diff --git a/docs/specs/vscode.md b/docs/specs/vscode.md
index a19b18a..1e42dce 100644
--- a/docs/specs/vscode.md
+++ b/docs/specs/vscode.md
@@ -55,6 +55,7 @@ Frontend Library (lib/src/)
 - **Save before kill.** Deactivate must save session state *before* killing PTYs. CWD and scrollback queries need live processes. See ordering in `extension.ts:deactivate()`.
 - **Alarm state is global.** A single `AlarmManager` instance in `message-router.ts` is shared across all routers and survives router disposal. PTY data feeds into it at module level, regardless of webview visibility.
 - **PTY ownership.** Each router tracks its PTYs in `ownedPtyIds`. A module-level `globalOwnedPtyIds` set prevents a reconnecting router from stealing PTYs owned by another webview.
+- **Shell login args are shell-specific.** The shared `pty-core.js` launches POSIX shells with `-l` only for shells that accept it. `csh`/`tcsh` must be spawned without `-l` so both the standalone app and VS Code extension can open a usable terminal for users whose login shell is C shell-derived.
 - **mergeAlarmStates on every save path.** Both the frontend periodic save (`onSaveState` callback) and the backend deactivate refresh (`refreshSavedSessionStateFromPtys`) must merge current alarm states. Missing this causes alarm state to revert on restore.
 - **Scrollback trailing newline.** Restored scrollback must end with `\n` to avoid zsh printing a `%` artifact at the top of the terminal.
 - **retainContextWhenHidden.** Set on `WebviewPanel` (editor tabs) but NOT on `WebviewView` (bottom panel). The view relies on reconnect/replay when it becomes visible again; the panel keeps its DOM alive.
diff --git a/standalone/sidecar/pty-core.js b/standalone/sidecar/pty-core.js
index 9e1e606..03d1065 100644
--- a/standalone/sidecar/pty-core.js
+++ b/standalone/sidecar/pty-core.js
@@ -23,6 +23,17 @@ function resolveDefaultShell(platform = process.platform, env = process.env) {
   return env.SHELL || '/bin/sh';
 }
 
+const LOGIN_ARG_UNSUPPORTED_SHELLS = new Set(['csh', 'tcsh']);
+
+function resolveLoginArg(shell, platform = process.platform) {
+  if (platform === 'win32') {
+    return [];
+  }
+
+  const shellName = path.posix.basename(shell || '').toLowerCase();
+  return LOGIN_ARG_UNSUPPORTED_SHELLS.has(shellName) ? [] : ['-l'];
+}
+
 function resolveDefaultCwd(platform = process.platform, env = process.env, osModule = os) {
   const homedir = safeResolve(() => osModule.homedir());
   const tmpdir = safeResolve(() => osModule.tmpdir());
@@ -51,6 +62,7 @@ function resolveSpawnConfig(options, runtime = {}) {
   const fsModule = runtime.fsModule || fs;
   const defaultCwd = resolveDefaultCwd(platform, env, osModule);
   const missingExplicitCwd = Boolean(cwd) && !directoryExists(cwd, fsModule);
+  const shell = resolveDefaultShell(platform, env);
 
   return {
     cols,
@@ -58,7 +70,8 @@ function resolveSpawnConfig(options, runtime = {}) {
     cwd: missingExplicitCwd ? defaultCwd : (cwd || defaultCwd),
     cwdWarning: missingExplicitCwd ? `unable to restore because directory ${cwd} was removed` : null,
     env: { ...env, TERM_PROGRAM: 'MouseTerm' },
-    shell: resolveDefaultShell(platform, env),
+    shell,
+    loginArg: resolveLoginArg(shell, platform),
   };
 }
 
@@ -160,7 +173,7 @@ module.exports.create = function create(send, ptyModule) {
 
     let p;
     try {
-      p = pty.spawn(config.shell, [], {
+      p = pty.spawn(config.shell, config.loginArg, {
         name: 'xterm-256color',
         cols: config.cols,
         rows: config.rows,
diff --git a/standalone/sidecar/pty-core.test.js b/standalone/sidecar/pty-core.test.js
index 6632155..a642c1e 100644
--- a/standalone/sidecar/pty-core.test.js
+++ b/standalone/sidecar/pty-core.test.js
@@ -19,6 +19,7 @@ test('resolveSpawnConfig uses POSIX shell and home defaults', () => {
   assert.equal(config.cols, 80);
   assert.equal(config.rows, 30);
   assert.equal(config.env.TERM_PROGRAM, 'MouseTerm');
+  assert.deepEqual(config.loginArg, ['-l']);
 });
 
 test('resolveSpawnConfig uses Windows shell and profile defaults', () => {
@@ -35,6 +36,7 @@ test('resolveSpawnConfig uses Windows shell and profile defaults', () => {
   assert.equal(config.cwd, 'C:\\Users\\tester');
   assert.equal(config.cwdWarning, null);
   assert.equal(config.env.TERM_PROGRAM, 'MouseTerm');
+  assert.deepEqual(config.loginArg, []);
 });
 
 test('resolveSpawnConfig preserves explicit cwd', () => {
@@ -58,6 +60,21 @@ test('resolveSpawnConfig preserves explicit cwd', () => {
   assert.equal(config.cwdWarning, null);
   assert.equal(config.cols, 120);
   assert.equal(config.rows, 40);
+  assert.deepEqual(config.loginArg, ['-l']);
+});
+
+test('resolveSpawnConfig skips -l for csh-style shells that reject it', () => {
+  const config = resolveSpawnConfig(undefined, {
+    platform: 'linux',
+    env: { SHELL: '/bin/tcsh' },
+    osModule: {
+      homedir: () => '/home/tester',
+      tmpdir: () => '/tmp/fallback',
+    },
+  });
+
+  assert.equal(config.shell, '/bin/tcsh');
+  assert.deepEqual(config.loginArg, []);
 });
 
 test('resolveSpawnConfig falls back to the default directory when explicit cwd is missing', () => {
@@ -83,6 +100,20 @@ test('resolveSpawnConfig falls back to the default directory when explicit cwd i
   assert.equal(config.rows, 40);
 });
 
+test('resolveSpawnConfig skips -l for csh', () => {
+  const config = resolveSpawnConfig(undefined, {
+    platform: 'darwin',
+    env: { SHELL: '/bin/csh' },
+    osModule: {
+      homedir: () => '/Users/tester',
+      tmpdir: () => '/tmp/fallback',
+    },
+  });
+
+  assert.equal(config.shell, '/bin/csh');
+  assert.deepEqual(config.loginArg, []);
+});
+
 test('create buffers scrollback for getScrollback requests', () => {
   const events = [];
   const listeners = {};
diff --git a/vscode-ext/src/message-router.ts b/vscode-ext/src/message-router.ts
index f985ae6..dad7541 100644
--- a/vscode-ext/src/message-router.ts
+++ b/vscode-ext/src/message-router.ts
@@ -142,10 +142,15 @@ export function attachRouter(
   // Route webview messages to the PTY manager
   const messageDisposable = webview.onDidReceiveMessage((msg: WebviewMessage) => {
     switch (msg.type) {
-      case 'pty:spawn':
+      case 'pty:spawn': {
         claim(msg.id);
-        ptyManager.spawn(msg.id, msg.options);
+        const spawnOptions = { ...msg.options };
+        if (!spawnOptions.cwd) {
+          spawnOptions.cwd = vscode.workspace.workspaceFolders?.[0]?.uri.fsPath;
+        }
+        ptyManager.spawn(msg.id, spawnOptions);
         break;
+      }
       case 'pty:input':
         ptyManager.write(msg.id, msg.data);
         break;