diff --git a/README.md b/README.md
index e174f8d3..866c41f6 100644
--- a/README.md
+++ b/README.md
@@ -227,12 +227,35 @@ deepseek resume --last                           # resume the most recent sessio
 deepseek resume <SESSION_ID>                     # resume a specific session by UUID
 deepseek fork <SESSION_ID>                       # fork a session at a chosen turn
 deepseek serve --http                            # HTTP/SSE API server
+deepseek serve --acp                             # ACP stdio adapter for Zed/custom agents
 deepseek pr <N>                                  # fetch PR and pre-seed review prompt
 deepseek mcp list                                # list configured MCP servers
 deepseek mcp validate                            # validate MCP config/connectivity
 deepseek mcp-server                              # run dispatcher MCP stdio server
 ```
 
+### Zed / ACP
+
+DeepSeek can run as a custom Agent Client Protocol server for editors that
+spawn local ACP agents over stdio. In Zed, add a custom agent server:
+
+```json
+{
+  "agent_servers": {
+    "DeepSeek": {
+      "type": "custom",
+      "command": "deepseek",
+      "args": ["serve", "--acp"],
+      "env": {}
+    }
+  }
+}
+```
+
+The first ACP slice supports new sessions and prompt responses through your
+existing DeepSeek config/API key. Tool-backed editing and checkpoint replay are
+not exposed through ACP yet.
+
 ### Keyboard Shortcuts
 
 | Key | Action |
diff --git a/crates/tui/src/acp_server.rs b/crates/tui/src/acp_server.rs
new file mode 100644
index 00000000..4cc4fdb3
--- /dev/null
+++ b/crates/tui/src/acp_server.rs
@@ -0,0 +1,461 @@
+//! Minimal Agent Client Protocol stdio adapter.
+//!
+//! This intentionally starts with the ACP baseline: initialize, new session,
+//! prompt, and cancel. It keeps stdout protocol-clean for editor clients and
+//! routes prompts through the same configured DeepSeek client as one-shot CLI
+//! mode.
+
+use std::collections::HashMap;
+use std::path::PathBuf;
+
+use anyhow::{Result, anyhow};
+use serde_json::{Value, json};
+use tokio::io::{AsyncBufReadExt, AsyncWrite, AsyncWriteExt, BufReader};
+
+use crate::client::DeepSeekClient;
+use crate::config::Config;
+use crate::llm_client::LlmClient;
+use crate::models::{ContentBlock, Message, MessageRequest, SystemPrompt};
+
+const ACP_PROTOCOL_VERSION: u64 = 1;
+
+pub async fn run_acp_server(config: Config, model: String, default_cwd: PathBuf) -> Result<()> {
+    let stdin = tokio::io::stdin();
+    let stdout = tokio::io::stdout();
+    let mut reader = BufReader::new(stdin).lines();
+    let mut writer = tokio::io::BufWriter::new(stdout);
+    let mut server = AcpServer::new(config, model, default_cwd);
+
+    while let Some(line) = reader.next_line().await? {
+        if line.trim().is_empty() {
+            continue;
+        }
+
+        let message: Value = match serde_json::from_str(&line) {
+            Ok(value) => value,
+            Err(err) => {
+                write_jsonrpc_error(&mut writer, None, -32700, format!("invalid json: {err}"))
+                    .await?;
+                continue;
+            }
+        };
+
+        if message.get("jsonrpc").and_then(Value::as_str) != Some("2.0") {
+            write_jsonrpc_error(
+                &mut writer,
+                message.get("id").cloned(),
+                -32600,
+                "jsonrpc version must be 2.0",
+            )
+            .await?;
+            continue;
+        }
+
+        let id = message.get("id").cloned();
+        let method = match message.get("method").and_then(Value::as_str) {
+            Some(method) => method,
+            None => {
+                write_jsonrpc_error(&mut writer, id, -32600, "missing method").await?;
+                continue;
+            }
+        };
+        let params = message.get("params").cloned().unwrap_or_else(|| json!({}));
+
+        match server.handle_request(method, params, &mut writer).await {
+            Ok(AcpDispatch::Response(result)) => {
+                if let Some(id) = id {
+                    write_jsonrpc_result(&mut writer, id, result).await?;
+                }
+            }
+            Ok(AcpDispatch::Shutdown) => {
+                if let Some(id) = id {
+                    write_jsonrpc_result(&mut writer, id, json!(null)).await?;
+                }
+                break;
+            }
+            Err(err) => {
+                write_jsonrpc_error(&mut writer, id, err.code, err.message).await?;
+            }
+        }
+    }
+
+    Ok(())
+}
+
+struct AcpServer {
+    config: Config,
+    model: String,
+    default_cwd: PathBuf,
+    sessions: HashMap<String, AcpSession>,
+}
+
+struct AcpSession {
+    cwd: PathBuf,
+}
+
+enum AcpDispatch {
+    Response(Value),
+    Shutdown,
+}
+
+struct AcpError {
+    code: i32,
+    message: String,
+}
+
+impl AcpServer {
+    fn new(config: Config, model: String, default_cwd: PathBuf) -> Self {
+        Self {
+            config,
+            model,
+            default_cwd,
+            sessions: HashMap::new(),
+        }
+    }
+
+    async fn handle_request<W>(
+        &mut self,
+        method: &str,
+        params: Value,
+        writer: &mut W,
+    ) -> std::result::Result<AcpDispatch, AcpError>
+    where
+        W: AsyncWrite + Unpin,
+    {
+        match method {
+            "initialize" => Ok(AcpDispatch::Response(initialize_result(
+                params.get("protocolVersion").and_then(Value::as_u64),
+            ))),
+            "session/new" => Ok(AcpDispatch::Response(self.new_session(params)?)),
+            "session/prompt" => {
+                self.prompt(params, writer).await?;
+                Ok(AcpDispatch::Response(json!({ "stopReason": "end_turn" })))
+            }
+            "session/cancel" => Ok(AcpDispatch::Response(json!(null))),
+            "shutdown" => Ok(AcpDispatch::Shutdown),
+            _ => Err(AcpError::method_not_found(method)),
+        }
+    }
+
+    fn new_session(&mut self, params: Value) -> std::result::Result<Value, AcpError> {
+        let cwd = params
+            .get("cwd")
+            .and_then(Value::as_str)
+            .map(PathBuf::from)
+            .unwrap_or_else(|| self.default_cwd.clone());
+        let session_id = format!("deepseek-{}", uuid::Uuid::new_v4());
+        self.sessions.insert(session_id.clone(), AcpSession { cwd });
+        Ok(json!({ "sessionId": session_id }))
+    }
+
+    async fn prompt<W>(&self, params: Value, writer: &mut W) -> std::result::Result<(), AcpError>
+    where
+        W: AsyncWrite + Unpin,
+    {
+        let session_id = params
+            .get("sessionId")
+            .and_then(Value::as_str)
+            .ok_or_else(|| AcpError::invalid_params("sessionId is required"))?;
+        let session = self
+            .sessions
+            .get(session_id)
+            .ok_or_else(|| AcpError::invalid_params("unknown sessionId"))?;
+        let prompt = extract_prompt_text(params.get("prompt"))
+            .filter(|text| !text.trim().is_empty())
+            .ok_or_else(|| AcpError::invalid_params("prompt must include text content"))?;
+
+        let output = self
+            .run_prompt(&prompt, &session.cwd)
+            .await
+            .map_err(|err| AcpError::internal(err.to_string()))?;
+
+        if !output.is_empty() {
+            write_session_update(writer, session_id, output)
+                .await
+                .map_err(|err| AcpError::internal(err.to_string()))?;
+        }
+
+        Ok(())
+    }
+
+    async fn run_prompt(&self, prompt: &str, cwd: &PathBuf) -> Result<String> {
+        let _cwd_guard = ScopedCurrentDir::new(cwd)?;
+        let client = DeepSeekClient::new(&self.config)?;
+        let route = crate::resolve_cli_auto_route(&self.config, &self.model, prompt).await;
+        let reasoning_effort = route
+            .reasoning_effort
+            .map(|effort| effort.as_setting().to_string());
+
+        let request = MessageRequest {
+            model: route.model,
+            messages: vec![Message {
+                role: "user".to_string(),
+                content: vec![ContentBlock::Text {
+                    text: prompt.to_string(),
+                    cache_control: None,
+                }],
+            }],
+            max_tokens: 4096,
+            system: Some(SystemPrompt::Text(
+                "You are a coding assistant inside an ACP-compatible editor. Give concise, actionable responses.".to_string(),
+            )),
+            tools: None,
+            tool_choice: None,
+            metadata: None,
+            thinking: None,
+            reasoning_effort,
+            stream: Some(false),
+            temperature: Some(0.2),
+            top_p: Some(0.9),
+        };
+
+        let response = client.create_message(request).await?;
+        let mut output = String::new();
+        for block in response.content {
+            if let ContentBlock::Text { text, .. } = block {
+                output.push_str(&text);
+            }
+        }
+        Ok(output)
+    }
+}
+
+struct ScopedCurrentDir {
+    prior: PathBuf,
+}
+
+impl ScopedCurrentDir {
+    fn new(cwd: &PathBuf) -> Result<Self> {
+        let prior = std::env::current_dir()?;
+        if cwd.as_os_str().is_empty() {
+            return Ok(Self { prior });
+        }
+        std::env::set_current_dir(cwd)
+            .map_err(|err| anyhow!("failed to enter ACP session cwd {}: {err}", cwd.display()))?;
+        Ok(Self { prior })
+    }
+}
+
+impl Drop for ScopedCurrentDir {
+    fn drop(&mut self) {
+        let _ = std::env::set_current_dir(&self.prior);
+    }
+}
+
+impl AcpError {
+    fn invalid_params(message: impl Into<String>) -> Self {
+        Self {
+            code: -32602,
+            message: message.into(),
+        }
+    }
+
+    fn method_not_found(method: &str) -> Self {
+        Self {
+            code: -32601,
+            message: format!("method not found: {method}"),
+        }
+    }
+
+    fn internal(message: impl Into<String>) -> Self {
+        Self {
+            code: -32603,
+            message: message.into(),
+        }
+    }
+}
+
+fn initialize_result(client_protocol_version: Option<u64>) -> Value {
+    json!({
+        "protocolVersion": client_protocol_version
+            .map(|version| version.min(ACP_PROTOCOL_VERSION))
+            .unwrap_or(ACP_PROTOCOL_VERSION),
+        "agentCapabilities": {
+            "loadSession": false,
+            "promptCapabilities": {
+                "image": false,
+                "audio": false,
+                "embeddedContext": true
+            },
+            "mcpCapabilities": {
+                "http": false,
+                "sse": false
+            },
+            "sessionCapabilities": {}
+        },
+        "agentInfo": {
+            "name": "deepseek",
+            "title": "DeepSeek TUI",
+            "version": env!("CARGO_PKG_VERSION")
+        },
+        "authMethods": []
+    })
+}
+
+fn extract_prompt_text(prompt: Option<&Value>) -> Option<String> {
+    match prompt? {
+        Value::String(text) => Some(text.clone()),
+        Value::Array(blocks) => {
+            let parts = blocks
+                .iter()
+                .filter_map(content_block_text)
+                .collect::<Vec<_>>();
+            (!parts.is_empty()).then(|| parts.join("\n\n"))
+        }
+        _ => None,
+    }
+}
+
+fn content_block_text(block: &Value) -> Option<String> {
+    match block.get("type").and_then(Value::as_str)? {
+        "text" => block
+            .get("text")
+            .and_then(Value::as_str)
+            .map(str::to_string),
+        "resource" => resource_text(block),
+        "resource_link" | "resourceLink" => resource_link_text(block),
+        _ => None,
+    }
+}
+
+fn resource_text(block: &Value) -> Option<String> {
+    let resource = block.get("resource").unwrap_or(block);
+    if let Some(text) = resource.get("text").and_then(Value::as_str) {
+        return Some(text.to_string());
+    }
+    resource_link_text(resource)
+}
+
+fn resource_link_text(block: &Value) -> Option<String> {
+    let uri = block
+        .get("uri")
+        .or_else(|| block.pointer("/resource/uri"))
+        .and_then(Value::as_str)?;
+    Some(format!("@{uri}"))
+}
+
+async fn write_session_update<W>(writer: &mut W, session_id: &str, text: String) -> Result<()>
+where
+    W: AsyncWrite + Unpin,
+{
+    let notification = json!({
+        "jsonrpc": "2.0",
+        "method": "session/update",
+        "params": {
+            "sessionId": session_id,
+            "update": {
+                "sessionUpdate": "agent_message_chunk",
+                "content": {
+                    "type": "text",
+                    "text": text
+                }
+            }
+        }
+    });
+    write_json_line(writer, notification).await
+}
+
+async fn write_jsonrpc_result<W>(writer: &mut W, id: Value, result: Value) -> Result<()>
+where
+    W: AsyncWrite + Unpin,
+{
+    write_json_line(
+        writer,
+        json!({
+            "jsonrpc": "2.0",
+            "id": id,
+            "result": result
+        }),
+    )
+    .await
+}
+
+async fn write_jsonrpc_error<W>(
+    writer: &mut W,
+    id: Option<Value>,
+    code: i32,
+    message: impl Into<String>,
+) -> Result<()>
+where
+    W: AsyncWrite + Unpin,
+{
+    write_json_line(
+        writer,
+        json!({
+            "jsonrpc": "2.0",
+            "id": id,
+            "error": {
+                "code": code,
+                "message": message.into()
+            }
+        }),
+    )
+    .await
+}
+
+async fn write_json_line<W>(writer: &mut W, value: Value) -> Result<()>
+where
+    W: AsyncWrite + Unpin,
+{
+    writer.write_all(value.to_string().as_bytes()).await?;
+    writer.write_all(b"\n").await?;
+    writer.flush().await?;
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn initialize_advertises_baseline_acp_agent() {
+        let result = initialize_result(Some(1));
+
+        assert_eq!(result["protocolVersion"], 1);
+        assert_eq!(result["agentInfo"]["name"], "deepseek");
+        assert_eq!(result["agentCapabilities"]["loadSession"], false);
+        assert_eq!(
+            result["agentCapabilities"]["promptCapabilities"]["embeddedContext"],
+            true
+        );
+        assert_eq!(result["authMethods"], json!([]));
+    }
+
+    #[test]
+    fn extract_prompt_text_accepts_text_and_resource_blocks() {
+        let prompt = json!([
+            { "type": "text", "text": "Review this file" },
+            {
+                "type": "resource",
+                "resource": {
+                    "uri": "file:///tmp/app.rs",
+                    "mimeType": "text/rust",
+                    "text": "fn main() {}"
+                }
+            },
+            { "type": "resource_link", "uri": "file:///tmp/lib.rs" }
+        ]);
+
+        let text = extract_prompt_text(Some(&prompt)).expect("prompt text");
+
+        assert!(text.contains("Review this file"));
+        assert!(text.contains("fn main() {}"));
+        assert!(text.contains("@file:///tmp/lib.rs"));
+    }
+
+    #[tokio::test]
+    async fn session_update_is_protocol_clean_single_line_json() {
+        let mut out = Vec::new();
+
+        write_session_update(&mut out, "sess_1", "hello\nworld".to_string())
+            .await
+            .expect("write update");
+
+        let line = String::from_utf8(out).expect("utf8");
+        assert_eq!(line.lines().count(), 1);
+        let value: Value = serde_json::from_str(line.trim()).expect("json");
+        assert_eq!(value["method"], "session/update");
+        assert_eq!(value["params"]["sessionId"], "sess_1");
+        assert_eq!(value["params"]["update"]["content"]["text"], "hello\nworld");
+    }
+}
diff --git a/crates/tui/src/main.rs b/crates/tui/src/main.rs
index 33270850..bf633c15 100644
--- a/crates/tui/src/main.rs
+++ b/crates/tui/src/main.rs
@@ -12,6 +12,7 @@ use dotenvy::dotenv;
 use tempfile::NamedTempFile;
 use wait_timeout::ChildExt;
 
+mod acp_server;
 mod audit;
 mod auto_reasoning;
 mod automation_manager;
@@ -387,6 +388,9 @@ struct ServeArgs {
     /// Start runtime HTTP/SSE API server
     #[arg(long)]
     http: bool,
+    /// Start ACP server over stdio for editor clients such as Zed
+    #[arg(long)]
+    acp: bool,
     /// Bind host for HTTP server (default localhost)
     #[arg(long, default_value = "127.0.0.1")]
     host: String,
@@ -689,8 +693,12 @@ async fn main() -> Result<()> {
                 let workspace = cli.workspace.clone().unwrap_or_else(|| {
                     std::env::current_dir().unwrap_or_else(|_| PathBuf::from("."))
                 });
-                if args.mcp && args.http {
-                    bail!("Choose exactly one server mode: --mcp or --http");
+                let selected_modes = [args.mcp, args.http, args.acp]
+                    .into_iter()
+                    .filter(|selected| *selected)
+                    .count();
+                if selected_modes != 1 {
+                    bail!("Choose exactly one server mode: --mcp, --http, or --acp");
                 }
                 if args.mcp {
                     mcp_server::run_mcp_server(workspace)
@@ -708,8 +716,12 @@ async fn main() -> Result<()> {
                         },
                     )
                     .await
+                } else if args.acp {
+                    let config = load_config_from_cli(&cli)?;
+                    let model = config.default_model();
+                    acp_server::run_acp_server(config, model, workspace).await
                 } else {
-                    bail!("No server mode specified. Use --mcp or --http.")
+                    unreachable!("server mode count checked above")
                 }
             }
             Commands::Resume { session_id, last } => {
diff --git a/crates/tui/src/tui/osc8.rs b/crates/tui/src/tui/osc8.rs
index b6a83523..156733be 100644
--- a/crates/tui/src/tui/osc8.rs
+++ b/crates/tui/src/tui/osc8.rs
@@ -139,9 +139,7 @@ pub fn strip_ansi_into(s: &str, out: &mut String) {
 /// to `1` for continuation bytes / invalid leads so callers always make
 /// forward progress.
 fn utf8_seq_len(lead: u8) -> usize {
-    if lead < 0x80 {
-        1
-    } else if lead < 0xc0 {
+    if lead < 0xc0 {
         1
     } else if lead < 0xe0 {
         2
diff --git a/docs/MCP.md b/docs/MCP.md
index f0396adf..15a0d2c1 100644
--- a/docs/MCP.md
+++ b/docs/MCP.md
@@ -176,16 +176,18 @@ Tools from a self-hosted DeepSeek server follow the standard naming convention:
 
 For example, the `shell` tool becomes `mcp_deepseek_shell`.
 
-### MCP Server vs HTTP/SSE API
+### MCP Server vs HTTP/SSE API vs ACP
 
-| | `deepseek-tui serve --mcp` | `deepseek-tui serve --http` |
-|---|---|---|
-| **Protocol** | MCP stdio | HTTP/SSE JSON-RPC |
-| **Use case** | Tool server for MCP clients | Runtime API for apps |
-| **Config** | `~/.deepseek/mcp.json` entry | Direct URL connection |
-| **Lifecycle** | Spawned per client session | Long-running daemon |
+| | `deepseek-tui serve --mcp` | `deepseek-tui serve --http` | `deepseek-tui serve --acp` |
+|---|---|---|---|
+| **Protocol** | MCP stdio | HTTP/SSE JSON-RPC | ACP stdio |
+| **Use case** | Tool server for MCP clients | Runtime API for apps | Editor agent for Zed/custom ACP clients |
+| **Config** | `~/.deepseek/mcp.json` entry | Direct URL connection | Editor `agent_servers` custom command |
+| **Lifecycle** | Spawned per client session | Long-running daemon | Spawned per editor agent session |
 
-Use `mcp add-self` when you want DeepSeek tools available to other MCP clients. Use `serve --http` when building applications that consume the API directly.
+Use `mcp add-self` when you want DeepSeek tools available to other MCP clients.
+Use `serve --http` when building applications that consume the API directly.
+Use `serve --acp` when an editor wants to talk to DeepSeek as an ACP agent.
 
 ### Verification
 
diff --git a/docs/RUNTIME_API.md b/docs/RUNTIME_API.md
index a4a43859..eab38911 100644
--- a/docs/RUNTIME_API.md
+++ b/docs/RUNTIME_API.md
@@ -1,10 +1,11 @@
 # Runtime API & Integration Contract
 
 DeepSeek TUI exposes a local runtime API through `deepseek serve --http` and
-machine-readable health via `deepseek doctor --json`. This document is the
-stable integration contract for native macOS workbench applications (and other
-local supervisors) that embed the DeepSeek engine without screen-scraping
-terminal output.
+machine-readable health via `deepseek doctor --json`. It also exposes
+`deepseek serve --acp` for editor clients that speak the Agent Client Protocol
+over stdio. This document is the stable integration contract for native macOS
+workbench applications (and other local supervisors) that embed the DeepSeek
+engine without screen-scraping terminal output.
 
 ## Architecture
 
@@ -13,6 +14,7 @@ macOS workbench (or any local supervisor)
         │
         ├─ deepseek doctor --json   → machine-readable health & capability
         ├─ deepseek serve --http    → HTTP/SSE runtime API
+        ├─ deepseek serve --acp     → ACP stdio agent for editors such as Zed
         ├─ deepseek serve --mcp     → MCP stdio server
         └─ deepseek [args]          → interactive TUI session
 ```
@@ -20,6 +22,25 @@ macOS workbench (or any local supervisor)
 The engine runs as a local-only process. All APIs bind to `localhost` by
 default. No hosted relay, no provider-token custody, no secret leakage.
 
+## ACP stdio adapter: `deepseek serve --acp`
+
+`deepseek serve --acp` speaks JSON-RPC 2.0 over newline-delimited stdio for
+ACP-compatible editor clients. The initial adapter implements the ACP baseline:
+
+- `initialize`
+- `session/new`
+- `session/prompt`
+- `session/cancel`
+
+Prompt requests are routed through the configured DeepSeek client and current
+default model. Responses are emitted as `session/update` agent message chunks
+followed by a `session/prompt` response with `stopReason: "end_turn"`.
+
+The adapter is intentionally conservative: it does not yet expose shell tools,
+file-write tools, checkpoint replay, or session loading through ACP. Use
+`deepseek serve --http` for the full local runtime API and `deepseek serve --mcp`
+when another client needs DeepSeek's tools as MCP tools.
+
 ## Capability endpoint: `deepseek doctor --json`
 
 Returns a JSON object describing the current installation's readiness state.