fix: buildNpmScriptCommand always uses cmd.exe on Windows

__tests__/scripts/dev-safe.test.ts

@@ -655,24 +655,45 @@ describe("getOrCreatePersistedSessionApiKey", () => {
 });
 
 describe("buildNpmScriptCommand", () => {
-  it("reuses npm's own CLI path when available", () => {
+  it("runs npm through cmd.exe on Windows even when npm_execpath is set", () => {
+    // npm_execpath points to a path with spaces like
+    // "C:\Program Files\nodejs\node_modules\npm\bin\npm-cli.js".
+    // spawnService uses shell:true on Windows, so passing that path as an
+    // argument causes cmd.exe to split on the space and fail with
+    // "'C:\Program' is not recognized as an internal or external command".
+    // The win32 branch must fire BEFORE the npm_execpath branch.
     const command = buildNpmScriptCommand(
       "dev:frontend",
       "win32",
       {
-        npm_execpath: "C:\\nodejs\\node_modules\\npm\\bin\\npm-cli.js",
-        npm_node_execpath: "C:\\nodejs\\node.exe",
+        ComSpec: "C:\\Windows\\System32\\cmd.exe",
+        npm_execpath:
+          "C:\\Program Files\\nodejs\\node_modules\\npm\\bin\\npm-cli.js",
+        npm_node_execpath: "C:\\Program Files\\nodejs\\node.exe",
       },
-      "C:\\fallback\\node.exe",
+      "C:\\Program Files\\nodejs\\node.exe",
     );
 
     expect(command).toEqual({
-      command: "C:\\nodejs\\node.exe",
-      args: [
-        "C:\\nodejs\\node_modules\\npm\\bin\\npm-cli.js",
-        "run",
-        "dev:frontend",
-      ],
+      command: "C:\\Windows\\System32\\cmd.exe",
+      args: ["/d", "/s", "/c", "npm", "run", "dev:frontend"],
+    });
+  });
+
+  it("reuses npm's own CLI path when available on POSIX", () => {
+    const command = buildNpmScriptCommand(
+      "dev:frontend",
+      "linux",
+      {
+        npm_execpath: "/usr/lib/node_modules/npm/bin/npm-cli.js",
+        npm_node_execpath: "/usr/bin/node",
+      },
+      "/fallback/node",
+    );
+
+    expect(command).toEqual({
+      command: "/usr/bin/node",
+      args: ["/usr/lib/node_modules/npm/bin/npm-cli.js", "run", "dev:frontend"],
     });
   });
 

scripts/dev-safe.mjs

@@ -606,6 +606,17 @@ function buildConfigFromPorts(ports, cwd, env) {
  */
 export function buildAgentServerEnv(config) {
   return {
+    // Force Python to use UTF-8 for all file I/O and streams.
+    //
+    // On Windows, Python defaults to the system ANSI codepage (e.g. cp1252).
+    // The agent-server writes conversation metadata JSON that can contain
+    // emoji (e.g. ✅ U+2705) which cp1252 cannot encode, producing:
+    //   UnicodeEncodeError: 'charmap' codec can't encode character '\u2705'
+    // Setting PYTHONUTF8=1 enables Python's UTF-8 mode (PEP 540) for the
+    // entire agent-server process, matching the behaviour on Linux/macOS
+    // where the locale is already UTF-8.
+    // This is a no-op on Linux/macOS where the locale is already UTF-8.
+    PYTHONUTF8: "1",
     TMUX_TMPDIR: config.tmuxTmpDir,
     OH_CONVERSATIONS_PATH: config.conversationsPath,
     OH_BASH_EVENTS_DIR: config.bashEventsDir,
@@ -753,17 +764,24 @@ export function buildNpmScriptCommand(
   env = process.env,
   nodeExecPath = process.execPath,
 ) {
-  if (env.npm_execpath) {
+  // On Windows, always use cmd.exe regardless of whether npm_execpath is set.
+  // npm_execpath points to a path like
+  // "C:\Program Files\nodejs\node_modules\npm\bin\npm-cli.js" which contains
+  // spaces. When that path is passed as an argument with shell:true in
+  // spawnService, cmd.exe splits on the space and tries to run "C:\Program"
+  // as a command, producing "not recognized as an internal or external command".
+  // Using "npm" via cmd.exe avoids the problem entirely.
+  if (platform === "win32") {
     return {
-      command: env.npm_node_execpath || nodeExecPath,
-      args: [env.npm_execpath, "run", scriptName],
+      command: env.ComSpec || "cmd.exe",
+      args: ["/d", "/s", "/c", "npm", "run", scriptName],
     };
   }
 
-  if (platform === "win32") {
+  if (env.npm_execpath) {
     return {
-      command: env.ComSpec || "cmd.exe",
-      args: ["/d", "/s", "/c", "npm", "run", scriptName],
+      command: env.npm_node_execpath || nodeExecPath,
+      args: [env.npm_execpath, "run", scriptName],
     };
   }
 

scripts/dev-with-automation.mjs

@@ -583,6 +583,9 @@ function startAutomationBackend(config) {
     {
       cwd: config.stateDir,
       env: {
+        // Force UTF-8 for all Python file I/O (same reason as agent-server;
+        // see buildAgentServerEnv in dev-safe.mjs).
+        PYTHONUTF8: "1",
         // The URL the automation backend itself uses to call the
         // agent-server's REST API (tarball upload + bash dispatch).
         //