feat: add CLI flags support to attach command

packages/opencode/src/cli/cmd/tui/attach.ts

@@ -1,5 +1,6 @@
 import { cmd } from "../cmd"
 import { tui } from "./app"
+import { iife } from "@/util/iife"
 
 export const AttachCommand = cmd({
   command: "attach <url>",
@@ -15,16 +16,48 @@ export const AttachCommand = cmd({
         type: "string",
         description: "directory to run in",
       })
+      .option("model", {
+        type: "string",
+        alias: ["m"],
+        describe: "model to use in the format of provider/model",
+      })
+      .option("continue", {
+        alias: ["c"],
+        describe: "continue the last session",
+        type: "boolean",
+      })
       .option("session", {
         alias: ["s"],
         type: "string",
         describe: "session id to continue",
+      })
+      .option("prompt", {
+        alias: ["p"],
+        type: "string",
+        describe: "prompt to use",
+      })
+      .option("agent", {
+        type: "string",
+        describe: "agent to use",
       }),
   handler: async (args) => {
     if (args.dir) process.chdir(args.dir)
+
+    const prompt = await iife(async () => {
+      const piped = !process.stdin.isTTY ? await Bun.stdin.text() : undefined
+      if (!args.prompt) return piped
+      return piped ? piped + "\n" + args.prompt : args.prompt
+    })
+
     await tui({
       url: args.url,
-      args: { sessionID: args.session },
+      args: {
+        continue: args.continue,
+        sessionID: args.session,
+        agent: args.agent,
+        model: args.model,
+        prompt,
+      },
     })
   },
 })

packages/web/src/content/docs/cli.mdx

@@ -79,6 +79,43 @@ opencode agent list
 
 ---
 
+### attach
+
+Attach to a running opencode server with a full terminal interface.
+
+```bash
+opencode attach <url>
+```
+
+This command connects to an existing `opencode serve` or `opencode spawn` instance and provides the full TUI experience, allowing you to interact with the server as if you started opencode directly.
+
+```bash
+# Start a headless server in one terminal
+opencode serve
+
+# In another terminal, attach with the TUI
+opencode attach http://localhost:4096
+```
+
+This is useful when you want to:
+
+- Connect to a long-running opencode server
+- Avoid MCP server cold boot times
+- Share a server instance across multiple sessions
+
+#### Flags
+
+| Flag         | Short | Description                                |
+| ------------ | ----- | ------------------------------------------ |
+| `--dir`      |       | Directory to run in                        |
+| `--model`    | `-m`  | Model to use in the form of provider/model |
+| `--continue` | `-c`  | Continue the last session                  |
+| `--session`  | `-s`  | Session ID to continue                     |
+| `--prompt`   | `-p`  | Prompt to use                              |
+| `--agent`    |       | Agent to use                               |
+
+---
+
 ### auth
 
 Command to manage credentials and login for providers.