diff --git a/nix/devShell.nix b/nix/devShell.nix
index 6fa1f14b1..5401ba0d1 100644
--- a/nix/devShell.nix
+++ b/nix/devShell.nix
@@ -59,6 +59,7 @@
   zlib,
   alejandra,
   jq,
+  kaitai-struct-compiler,
   minisign,
   pandoc,
   pinact,
@@ -85,6 +86,11 @@
   gi_typelib_path = import ./build-support/gi-typelib-path.nix {
     inherit pkgs lib stdenv;
   };
+  python = python3.withPackages (python-pkgs: [
+    python-pkgs.blake3
+    python-pkgs.kaitaistruct
+    python-pkgs.ucs-detect
+  ]);
 in
   mkShell {
     name = "ghostty";
@@ -116,9 +122,10 @@ in
 
         # Testing
         parallel
-        python3
+        python
         vttest
         hyperfine
+        kaitai-struct-compiler
 
         # wasm
         wabt
@@ -138,11 +145,6 @@ in
         blueprint-compiler
         libadwaita
         gtk4
-
-        # Python packages
-        (python3.withPackages (python-pkgs: [
-          python-pkgs.ucs-detect
-        ]))
       ]
       ++ lib.optionals stdenv.hostPlatform.isLinux [
         # My nix shell environment installs the non-interactive version
@@ -242,6 +244,6 @@ in
         # We need to remove "xcrun" from the PATH. It is injected by
         # some dependency but we need to rely on system Xcode tools
         export PATH=$(echo "$PATH" | awk -v RS=: -v ORS=: '$0 !~ /xcrun/ || $0 == "/usr/bin" {print}' | sed 's/:$//')
-        export PATH="/opt/homebrew/opt/llvm/bin:/opt/homebrew/bin:/usr/local/opt/llvm/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:$PATH"
+        export PATH="${python}/bin:/opt/homebrew/opt/llvm/bin:/opt/homebrew/bin:/usr/local/opt/llvm/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:$PATH"
       '');
   }
diff --git a/src/terminal/snapshot/envelope.zig b/src/terminal/snapshot/envelope.zig
index 9963ced2a..21fcefb9d 100644
--- a/src/terminal/snapshot/envelope.zig
+++ b/src/terminal/snapshot/envelope.zig
@@ -66,9 +66,7 @@ fn computeLen() usize {
     }
 }
 
-const test_golden_fixture = test_fixture.parse(
-    @embedFile("testdata/envelope-v1.hex"),
-);
+const test_golden_fixture = test_fixture.parse(@embedFile("testdata/envelope-v1.hex"));
 
 test "golden encoding" {
     var buf: [encoded_len]u8 = undefined;
diff --git a/src/terminal/snapshot/fixture.zig b/src/terminal/snapshot/fixture.zig
index 6d256ac3d..d5c86b2b7 100644
--- a/src/terminal/snapshot/fixture.zig
+++ b/src/terminal/snapshot/fixture.zig
@@ -49,6 +49,23 @@
 //!     );
 //! }
 //! ```
+//!
+//! ## Kaitai
+//!
+//! Every fixture has three machine-readable comment fields:
+//!
+//! ```text
+//! # Kaitai type: page_payload
+//! # Kaitai params:
+//! # Kaitai offset: 0
+//! ```
+//!
+//! These select a type from `snapshot.ksy`, its whitespace-separated
+//! parameters, and the byte offset where parsing begins. The Kaitai verifier
+//! discovers fixtures from the filesystem and uses this metadata instead of
+//! maintaining a parallel filename table. Generated candidates copy the
+//! metadata from their checked-in reference.
+//!
 
 const std = @import("std");
 const envelope = @import("envelope.zig");
@@ -128,6 +145,17 @@ pub fn expectEqual(
     var tmp = testing.tmpDir(.{});
     defer tmp.cleanup();
 
+    // Kaitai parser selection lives in the reference itself. Read the textual
+    // source so generated candidates preserve that metadata even though the
+    // byte comparison below uses the comptime-decoded reference.
+    const reference_source = try std.Io.Dir.cwd().readFileAlloc(
+        testing.io,
+        reference_path,
+        alloc,
+        .unlimited,
+    );
+    defer alloc.free(reference_source);
+
     // Always materialize a candidate, even when it will match. This keeps the
     // generation path exercised on every test run while avoiding repository
     // artifacts for the normal successful case.
@@ -143,7 +171,12 @@ pub fn expectEqual(
             testing.io,
             &write_buffer,
         );
-        try format(kind, actual, &candidate_writer.interface);
+        try format(
+            kind,
+            reference_source,
+            actual,
+            &candidate_writer.interface,
+        );
         try candidate_writer.interface.flush();
     }
 
@@ -267,14 +300,16 @@ fn hexNibble(comptime value: u8) u8 {
 
 fn format(
     kind: Kind,
+    reference_source: []const u8,
     bytes: []const u8,
     writer: *std.Io.Writer,
-) std.Io.Writer.Error!void {
+) (std.Io.Writer.Error || error{InvalidKaitaiMetadata})!void {
     // Every generated candidate starts with enough maintenance context to be
     // understandable when copied out of a failing test's temp directory.
+    try writer.writeAll("# Ghostty snapshot fixture\n");
+    try writeKaitaiMetadata(reference_source, writer);
     try writer.print(
-        "# Ghostty snapshot fixture\n" ++
-            "# Wire version: {}\n" ++
+        "# Wire version: {}\n" ++
             "# Generated by its snapshot test; review before replacing.\n" ++
             "# On mismatch, the candidate is copied to the repository root.\n",
         .{envelope.version},
@@ -295,6 +330,34 @@ fn format(
     }
 }
 
+fn writeKaitaiMetadata(
+    reference_source: []const u8,
+    writer: *std.Io.Writer,
+) (std.Io.Writer.Error || error{InvalidKaitaiMetadata})!void {
+    const prefixes = [_][]const u8{
+        "# Kaitai type:",
+        "# Kaitai params:",
+        "# Kaitai offset:",
+    };
+    var found = [_]bool{false} ** prefixes.len;
+
+    var lines = std.mem.splitScalar(u8, reference_source, '\n');
+    while (lines.next()) |untrimmed| {
+        const line = std.mem.trim(u8, untrimmed, " \r");
+        for (prefixes, &found) |prefix, *seen| {
+            if (!std.mem.startsWith(u8, line, prefix)) continue;
+            if (seen.*) return error.InvalidKaitaiMetadata;
+            seen.* = true;
+            try writer.print("{s}\n", .{line});
+            break;
+        }
+    }
+
+    for (found) |seen| {
+        if (!seen) return error.InvalidKaitaiMetadata;
+    }
+}
+
 fn formatPage(
     bytes: []const u8,
     writer: *std.Io.Writer,
diff --git a/src/terminal/snapshot/history.zig b/src/terminal/snapshot/history.zig
index 8422c4f73..d4ea5a60d 100644
--- a/src/terminal/snapshot/history.zig
+++ b/src/terminal/snapshot/history.zig
@@ -288,9 +288,7 @@ pub fn decode(
         // the destination PageList to allocate the final backing memory once.
         var decoder: page.Decoder = undefined;
         try decoder.init(source);
-        var allocation = try terminal_screen.pages.allocatePage(
-            decoder.capacity(),
-        );
+        var allocation = try terminal_screen.pages.allocatePage(decoder.capacity());
         defer allocation.deinit();
         try decoder.decode(allocation.page(), alloc);
 
@@ -319,9 +317,7 @@ pub fn decode(
 }
 
 fn hasSemanticPrompt(terminal_page: *const TerminalPage) bool {
-    const rows = terminal_page.rows.ptr(
-        terminal_page.memory,
-    )[0..terminal_page.size.rows];
+    const rows = terminal_page.rows.ptr(terminal_page.memory)[0..terminal_page.size.rows];
     for (rows) |row| {
         if (row.semantic_prompt != .none) return true;
 
@@ -335,9 +331,7 @@ fn hasSemanticPrompt(terminal_page: *const TerminalPage) bool {
     return false;
 }
 
-const test_header_fixture = test_fixture.parse(
-    @embedFile("testdata/history-header-v1.hex"),
-);
+const test_header_fixture = test_fixture.parse(@embedFile("testdata/history-header-v1.hex"));
 
 test "HISTORY header golden encoding and decoding" {
     const expected: Header = .{
diff --git a/src/terminal/snapshot/hyperlink.zig b/src/terminal/snapshot/hyperlink.zig
index 6baade906..ec3b14efe 100644
--- a/src/terminal/snapshot/hyperlink.zig
+++ b/src/terminal/snapshot/hyperlink.zig
@@ -271,13 +271,8 @@ fn decodePageString(
     };
 }
 
-const test_implicit_fixture = test_fixture.parse(
-    @embedFile("testdata/hyperlink-implicit-v1.hex"),
-);
-
-const test_explicit_fixture = test_fixture.parse(
-    @embedFile("testdata/hyperlink-explicit-v1.hex"),
-);
+const test_implicit_fixture = test_fixture.parse(@embedFile("testdata/hyperlink-implicit-v1.hex"));
+const test_explicit_fixture = test_fixture.parse(@embedFile("testdata/hyperlink-explicit-v1.hex"));
 
 test "golden implicit encoding" {
     const value: terminal_hyperlink.Hyperlink = .{
diff --git a/src/terminal/snapshot/page.zig b/src/terminal/snapshot/page.zig
index 2c6c1b4d6..05ad3c03a 100644
--- a/src/terminal/snapshot/page.zig
+++ b/src/terminal/snapshot/page.zig
@@ -547,17 +547,9 @@ fn pageHyperlink(
     };
 }
 
-const test_page_fixture = test_fixture.parse(
-    @embedFile("testdata/page-v1.hex"),
-);
-
-const test_header_fixture = test_fixture.parse(
-    @embedFile("testdata/page-header-v1.hex"),
-);
-
-const test_empty_framed_page_fixture = test_fixture.parse(
-    @embedFile("testdata/page-empty-record-v1.hex"),
-);
+const test_page_fixture = test_fixture.parse(@embedFile("testdata/page-v1.hex"));
+const test_header_fixture = test_fixture.parse(@embedFile("testdata/page-header-v1.hex"));
+const test_empty_framed_page_fixture = test_fixture.parse(@embedFile("testdata/page-empty-record-v1.hex"));
 
 test "PAGE header golden encoding and decoding" {
     const header: Header = .{
diff --git a/src/terminal/snapshot/screen.zig b/src/terminal/snapshot/screen.zig
index e9de03c66..505c9c5ff 100644
--- a/src/terminal/snapshot/screen.zig
+++ b/src/terminal/snapshot/screen.zig
@@ -1117,13 +1117,8 @@ pub fn decodeCursorHyperlink(
     return try hyperlink.decode(reader, alloc);
 }
 
-const test_header_fixture = test_fixture.parse(
-    @embedFile("testdata/screen-header-v1.hex"),
-);
-
-const test_saved_cursor_fixture = test_fixture.parse(
-    @embedFile("testdata/screen-saved-cursor-v1.hex"),
-);
+const test_header_fixture = test_fixture.parse(@embedFile("testdata/screen-header-v1.hex"));
+const test_saved_cursor_fixture = test_fixture.parse(@embedFile("testdata/screen-saved-cursor-v1.hex"));
 
 fn testCharsetState() TerminalScreen.CharsetState {
     var result: TerminalScreen.CharsetState = .{
diff --git a/src/terminal/snapshot/snapshot.ksy b/src/terminal/snapshot/snapshot.ksy
new file mode 100644
index 000000000..a800b2782
--- /dev/null
+++ b/src/terminal/snapshot/snapshot.ksy
@@ -0,0 +1,998 @@
+meta:
+  id: ghostty_snapshot
+  title: Ghostty terminal snapshot
+  application: Ghostty
+  license: MIT
+  endian: le
+doc: |
+  Ghostty terminal snapshot format version 1.
+
+  A complete snapshot contains an envelope, terminal-wide state, one or two
+  renderable screen sequences, a READY checkpoint, matching history sequences,
+  and a FINISH checkpoint. SCREEN pages are oldest-to-newest. HISTORY pages are
+  newest-to-oldest.
+
+  Record CRC32C values and checkpoint BLAKE3-256 digests are represented here
+  but cannot be calculated by portable Kaitai Struct expressions. The adjacent
+  verify-kaitai.py script validates those values after parsing.
+seq:
+  - id: envelope
+    type: envelope
+  - id: terminal
+    type: terminal_record
+  - id: screens
+    type: screen_sequence
+    repeat: expr
+    repeat-expr: terminal.payload.header.screen_count
+  - id: ready
+    type: checkpoint_record(5)
+  - id: histories
+    type: history_sequence
+    repeat: expr
+    repeat-expr: terminal.payload.header.screen_count
+  - id: finish
+    type: checkpoint_record(6)
+  - id: trailing_data
+    size-eos: true
+    valid:
+      expr: _.size == 0
+enums:
+  record_tag:
+    1: terminal
+    2: screen
+    3: page
+    4: history
+    5: ready
+    6: finish
+  screen_key:
+    0: primary
+    1: alternate
+  cursor_style:
+    0: bar
+    1: block
+    2: underline
+    3: block_hollow
+  status_display:
+    0: main
+    1: status_line
+  shell_redraw:
+    0: full
+    1: none
+    2: last
+  mouse_event:
+    0: none
+    1: x10
+    2: normal
+    3: button
+    4: any
+  mouse_format:
+    0: x10
+    1: utf8
+    2: sgr
+    3: urxvt
+    4: sgr_pixels
+  mouse_shape:
+    0: default
+    1: context_menu
+    2: help
+    3: pointer
+    4: progress
+    5: wait
+    6: cell
+    7: crosshair
+    8: text
+    9: vertical_text
+    10: alias
+    11: copy
+    12: move
+    13: no_drop
+    14: not_allowed
+    15: grab
+    16: grabbing
+    17: all_scroll
+    18: col_resize
+    19: row_resize
+    20: n_resize
+    21: e_resize
+    22: s_resize
+    23: w_resize
+    24: ne_resize
+    25: nw_resize
+    26: se_resize
+    27: sw_resize
+    28: ew_resize
+    29: ns_resize
+    30: nesw_resize
+    31: nwse_resize
+    32: zoom_in
+    33: zoom_out
+  protected_mode:
+    0: "off"
+    1: iso
+    2: dec
+  semantic_click_kind:
+    0: none
+    1: click_events
+    2: cl
+  color_kind:
+    0: none
+    1: palette
+    2: rgb
+  hyperlink_kind:
+    0: none
+    1: implicit
+    2: explicit
+  cell_content_kind:
+    0: codepoint
+    1: background_palette
+    2: background_rgb
+  cell_width:
+    0: narrow
+    1: wide
+    2: spacer_tail
+    3: spacer_head
+  underline:
+    0: none
+    1: single
+    2: double
+    3: curly
+    4: dotted
+    5: dashed
+  semantic_content:
+    0: output
+    1: input
+    2: prompt
+  semantic_prompt:
+    0: none
+    1: prompt
+    2: prompt_continuation
+types:
+  envelope:
+    doc: Fixed ten-byte snapshot identification and version header.
+    seq:
+      - id: magic
+        contents: [0x47, 0x48, 0x4f, 0x53, 0x54, 0x53, 0x4e, 0x50]
+      - id: version
+        type: u2
+        valid: 1
+
+  record_header:
+    doc: |
+      Common record framing. crc32c covers the encoded tag, payload length,
+      and payload bytes, excluding the crc32c field itself.
+    params:
+      - id: expected_tag
+        type: u2
+    seq:
+      - id: tag
+        type: u2
+        valid: expected_tag
+      - id: payload_length
+        type: u4
+      - id: crc32c
+        type: u4
+
+  terminal_record:
+    seq:
+      - id: header
+        type: record_header(1)
+      - id: payload
+        type: terminal_payload
+        size: header.payload_length
+
+  screen_record:
+    seq:
+      - id: header
+        type: record_header(2)
+      - id: payload
+        type: screen_payload
+        size: header.payload_length
+
+  page_record:
+    seq:
+      - id: header
+        type: record_header(3)
+      - id: payload
+        type: page_payload
+        size: header.payload_length
+
+  history_record:
+    seq:
+      - id: header
+        type: record_header(4)
+      - id: payload
+        type: history_payload
+        size: header.payload_length
+
+  checkpoint_record:
+    params:
+      - id: expected_tag
+        type: u2
+    seq:
+      - id: header
+        type: record_header(expected_tag)
+      - id: payload
+        type: checkpoint_payload
+        size: header.payload_length
+
+  screen_sequence:
+    doc: SCREEN followed by its declared PAGE records, oldest-to-newest.
+    seq:
+      - id: screen
+        type: screen_record
+      - id: pages
+        type: page_record
+        repeat: expr
+        repeat-expr: screen.payload.header.page_count
+
+  history_sequence:
+    doc: HISTORY followed by its declared PAGE records, newest-to-oldest.
+    seq:
+      - id: history
+        type: history_record
+      - id: pages
+        type: page_record
+        repeat: expr
+        repeat-expr: history.payload.page_count
+
+  checkpoint_payload:
+    seq:
+      - id: prefix_digest
+        size: 32
+      - id: trailing_data
+        size-eos: true
+        valid:
+          expr: _.size == 0
+
+  terminal_payload:
+    seq:
+      - id: header
+        type: terminal_header
+      - id: tab_stops
+        type: tab_stops(header.columns)
+      - id: original_palette
+        type: rgb
+        repeat: expr
+        repeat-expr: 256
+      - id: palette_override_mask
+        size: 32
+      - id: palette_overrides
+        type: palette_override(palette_override_mask, _index)
+        repeat: expr
+        repeat-expr: 256
+      - id: len_pwd
+        type: u4
+      - id: pwd
+        size: len_pwd
+      - id: len_title
+        type: u4
+      - id: title
+        size: len_title
+      - id: trailing_data
+        size-eos: true
+        valid:
+          expr: _.size == 0
+
+  terminal_header:
+    seq:
+      - id: columns
+        type: u2
+        valid:
+          min: 1
+      - id: rows
+        type: u2
+        valid:
+          min: 1
+      - id: width_px
+        type: u4
+      - id: height_px
+        type: u4
+      - id: scrolling_region_top
+        type: u2
+      - id: scrolling_region_bottom
+        type: u2
+        valid:
+          expr: _ >= scrolling_region_top and _ < rows
+      - id: scrolling_region_left
+        type: u2
+      - id: scrolling_region_right
+        type: u2
+        valid:
+          expr: _ >= scrolling_region_left and _ < columns
+      - id: status_display
+        type: u1
+        enum: status_display
+        valid:
+          expr: _.to_i <= 1
+      - id: active_screen_key
+        type: u2
+        enum: screen_key
+        valid:
+          expr: _.to_i <= 1
+      - id: screen_count
+        type: u2
+        valid:
+          expr: (_ == 1 or _ == 2) and (active_screen_key.to_i == 0 or _ == 2)
+      - id: previous_codepoint
+        type: u4
+        valid:
+          expr: _ == 0xffffffff or (_ <= 0x10ffff and not (_ >= 0xd800 and _ <= 0xdfff))
+      - id: cursor_is_default
+        type: u1
+        valid:
+          max: 1
+      - id: cursor_default_style
+        type: u1
+        enum: cursor_style
+        valid:
+          expr: _.to_i <= 3
+      - id: cursor_default_blink
+        type: u1
+        valid:
+          max: 2
+      - id: shell_redraw
+        type: u1
+        enum: shell_redraw
+        valid:
+          expr: _.to_i <= 2
+      - id: modify_other_keys_2
+        type: u1
+        valid:
+          max: 1
+      - id: mouse_event
+        type: u1
+        enum: mouse_event
+        valid:
+          expr: _.to_i <= 4
+      - id: mouse_format
+        type: u1
+        enum: mouse_format
+        valid:
+          expr: _.to_i <= 4
+      - id: mouse_shift_capture
+        type: u1
+        valid:
+          max: 2
+      - id: mouse_shape
+        type: u1
+        enum: mouse_shape
+        valid:
+          expr: _.to_i <= 33
+      - id: password_input
+        type: u1
+        valid:
+          max: 1
+      - id: current_modes
+        type: mode_set
+      - id: saved_modes
+        type: mode_set
+      - id: default_modes
+        type: mode_set
+      - id: background
+        type: dynamic_rgb
+      - id: foreground
+        type: dynamic_rgb
+      - id: cursor_color
+        type: dynamic_rgb
+      - id: max_scrollback_bytes
+        type: u8
+      - id: max_scrollback_rows
+        type: u8
+
+  mode_set:
+    doc: |
+      The stable packed registry shared by current, saved, and default modes.
+      Each named instance exposes one bit from the little-endian integer.
+      Arithmetic division is used instead of bitwise operations because the
+      JavaScript target implements those operations with signed 32-bit values.
+      All values remain exact because the registry occupies only 42 bits,
+      within JavaScript's 53-bit safe integer range.
+    seq:
+      - id: raw
+        type: u8
+        valid:
+          max: 4398046511103
+    instances:
+      disable_keyboard:
+        value: (raw / 1) % 2 != 0
+      insert:
+        value: (raw / 2) % 2 != 0
+      send_receive_mode:
+        value: (raw / 4) % 2 != 0
+      linefeed:
+        value: (raw / 8) % 2 != 0
+      cursor_keys:
+        value: (raw / 16) % 2 != 0
+      column_132:
+        value: (raw / 32) % 2 != 0
+      slow_scroll:
+        value: (raw / 64) % 2 != 0
+      reverse_colors:
+        value: (raw / 128) % 2 != 0
+      origin:
+        value: (raw / 256) % 2 != 0
+      wraparound:
+        value: (raw / 512) % 2 != 0
+      autorepeat:
+        value: (raw / 1024) % 2 != 0
+      mouse_event_x10:
+        value: (raw / 2048) % 2 != 0
+      cursor_blinking:
+        value: (raw / 4096) % 2 != 0
+      cursor_visible:
+        value: (raw / 8192) % 2 != 0
+      enable_mode_3:
+        value: (raw / 16384) % 2 != 0
+      reverse_wrap:
+        value: (raw / 32768) % 2 != 0
+      alt_screen_legacy:
+        value: (raw / 65536) % 2 != 0
+      keypad_keys:
+        value: (raw / 131072) % 2 != 0
+      backarrow_key_mode:
+        value: (raw / 262144) % 2 != 0
+      enable_left_and_right_margin:
+        value: (raw / 524288) % 2 != 0
+      mouse_event_normal:
+        value: (raw / 1048576) % 2 != 0
+      mouse_event_button:
+        value: (raw / 2097152) % 2 != 0
+      mouse_event_any:
+        value: (raw / 4194304) % 2 != 0
+      focus_event:
+        value: (raw / 8388608) % 2 != 0
+      mouse_format_utf8:
+        value: (raw / 16777216) % 2 != 0
+      mouse_format_sgr:
+        value: (raw / 33554432) % 2 != 0
+      mouse_alternate_scroll:
+        value: (raw / 67108864) % 2 != 0
+      mouse_format_urxvt:
+        value: (raw / 134217728) % 2 != 0
+      mouse_format_sgr_pixels:
+        value: (raw / 268435456) % 2 != 0
+      ignore_keypad_with_numlock:
+        value: (raw / 536870912) % 2 != 0
+      alt_esc_prefix:
+        value: (raw / 1073741824) % 2 != 0
+      alt_sends_escape:
+        value: (raw / 2147483648) % 2 != 0
+      reverse_wrap_extended:
+        value: (raw / 4294967296) % 2 != 0
+      alt_screen:
+        value: (raw / 8589934592) % 2 != 0
+      save_cursor:
+        value: (raw / 17179869184) % 2 != 0
+      alt_screen_save_cursor_clear_enter:
+        value: (raw / 34359738368) % 2 != 0
+      bracketed_paste:
+        value: (raw / 68719476736) % 2 != 0
+      synchronized_output:
+        value: (raw / 137438953472) % 2 != 0
+      grapheme_cluster:
+        value: (raw / 274877906944) % 2 != 0
+      report_color_scheme:
+        value: (raw / 549755813888) % 2 != 0
+      report_visibility:
+        value: (raw / 1099511627776) % 2 != 0
+      in_band_size_reports:
+        value: (raw / 2199023255552) % 2 != 0
+
+  tab_stops:
+    params:
+      - id: columns
+        type: u2
+    seq:
+      - id: complete_bytes
+        size: columns / 8
+      - id: partial_byte
+        type: u1
+        if: columns % 8 != 0
+        valid:
+          expr: _ < (1 << (columns % 8))
+
+  rgb:
+    seq:
+      - id: red
+        type: u1
+      - id: green
+        type: u1
+      - id: blue
+        type: u1
+
+  dynamic_rgb:
+    seq:
+      - id: default_present
+        type: u1
+        valid:
+          max: 1
+      - id: default_red
+        type: u1
+        valid:
+          expr: default_present == 1 or _ == 0
+      - id: default_green
+        type: u1
+        valid:
+          expr: default_present == 1 or _ == 0
+      - id: default_blue
+        type: u1
+        valid:
+          expr: default_present == 1 or _ == 0
+      - id: override_present
+        type: u1
+        valid:
+          max: 1
+      - id: override_red
+        type: u1
+        valid:
+          expr: override_present == 1 or _ == 0
+      - id: override_green
+        type: u1
+        valid:
+          expr: override_present == 1 or _ == 0
+      - id: override_blue
+        type: u1
+        valid:
+          expr: override_present == 1 or _ == 0
+
+  palette_override:
+    params:
+      - id: mask
+        type: bytes
+      - id: index
+        type: u2
+    seq:
+      - id: color
+        type: rgb
+        if: (mask[index / 8] & (1 << (index % 8))) != 0
+
+  screen_payload:
+    seq:
+      - id: header
+        type: screen_header
+      - id: saved_cursor
+        type: saved_cursor
+        if: header.saved_cursor_present == 1
+      - id: cursor_hyperlink
+        type: hyperlink(true, false)
+      - id: trailing_data
+        size-eos: true
+        valid:
+          expr: _.size == 0
+
+  screen_header:
+    seq:
+      - id: key
+        type: u2
+        enum: screen_key
+        valid:
+          expr: _.to_i <= 1
+      - id: page_count
+        type: u2
+        valid:
+          min: 1
+      - id: cursor_x
+        type: u2
+      - id: cursor_y
+        type: u2
+      - id: cursor_style
+        type: u1
+        enum: cursor_style
+        valid:
+          expr: _.to_i <= 3
+      - id: cursor_flags
+        type: cursor_flags
+      - id: cursor_pen
+        type: style
+      - id: hyperlink_implicit_id
+        type: u4
+      - id: charset
+        type: charset_state
+      - id: protected_mode
+        type: u1
+        enum: protected_mode
+        valid:
+          expr: _.to_i <= 2
+      - id: kitty_keyboard_index
+        type: u1
+        valid:
+          max: 7
+      - id: kitty_keyboard_flags
+        type: kitty_keyboard_flags
+        repeat: expr
+        repeat-expr: 8
+      - id: semantic_click_kind
+        type: u1
+        enum: semantic_click_kind
+        valid:
+          expr: _.to_i <= 2
+      - id: semantic_click_value
+        type: u1
+        valid:
+          expr: |
+            semantic_click_kind.to_i == 0 ? _ == 0 :
+            semantic_click_kind.to_i == 1 ? _ <= 1 :
+            _ <= 3
+      - id: saved_cursor_present
+        type: u1
+        valid:
+          max: 1
+
+  cursor_flags:
+    seq:
+      - id: raw
+        type: u1
+        valid:
+          expr: (_ & 0xe0) == 0 and ((_ >> 2) & 0x3) <= 2
+    instances:
+      pending_wrap:
+        value: (raw & (1 << 0)) != 0
+      protected:
+        value: (raw & (1 << 1)) != 0
+      semantic_content:
+        value: (raw >> 2) & 0x3
+      semantic_content_clear_eol:
+        value: (raw & (1 << 4)) != 0
+
+  charset_state:
+    doc: |
+      Four selected character sets, the GL and GR slots, and an optional
+      single-shift slot. single_shift is zero for none or one plus a slot.
+    seq:
+      - id: raw
+        type: u2
+        valid:
+          expr: (_ & 0x8000) == 0 and ((_ >> 12) & 0x7) <= 4
+    instances:
+      g0:
+        value: (raw >> 0) & 0x3
+      g1:
+        value: (raw >> 2) & 0x3
+      g2:
+        value: (raw >> 4) & 0x3
+      g3:
+        value: (raw >> 6) & 0x3
+      gl:
+        value: (raw >> 8) & 0x3
+      gr:
+        value: (raw >> 10) & 0x3
+      single_shift:
+        value: (raw >> 12) & 0x7
+
+  kitty_keyboard_flags:
+    seq:
+      - id: raw
+        type: u1
+        valid:
+          expr: (_ & 0xe0) == 0
+    instances:
+      disambiguate:
+        value: (raw & (1 << 0)) != 0
+      report_events:
+        value: (raw & (1 << 1)) != 0
+      report_alternates:
+        value: (raw & (1 << 2)) != 0
+      report_all:
+        value: (raw & (1 << 3)) != 0
+      report_associated:
+        value: (raw & (1 << 4)) != 0
+
+  saved_cursor:
+    seq:
+      - id: x
+        type: u2
+      - id: y
+        type: u2
+      - id: pen
+        type: style
+      - id: flags
+        type: saved_cursor_flags
+      - id: charset
+        type: charset_state
+
+  saved_cursor_flags:
+    seq:
+      - id: raw
+        type: u1
+        valid:
+          expr: (_ & 0xf8) == 0
+    instances:
+      protected:
+        value: (raw & (1 << 0)) != 0
+      pending_wrap:
+        value: (raw & (1 << 1)) != 0
+      origin:
+        value: (raw & (1 << 2)) != 0
+
+  history_payload:
+    seq:
+      - id: key
+        type: u2
+        enum: screen_key
+        valid:
+          expr: _.to_i <= 1
+      - id: page_count
+        type: u4
+      - id: total_rows
+        type: u8
+      - id: screen_overlap_rows
+        type: u2
+      - id: trailing_data
+        size-eos: true
+        valid:
+          expr: _.size == 0
+
+  page_payload:
+    seq:
+      - id: header
+        type: page_header
+      - id: styles
+        type: style_table_entry
+        repeat: expr
+        repeat-expr: header.style_count
+      - id: hyperlinks
+        type: hyperlink_table_entry
+        repeat: expr
+        repeat-expr: header.hyperlink_count
+      - id: grid
+        type: grid(header.rows, header.columns)
+      - id: trailing_data
+        size-eos: true
+        valid:
+          expr: _.size == 0
+
+  page_header:
+    seq:
+      - id: columns
+        type: u2
+        valid:
+          min: 1
+      - id: rows
+        type: u2
+        valid:
+          min: 1
+      - id: style_count
+        type: u2
+      - id: hyperlink_count
+        type: u2
+      - id: style_capacity
+        type: u2
+      - id: hyperlink_capacity_bytes
+        type: u2
+      - id: grapheme_capacity_bytes
+        type: u4
+      - id: string_capacity_bytes
+        type: u4
+
+  style_table_entry:
+    seq:
+      - id: encoded_id
+        type: u2
+        valid:
+          min: 1
+      - id: value
+        type: style
+
+  hyperlink_table_entry:
+    seq:
+      - id: encoded_id
+        type: u2
+        valid:
+          min: 1
+      - id: value
+        type: hyperlink(false, true)
+
+  style:
+    seq:
+      - id: foreground
+        type: style_color
+      - id: background
+        type: style_color
+      - id: underline_color
+        type: style_color
+      - id: flags
+        type: style_flags
+      - id: reserved
+        type: u2
+        valid: 0
+
+  style_flags:
+    seq:
+      - id: raw
+        type: u2
+        valid:
+          expr: (_ & 0xf800) == 0 and ((_ >> 8) & 0x7) <= 5
+    instances:
+      bold:
+        value: (raw & (1 << 0)) != 0
+      italic:
+        value: (raw & (1 << 1)) != 0
+      faint:
+        value: (raw & (1 << 2)) != 0
+      blink:
+        value: (raw & (1 << 3)) != 0
+      inverse:
+        value: (raw & (1 << 4)) != 0
+      invisible:
+        value: (raw & (1 << 5)) != 0
+      strikethrough:
+        value: (raw & (1 << 6)) != 0
+      overline:
+        value: (raw & (1 << 7)) != 0
+      underline:
+        value: (raw >> 8) & 0x7
+
+  style_color:
+    seq:
+      - id: kind
+        type: u1
+        enum: color_kind
+        valid:
+          expr: _.to_i <= 2
+      - id: first
+        type: u1
+        valid:
+          expr: kind.to_i != 0 or _ == 0
+      - id: second
+        type: u1
+        valid:
+          expr: kind.to_i == 2 or _ == 0
+      - id: third
+        type: u1
+        valid:
+          expr: kind.to_i == 2 or _ == 0
+
+  hyperlink:
+    params:
+      - id: allow_none
+        type: bool
+      - id: allow_empty
+        type: bool
+    seq:
+      - id: kind
+        type: u1
+        enum: hyperlink_kind
+        valid:
+          expr: _.to_i <= 2 and (allow_none or _.to_i != 0)
+      - id: implicit
+        type: implicit_hyperlink(allow_empty)
+        if: kind.to_i == 1
+      - id: explicit
+        type: explicit_hyperlink(allow_empty)
+        if: kind.to_i == 2
+
+  implicit_hyperlink:
+    params:
+      - id: allow_empty
+        type: bool
+    seq:
+      - id: id
+        type: u4
+      - id: len_uri
+        type: u4
+        valid:
+          expr: allow_empty or _ >= 1
+      - id: uri
+        size: len_uri
+
+  explicit_hyperlink:
+    params:
+      - id: allow_empty
+        type: bool
+    seq:
+      - id: len_id
+        type: u4
+        valid:
+          expr: allow_empty or _ >= 1
+      - id: id
+        size: len_id
+      - id: len_uri
+        type: u4
+        valid:
+          expr: allow_empty or _ >= 1
+      - id: uri
+        size: len_uri
+
+  grid:
+    params:
+      - id: num_rows
+        type: u2
+      - id: columns
+        type: u2
+    seq:
+      - id: rows
+        type: grid_row(columns)
+        repeat: expr
+        repeat-expr: num_rows
+
+  grid_row:
+    params:
+      - id: num_cells
+        type: u2
+    seq:
+      - id: flags
+        type: grid_row_flags
+      - id: cells
+        type: grid_cell(_index, num_cells, flags.wrap)
+        repeat: expr
+        repeat-expr: num_cells
+
+  grid_row_flags:
+    seq:
+      - id: raw
+        type: u1
+        valid:
+          expr: (_ & 0xf0) == 0 and ((_ >> 2) & 0x3) <= 2
+    instances:
+      wrap:
+        value: (raw & 1) != 0
+      wrap_continuation:
+        value: (raw & 2) != 0
+      semantic_prompt:
+        value: (raw >> 2) & 0x3
+
+  grid_cell:
+    params:
+      - id: index
+        type: u2
+      - id: columns
+        type: u2
+      - id: row_wrap
+        type: bool
+    seq:
+      - id: content_kind
+        type: u1
+        valid:
+          max: 2
+      - id: width
+        type: u1
+        valid:
+          expr: |
+            _ <= 3 and
+            (_ != 2 or
+              (index > 0 and _parent.cells[index - 1].width == 1)) and
+            (_ != 3 or
+              (index + 1 == columns and row_wrap))
+      - id: flags
+        type: grid_cell_flags
+      - id: reserved
+        type: u1
+        valid: 0
+      - id: style_id
+        type: u2
+      - id: hyperlink_id
+        type: u2
+      - id: value
+        type: u4
+        valid:
+          expr: |
+            content_kind == 0 ?
+              (_ <= 0x10ffff and not (_ >= 0xd800 and _ <= 0xdfff) and _ != 0x10eeee) :
+            content_kind == 1 ?
+              _ <= 0xff :
+              _ <= 0xffffff
+      - id: num_graphemes
+        type: u4
+        valid:
+          expr: |
+            content_kind == 0 ?
+              (_ == 0 or value != 0) :
+              _ == 0
+      - id: graphemes
+        type: u4
+        repeat: expr
+        repeat-expr: num_graphemes
+        valid:
+          expr: _ <= 0x10ffff and not (_ >= 0xd800 and _ <= 0xdfff) and _ != 0x10eeee
+
+  grid_cell_flags:
+    seq:
+      - id: raw
+        type: u1
+        valid:
+          expr: (_ & 0xf8) == 0 and ((_ >> 1) & 0x3) <= 2
+    instances:
+      protected:
+        value: (raw & (1 << 0)) != 0
+      semantic_content:
+        value: (raw >> 1) & 0x3
diff --git a/src/terminal/snapshot/style.zig b/src/terminal/snapshot/style.zig
index 268c29289..69e0973c2 100644
--- a/src/terminal/snapshot/style.zig
+++ b/src/terminal/snapshot/style.zig
@@ -216,9 +216,7 @@ fn computeLen() usize {
     }
 }
 
-const test_golden_fixture = test_fixture.parse(
-    @embedFile("testdata/style-v1.hex"),
-);
+const test_golden_fixture = test_fixture.parse(@embedFile("testdata/style-v1.hex"));
 
 test "golden encoding and decoding" {
     const value: terminal_style.Style = .{
diff --git a/src/terminal/snapshot/testdata/checkpoint-ready-v1.hex b/src/terminal/snapshot/testdata/checkpoint-ready-v1.hex
index b3a24104b..51381196c 100644
--- a/src/terminal/snapshot/testdata/checkpoint-ready-v1.hex
+++ b/src/terminal/snapshot/testdata/checkpoint-ready-v1.hex
@@ -1,4 +1,7 @@
 # Ghostty snapshot fixture
+# Kaitai type: checkpoint_record
+# Kaitai params: 5
+# Kaitai offset: 3
 # Wire version: 1
 # Generated by its snapshot test; review before replacing.
 # On mismatch, the candidate is copied to the repository root.
diff --git a/src/terminal/snapshot/testdata/complete-v1.hex b/src/terminal/snapshot/testdata/complete-v1.hex
index 8982c2add..01a72f1ea 100644
--- a/src/terminal/snapshot/testdata/complete-v1.hex
+++ b/src/terminal/snapshot/testdata/complete-v1.hex
@@ -1,4 +1,7 @@
 # Ghostty snapshot fixture
+# Kaitai type: ghostty_snapshot
+# Kaitai params:
+# Kaitai offset: 0
 # Wire version: 1
 # Generated by its snapshot test; review before replacing.
 # On mismatch, the candidate is copied to the repository root.
diff --git a/src/terminal/snapshot/testdata/envelope-v1.hex b/src/terminal/snapshot/testdata/envelope-v1.hex
index 3e4ddadfa..04a7eb6d5 100644
--- a/src/terminal/snapshot/testdata/envelope-v1.hex
+++ b/src/terminal/snapshot/testdata/envelope-v1.hex
@@ -1,4 +1,7 @@
 # Ghostty snapshot fixture
+# Kaitai type: envelope
+# Kaitai params:
+# Kaitai offset: 0
 # Wire version: 1
 # Generated by its snapshot test; review before replacing.
 # On mismatch, the candidate is copied to the repository root.
diff --git a/src/terminal/snapshot/testdata/grid-v1.hex b/src/terminal/snapshot/testdata/grid-v1.hex
index 83a668326..3389a876f 100644
--- a/src/terminal/snapshot/testdata/grid-v1.hex
+++ b/src/terminal/snapshot/testdata/grid-v1.hex
@@ -1,4 +1,7 @@
 # Ghostty snapshot fixture
+# Kaitai type: grid
+# Kaitai params: 2 3
+# Kaitai offset: 0
 # Wire version: 1
 # Generated by its snapshot test; review before replacing.
 # On mismatch, the candidate is copied to the repository root.
diff --git a/src/terminal/snapshot/testdata/history-header-v1.hex b/src/terminal/snapshot/testdata/history-header-v1.hex
index 7949ca620..6e44379dc 100644
--- a/src/terminal/snapshot/testdata/history-header-v1.hex
+++ b/src/terminal/snapshot/testdata/history-header-v1.hex
@@ -1,4 +1,7 @@
 # Ghostty snapshot fixture
+# Kaitai type: history_payload
+# Kaitai params:
+# Kaitai offset: 0
 # Wire version: 1
 # Generated by its snapshot test; review before replacing.
 # On mismatch, the candidate is copied to the repository root.
diff --git a/src/terminal/snapshot/testdata/hyperlink-explicit-v1.hex b/src/terminal/snapshot/testdata/hyperlink-explicit-v1.hex
index 6f925099a..7643b203a 100644
--- a/src/terminal/snapshot/testdata/hyperlink-explicit-v1.hex
+++ b/src/terminal/snapshot/testdata/hyperlink-explicit-v1.hex
@@ -1,4 +1,7 @@
 # Ghostty snapshot fixture
+# Kaitai type: hyperlink
+# Kaitai params: false false
+# Kaitai offset: 0
 # Wire version: 1
 # Generated by its snapshot test; review before replacing.
 # On mismatch, the candidate is copied to the repository root.
diff --git a/src/terminal/snapshot/testdata/hyperlink-implicit-v1.hex b/src/terminal/snapshot/testdata/hyperlink-implicit-v1.hex
index 8ae474676..cb15cf123 100644
--- a/src/terminal/snapshot/testdata/hyperlink-implicit-v1.hex
+++ b/src/terminal/snapshot/testdata/hyperlink-implicit-v1.hex
@@ -1,4 +1,7 @@
 # Ghostty snapshot fixture
+# Kaitai type: hyperlink
+# Kaitai params: false false
+# Kaitai offset: 0
 # Wire version: 1
 # Generated by its snapshot test; review before replacing.
 # On mismatch, the candidate is copied to the repository root.
diff --git a/src/terminal/snapshot/testdata/page-empty-record-v1.hex b/src/terminal/snapshot/testdata/page-empty-record-v1.hex
index 06db7cc54..4b759b704 100644
--- a/src/terminal/snapshot/testdata/page-empty-record-v1.hex
+++ b/src/terminal/snapshot/testdata/page-empty-record-v1.hex
@@ -1,4 +1,7 @@
 # Ghostty snapshot fixture
+# Kaitai type: page_record
+# Kaitai params:
+# Kaitai offset: 0
 # Wire version: 1
 # Generated by its snapshot test; review before replacing.
 # On mismatch, the candidate is copied to the repository root.
diff --git a/src/terminal/snapshot/testdata/page-header-v1.hex b/src/terminal/snapshot/testdata/page-header-v1.hex
index 811ad80fc..b7b00765f 100644
--- a/src/terminal/snapshot/testdata/page-header-v1.hex
+++ b/src/terminal/snapshot/testdata/page-header-v1.hex
@@ -1,4 +1,7 @@
 # Ghostty snapshot fixture
+# Kaitai type: page_header
+# Kaitai params:
+# Kaitai offset: 0
 # Wire version: 1
 # Generated by its snapshot test; review before replacing.
 # On mismatch, the candidate is copied to the repository root.
diff --git a/src/terminal/snapshot/testdata/page-v1.hex b/src/terminal/snapshot/testdata/page-v1.hex
index d3c04d0c4..dfc53eeaa 100644
--- a/src/terminal/snapshot/testdata/page-v1.hex
+++ b/src/terminal/snapshot/testdata/page-v1.hex
@@ -1,4 +1,7 @@
 # Ghostty snapshot fixture
+# Kaitai type: page_payload
+# Kaitai params:
+# Kaitai offset: 0
 # Wire version: 1
 # Generated by its snapshot test; review before replacing.
 # On mismatch, the candidate is copied to the repository root.
diff --git a/src/terminal/snapshot/testdata/record-page-header-v1.hex b/src/terminal/snapshot/testdata/record-page-header-v1.hex
index 339246dab..28e6269ae 100644
--- a/src/terminal/snapshot/testdata/record-page-header-v1.hex
+++ b/src/terminal/snapshot/testdata/record-page-header-v1.hex
@@ -1,4 +1,7 @@
 # Ghostty snapshot fixture
+# Kaitai type: record_header
+# Kaitai params: 3
+# Kaitai offset: 0
 # Wire version: 1
 # Generated by its snapshot test; review before replacing.
 # On mismatch, the candidate is copied to the repository root.
diff --git a/src/terminal/snapshot/testdata/screen-header-v1.hex b/src/terminal/snapshot/testdata/screen-header-v1.hex
index 3b8f9ef92..950d5736b 100644
--- a/src/terminal/snapshot/testdata/screen-header-v1.hex
+++ b/src/terminal/snapshot/testdata/screen-header-v1.hex
@@ -1,4 +1,7 @@
 # Ghostty snapshot fixture
+# Kaitai type: screen_header
+# Kaitai params:
+# Kaitai offset: 0
 # Wire version: 1
 # Generated by its snapshot test; review before replacing.
 # On mismatch, the candidate is copied to the repository root.
diff --git a/src/terminal/snapshot/testdata/screen-saved-cursor-v1.hex b/src/terminal/snapshot/testdata/screen-saved-cursor-v1.hex
index 62470761c..f4bd7e3ab 100644
--- a/src/terminal/snapshot/testdata/screen-saved-cursor-v1.hex
+++ b/src/terminal/snapshot/testdata/screen-saved-cursor-v1.hex
@@ -1,4 +1,7 @@
 # Ghostty snapshot fixture
+# Kaitai type: saved_cursor
+# Kaitai params:
+# Kaitai offset: 0
 # Wire version: 1
 # Generated by its snapshot test; review before replacing.
 # On mismatch, the candidate is copied to the repository root.
diff --git a/src/terminal/snapshot/testdata/style-v1.hex b/src/terminal/snapshot/testdata/style-v1.hex
index 94e381cda..0e834f870 100644
--- a/src/terminal/snapshot/testdata/style-v1.hex
+++ b/src/terminal/snapshot/testdata/style-v1.hex
@@ -1,4 +1,7 @@
 # Ghostty snapshot fixture
+# Kaitai type: style
+# Kaitai params:
+# Kaitai offset: 0
 # Wire version: 1
 # Generated by its snapshot test; review before replacing.
 # On mismatch, the candidate is copied to the repository root.
diff --git a/src/terminal/snapshot/testdata/terminal-header-v1.hex b/src/terminal/snapshot/testdata/terminal-header-v1.hex
index 690891c65..9c9eb4bfb 100644
--- a/src/terminal/snapshot/testdata/terminal-header-v1.hex
+++ b/src/terminal/snapshot/testdata/terminal-header-v1.hex
@@ -1,4 +1,7 @@
 # Ghostty snapshot fixture
+# Kaitai type: terminal_header
+# Kaitai params:
+# Kaitai offset: 0
 # Wire version: 1
 # Generated by its snapshot test; review before replacing.
 # On mismatch, the candidate is copied to the repository root.
diff --git a/src/terminal/snapshot/verify-kaitai.py b/src/terminal/snapshot/verify-kaitai.py
new file mode 100755
index 000000000..1a88ab41c
--- /dev/null
+++ b/src/terminal/snapshot/verify-kaitai.py
@@ -0,0 +1,422 @@
+#!/usr/bin/env python3
+"""Compile the snapshot Kaitai schema and parse every checked-in fixture.
+
+Run this from a Ghostty development shell:
+
+    src/terminal/snapshot/verify-kaitai.py
+
+To turn an annotated fixture into a binary suitable for the Kaitai Web IDE:
+
+    src/terminal/snapshot/verify-kaitai.py \
+        --write-binary \
+        src/terminal/snapshot/testdata/complete-v1.hex \
+        /tmp/complete-v1.bin
+
+Then load `snapshot.ksy` and the generated binary into
+https://ide.kaitai.io/.
+
+The generated Python parser exists only in a temporary directory. This keeps
+snapshot.ksy as the source of truth and ensures this check cannot accidentally
+pass against stale generated code. After structural parsing, the script checks
+record CRC32C values, checkpoint BLAKE3 digests, and cross-record invariants
+that portable Kaitai expressions cannot represent.
+"""
+
+from __future__ import annotations
+
+import argparse
+import importlib
+import io
+import shutil
+import struct
+import subprocess
+import sys
+import tempfile
+from dataclasses import dataclass
+from pathlib import Path
+from typing import Any
+
+try:
+    from blake3 import blake3
+    from kaitaistruct import KaitaiStream
+except ImportError as error:
+    raise SystemExit(
+        "missing Kaitai verifier dependencies; run this inside "
+        "`nix develop`"
+    ) from error
+
+
+SNAPSHOT_DIR = Path(__file__).resolve().parent
+SCHEMA_PATH = SNAPSHOT_DIR / "snapshot.ksy"
+TESTDATA_DIR = SNAPSHOT_DIR / "testdata"
+SNAPSHOT_ENVELOPE_SIZE = 10
+RECORD_HEADER_SIZE = struct.calcsize("<HII")
+
+
+@dataclass(frozen=True)
+class Fixture:
+    path: Path
+    type_name: str
+    params: tuple[object, ...]
+    offset: int
+    data: bytes
+
+
+def load_fixture(path: Path) -> Fixture:
+    """Load one self-describing annotated hexadecimal fixture."""
+    metadata: dict[str, str] = {}
+    chunks: list[str] = []
+    for line in path.read_text(encoding="utf-8").splitlines():
+        content, separator, comment = line.partition("#")
+        chunks.extend(content.split())
+
+        if not separator:
+            continue
+        comment = comment.strip()
+        if not comment.startswith("Kaitai "):
+            continue
+        key, colon, value = comment.removeprefix("Kaitai ").partition(":")
+        if not colon or key not in {"type", "params", "offset"}:
+            raise ValueError(f"{path}: invalid Kaitai metadata: {comment}")
+        if key in metadata:
+            raise ValueError(f"{path}: duplicate Kaitai {key} metadata")
+        metadata[key] = value.strip()
+
+    try:
+        data = bytes.fromhex(" ".join(chunks))
+    except ValueError as error:
+        raise ValueError(f"{path}: invalid annotated hexadecimal") from error
+
+    required = {"type", "params", "offset"}
+    if metadata.keys() != required:
+        missing = sorted(required - metadata.keys())
+        extra = sorted(metadata.keys() - required)
+        raise ValueError(
+            f"{path}: Kaitai metadata drift: missing={missing}, extra={extra}"
+        )
+    if not metadata["type"]:
+        raise ValueError(f"{path}: empty Kaitai type")
+
+    params: list[object] = []
+    for value in metadata["params"].split():
+        if value == "true":
+            params.append(True)
+        elif value == "false":
+            params.append(False)
+        else:
+            try:
+                params.append(int(value, 0))
+            except ValueError as error:
+                raise ValueError(
+                    f"{path}: invalid Kaitai parameter {value!r}"
+                ) from error
+
+    try:
+        offset = int(metadata["offset"], 0)
+    except ValueError as error:
+        raise ValueError(f"{path}: invalid Kaitai offset") from error
+    if offset < 0 or offset > len(data):
+        raise ValueError(f"{path}: Kaitai offset is outside the fixture")
+
+    return Fixture(
+        path=path,
+        type_name=metadata["type"],
+        params=tuple(params),
+        offset=offset,
+        data=data,
+    )
+
+
+def parse_type(
+    parser_type: type[Any],
+    data: bytes,
+    *params: object,
+) -> Any:
+    """Construct one generated Kaitai type and require exact exhaustion."""
+    stream = KaitaiStream(io.BytesIO(data))
+    result = parser_type(*params, stream)
+    if not stream.is_eof():
+        raise ValueError(
+            f"{parser_type.__name__} left "
+            f"{stream.size() - stream.pos()} trailing bytes"
+        )
+    return result
+
+
+def crc32c(data: bytes) -> int:
+    """Return CRC32C using the reflected Castagnoli polynomial."""
+    result = 0xFFFFFFFF
+    for byte in data:
+        result ^= byte
+        for _ in range(8):
+            result = (
+                (result >> 1) ^ 0x82F63B78
+                if result & 1
+                else result >> 1
+            )
+    return result ^ 0xFFFFFFFF
+
+
+def validate_record(record: Any, data: bytes, offset: int) -> int:
+    """Validate one parsed record's source bytes and CRC32C."""
+    payload = record._raw_payload
+    header = record.header
+    if header.payload_length != len(payload):
+        raise ValueError(
+            f"record at 0x{offset:x}: declared {header.payload_length} "
+            f"payload bytes but parsed {len(payload)}"
+        )
+
+    encoded_header = data[offset : offset + RECORD_HEADER_SIZE]
+    expected_header = struct.pack(
+        "<HII",
+        header.tag,
+        header.payload_length,
+        header.crc32c,
+    )
+    if encoded_header != expected_header:
+        raise ValueError(f"record at 0x{offset:x}: parsed header drift")
+
+    covered = struct.pack("<HI", header.tag, header.payload_length) + payload
+    actual_crc = crc32c(covered)
+    if header.crc32c != actual_crc:
+        raise ValueError(
+            f"record at 0x{offset:x}: CRC32C 0x{header.crc32c:08x} "
+            f"does not match 0x{actual_crc:08x}"
+        )
+
+    return offset + RECORD_HEADER_SIZE + len(payload)
+
+
+def all_snapshot_records(snapshot: Any) -> list[Any]:
+    """Return complete-snapshot records in their authenticated wire order."""
+    records = [snapshot.terminal]
+    for sequence in snapshot.screens:
+        records.append(sequence.screen)
+        records.extend(sequence.pages)
+    records.append(snapshot.ready)
+    for sequence in snapshot.histories:
+        records.append(sequence.history)
+        records.extend(sequence.pages)
+    records.append(snapshot.finish)
+    return records
+
+
+def validate_complete_snapshot(snapshot: Any, data: bytes) -> None:
+    """Validate ordering relationships, record CRCs, and checkpoints."""
+    screen_keys = [
+        sequence.screen.payload.header.key for sequence in snapshot.screens
+    ]
+    history_keys = [
+        sequence.history.payload.key for sequence in snapshot.histories
+    ]
+    if len(set(screen_keys)) != len(screen_keys):
+        raise ValueError("complete snapshot contains a duplicate SCREEN key")
+    if len(set(history_keys)) != len(history_keys):
+        raise ValueError("complete snapshot contains a duplicate HISTORY key")
+    if set(screen_keys) != set(history_keys):
+        raise ValueError("SCREEN and HISTORY keys do not match")
+
+    terminal_header = snapshot.terminal.payload.header
+    expected_key_values = (
+        {0} if terminal_header.screen_count == 1 else {0, 1}
+    )
+    screen_key_values = {key.value for key in screen_keys}
+    if screen_key_values != expected_key_values:
+        raise ValueError(
+            f"TERMINAL declares screen keys {expected_key_values}, "
+            f"but SCREEN records contain {screen_key_values}"
+        )
+
+    screens_by_key = {
+        sequence.screen.payload.header.key: sequence
+        for sequence in snapshot.screens
+    }
+    for sequence in snapshot.screens:
+        header = sequence.screen.payload.header
+        if (
+            header.cursor_x >= terminal_header.columns
+            or header.cursor_y >= terminal_header.rows
+            or (
+                header.cursor_flags.pending_wrap
+                and header.cursor_x != terminal_header.columns - 1
+            )
+        ):
+            raise ValueError(f"SCREEN key {header.key}: invalid cursor position")
+
+    for sequence in snapshot.histories:
+        payload = sequence.history.payload
+        screen = screens_by_key[payload.key]
+        screen_rows = sum(
+            page.payload.header.rows for page in screen.pages
+        )
+        if screen_rows < terminal_header.rows:
+            raise ValueError(
+                f"SCREEN key {payload.key}: PAGE rows do not cover "
+                "the active area"
+            )
+        overlap_rows = screen_rows - terminal_header.rows
+        if payload.screen_overlap_rows != overlap_rows:
+            raise ValueError(
+                f"HISTORY key {payload.key}: screen_overlap_rows "
+                f"{payload.screen_overlap_rows} does not match {overlap_rows}"
+            )
+
+        total_rows = payload.screen_overlap_rows + sum(
+            page.payload.header.rows for page in sequence.pages
+        )
+        if total_rows != payload.total_rows:
+            raise ValueError(
+                f"HISTORY key {payload.key}: total_rows "
+                f"{payload.total_rows} does not match {total_rows}"
+            )
+
+    for record in all_snapshot_records(snapshot):
+        if not hasattr(record, "payload"):
+            continue
+        payload = record.payload
+        if not hasattr(payload, "styles"):
+            continue
+        style_ids = [entry.encoded_id for entry in payload.styles]
+        hyperlink_ids = [entry.encoded_id for entry in payload.hyperlinks]
+        if len(set(style_ids)) != len(style_ids):
+            raise ValueError("PAGE contains a duplicate style ID")
+        if len(set(hyperlink_ids)) != len(hyperlink_ids):
+            raise ValueError("PAGE contains a duplicate hyperlink ID")
+
+    offset = SNAPSHOT_ENVELOPE_SIZE
+    for record in all_snapshot_records(snapshot):
+        if record is snapshot.ready:
+            expected = blake3(data[:offset]).digest()
+            if record.payload.prefix_digest != expected:
+                raise ValueError("READY BLAKE3-256 digest does not match")
+        elif record is snapshot.finish:
+            expected = blake3(data[:offset]).digest()
+            if record.payload.prefix_digest != expected:
+                raise ValueError("FINISH BLAKE3-256 digest does not match")
+        offset = validate_record(record, data, offset)
+
+    if offset != len(data):
+        raise ValueError(
+            f"complete snapshot accounted for {offset} of {len(data)} bytes"
+        )
+
+
+def compile_schema(output_dir: Path) -> type[Any]:
+    """Compile snapshot.ksy and import its temporary Python parser."""
+    compiler = shutil.which("kaitai-struct-compiler") or shutil.which("ksc")
+    if compiler is None:
+        raise SystemExit(
+            "kaitai-struct-compiler is not available; run this inside "
+            "`nix develop`"
+        )
+
+    subprocess.run(
+        [
+            compiler,
+            "--target=python",
+            f"--outdir={output_dir}",
+            str(SCHEMA_PATH),
+        ],
+        check=True,
+    )
+
+    sys.path.insert(0, str(output_dir))
+    try:
+        module = importlib.import_module("ghostty_snapshot")
+    finally:
+        sys.path.pop(0)
+    return module.GhosttySnapshot
+
+
+def resolve_type(parser: type[Any], type_name: str) -> type[Any]:
+    """Resolve one KSY snake-case type name on the generated parser."""
+    root_type_name = "".join(
+        f"_{character.lower()}" if character.isupper() else character
+        for character in parser.__name__
+    ).lstrip("_")
+    if type_name == root_type_name:
+        return parser
+
+    class_name = "".join(
+        part[:1].upper() + part[1:] for part in type_name.split("_")
+    )
+    try:
+        return getattr(parser, class_name)
+    except AttributeError as error:
+        raise ValueError(f"snapshot.ksy has no type {type_name!r}") from error
+
+
+def main() -> int:
+    cli = argparse.ArgumentParser(description=__doc__)
+    cli.add_argument(
+        "--write-binary",
+        nargs=2,
+        metavar=("FIXTURE", "OUTPUT"),
+        type=Path,
+        help="decode one annotated fixture into a raw binary",
+    )
+    args = cli.parse_args()
+
+    if args.write_binary:
+        fixture_path, output_path = args.write_binary
+        fixture = load_fixture(fixture_path)
+        output_path.write_bytes(fixture.data)
+        print(f"wrote {len(fixture.data)} bytes to {output_path}")
+        return 0
+
+    with tempfile.TemporaryDirectory(prefix="ghostty-kaitai-") as temp:
+        parser = compile_schema(Path(temp))
+
+        fixture_paths = sorted(TESTDATA_DIR.rglob("*.hex"))
+        if not fixture_paths:
+            raise ValueError(f"{TESTDATA_DIR}: no snapshot fixtures")
+
+        for path in fixture_paths:
+            fixture = load_fixture(path)
+            parser_type = resolve_type(parser, fixture.type_name)
+            fixture_label = path.relative_to(TESTDATA_DIR)
+            try:
+                parsed = parse_type(
+                    parser_type,
+                    fixture.data[fixture.offset:],
+                    *fixture.params,
+                )
+            except Exception as error:
+                raise ValueError(
+                    f"{fixture_label}: Kaitai parse failed"
+                ) from error
+
+            if parser_type is parser:
+                if fixture.offset != 0:
+                    raise ValueError(
+                        f"{fixture_label}: root parser must begin at offset zero"
+                    )
+                validate_complete_snapshot(parsed, fixture.data)
+            elif hasattr(parsed, "_raw_payload"):
+                record_end = validate_record(
+                    parsed,
+                    fixture.data,
+                    fixture.offset,
+                )
+                if record_end != len(fixture.data):
+                    raise ValueError(
+                        f"{fixture_label}: record has trailing data"
+                    )
+                if hasattr(parsed.payload, "prefix_digest"):
+                    expected = blake3(
+                        fixture.data[:fixture.offset]
+                    ).digest()
+                    if parsed.payload.prefix_digest != expected:
+                        raise ValueError(
+                            f"{fixture_label}: checkpoint digest does not match"
+                        )
+
+            print(f"ok {fixture_label}")
+
+    print(f"validated {len(fixture_paths)} snapshot fixtures")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())