Derive SSH srcBaseDir from username

When parsing SSH runtime strings, extract the username from user@host format
and use it to construct the srcBaseDir path. This ensures workspace creation
targets the correct user's home directory.

- 'ssh user@host' -> srcBaseDir: /home/user/cmux
- 'ssh hostname' -> srcBaseDir: /home/$USER/cmux (current user)

Resolves Codex review comment about hard-coded /home/cmux.

Author: ammar-agent

src/utils/chatCommands.test.ts

@@ -18,7 +18,7 @@ describe("parseRuntimeString", () => {
     expect(result).toEqual({
       type: "ssh",
       host: "user@host",
-      srcBaseDir: "/home/cmux",
+      srcBaseDir: "/home/user/cmux",
     });
   });
 
@@ -27,7 +27,7 @@ describe("parseRuntimeString", () => {
     expect(result).toEqual({
       type: "ssh",
       host: "User@Host.Example.Com",
-      srcBaseDir: "/home/cmux",
+      srcBaseDir: "/home/User/cmux",
     });
   });
 
@@ -36,7 +36,7 @@ describe("parseRuntimeString", () => {
     expect(result).toEqual({
       type: "ssh",
       host: "user@host",
-      srcBaseDir: "/home/cmux",
+      srcBaseDir: "/home/user/cmux",
     });
   });
 
@@ -47,19 +47,23 @@ describe("parseRuntimeString", () => {
 
   test("accepts SSH with hostname only (user will be inferred)", () => {
     const result = parseRuntimeString("ssh hostname", workspaceName);
+    // When no user is specified, uses current user (process.env.USER)
+    const expectedUser = process.env.USER || "user";
     expect(result).toEqual({
       type: "ssh",
       host: "hostname",
-      srcBaseDir: "/home/cmux",
+      srcBaseDir: `/home/${expectedUser}/cmux`,
     });
   });
 
   test("accepts SSH with hostname.domain only", () => {
     const result = parseRuntimeString("ssh dev.example.com", workspaceName);
+    // When no user is specified, uses current user (process.env.USER)
+    const expectedUser = process.env.USER || "user";
     expect(result).toEqual({
       type: "ssh",
       host: "dev.example.com",
-      srcBaseDir: "/home/cmux",
+      srcBaseDir: `/home/${expectedUser}/cmux`,
     });
   });
 

src/utils/chatCommands.ts

@@ -51,12 +51,16 @@ export function parseRuntimeString(
       throw new Error("SSH runtime requires host (e.g., 'ssh hostname' or 'ssh user@host')");
     }
 
+    // Extract username from user@host format, or default to current user
+    const atIndex = hostPart.indexOf("@");
+    const user = atIndex > 0 ? hostPart.substring(0, atIndex) : process.env.USER || "user";
+
     // Accept both "hostname" and "user@hostname" formats
     // SSH will use current user or ~/.ssh/config if user not specified
     return {
       type: RUNTIME_MODE.SSH,
       host: hostPart,
-      srcBaseDir: "/home/cmux", // Default remote base directory (NOT including workspace name)
+      srcBaseDir: `/home/${user}/cmux`, // Default remote base directory (NOT including workspace name)
     };
   }