diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index f59a5bd67..b49fd3b4b 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -105,6 +105,7 @@ jobs:
       - test-sentry-linux
       - test-i18n
       - test-fuzz-libghostty
+      - test-lib-vt
       - test-macos
       - pinact
       - prettier
@@ -911,6 +912,36 @@ jobs:
       - name: Test System Build
         run: nix develop -c zig build --system ${ZIG_GLOBAL_CACHE_DIR}/p
 
+  test-lib-vt:
+    if: github.repository == 'ghostty-org/ghostty' && needs.skip.outputs.skip != 'true'
+    needs: skip
+    runs-on: namespace-profile-ghostty-md
+    env:
+      ZIG_LOCAL_CACHE_DIR: /zig/local-cache
+      ZIG_GLOBAL_CACHE_DIR: /zig/global-cache
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+
+      - name: Setup Cache
+        uses: namespacelabs/nscloud-cache-action@a90bb5d4b27522ce881c6e98eebd7d7e6d1653f9 # v1.4.2
+        with:
+          path: |
+            /nix
+            /zig
+
+      # Install Nix and use that to run our tests so our environment matches exactly.
+      - uses: cachix/install-nix-action@1ca7d21a94afc7c957383a2d217460d980de4934 # v31.10.1
+        with:
+          nix_path: nixpkgs=channel:nixos-unstable
+      - uses: cachix/cachix-action@1eb2ef646ac0255473d23a5907ad7b04ce94065c # v17
+        with:
+          name: ghostty
+          authToken: "${{ secrets.CACHIX_AUTH_TOKEN }}"
+
+      - name: Test
+        run: nix develop -c zig build test-lib-vt
+
   test-gtk:
     strategy:
       fail-fast: false
diff --git a/src/config.zig b/src/config.zig
index 314fb49ee..289b6a811 100644
--- a/src/config.zig
+++ b/src/config.zig
@@ -2,6 +2,7 @@ const builtin = @import("builtin");
 
 const file_load = @import("config/file_load.zig");
 const formatter = @import("config/formatter.zig");
+const formatter_file = @import("config/formatter_file.zig");
 pub const Config = @import("config/Config.zig");
 pub const conditional = @import("config/conditional.zig");
 pub const io = @import("config/io.zig");
@@ -10,7 +11,7 @@ pub const edit = @import("config/edit.zig");
 pub const url = @import("config/url.zig");
 
 pub const ConditionalState = conditional.State;
-pub const FileFormatter = formatter.FileFormatter;
+pub const FileFormatter = formatter_file.FileFormatter;
 pub const entryFormatter = formatter.entryFormatter;
 pub const formatEntry = formatter.formatEntry;
 pub const preferredDefaultFilePath = file_load.preferredDefaultFilePath;
diff --git a/src/config/Config.zig b/src/config/Config.zig
index d32740783..facbdb21d 100644
--- a/src/config/Config.zig
+++ b/src/config/Config.zig
@@ -39,6 +39,7 @@ pub const Path = @import("path.zig").Path;
 pub const RepeatablePath = @import("path.zig").RepeatablePath;
 const ClipboardCodepointMap = @import("ClipboardCodepointMap.zig");
 const KeyRemapSet = @import("../input/key_mods.zig").RemapSet;
+pub const WindowPaddingBalance = @import("../renderer/size.zig").PaddingBalance;
 const string = @import("string.zig");
 
 // We do this instead of importing all of terminal/main.zig to
@@ -5245,12 +5246,6 @@ pub const Fullscreen = enum(c_int) {
     @"non-native-padded-notch",
 };
 
-pub const WindowPaddingBalance = enum {
-    false,
-    true,
-    equal,
-};
-
 pub const WindowPaddingColor = enum {
     background,
     extend,
diff --git a/src/config/formatter.zig b/src/config/formatter.zig
index dcf99167d..00d946f88 100644
--- a/src/config/formatter.zig
+++ b/src/config/formatter.zig
@@ -1,8 +1,7 @@
 const formatter = @This();
+
 const std = @import("std");
 const Allocator = std.mem.Allocator;
-const help_strings = @import("help_strings");
-const Config = @import("Config.zig");
 const Key = @import("key.zig").Key;
 
 /// Returns a single entry formatter for the given field name and writer.
@@ -125,106 +124,6 @@ pub fn formatEntry(
     @compileError("missing case for type");
 }
 
-/// FileFormatter is a formatter implementation that outputs the
-/// config in a file-like format. This uses more generous whitespace,
-/// can include comments, etc.
-pub const FileFormatter = struct {
-    alloc: Allocator,
-    config: *const Config,
-
-    /// Include comments for documentation of each key
-    docs: bool = false,
-
-    /// Only include changed values from the default.
-    changed: bool = false,
-
-    /// Implements std.fmt so it can be used directly with std.fmt.
-    pub fn format(
-        self: FileFormatter,
-        writer: *std.Io.Writer,
-    ) std.Io.Writer.Error!void {
-        @setEvalBranchQuota(10_000);
-
-        // If we're change-tracking then we need the default config to
-        // compare against.
-        var default: ?Config = if (self.changed)
-            Config.default(self.alloc) catch return error.WriteFailed
-        else
-            null;
-        defer if (default) |*v| v.deinit();
-
-        inline for (@typeInfo(Config).@"struct".fields) |field| {
-            if (field.name[0] == '_') continue;
-
-            const value = @field(self.config, field.name);
-            const do_format = if (default) |d| format: {
-                const key = @field(Key, field.name);
-                break :format d.changed(self.config, key);
-            } else true;
-
-            if (do_format) {
-                const do_docs = self.docs and @hasDecl(help_strings.Config, field.name);
-                if (do_docs) {
-                    const help = @field(help_strings.Config, field.name);
-                    var lines = std.mem.splitScalar(u8, help, '\n');
-                    while (lines.next()) |line| {
-                        try writer.print("# {s}\n", .{line});
-                    }
-                }
-
-                formatEntry(
-                    field.type,
-                    field.name,
-                    value,
-                    writer,
-                ) catch return error.WriteFailed;
-
-                if (do_docs) try writer.print("\n", .{});
-            }
-        }
-    }
-};
-
-test "format default config" {
-    const testing = std.testing;
-    const alloc = testing.allocator;
-    var cfg = try Config.default(alloc);
-    defer cfg.deinit();
-
-    var buf: std.Io.Writer.Allocating = .init(alloc);
-    defer buf.deinit();
-
-    // We just make sure this works without errors. We aren't asserting output.
-    const fmt: FileFormatter = .{
-        .alloc = alloc,
-        .config = &cfg,
-    };
-    try fmt.format(&buf.writer);
-
-    //std.log.warn("{s}", .{buf.written()});
-}
-
-test "format default config changed" {
-    const testing = std.testing;
-    const alloc = testing.allocator;
-    var cfg = try Config.default(alloc);
-    defer cfg.deinit();
-    cfg.@"font-size" = 42;
-
-    var buf: std.Io.Writer.Allocating = .init(alloc);
-    defer buf.deinit();
-
-    // We just make sure this works without errors. We aren't asserting output.
-    const fmt: FileFormatter = .{
-        .alloc = alloc,
-        .config = &cfg,
-        .changed = true,
-    };
-    try fmt.format(&buf.writer);
-
-    //std.log.warn("{s}", .{buf.written()});
-}
-
 test "formatEntry bool" {
     const testing = std.testing;
 
diff --git a/src/config/formatter_file.zig b/src/config/formatter_file.zig
new file mode 100644
index 000000000..37beb7b54
--- /dev/null
+++ b/src/config/formatter_file.zig
@@ -0,0 +1,110 @@
+const std = @import("std");
+const Allocator = std.mem.Allocator;
+const Config = @import("Config.zig");
+const Key = @import("key.zig").Key;
+const help_strings = @import("help_strings");
+const formatter = @import("formatter.zig");
+
+// IMPORTANT: This is in a separate file from formatter.zig because it
+// puts a build-time dependency on Config.zig which brings in too much
+// into libghostty-vt tests which reference some formattable types.
+
+/// FileFormatter is a formatter implementation that outputs the
+/// config in a file-like format. This uses more generous whitespace,
+/// can include comments, etc.
+pub const FileFormatter = struct {
+    alloc: Allocator,
+    config: *const Config,
+
+    /// Include comments for documentation of each key
+    docs: bool = false,
+
+    /// Only include changed values from the default.
+    changed: bool = false,
+
+    /// Implements std.fmt so it can be used directly with std.fmt.
+    pub fn format(
+        self: FileFormatter,
+        writer: *std.Io.Writer,
+    ) std.Io.Writer.Error!void {
+        @setEvalBranchQuota(10_000);
+
+        // If we're change-tracking then we need the default config to
+        // compare against.
+        var default: ?Config = if (self.changed)
+            Config.default(self.alloc) catch return error.WriteFailed
+        else
+            null;
+        defer if (default) |*v| v.deinit();
+
+        inline for (@typeInfo(Config).@"struct".fields) |field| {
+            if (field.name[0] == '_') continue;
+
+            const value = @field(self.config, field.name);
+            const do_format = if (default) |d| format: {
+                const key = @field(Key, field.name);
+                break :format d.changed(self.config, key);
+            } else true;
+
+            if (do_format) {
+                const do_docs = self.docs and @hasDecl(help_strings.Config, field.name);
+                if (do_docs) {
+                    const help = @field(help_strings.Config, field.name);
+                    var lines = std.mem.splitScalar(u8, help, '\n');
+                    while (lines.next()) |line| {
+                        try writer.print("# {s}\n", .{line});
+                    }
+                }
+
+                formatter.formatEntry(
+                    field.type,
+                    field.name,
+                    value,
+                    writer,
+                ) catch return error.WriteFailed;
+
+                if (do_docs) try writer.print("\n", .{});
+            }
+        }
+    }
+};
+
+test "format default config" {
+    const testing = std.testing;
+    const alloc = testing.allocator;
+    var cfg = try Config.default(alloc);
+    defer cfg.deinit();
+
+    var buf: std.Io.Writer.Allocating = .init(alloc);
+    defer buf.deinit();
+
+    // We just make sure this works without errors. We aren't asserting output.
+    const fmt: FileFormatter = .{
+        .alloc = alloc,
+        .config = &cfg,
+    };
+    try fmt.format(&buf.writer);
+
+    //std.log.warn("{s}", .{buf.written()});
+}
+
+test "format default config changed" {
+    const testing = std.testing;
+    const alloc = testing.allocator;
+    var cfg = try Config.default(alloc);
+    defer cfg.deinit();
+    cfg.@"font-size" = 42;
+
+    var buf: std.Io.Writer.Allocating = .init(alloc);
+    defer buf.deinit();
+
+    // We just make sure this works without errors. We aren't asserting output.
+    const fmt: FileFormatter = .{
+        .alloc = alloc,
+        .config = &cfg,
+        .changed = true,
+    };
+    try fmt.format(&buf.writer);
+
+    //std.log.warn("{s}", .{buf.written()});
+}
diff --git a/src/input/key.zig b/src/input/key.zig
index a929a0323..9c04f01e0 100644
--- a/src/input/key.zig
+++ b/src/input/key.zig
@@ -2,7 +2,6 @@ const std = @import("std");
 const builtin = @import("builtin");
 const Allocator = std.mem.Allocator;
 const cimgui = @import("dcimgui");
-const OptionAsAlt = @import("config.zig").OptionAsAlt;
 
 pub const Mods = @import("key_mods.zig").Mods;
 
diff --git a/src/lib/enum.zig b/src/lib/enum.zig
index bdec2ab88..f40a40b54 100644
--- a/src/lib/enum.zig
+++ b/src/lib/enum.zig
@@ -95,7 +95,10 @@ test "abi by removing a key" {
 /// Verify that for every key in enum T, there is a matching declaration in
 /// `ghostty.h` with the correct value. This should only ever be called inside a `test`
 /// because the `ghostty.h` module is only available then.
-pub fn checkGhosttyHEnum(comptime T: type, comptime prefix: []const u8) !void {
+pub fn checkGhosttyHEnum(
+    comptime T: type,
+    comptime prefix: []const u8,
+) !void {
     const info = @typeInfo(T);
 
     try std.testing.expect(info == .@"enum");
diff --git a/src/renderer/size.zig b/src/renderer/size.zig
index 7a022cdb4..6cf05f58a 100644
--- a/src/renderer/size.zig
+++ b/src/renderer/size.zig
@@ -1,10 +1,22 @@
 const std = @import("std");
 const Allocator = std.mem.Allocator;
-const configpkg = @import("../config.zig");
 const terminal_size = @import("../terminal/size.zig");
 
 const log = std.log.scoped(.renderer_size);
 
+/// Controls how extra whitespace around the terminal grid is distributed.
+pub const PaddingBalance = enum {
+    /// No balancing; padding is applied as specified explicitly.
+    false,
+    /// Balances padding but caps the top padding so the first row doesn't
+    /// drift too far from the top of the window. Excess vertical space is
+    /// shifted to the bottom.
+    true,
+    /// Distributes leftover space equally on all sides so the grid is
+    /// centered within the screen.
+    equal,
+};
+
 /// All relevant sizes for a rendered terminal. These are all the sizes that
 /// any functionality should need to know about the terminal in order to
 /// convert between any coordinate systems.
@@ -37,7 +49,7 @@ pub const Size = struct {
     pub fn balancePadding(
         self: *Size,
         explicit: Padding,
-        mode: configpkg.Config.WindowPaddingBalance,
+        mode: PaddingBalance,
     ) void {
         // This ensure grid() does the right thing
         self.padding = explicit;
diff --git a/src/terminal/c/build_info.zig b/src/terminal/c/build_info.zig
index d65a3b562..312d94fec 100644
--- a/src/terminal/c/build_info.zig
+++ b/src/terminal/c/build_info.zig
@@ -43,6 +43,7 @@ pub fn get(
     }
 
     return switch (data) {
+        .invalid => .invalid_value,
         inline else => |comptime_data| getTyped(
             comptime_data,
             @ptrCast(@alignCast(out)),
diff --git a/src/terminal/c/cell.zig b/src/terminal/c/cell.zig
index 2ff9b35f9..171867048 100644
--- a/src/terminal/c/cell.zig
+++ b/src/terminal/c/cell.zig
@@ -110,6 +110,7 @@ pub fn get(
     }
 
     return switch (data) {
+        .invalid => .invalid_value,
         inline else => |comptime_data| getTyped(
             cell_,
             comptime_data,
diff --git a/src/terminal/c/key_encode.zig b/src/terminal/c/key_encode.zig
index 2cdb765af..616a438d9 100644
--- a/src/terminal/c/key_encode.zig
+++ b/src/terminal/c/key_encode.zig
@@ -259,7 +259,7 @@ test "setopt_from_terminal" {
 
     // Options should reflect defaults from a fresh terminal
     try testing.expect(!e.?.opts.cursor_key_application);
-    try testing.expect(!e.?.opts.alt_esc_prefix);
+    try testing.expect(e.?.opts.alt_esc_prefix);
     try testing.expectEqual(KittyFlags.disabled, e.?.opts.kitty_flags);
     try testing.expectEqual(OptionAsAlt.false, e.?.opts.macos_option_as_alt);
 }
diff --git a/src/terminal/c/osc.zig b/src/terminal/c/osc.zig
index c4cdaad3b..648e448fd 100644
--- a/src/terminal/c/osc.zig
+++ b/src/terminal/c/osc.zig
@@ -76,6 +76,7 @@ pub fn commandData(
     }
 
     return switch (data) {
+        .invalid => false,
         inline else => |comptime_data| commandDataTyped(
             command_,
             comptime_data,
diff --git a/src/terminal/c/render.zig b/src/terminal/c/render.zig
index f8a107979..020dbc202 100644
--- a/src/terminal/c/render.zig
+++ b/src/terminal/c/render.zig
@@ -193,6 +193,7 @@ pub fn get(
     }
 
     return switch (data) {
+        .invalid => .invalid_value,
         inline else => |comptime_data| getTyped(
             state_,
             comptime_data,
@@ -336,11 +337,7 @@ pub fn colors_get(
         out_colors.cursor_has_value = colors.cursor != null;
     }
 
-    if (lib.structSizedFieldFits(
-        Colors,
-        out_size,
-        "palette",
-    )) {
+    {
         const palette_offset = @offsetOf(Colors, "palette");
         if (out_size > palette_offset) {
             const available = out_size - palette_offset;
@@ -467,6 +464,7 @@ pub fn row_cells_get(
     }
 
     return switch (data) {
+        .invalid => .invalid_value,
         inline else => |comptime_data| rowCellsGetTyped(
             cells_,
             comptime_data,
@@ -566,6 +564,7 @@ pub fn row_get(
     }
 
     return switch (data) {
+        .invalid => .invalid_value,
         inline else => |comptime_data| rowGetTyped(
             iterator_,
             comptime_data,
diff --git a/src/terminal/c/row.zig b/src/terminal/c/row.zig
index 6614d922e..7b765b56a 100644
--- a/src/terminal/c/row.zig
+++ b/src/terminal/c/row.zig
@@ -73,6 +73,7 @@ pub fn get(
     }
 
     return switch (data) {
+        .invalid => .invalid_value,
         inline else => |comptime_data| getTyped(
             row_,
             comptime_data,
diff --git a/src/terminal/c/terminal.zig b/src/terminal/c/terminal.zig
index 97b76985d..2dd56a519 100644
--- a/src/terminal/c/terminal.zig
+++ b/src/terminal/c/terminal.zig
@@ -196,6 +196,7 @@ pub fn get(
     }
 
     return switch (data) {
+        .invalid => .invalid_value,
         inline else => |comptime_data| getTyped(
             terminal_,
             comptime_data,
diff --git a/src/terminal/mouse.zig b/src/terminal/mouse.zig
index e72e166f7..5286ab856 100644
--- a/src/terminal/mouse.zig
+++ b/src/terminal/mouse.zig
@@ -92,6 +92,7 @@ pub const Shape = enum(c_int) {
     };
 
     test "ghostty.h MouseShape" {
+        if (comptime build_options.artifact == .lib) return error.SkipZigTest;
         try lib.checkGhosttyHEnum(Shape, "GHOSTTY_MOUSE_SHAPE_");
     }
 };
diff --git a/src/terminal/osc.zig b/src/terminal/osc.zig
index 0086e48bc..920ce3f7e 100644
--- a/src/terminal/osc.zig
+++ b/src/terminal/osc.zig
@@ -205,6 +205,7 @@ pub const Command = union(Key) {
             pause,
 
             test "ghostty.h Command.ProgressReport.State" {
+                if (comptime build_options.artifact == .lib) return error.SkipZigTest;
                 try lib.checkGhosttyHEnum(State, "GHOSTTY_PROGRESS_STATE_");
             }
         };