Specify custom container mount paths using the host:container format

Directory.Packages.props

@@ -3,7 +3,8 @@
     <ManagePackageVersionsCentrally>true</ManagePackageVersionsCentrally>
   </PropertyGroup>
   <ItemGroup>
+    <PackageVersion Include="Microsoft.Testing.Platform.MSBuild" Version="2.1.0" />
     <PackageVersion Include="System.CommandLine" Version="2.0.0" />
     <PackageVersion Include="TUnit" Version="1.2.11" />
   </ItemGroup>
-</Project>
+</Project>

README.md

@@ -54,8 +54,8 @@ All functions support switching between Docker image variants using flags:
 - **`-h` or `--help`** - Show usage help and examples
 - **`--no-cleanup`** - Skip cleanup of unused Docker images
 - **`--no-pull`** - Skip pulling the latest image
-- **`--mount <path>`** - Mount a directory as read-only
-- **`--mount-rw <path>`** - Mount a directory as read-write
+- **`--mount <path>`** - Mount a directory as read-only (supports `path` or `host:container` format)
+- **`--mount-rw <path>`** - Mount a directory as read-write (supports `path` or `host:container` format)
 - **`--save-mount <path>`** - Save a mount to local config
 - **`--save-mount-global <path>`** - Save a mount to global config
 - **`--remove-mount <path>`** - Remove a saved mount
@@ -78,8 +78,10 @@ These options are passed directly to the GitHub Copilot CLI:
 By default, `copilot_here` only mounts the current working directory. You can mount additional directories using flags or configuration files.
 
 **CLI Flags:**
-- `--mount ./path/to/dir` (Read-only)
-- `--mount-rw ./path/to/dir` (Read-write)
+- `--mount ./path/to/dir` (Read-only, auto-computed container path)
+- `--mount-rw ./path/to/dir` (Read-write, auto-computed container path)
+- `--mount /host/path:/container/path` (Read-only, custom container path)
+- `--mount-rw /host/path:/container/path` (Read-write, custom container path)
 
 **Configuration Files:**
 - Global: `~/.config/copilot_here/mounts.conf`

app/Commands/Mounts/ListMounts.cs

@@ -28,13 +28,13 @@ private static Command SetListMountsCommand()
       foreach (var mount in config.GlobalMounts)
       {
         var mode = mount.IsReadWrite ? "rw" : "ro";
-        Console.WriteLine($"  🌍 {mount.Path} ({mode})");
+        Console.WriteLine($"  🌍 {mount.HostPath} ({mode})");
       }
 
       foreach (var mount in config.LocalMounts)
       {
         var mode = mount.IsReadWrite ? "rw" : "ro";
-        Console.WriteLine($"  📍 {mount.Path} ({mode})");
+        Console.WriteLine($"  📍 {mount.HostPath} ({mode})");
       }
 
       Console.WriteLine();

app/Commands/Mounts/_MountsConfig.cs

@@ -36,19 +36,32 @@
     foreach (var line in ConfigFile.ReadLines(path))
     {
       var isReadWrite = false;
-      var mountPath = line;
+      var workingLine = line;
 
-      if (line.EndsWith(":rw", StringComparison.OrdinalIgnoreCase))
+      // Check for :rw or :ro suffix
+      if (workingLine.EndsWith(":rw", StringComparison.OrdinalIgnoreCase))
       {
         isReadWrite = true;
-        mountPath = line[..^3];
+        workingLine = workingLine[..^3];
       }
-      else if (line.EndsWith(":ro", StringComparison.OrdinalIgnoreCase))
+      else if (workingLine.EndsWith(":ro", StringComparison.OrdinalIgnoreCase))
       {
-        mountPath = line[..^3];
+        workingLine = workingLine[..^3];
       }
 
-      mounts.Add(new MountEntry(mountPath, isReadWrite, source));
+      // Parse hostPath:containerPath format
+      var colonIndex = workingLine.IndexOf(':');
+      if (colonIndex > 0)
+      {
+        var hostPath = workingLine[..colonIndex];
+        var containerPath = workingLine[(colonIndex + 1)..];
+        mounts.Add(new MountEntry(hostPath, containerPath, isReadWrite, source));
+      }
+      else
+      {
+        var hostPath = workingLine;
+        mounts.Add(new MountEntry(hostPath, null, isReadWrite, source));
+      }
     }
 
     return mounts;
@@ -133,14 +146,35 @@
 /// <summary>
 /// A single mount entry with its path, mode, and source.
 /// </summary>
-public readonly record struct MountEntry(string Path, bool IsReadWrite, MountSource Source)
+public readonly record struct MountEntry
 {
+  /// <summary>
+  /// A single mount entry with its path, mode, and source.
+  /// </summary>
+  public MountEntry(string HostPath, bool IsReadWrite, MountSource Source)
+  {
+    this.HostPath = HostPath;
+    this.IsReadWrite = IsReadWrite;
+    this.Source = Source;
+  }
+
+  /// <summary>
+  /// A single mount entry with its host/container paths, mode, and source.
+  /// </summary>
+  public MountEntry(string HostPath, string ContainerPath, bool IsReadWrite, MountSource Source)
+  {
+    this.HostPath = HostPath;
+    this.ContainerPath = ContainerPath;
+    this.IsReadWrite = IsReadWrite;
+    this.Source = Source;
+  }
+
   /// <summary>
   /// Resolves ~ and relative paths to absolute paths, following symlinks.
   /// </summary>
-  public string ResolvePath(string userHome)
+  public string ResolveHostPath(string userHome)
   {
-    return PathValidator.ResolvePath(Path, userHome);
+    return PathValidator.ResolvePath(HostPath, userHome);
   }
 
   /// <summary>
@@ -149,7 +183,7 @@
   /// </summary>
   public bool Validate(string userHome)
   {
-    var resolved = ResolvePath(userHome);
+    var resolved = ResolveHostPath(userHome);
 
     // Warn if path doesn't exist
     PathValidator.WarnIfNotExists(resolved);
@@ -166,7 +200,13 @@
   /// <summary>Calculates the container path for this mount.</summary>
   public string GetContainerPath(string userHome)
   {
-    var hostPath = ResolvePath(userHome);
+    // If custom container path is specified, expand tilde to container user home
+    if (!string.IsNullOrWhiteSpace(ContainerPath))
+    {
+      return ExpandContainerTilde(ContainerPath);
+    }
+
+    var hostPath = ResolveHostPath(userHome);
     if (hostPath.StartsWith(userHome))
     {
       return $"/home/appuser/{System.IO.Path.GetRelativePath(userHome, hostPath).Replace("\\", "/")}";
@@ -185,10 +225,28 @@
     return $"/work{hostPath}";
   }
 
+  /// <summary>
+  /// Expands tilde in container paths to /home/appuser (the container user's home).
+  /// </summary>
+  private static string ExpandContainerTilde(string containerPath)
+  {
+    if (containerPath == "~")
+    {
+      return "/home/appuser";
+    }
+
+    if (containerPath.StartsWith("~/"))
+    {
+      return $"/home/appuser/{containerPath.Substring(2)}";
+    }
+
+    return containerPath;
+  }
+
   /// <summary>Gets the Docker volume mount string.</summary>
   public string ToDockerVolume(string userHome)
   {
-    var hostPath = ResolvePath(userHome);
+    var hostPath = ResolveHostPath(userHome);
     var dockerHostPath = ConvertToDockerPath(hostPath);
     var containerPath = GetContainerPath(userHome);
     var mode = IsReadWrite ? "rw" : "ro";
@@ -217,6 +275,11 @@
 
     return normalizedPath;
   }
+
+  public string HostPath { get; init; }
+  public bool IsReadWrite { get; init; }
+  public MountSource Source { get; init; }
+  public string? ContainerPath { get; init; }
 }
 
 public enum MountSource

app/Commands/Run/RunCommand.cs

@@ -99,9 +99,9 @@ public RunCommand(bool isYolo = false)
 
     _golangOption = new Option<bool>("--golang") { Description = "[-go] Use Golang image variant" };
 
-    _mountOption = new Option<string[]>("--mount") { Description = "Mount additional directory (read-only)" };
+    _mountOption = new Option<string[]>("--mount") { Description = "Mount directory (read-only). Format: path or host:container" };
 
-    _mountRwOption = new Option<string[]>("--mount-rw") { Description = "Mount additional directory (read-write)" };
+    _mountRwOption = new Option<string[]>("--mount-rw") { Description = "Mount directory (read-write). Format: path or host:container" };
 
     _noCleanupOption = new Option<bool>("--no-cleanup") { Description = "Skip cleanup of unused Docker images" };
 
@@ -447,6 +447,7 @@ public void Configure(RootCommand root)
       var allMounts = new List<MountEntry>();
 
       // Parse CLI mounts first (highest priority)
+      // Supports both simple paths and host:container format
       foreach (var path in cliMountsRo)
         allMounts.Add(ParseCliMount(path, defaultReadWrite: false));
       foreach (var path in cliMountsRw)
@@ -469,7 +470,7 @@ public void Configure(RootCommand root)
         else
         {
           // User cancelled due to sensitive path - skip this mount
-          Console.WriteLine($"⏭️  Skipping mount: {mount.Path}");
+          Console.WriteLine($"⏭️  Skipping mount: {mount.HostPath}");
         }
       }
       allMounts = validatedMounts;
@@ -622,26 +623,60 @@ private static List<string> BuildDockerArgs(
   }
 
   /// <summary>
-  /// Parses a CLI mount path, handling :rw/:ro suffix.
-  /// Format: "path" or "path:rw" or "path:ro"
+  /// Parses a CLI mount path, handling both simple paths and host:container format.
+  /// Format: "path", "path:rw", "path:ro", "host:container", "host:container:rw", "host:container:ro"
   /// </summary>
-  private static MountEntry ParseCliMount(string input, bool defaultReadWrite)
+  internal static MountEntry ParseCliMount(string input, bool defaultReadWrite)
   {
     var isReadWrite = defaultReadWrite;
-    var mountPath = input;
+    var spec = input.Trim('\'', '"'); // Remove any surrounding quotes
 
-    if (input.EndsWith(":rw", StringComparison.OrdinalIgnoreCase))
+    // Check for trailing :rw or :ro
+    if (spec.EndsWith(":rw", StringComparison.OrdinalIgnoreCase))
     {
       isReadWrite = true;
-      mountPath = input[..^3];
+      spec = spec[..^3];
     }
-    else if (input.EndsWith(":ro", StringComparison.OrdinalIgnoreCase))
+    else if (spec.EndsWith(":ro", StringComparison.OrdinalIgnoreCase))
     {
       isReadWrite = false;
-      mountPath = input[..^3];
+      spec = spec[..^3];
     }
 
-    return new MountEntry(mountPath, isReadWrite, MountSource.CommandLine);
+    // Check if this is a host:container format
+    var separatorIndex = FindBindSeparator(spec);
+
+    if (separatorIndex == -1)
+    {
+      // Simple path format - auto-compute container path
+      return new MountEntry(spec, isReadWrite, MountSource.CommandLine);
+    }
+
+    // host:container format
+    var hostPath = spec[..separatorIndex];
+    var containerPath = spec[(separatorIndex + 1)..];
+
+    return new MountEntry(hostPath, containerPath, isReadWrite, MountSource.CommandLine);
+  }
+
+  /// <summary>
+  /// Finds the separator between host and container paths in a bind spec.
+  /// On Windows, skips the colon after drive letter (e.g., C:\path).
+  /// </summary>
+  private static int FindBindSeparator(string bindSpec)
+  {
+    var startIndex = 0;
+
+    // On Windows, skip past drive letter colon (e.g., C:)
+    if (OperatingSystem.IsWindows() && 
+        bindSpec.Length >= 2 && 
+        char.IsLetter(bindSpec[0]) && 
+        bindSpec[1] == ':')
+    {
+      startIndex = 2;
+    }
+
+    return bindSpec.IndexOf(':', startIndex);
   }
 
   /// <summary>

app/Infrastructure/AirlockRunner.cs

@@ -244,7 +244,7 @@ private static void SetupLogsDirectory(AppPaths paths, string rulesPath)
       {
         var mode = mount.IsReadWrite ? "rw" : "ro";
         var containerPath = mount.GetContainerPath(ctx.Paths.UserHome);
-        var resolvedPath = mount.ResolvePath(ctx.Paths.UserHome);
+        var resolvedPath = mount.ResolveHostPath(ctx.Paths.UserHome);
         var dockerPath = ConvertToDockerPath(resolvedPath);
         extraMounts.AppendLine($"      - {dockerPath}:{containerPath}:{mode}");
       }

app/Infrastructure/SessionInfo.cs

@@ -34,7 +34,7 @@ public static string Generate(
       var m = mounts[i];
       if (i > 0) json.Append(',');
       json.Append('{');
-      json.Append($"\"host_path\":\"{JsonEncode(m.ResolvePath(ctx.Paths.UserHome))}\",");
+      json.Append($"\"host_path\":\"{JsonEncode(m.ResolveHostPath(ctx.Paths.UserHome))}\",");
       json.Append($"\"container_path\":\"{JsonEncode(m.GetContainerPath(ctx.Paths.UserHome))}\",");
       json.Append($"\"mode\":\"{(m.IsReadWrite ? "rw" : "ro")}\",");
       json.Append($"\"source\":\"{m.Source.ToString().ToLowerInvariant()}\"");

tests/CopilotHere.UnitTests/CopilotHere.UnitTests.csproj

@@ -17,6 +17,7 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <PackageReference Include="Microsoft.Testing.Platform.MSBuild" />
     <PackageReference Include="TUnit" />
   </ItemGroup>