-1. Compile `native-host/NativeMessagingHost.swift` to binary
-2. Place at `/Applications/DemoSafe.app/Contents/Helpers/demosafe-nmh`
-3. Copy `com.demosafe.nmh.json` to NativeMessagingHosts directory
-4. Replace `EXTENSION_ID_HERE` with actual Chrome Extension ID
-
 ---
 
 ## Content Script Target Websites
diff --git a/docs/en/02-technical-architecture/extension-boundaries.md b/docs/en/02-technical-architecture/extension-boundaries.md
index 6f93a9c..2f596b4 100644
--- a/docs/en/02-technical-architecture/extension-boundaries.md
+++ b/docs/en/02-technical-architecture/extension-boundaries.md
@@ -60,20 +60,22 @@ File open/change → regex scan (using cached patterns)
 ### Connection Architecture
 
 - Background Service Worker maintains WebSocket connection to Core
-- Native Messaging Host (Swift helper) reads `ipc.json` for discovery
+- Native Messaging Host (Swift helper) provides config query + WS relay dual-path fallback
 
 ### Native Messaging Host Specification
 
-Chrome Extensions cannot directly read the file system (`~/.demosafe/ipc.json`), so a Native Messaging Host is needed as a bridge:
+Chrome Extensions cannot directly read the file system (`~/.demosafe/ipc.json`), so a Native Messaging Host is needed as a bridge. NMH also serves as a fallback relay when WebSocket is disconnected.
 
 | Item | Description |
 |------|-------------|
-| Implementation language | Swift (macOS helper binary) |
-| Installation location | `~/Library/Application Support/Google/Chrome/NativeMessagingHosts/com.demosafe.nmh.json` |
-| Responsibility | Read `ipc.json` → return `{port, token}` to Background Service Worker |
+| Implementation language | Swift (macOS helper binary, standalone swiftc compilation, ~93KB) |
+| Installation location | binary: `~/.demosafe/bin/demosafe-nmh`, manifest: `~/Library/Application Support/Google/Chrome/NativeMessagingHosts/com.demosafe.nmh.json` |
+| Responsibility | (1) Read `ipc.json` → return `{port, token}`; (2) WS relay: get_state / submit_captured_key / toggle_demo_mode |
 | Communication protocol | Chrome Native Messaging (stdin/stdout JSON) |
-| Trigger timing | Called once on Extension startup to get connection info; re-called after Core restart |
-| Security | Manifest restricts `allowed_origins` to only this Extension ID |
+| WS Relay | Short-lived connection (connect → handshake → 1 request → 1 response → close), clientType: `"nmh"`, 5s timeout |
+| Trigger timing | On Extension startup for connection info; as fallback relay when WS is disconnected |
+| Installation | NMHInstaller auto-installs on Core startup; `install.sh` as manual fallback |
+| Security | Manifest restricts `allowed_origins`; NMH stores no data, only relays |
 
 ---
 
diff --git a/docs/en/05-ipc-protocol/protocol-spec.md b/docs/en/05-ipc-protocol/protocol-spec.md
index 2ca9208..cbb1cb9 100644
--- a/docs/en/05-ipc-protocol/protocol-spec.md
+++ b/docs/en/05-ipc-protocol/protocol-spec.md
@@ -36,7 +36,7 @@ All messages follow a JSON envelope structure:
 
 | Action | Payload | Response |
 |--------|---------|----------|
-| `handshake` | `clientType`, `token`, `version` | port, pid, patternCache version, connection status |
+| `handshake` | `clientType` (`vscode` / `chrome` / `accessibility` / `nmh`), `token`, `version` | port, pid, patternCache version, connection status |
 | `get_state` | (none) | isDemoMode, activeContext, patternCache, version |
 | `request_paste` | `keyId` | status (`success` \| `denied` \| `offline`) |
 | `request_paste_group` | `groupId`, `fieldIndex` (optional) | status, groupId |
@@ -159,6 +159,19 @@ Core maintains a `patternCacheVersion` that increments with each pattern change.
 
 ---
 
+## NMH Relay (Native Messaging Host Short-lived Connection)
+
+clientType `"nmh"` is used by Chrome Native Messaging Host to relay requests via short-lived WS connections.
+
+| Characteristic | Description |
+|----------------|-------------|
+| Connection lifecycle | connect → handshake → 1 request → 1 response → close (~20-60ms) |
+| Supported actions | `get_state`, `submit_captured_key`, `toggle_demo_mode` |
+| Broadcast exclusion | Core automatically skips `.nmh` clients when broadcasting events |
+| Use case | Fallback path when Chrome Extension WS is disconnected |
+
+---
+
 ## Security Constraints
 
 | Rule | Description |
@@ -166,4 +179,5 @@ Core maintains a `patternCacheVersion` that increments with each pattern change.
 | WebSocket on 127.0.0.1 only | Binding to external interfaces is prohibited |
 | Handshake authentication | Token from `ipc.json` is required |
 | **Plaintext never traverses IPC** | Only masked representations and references flow over the network |
+| **Plaintext not stored in chrome.storage** | submit_captured_key failures are not queued — security red line |
 | `ipc.json` permissions 600 | User read/write only |
diff --git a/packages/chrome-extension/native-host/NativeMessagingHost.swift b/packages/chrome-extension/native-host/NativeMessagingHost.swift
index db2bbd1..459b003 100644
--- a/packages/chrome-extension/native-host/NativeMessagingHost.swift
+++ b/packages/chrome-extension/native-host/NativeMessagingHost.swift
@@ -1,7 +1,9 @@
 import Foundation
 
 /// Native Messaging Host for Chrome Extension.
-/// Reads ~/.demosafe/ipc.json and returns {port, token} to the extension.
+/// Supports:
+///   - get_config: Read ~/.demosafe/ipc.json and return {port, token}
+///   - get_state / submit_captured_key / toggle_demo_mode: Relay via short-lived WS to Core
 /// Protocol: Chrome Native Messaging (stdin/stdout with 4-byte length prefix).
 
 struct IPCConfig: Codable {
@@ -11,6 +13,8 @@ struct IPCConfig: Codable {
     let token: String
 }
 
+// MARK: - Chrome Native Messaging I/O
+
 func readMessage() -> Data? {
     var lengthBytes = [UInt8](repeating: 0, count: 4)
     guard fread(&lengthBytes, 1, 4, stdin) == 4 else { return nil }
@@ -28,22 +32,205 @@ func writeMessage(_ data: Data) {
     fflush(stdout)
 }
 
-func main() {
-    guard readMessage() != nil else { return }
+func writeJSON(_ dict: [String: Any]) {
+    do {
+        let data = try JSONSerialization.data(withJSONObject: dict)
+        writeMessage(data)
+    } catch {
+        // Last-resort fallback: write a hardcoded error directly
+        let fallback = Data(#"{"error":"encode_failed"}"#.utf8)
+        writeMessage(fallback)
+        fputs("NMH: writeJSON serialization failed: \(error)\n", stderr)
+    }
+}
+
+func writeError(_ code: String, message: String = "") {
+    writeJSON(["error": code, "message": message])
+}
+
+// MARK: - IPC Config
 
+func loadIPCConfig() -> IPCConfig? {
     let configPath = FileManager.default.homeDirectoryForCurrentUser
         .appendingPathComponent(".demosafe/ipc.json")
+    guard let data = try? Data(contentsOf: configPath),
+          let config = try? JSONDecoder().decode(IPCConfig.self, from: data) else {
+        return nil
+    }
+    return config
+}
+
+// MARK: - WebSocket Relay
+
+let relayActions: Set<String> = ["get_state", "submit_captured_key", "toggle_demo_mode"]
+
+/// Connect to Core WS, handshake, send one request, return one response, then close.
+/// Uses DispatchQueue for URLSession callbacks; blocks main thread with semaphore.
+func relayToCore(config: IPCConfig, action: String, payload: [String: Any]) -> [String: Any] {
+    let semaphore = DispatchSemaphore(value: 0)
+    var result: [String: Any] = ["error": "timeout"]
+
+    // URLSession with delegate queue so callbacks don't need RunLoop
+    let delegateQueue = OperationQueue()
+    delegateQueue.name = "nmh.ws"
+    let session = URLSession(configuration: .default, delegate: nil, delegateQueue: delegateQueue)
+
+    let url = URL(string: "ws://127.0.0.1:\(config.port)")!
+    let wsTask = session.webSocketTask(with: url)
+    wsTask.resume()
+
+    let messageId = UUID().uuidString
+
+    // Step 1: Send handshake
+    let handshake: [String: Any] = [
+        "id": UUID().uuidString,
+        "type": "request",
+        "action": "handshake",
+        "payload": ["clientType": "nmh", "token": config.token, "version": "0.1.0"],
+        "timestamp": ISO8601DateFormatter().string(from: Date()),
+    ]
+
+    guard let handshakeData = try? JSONSerialization.data(withJSONObject: handshake),
+          let handshakeStr = String(data: handshakeData, encoding: .utf8) else {
+        return ["error": "encode_failed"]
+    }
+
+    wsTask.send(.string(handshakeStr)) { error in
+        if error != nil {
+            result = ["error": "core_unreachable"]
+            semaphore.signal()
+            return
+        }
+
+        // Step 2: Receive handshake response
+        wsTask.receive { receiveResult in
+            guard case .success(let msg) = receiveResult,
+                  case .string(let text) = msg,
+                  let data = text.data(using: .utf8),
+                  let json = try? JSONSerialization.jsonObject(with: data) as? [String: Any],
+                  let hsPayload = json["payload"] as? [String: Any],
+                  hsPayload["status"] as? String == "success" else {
+                result = ["error": "auth_failed"]
+                wsTask.cancel(with: .goingAway, reason: nil)
+                semaphore.signal()
+                return
+            }
+
+            // Step 3: Send the actual request
+            let request: [String: Any] = [
+                "id": messageId,
+                "type": "request",
+                "action": action,
+                "payload": payload,
+                "timestamp": ISO8601DateFormatter().string(from: Date()),
+            ]
+
+            guard let reqData = try? JSONSerialization.data(withJSONObject: request),
+                  let reqStr = String(data: reqData, encoding: .utf8) else {
+                result = ["error": "encode_failed"]
+                wsTask.cancel(with: .goingAway, reason: nil)
+                semaphore.signal()
+                return
+            }
+
+            wsTask.send(.string(reqStr)) { error in
+                if error != nil {
+                    result = ["error": "core_unreachable"]
+                    wsTask.cancel(with: .goingAway, reason: nil)
+                    semaphore.signal()
+                    return
+                }
+
+                // Step 4: Receive response (skip event messages)
+                receiveResponse(wsTask: wsTask, expectedId: messageId, attemptsLeft: 5) { response in
+                    result = response
+                    wsTask.cancel(with: .goingAway, reason: nil)
+                    semaphore.signal()
+                }
+            }
+        }
+    }
+
+    let timeout = DispatchTime.now() + .seconds(5)
+    if semaphore.wait(timeout: timeout) == .timedOut {
+        wsTask.cancel(with: .goingAway, reason: nil)
+        session.invalidateAndCancel()
+        return ["error": "timeout"]
+    }
+
+    session.invalidateAndCancel()
+    return result
+}
+
+func receiveResponse(wsTask: URLSessionWebSocketTask, expectedId: String, attemptsLeft: Int, completion: @escaping ([String: Any]) -> Void) {
+    guard attemptsLeft > 0 else {
+        completion(["error": "no_response"])
+        return
+    }
+
+    wsTask.receive { receiveResult in
+        guard case .success(let msg) = receiveResult,
+              case .string(let text) = msg,
+              let data = text.data(using: .utf8),
+              let json = try? JSONSerialization.jsonObject(with: data) as? [String: Any] else {
+            completion(["error": "core_unreachable"])
+            return
+        }
+
+        let msgType = json["type"] as? String
+        let msgId = json["id"] as? String
+
+        // Skip event messages (e.g., pattern_cache_sync sent after handshake)
+        if msgType == "event" {
+            receiveResponse(wsTask: wsTask, expectedId: expectedId, attemptsLeft: attemptsLeft - 1, completion: completion)
+            return
+        }
+
+        // Check if this is our response
+        if msgType == "response" && msgId == expectedId {
+            completion(json)
+            return
+        }
+
+        // Not our message, try again
+        receiveResponse(wsTask: wsTask, expectedId: expectedId, attemptsLeft: attemptsLeft - 1, completion: completion)
+    }
+}
+
+// MARK: - Main
+
+func nmhMain() {
+    guard let messageData = readMessage(),
+          let json = try? JSONSerialization.jsonObject(with: messageData) as? [String: Any],
+          let action = json["action"] as? String else {
+        writeError("invalid_request")
+        return
+    }
+
+    // get_config: read ipc.json directly (no WS needed)
+    if action == "get_config" {
+        guard let config = loadIPCConfig() else {
+            writeError("ipc_not_found", message: "ipc.json not found or unreadable")
+            return
+        }
+        writeJSON(["port": config.port, "token": config.token])
+        return
+    }
+
+    // Relay actions: connect to Core WS, forward request, return response
+    if relayActions.contains(action) {
+        guard let config = loadIPCConfig() else {
+            writeError("ipc_not_found", message: "ipc.json not found or unreadable")
+            return
+        }
 
-    guard let configData = try? Data(contentsOf: configPath),
-          let config = try? JSONDecoder().decode(IPCConfig.self, from: configData) else {
-        let error = try! JSONSerialization.data(withJSONObject: ["error": "ipc.json not found"])
-        writeMessage(error)
+        let payload = json["payload"] as? [String: Any] ?? [:]
+        let response = relayToCore(config: config, action: action, payload: payload)
+        writeJSON(response)
         return
     }
 
-    let response: [String: Any] = ["port": config.port, "token": config.token]
-    let responseData = try! JSONSerialization.data(withJSONObject: response)
-    writeMessage(responseData)
+    writeError("unknown_action", message: "Unknown action: \(action)")
 }
 
-main()
+nmhMain()
diff --git a/packages/chrome-extension/src/background/service-worker.ts b/packages/chrome-extension/src/background/service-worker.ts
index 0b94513..d4d9466 100644
--- a/packages/chrome-extension/src/background/service-worker.ts
+++ b/packages/chrome-extension/src/background/service-worker.ts
@@ -1,19 +1,23 @@
 /**
  * Background Service Worker — maintains WebSocket connection to DemoSafe Core.
  * Uses Native Messaging Host to read ipc.json for connection info.
+ * Falls back to NMH relay when WebSocket is disconnected.
  *
  * Responsibilities:
  * - WebSocket lifecycle (connect, handshake, reconnect with exponential backoff)
+ * - NMH fallback for critical actions (get_state, submit_captured_key, toggle_demo_mode)
  * - Forward Core events to content scripts
  * - Persist pattern cache to chrome.storage.local
  * - Respond to popup/options requests
  * - Manage Active Key Capture mode with alarm-based timeout
+ * - Queue failed submissions for retry on reconnect
  */
 
 const NATIVE_HOST_ID = 'com.demosafe.nmh';
 const MAX_RECONNECT_DELAY = 30000;
 const CAPTURE_TIMEOUT_MS = 300_000; // 5 minutes
 const CAPTURE_ALARM_NAME = 'demosafe_capture_timeout';
+const WS_REQUEST_TIMEOUT = 5000;
 
 interface IPCConfig {
     port: number;
@@ -28,6 +32,8 @@ interface IPCMessage {
     timestamp: string;
 }
 
+type ConnectionPath = 'ws' | 'nmh' | 'offline';
+
 interface DemoSafeState {
     isConnected: boolean;
     isDemoMode: boolean;
@@ -36,12 +42,19 @@ interface DemoSafeState {
     isCaptureMode: boolean;
     captureTimeoutEnd: number | null; // timestamp ms
     capturedCount: number;
+    connectionPath: ConnectionPath;
 }
 
+// NMH relay actions — these can be forwarded via Native Messaging Host when WS is down
+const NMH_RELAY_ACTIONS = new Set(['get_state', 'submit_captured_key', 'toggle_demo_mode']);
+
 let ws: WebSocket | null = null;
 let reconnectDelay = 1000;
 let reconnectTimer: ReturnType<typeof setTimeout> | null = null;
 
+// Pending WS request tracking (request-response correlation)
+const pendingRequests = new Map<string, { resolve: (response: IPCMessage) => void; reject: (error: Error) => void; timer: ReturnType<typeof setTimeout> }>();
+
 const state: DemoSafeState = {
     isConnected: false,
     isDemoMode: false,
@@ -50,6 +63,7 @@ const state: DemoSafeState = {
     isCaptureMode: false,
     captureTimeoutEnd: null,
     capturedCount: 0,
+    connectionPath: 'offline',
 };
 
 // MARK: - Native Messaging Host
@@ -70,7 +84,10 @@ async function getNativeConfig(): Promise<IPCConfig | null> {
     return new Promise((resolve) => {
         try {
             chrome.runtime.sendNativeMessage(NATIVE_HOST_ID, { action: 'get_config' }, (response) => {
-                if (chrome.runtime.lastError || !response) {
+                if (chrome.runtime.lastError) {
+                    console.warn('[DemoSafe BG] getNativeConfig error:', chrome.runtime.lastError.message);
+                    resolve(null);
+                } else if (!response) {
                     resolve(null);
                 } else {
                     resolve(response as IPCConfig);
@@ -82,6 +99,109 @@ async function getNativeConfig(): Promise<IPCConfig | null> {
     });
 }
 
+// MARK: - NMH Relay (fallback path)
+
+async function sendViaNMH(action: string, payload: Record<string, unknown>): Promise<Record<string, unknown> | null> {
+    return new Promise((resolve) => {
+        try {
+            chrome.runtime.sendNativeMessage(
+                NATIVE_HOST_ID,
+                { action, payload },
+                (response) => {
+                    if (chrome.runtime.lastError) {
+                        console.warn(`[DemoSafe NMH] ${action} native error:`, chrome.runtime.lastError.message);
+                        resolve(null);
+                    } else if (!response) {
+                        console.warn(`[DemoSafe NMH] ${action}: no response`);
+                        resolve(null);
+                    } else if (response.error) {
+                        console.warn(`[DemoSafe NMH] ${action} error:`, response.error, response.message);
+                        resolve(null);
+                    } else {
+                        resolve(response as Record<string, unknown>);
+                    }
+                }
+            );
+        } catch (e) {
+            console.warn(`[DemoSafe NMH] ${action} exception:`, e);
+            resolve(null);
+        }
+    });
+}
+
+// MARK: - Unified Request Dispatch
+
+/**
+ * Send a request to Core, trying WS first, then NMH fallback for relay-eligible actions.
+ * For submit_captured_key, queues to storage if both paths fail.
+ */
+async function sendRequest(action: string, payload: Record<string, unknown>): Promise<Record<string, unknown> | null> {
+    // Try WebSocket first
+    if (ws && ws.readyState === WebSocket.OPEN) {
+        try {
+            const response = await sendRequestViaWS(action, payload);
+            if (response) return response.payload as Record<string, unknown>;
+        } catch (err) {
+            console.warn(`[DemoSafe BG] WS request '${action}' failed, trying NMH fallback:`, err);
+        }
+    }
+
+    // Try NMH fallback for relay-eligible actions
+    if (NMH_RELAY_ACTIONS.has(action)) {
+        const nmhResponse = await sendViaNMH(action, payload);
+        if (nmhResponse && !nmhResponse.error) {
+            // Extract payload from the full IPC response envelope
+            const responsePayload = nmhResponse.payload as Record<string, unknown> | undefined;
+            if (responsePayload) {
+                state.connectionPath = 'nmh';
+                return responsePayload;
+            }
+            // If response has no payload wrapper, it's already the payload
+            state.connectionPath = 'nmh';
+            return nmhResponse;
+        }
+    }
+
+    // Both failed — do NOT queue plaintext keys to chrome.storage (security red line)
+    if (action === 'submit_captured_key') {
+        console.warn('[DemoSafe BG] submit_captured_key failed via both WS and NMH — key not stored');
+    }
+
+    state.connectionPath = 'offline';
+    return null;
+}
+
+// MARK: - WS Request-Response Tracking
+
+function sendRequestViaWS(action: string, payload: Record<string, unknown>): Promise<IPCMessage> {
+    return new Promise((resolve, reject) => {
+        const id = crypto.randomUUID();
+        const timer = setTimeout(() => {
+            pendingRequests.delete(id);
+            reject(new Error('WS request timeout'));
+        }, WS_REQUEST_TIMEOUT);
+
+        pendingRequests.set(id, { resolve, reject, timer });
+
+        sendToCore({
+            id,
+            type: 'request',
+            action,
+            payload,
+            timestamp: new Date().toISOString(),
+        });
+    });
+}
+
+function resolvePendingRequest(message: IPCMessage) {
+    const pending = pendingRequests.get(message.id);
+    if (pending) {
+        clearTimeout(pending.timer);
+        pendingRequests.delete(message.id);
+        pending.resolve(message);
+    }
+}
+
 // MARK: - WebSocket Connection
 
 async function connect() {
@@ -94,6 +214,7 @@ async function connect() {
     const config = await getIPCConfig();
     if (!config) {
         state.isConnected = false;
+        state.connectionPath = 'offline';
         scheduleReconnect();
         return;
     }
@@ -102,6 +223,7 @@ async function connect() {
         ws = new WebSocket(`ws://127.0.0.1:${config.port}`);
     } catch {
         state.isConnected = false;
+        state.connectionPath = 'offline';
         scheduleReconnect();
         return;
     }
@@ -115,13 +237,20 @@ async function connect() {
         try {
             const message: IPCMessage = JSON.parse(event.data as string);
             handleMessage(message);
-        } catch {
-            // Ignore malformed messages
+        } catch (err) {
+            console.warn('[DemoSafe BG] Failed to parse WS message:', err);
         }
     };
 
     ws.onclose = () => {
         state.isConnected = false;
+        state.connectionPath = 'offline';
+        // Reject all pending WS requests so sendRequest can fall through to NMH
+        for (const [, pending] of pendingRequests) {
+            clearTimeout(pending.timer);
+            pending.reject(new Error('WebSocket closed'));
+        }
+        pendingRequests.clear();
         broadcastStateToPopup();
         scheduleReconnect();
     };
@@ -159,9 +288,15 @@ function sendRequestToCore(action: string, payload: Record<string, unknown>) {
 // MARK: - Message Handling (from Core)
 
 function handleMessage(message: IPCMessage) {
+    // Resolve any pending request-response
+    if (message.type === 'response') {
+        resolvePendingRequest(message);
+    }
+
     if (message.type === 'response' && message.action === 'handshake') {
         if (message.payload.status === 'success') {
             state.isConnected = true;
+            state.connectionPath = 'ws';
             state.isDemoMode = message.payload.isDemoMode as boolean;
             broadcastStateToPopup();
         }
@@ -312,12 +447,30 @@ function broadcastStateToPopup() {
 // Listen for messages from popup and content scripts
 chrome.runtime.onMessage.addListener((message, _sender, sendResponse) => {
     if (message.type === 'get_state') {
-        sendResponse(state);
+        // If WS is disconnected, try NMH to get fresh state
+        if (!state.isConnected) {
+            sendViaNMH('get_state', {}).then((nmhResponse) => {
+                if (nmhResponse && !nmhResponse.error) {
+                    const payload = (nmhResponse.payload ?? nmhResponse) as Record<string, unknown>;
+                    state.isDemoMode = (payload.isDemoMode as boolean) ?? state.isDemoMode;
+                    // NMH is one-shot relay, not a persistent connection — don't claim isConnected
+                    state.connectionPath = 'nmh';
+                }
+                sendResponse(state);
+            });
+        } else {
+            sendResponse(state);
+        }
         return true;
     }
 
     if (message.type === 'toggle_demo_mode') {
-        sendRequestToCore('toggle_demo_mode', {});
+        sendRequest('toggle_demo_mode', {}).then((result) => {
+            if (result) {
+                state.isDemoMode = (result.isDemoMode as boolean) ?? state.isDemoMode;
+                broadcastStateToPopup();
+            }
+        });
         sendResponse({ ok: true });
         return true;
     }
@@ -326,21 +479,20 @@ chrome.runtime.onMessage.addListener((message, _sender, sendResponse) => {
         const newState = !state.isCaptureMode;
         if (newState) state.capturedCount = 0;
         updateCaptureState(newState);
-        if (state.isConnected) {
-            sendRequestToCore('toggle_capture_mode', { isActive: newState });
-        }
+        sendRequest('toggle_capture_mode', { isActive: newState });
         sendResponse({ ok: true });
         return true;
     }
 
     if (message.type === 'submit_captured_key') {
         console.log('[DemoSafe BG] submit_captured_key received:', message.payload?.suggestedService, 'connected:', state.isConnected, 'rawValue length:', message.payload?.rawValue?.length);
-        if (state.isConnected) {
-            sendRequestToCore('submit_captured_key', message.payload);
-            console.log('[DemoSafe BG] forwarded to Core');
-        } else {
-            console.log('[DemoSafe BG] NOT connected, cannot forward');
-        }
+        sendRequest('submit_captured_key', message.payload).then((result) => {
+            if (result) {
+                console.log('[DemoSafe BG] submit_captured_key success via', state.connectionPath);
+            } else {
+                console.log('[DemoSafe BG] submit_captured_key queued for retry');
+            }
+        });
         state.capturedCount++;
         broadcastStateToPopup();
         sendResponse({ ok: true });
@@ -368,6 +520,20 @@ chrome.runtime.onMessage.addListener((message, _sender, sendResponse) => {
     return false;
 });
 
+// DEBUG: uncomment to expose debug functions on SW DevTools console
+// Object.assign(self, {
+//     debugState: () => { console.log(JSON.stringify(state, null, 2)); return state; },
+//     debugDisconnectWS: () => {
+//         if (ws) { ws.onclose = null; ws.close(); ws = null; }
+//         if (reconnectTimer) { clearTimeout(reconnectTimer); reconnectTimer = null; }
+//         state.isConnected = false;
+//         state.connectionPath = 'offline';
+//         broadcastStateToPopup();
+//         console.log('[DEBUG] WS disconnected, reconnect disabled');
+//     },
+//     debugReconnectWS: () => { reconnectDelay = 1000; connect(); },
+// });
+
 // MARK: - Reconnection
 
 function scheduleReconnect() {
diff --git a/packages/chrome-extension/src/popup/popup.html b/packages/chrome-extension/src/popup/popup.html
index 83e3f04..317234f 100644
--- a/packages/chrome-extension/src/popup/popup.html
+++ b/packages/chrome-extension/src/popup/popup.html
@@ -49,6 +49,7 @@
       vertical-align: middle;
     }
     .dot.connected { background: #22c55e; }
+    .dot.nmh { background: #3b82f6; }
     .dot.offline { background: #ef4444; }
     .dot.capture { background: #f59e0b; }
     .actions {
diff --git a/packages/chrome-extension/src/popup/popup.ts b/packages/chrome-extension/src/popup/popup.ts
index d821f76..9c11bdc 100644
--- a/packages/chrome-extension/src/popup/popup.ts
+++ b/packages/chrome-extension/src/popup/popup.ts
@@ -10,8 +10,15 @@ interface DemoSafeState {
     isCaptureMode: boolean;
     captureTimeoutEnd: number | null;
     capturedCount: number;
+    connectionPath: 'ws' | 'nmh' | 'offline';
 }
 
+const CONNECTION_LABELS: Record<DemoSafeState['connectionPath'], string> = {
+    ws: 'Connected (WebSocket)',
+    nmh: 'Connected (NMH)',
+    offline: 'Offline',
+};
+
 let countdownInterval: ReturnType<typeof setInterval> | null = null;
 
 function updateUI(state: DemoSafeState) {
@@ -28,13 +35,18 @@ function updateUI(state: DemoSafeState) {
     const captureDot = document.getElementById('captureDot')!;
     const captureBtn = document.getElementById('toggleCapture')!;
 
-    // Connection
-    if (state.isConnected) {
+    // Connection — show path info (NMH is one-shot relay, shown as reachable but not persistent)
+    const path = state.connectionPath ?? (state.isConnected ? 'ws' : 'offline');
+    const isReachable = state.isConnected || path === 'nmh';
+    if (path === 'nmh') {
+        connectionDot.className = 'dot nmh';
+        connectionText.textContent = CONNECTION_LABELS.nmh;
+    } else if (state.isConnected) {
         connectionDot.className = 'dot connected';
-        connectionText.textContent = 'Connected';
+        connectionText.textContent = CONNECTION_LABELS.ws;
     } else {
         connectionDot.className = 'dot offline';
-        connectionText.textContent = 'Offline';
+        connectionText.textContent = CONNECTION_LABELS.offline;
     }
 
     // Mode
@@ -56,8 +68,8 @@ function updateUI(state: DemoSafeState) {
     // Patterns
     patternCount.textContent = String(state.patternCount);
 
-    // Capture mode — only show when connected
-    if (state.isConnected) {
+    // Capture mode — show when reachable (WS or NMH)
+    if (isReachable) {
         captureRow.style.display = '';
         captureBtn.style.display = '';
 
diff --git a/packages/swift-core/DemoSafe/App/AppState.swift b/packages/swift-core/DemoSafe/App/AppState.swift
index 887124d..2dd2c55 100644
--- a/packages/swift-core/DemoSafe/App/AppState.swift
+++ b/packages/swift-core/DemoSafe/App/AppState.swift
@@ -64,6 +64,9 @@ final class AppState: ObservableObject {
         // Wire hotkey callbacks
         wireHotkeyCallbacks()
 
+        // Install NMH (Chrome Native Messaging Host) if bundled
+        NMHInstaller.installIfNeeded(extensionId: "cockodmaleagghfbaookajpcpnbdjocj")
+
         // Start IPC Server
         do {
             let port = try ipcServer.start()
diff --git a/packages/swift-core/DemoSafe/Services/IPC/IPCServer.swift b/packages/swift-core/DemoSafe/Services/IPC/IPCServer.swift
index 61a7838..251d696 100644
--- a/packages/swift-core/DemoSafe/Services/IPC/IPCServer.swift
+++ b/packages/swift-core/DemoSafe/Services/IPC/IPCServer.swift
@@ -27,6 +27,7 @@ final class IPCServer {
         case vscode
         case chrome
         case accessibility
+        case nmh
     }
 
     struct ClientInfo: Identifiable {
@@ -122,7 +123,8 @@ final class IPCServer {
         if let type = clientType {
             targets = connections.values.filter { $0.clientType == type && $0.isAuthenticated }
         } else {
-            targets = connections.values.filter { $0.isAuthenticated }
+            // Skip .nmh clients — they are short-lived relay connections, not event subscribers
+            targets = connections.values.filter { $0.isAuthenticated && $0.clientType != .nmh }
         }
 
         guard let data = encodeEvent(event) else { return }
diff --git a/packages/swift-core/DemoSafe/Services/NMHInstaller.swift b/packages/swift-core/DemoSafe/Services/NMHInstaller.swift
new file mode 100644
index 0000000..346580e
--- /dev/null
+++ b/packages/swift-core/DemoSafe/Services/NMHInstaller.swift
@@ -0,0 +1,96 @@
+import Foundation
+import os
+
+private let logger = Logger(subsystem: "com.demosafe", category: "NMHInstaller")
+
+/// Installs the Native Messaging Host binary and Chrome manifest on app launch.
+/// Copies from app bundle Resources → ~/.demosafe/bin/ and writes the Chrome NMH manifest.
+enum NMHInstaller {
+
+    private static let binaryName = "demosafe-nmh"
+    private static let hostName = "com.demosafe.nmh"
+    private static let installDir = FileManager.default.homeDirectoryForCurrentUser
+        .appendingPathComponent(".demosafe/bin")
+    private static let chromeNMHDir = FileManager.default.homeDirectoryForCurrentUser
+        .appendingPathComponent("Library/Application Support/Google/Chrome/NativeMessagingHosts")
+
+    /// Check and install NMH if needed. Call from AppState.init().
+    static func installIfNeeded(extensionId: String) {
+        let binaryDest = installDir.appendingPathComponent(binaryName)
+        let manifestDest = chromeNMHDir.appendingPathComponent("\(hostName).json")
+
+        let fm = FileManager.default
+
+        // Check if binary exists in app bundle Resources
+        guard let bundledBinary = Bundle.main.url(forResource: binaryName, withExtension: nil) else {
+            logger.warning("NMH binary not found in app bundle Resources, skipping auto-install")
+            return
+        }
+
+        // Check if binary needs updating (missing or different size)
+        let needsBinaryUpdate: Bool
+        if fm.fileExists(atPath: binaryDest.path) {
+            let bundledSize = (try? fm.attributesOfItem(atPath: bundledBinary.path)[.size] as? Int) ?? 0
+            let installedSize = (try? fm.attributesOfItem(atPath: binaryDest.path)[.size] as? Int) ?? -1
+            needsBinaryUpdate = bundledSize != installedSize
+        } else {
+            needsBinaryUpdate = true
+        }
+
+        // Install binary if needed
+        if needsBinaryUpdate {
+            do {
+                try fm.createDirectory(at: installDir, withIntermediateDirectories: true)
+                if fm.fileExists(atPath: binaryDest.path) {
+                    try fm.removeItem(at: binaryDest)
+                }
+                try fm.copyItem(at: bundledBinary, to: binaryDest)
+                // chmod 755
+                try fm.setAttributes([.posixPermissions: 0o755], ofItemAtPath: binaryDest.path)
+                logger.info("NMH binary installed: \(binaryDest.path)")
+            } catch {
+                logger.error("Failed to install NMH binary: \(error)")
+                return
+            }
+        }
+
+        // Check if manifest needs updating
+        let needsManifestUpdate: Bool
+        if fm.fileExists(atPath: manifestDest.path),
+           let existingData = try? Data(contentsOf: manifestDest),
+           let existing = try? JSONSerialization.jsonObject(with: existingData) as? [String: Any],
+           let origins = existing["allowed_origins"] as? [String],
+           origins.contains("chrome-extension://\(extensionId)/"),
+           existing["path"] as? String == binaryDest.path {
+            needsManifestUpdate = false
+        } else {
+            needsManifestUpdate = true
+        }
+
+        // Write manifest if needed
+        if needsManifestUpdate {
+            do {
+                try fm.createDirectory(at: chromeNMHDir, withIntermediateDirectories: true)
+
+                let manifest: [String: Any] = [
+                    "name": hostName,
+                    "description": "DemoSafe Native Messaging Host — relay for Chrome Extension",
+                    "path": binaryDest.path,
+                    "type": "stdio",
+                    "allowed_origins": ["chrome-extension://\(extensionId)/"],
+                ]
+
+                let data = try JSONSerialization.data(withJSONObject: manifest, options: .prettyPrinted)
+                try data.write(to: manifestDest)
+                logger.info("NMH manifest installed: \(manifestDest.path)")
+            } catch {
+                logger.error("Failed to install NMH manifest: \(error)")
+                return
+            }
+        }
+
+        if !needsBinaryUpdate && !needsManifestUpdate {
+            logger.info("NMH already installed and up to date")
+        }
+    }
+}
diff --git a/shared/ipc-protocol/src/index.ts b/shared/ipc-protocol/src/index.ts
index 3f00a0a..cd40ae2 100644
--- a/shared/ipc-protocol/src/index.ts
+++ b/shared/ipc-protocol/src/index.ts
@@ -27,7 +27,7 @@ export type RequestAction =
     | 'resolve_mask';
 
 export interface HandshakePayload {
-    clientType: 'vscode' | 'chrome' | 'accessibility';
+    clientType: 'vscode' | 'chrome' | 'accessibility' | 'nmh';
     token: string;
     version: string;
 }