Fix critical GUID parsing bugs to prevent crashes

Added proper error handling for invalid GUID inputs in:
1. focus-tab --session option parsing
2. new-tab --sessionId option parsing

Both now silently ignore invalid GUIDs instead of crashing, consistent
with how invalid tab colors are handled. Added test case for invalid GUID.

Co-authored-by: shanselman <2892+shanselman@users.noreply.github.com>

Author: Copilot

src/cascadia/LocalTests_TerminalApp/CommandlineTest.cpp

@@ -1180,6 +1180,16 @@ namespace TerminalAppLocalTests
                 VERIFY_ARE_NOT_EQUAL("", appArgs._exitMessage);
             }
         }
+        {
+            Log::Comment(NoThrowString().Format(
+                L"Test that --session with an invalid GUID doesn't crash"));
+            AppCommandlineArgs appArgs{};
+            std::vector<const wchar_t*> rawCommands{ L"wt.exe", subcommand, L"-s", L"invalid-guid-string" };
+            _buildCommandlinesHelper(appArgs, 1u, rawCommands);
+
+            // With an invalid GUID, the command should be silently skipped (no action created)
+            VERIFY_ARE_EQUAL(0u, appArgs._startupActions.size());
+        }
     }
 
     void CommandlineTest::ParseMoveFocusArgs()

src/cascadia/TerminalApp/AppCommandlineArgs.cpp

@@ -393,31 +393,45 @@ void AppCommandlineArgs::_buildFocusTabParser()
             if (!_focusTabSession.empty())
             {
                 // Focus tab by session GUID
-                focusTabAction.Action(ShortcutAction::SwitchToTab);
-                SwitchToTabArgs args{};
                 const auto str = winrt::to_hstring(_focusTabSession);
                 // GuidFromPlainString handles GUIDs without braces (e.g. "12345678-...")
                 // GuidFromString handles GUIDs with braces (e.g. "{12345678-...}")
                 // Try plain first (most common from WT_SESSION), fall back to braced
                 winrt::guid id{};
+                bool parsedSuccessfully = false;
                 try
                 {
-                    id = ::Microsoft::Console::Utils::GuidFromPlainString(str.c_str());
+                    try
+                    {
+                        id = ::Microsoft::Console::Utils::GuidFromPlainString(str.c_str());
+                    }
+                    catch (...)
+                    {
+                        id = ::Microsoft::Console::Utils::GuidFromString(str.c_str());
+                    }
+                    parsedSuccessfully = true;
                 }
                 catch (...)
                 {
-                    id = ::Microsoft::Console::Utils::GuidFromString(str.c_str());
+                    // Invalid GUID provided - silently ignore similar to how invalid
+                    // tab colors are handled. The command will be skipped.
                 }
-                args.SessionId(id);
-                focusTabAction.Args(args);
-                _startupActions.push_back(focusTabAction);
-                
-                // When targeting by session ID, route to an existing window on the 
-                // current desktop (if user didn't specify -w explicitly).
-                // The session ID uniquely identifies a pane in some window.
-                if (_windowTarget.empty())
+
+                if (parsedSuccessfully)
                 {
-                    _windowTarget = "0";
+                    focusTabAction.Action(ShortcutAction::SwitchToTab);
+                    SwitchToTabArgs args{};
+                    args.SessionId(id);
+                    focusTabAction.Args(args);
+                    _startupActions.push_back(focusTabAction);
+                    
+                    // When targeting by session ID, route to an existing window on the 
+                    // current desktop (if user didn't specify -w explicitly).
+                    // The session ID uniquely identifies a pane in some window.
+                    if (_windowTarget.empty())
+                    {
+                        _windowTarget = "0";
+                    }
                 }
             }
             else if (_focusTabIndex >= 0)
@@ -736,8 +750,16 @@ NewTerminalArgs AppCommandlineArgs::_getNewTerminalArgs(AppCommandlineArgs::NewT
     if (*subcommand.sessionIdOption)
     {
         const auto str = winrt::to_hstring(_sessionId);
-        const auto id = ::Microsoft::Console::Utils::GuidFromString(str.c_str());
-        args.SessionId(id);
+        try
+        {
+            const auto id = ::Microsoft::Console::Utils::GuidFromString(str.c_str());
+            args.SessionId(id);
+        }
+        catch (...)
+        {
+            // Invalid GUID provided - silently ignore similar to how invalid
+            // tab colors are handled.
+        }
     }
 
     if (*subcommand.startingDirectoryOption)