lib-vt: expose key encoding as a C API

example/c-vt-key-encode/README.md

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+# Example: `ghostty-vt` C Key Encoding
+
+This example demonstrates how to use the `ghostty-vt` C library to encode key
+events into terminal escape sequences.
+
+This example specifically shows how to:
+
+1. Create a key encoder with the C API
+2. Configure Kitty keyboard protocol flags (this example uses KKP)
+3. Create and configure a key event
+4. Encode the key event into a terminal escape sequence
+
+The example encodes a Ctrl key release event with the Ctrl modifier set,
+producing the escape sequence `\x1b[57442;5:3u`.
+
+## Usage
+
+Run the program:
+
+```shell-session
+zig build run
+```

example/c-vt-key-encode/build.zig

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+const std = @import("std");
+
+pub fn build(b: *std.Build) void {
+    const target = b.standardTargetOptions(.{});
+    const optimize = b.standardOptimizeOption(.{});
+
+    const run_step = b.step("run", "Run the app");
+
+    const exe_mod = b.createModule(.{
+        .target = target,
+        .optimize = optimize,
+    });
+    exe_mod.addCSourceFiles(.{
+        .root = b.path("src"),
+        .files = &.{"main.c"},
+    });
+
+    // You'll want to use a lazy dependency here so that ghostty is only
+    // downloaded if you actually need it.
+    if (b.lazyDependency("ghostty", .{
+        // Setting simd to false will force a pure static build that
+        // doesn't even require libc, but it has a significant performance
+        // penalty. If your embedding app requires libc anyway, you should
+        // always keep simd enabled.
+        // .simd = false,
+    })) |dep| {
+        exe_mod.linkLibrary(dep.artifact("ghostty-vt"));
+    }
+
+    // Exe
+    const exe = b.addExecutable(.{
+        .name = "c_vt_key_encode",
+        .root_module = exe_mod,
+    });
+    b.installArtifact(exe);
+
+    // Run
+    const run_cmd = b.addRunArtifact(exe);
+    run_cmd.step.dependOn(b.getInstallStep());
+    if (b.args) |args| run_cmd.addArgs(args);
+    run_step.dependOn(&run_cmd.step);
+}

example/c-vt-key-encode/build.zig.zon

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+.{
+    .name = .c_vt,
+    .version = "0.0.0",
+    .fingerprint = 0x413a8529b1255f9a,
+    .minimum_zig_version = "0.15.1",
+    .dependencies = .{
+        // Ghostty dependency. In reality, you'd probably use a URL-based
+        // dependency like the one showed (and commented out) below this one.
+        // We use a path dependency here for simplicity and to ensure our
+        // examples always test against the source they're bundled with.
+        .ghostty = .{ .path = "../../" },
+
+        // Example of what a URL-based dependency looks like:
+        // .ghostty = .{
+        //     .url = "https://github.com/ghostty-org/ghostty/archive/COMMIT.tar.gz",
+        //     .hash = "N-V-__8AAMVLTABmYkLqhZPLXnMl-KyN38R8UVYqGrxqO36s",
+        // },
+    },
+    .paths = .{
+        "build.zig",
+        "build.zig.zon",
+        "src",
+    },
+}

example/c-vt-key-encode/src/main.c

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+#include <assert.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <string.h>
+#include <ghostty/vt.h>
+
+int main() {
+  GhosttyKeyEncoder encoder;
+  GhosttyResult result = ghostty_key_encoder_new(NULL, &encoder);
+  assert(result == GHOSTTY_SUCCESS);
+
+  // Set kitty flags with all features enabled
+  ghostty_key_encoder_setopt(encoder, GHOSTTY_KEY_ENCODER_OPT_KITTY_FLAGS, &(uint8_t){GHOSTTY_KITTY_KEY_ALL});
+
+  // Create key event
+  GhosttyKeyEvent event;
+  result = ghostty_key_event_new(NULL, &event);
+  assert(result == GHOSTTY_SUCCESS);
+  ghostty_key_event_set_action(event, GHOSTTY_KEY_ACTION_RELEASE);
+  ghostty_key_event_set_key(event, GHOSTTY_KEY_CONTROL_LEFT);
+  ghostty_key_event_set_mods(event, GHOSTTY_MODS_CTRL);
+  printf("Encoding event: left ctrl release with all Kitty flags enabled\n");
+
+  // Optionally, encode with null buffer to get required size. You can
+  // skip this step and provide a sufficiently large buffer directly.
+  // If there isn't enoug hspace, the function will return an out of memory
+  // error.
+  size_t required = 0;
+  result = ghostty_key_encoder_encode(encoder, event, NULL, 0, &required);
+  assert(result == GHOSTTY_OUT_OF_MEMORY);
+  printf("Required buffer size: %zu bytes\n", required);
+
+  // Encode the key event. We don't use our required size above because
+  // that was just an example; we know 128 bytes is enough.
+  char buf[128];
+  size_t written = 0;
+  result = ghostty_key_encoder_encode(encoder, event, buf, sizeof(buf), &written);
+  assert(result == GHOSTTY_SUCCESS);
+  printf("Encoded %zu bytes\n", written);
+
+  // Print the encoded sequence (hex and string)
+  printf("Hex: ");
+  for (size_t i = 0; i < written; i++) printf("%02x ", (unsigned char)buf[i]);
+  printf("\n");
+
+  printf("String: ");
+  for (size_t i = 0; i < written; i++) {
+    if (buf[i] == 0x1b) {
+      printf("\\x1b");
+    } else {
+      printf("%c", buf[i]);
+    }
+  }
+  printf("\n");
+
+  ghostty_key_event_free(event);
+  ghostty_key_encoder_free(encoder);
+  return 0;
+}