diff --git a/README.md b/README.md
index 9d4c335..c9868e1 100644
--- a/README.md
+++ b/README.md
@@ -28,11 +28,13 @@
 - 將使用者選擇映射到對話狀態
 - 保留使用者直接打字而不按按鈕的能力
 
-### Phase 1 目標
+### 專案目標平台
 
-Phase 1 先做 **Telegram**。
+這個專案目前 **固定只做 Telegram**。
 
-原因很簡單：Telegram 已經支援 inline keyboard 和 callback payload，是最適合先驗證這個互動模型的平台。
+不考慮 Discord、Slack 或其他 channel。
+
+所有設計、狀態結構、callback 流程、驗證方式，都以 Telegram 為唯一目標平台。
 
 ### 預期行為
 
@@ -158,11 +160,13 @@ This repository is only for the reply-end control feature, including:
 - mapping user choice into conversation state
 - preserving the ability to type freely instead of pressing a button
 
-### Phase 1 target
+### Target platform
 
-Phase 1 targets **Telegram** first.
+This project is **Telegram-only** for now.
 
-Telegram is the easiest first platform because it already supports inline keyboards and callback payloads, which makes it a good place to validate the interaction model.
+Discord, Slack, and other channels are explicitly out of scope.
+
+All design, state handling, callback flow, and testing will assume Telegram as the only target platform.
 
 ### Expected behavior
 
@@ -250,4 +254,5 @@ Phase 1 will likely need at least these layers:
 
 - repository created
 - README expanded into a formal bilingual project description
+- scope narrowed to Telegram-only
 - technical design and implementation have not started yet
diff --git a/telegram-v1-design.md b/telegram-v1-design.md
new file mode 100644
index 0000000..819f878
--- /dev/null
+++ b/telegram-v1-design.md
@@ -0,0 +1,144 @@
+# reply-end-controls - Telegram V1 Design
+
+## Scope
+
+This project is Telegram-only.
+
+No Discord, Slack, or cross-channel abstraction is part of V1.
+
+## Product behavior
+
+At the end of every assistant reply sent to Telegram, attach two inline buttons:
+
+- `A. 繼續`
+- `B. 就這樣吧，不需要額外處理`
+
+Button selection must be captured and stored in conversation/session state.
+
+If the user types a new message instead of pressing a button, the typed message takes priority.
+
+## V1 rules
+
+### Rule 1
+
+Every assistant reply gets reply-end buttons.
+
+### Rule 2
+
+If the user taps `繼續`:
+
+- store `lastChoice=continue`
+- allow follow-up behavior on later turns
+
+### Rule 3
+
+If the user taps `就這樣吧，不需要額外處理`:
+
+- store `lastChoice=stop`
+- suppress unnecessary continuation behavior on later turns
+
+### Rule 4
+
+If the user sends a new typed message, that input overrides the button state.
+
+### Rule 5
+
+After a button is clicked, the original message buttons should be updated so the selection is visually resolved and repeated clicks are reduced.
+
+## State model
+
+Store this in Telegram conversation/session state:
+
+```json
+{
+  "replyEndControls": {
+    "lastChoice": "continue | stop",
+    "lastChoiceAt": "ISO timestamp",
+    "sourceMessageId": "telegram message id",
+    "sourceCallbackId": "telegram callback query id",
+    "active": true
+  }
+}
+```
+
+## Telegram callback payloads
+
+Suggested callback data format:
+
+- `rec:continue`
+- `rec:stop`
+
+If message-scoped state is needed later, extend to:
+
+- `rec:continue:<messageId>`
+- `rec:stop:<messageId>`
+
+## Technical flow
+
+### Outbound reply flow
+
+1. Assistant reply text is produced.
+2. Telegram reply payload is decorated with inline keyboard.
+3. Message is sent to Telegram.
+
+### Callback flow
+
+1. User clicks button.
+2. Telegram sends callback query.
+3. Callback handler parses `continue` or `stop`.
+4. State is persisted.
+5. Original message buttons are updated to reflect the chosen option.
+
+### Next-turn behavior
+
+1. A later turn begins.
+2. Runtime checks `replyEndControls.lastChoice`.
+3. If `stop`, do not proactively extend or continue the previous thread unless the user explicitly asks.
+4. If `continue`, normal continuation behavior is allowed.
+
+## Suggested implementation modules
+
+### 1. Reply decorator
+
+Responsibility:
+
+- append Telegram inline keyboard to every assistant reply
+
+### 2. Callback handler
+
+Responsibility:
+
+- receive Telegram callback queries
+- parse reply-end action
+- update state
+
+### 3. State storage helper
+
+Responsibility:
+
+- persist and retrieve the latest reply-end selection for the current conversation/session
+
+### 4. Behavior policy hook
+
+Responsibility:
+
+- inspect `lastChoice`
+- suppress proactive continuation when `stop` is active
+
+## Acceptance criteria for V1
+
+V1 is complete when all of the following are true:
+
+1. A normal Telegram assistant reply shows both buttons.
+2. Clicking `繼續` is received and stored.
+3. Clicking `就這樣吧，不需要額外處理` is received and stored.
+4. After click, the original message is updated to show the choice state.
+5. A new typed user message still works without pressing any button.
+6. A later turn can read the stored choice and alter continuation behavior.
+
+## Non-goals for V1
+
+- multi-channel abstraction
+- governance integration
+- analytics dashboard
+- complex branching controls beyond `continue` and `stop`