Add a cacheable Bazel app-server schema bundle (#42174)

## What changed

- Add a `schema_bundle` rule that generates stable and experimental app-server
  schema directories as declared Bazel actions.
- Include the pinned `zstd` executable in the bundle so consumers can normalize
  generated JSON without a separate `bazel run` invocation.
- Expose the app-server protocol test binary as the schema generator and add the
  manual `//bazel/schema:public-schema-bundle` target.

GitOrigin-RevId: 0a7ce47258d297dbf20db78626f2843145ee1b49

bazel/rules/BUILD.bazel

@@ -2,4 +2,5 @@ package(default_visibility = ["//visibility:public"])
 
 exports_files([
     "e2e_benchmark.bzl",
+    "schema_bundle.bzl",
 ])

bazel/rules/schema_bundle.bzl

@@ -0,0 +1,39 @@
+"""Cache schema generation from the filtered public Rust test executable."""
+
+def _schema_bundle_impl(ctx):
+    outputs = []
+    for mode in ["stable", "experimental"]:
+        schema = ctx.actions.declare_directory(ctx.label.name + "." + mode)
+        ctx.actions.run(
+            executable = ctx.executable.generator,
+            tools = [ctx.attr.generator[DefaultInfo].files_to_run],
+            arguments = [
+                "--exact",
+                "--ignored",
+                "schema_fixtures_tests::write_schema_fixtures_from_env",
+            ],
+            env = {
+                "CODEX_APP_SERVER_SCHEMA_ROOT": schema.path,
+                "CODEX_APP_SERVER_SCHEMA_EXPERIMENTAL": "1" if mode == "experimental" else "0",
+                "RUST_MIN_STACK": "8388608",
+            },
+            outputs = [schema],
+            mnemonic = "PublicSchema",
+            progress_message = "Generating %s public app-server schemas" % mode,
+        )
+        outputs.append(schema)
+
+    # Expose the pinned compressor alongside the cached directories so callers
+    # can normalize the JSON without a separate `bazel run` invocation.
+    zstd = ctx.actions.declare_file(ctx.label.name + ".zstd")
+    ctx.actions.symlink(output = zstd, target_file = ctx.executable.zstd, is_executable = True)
+    return [DefaultInfo(files = depset(outputs + [zstd]))]
+
+schema_bundle = rule(
+    implementation = _schema_bundle_impl,
+    attrs = {
+        "generator": attr.label(mandatory = True, executable = True, cfg = "exec"),
+        "zstd": attr.label(default = "@zstd//:zstd_cli", executable = True, cfg = "exec"),
+    },
+    doc = "Generates both schema modes as cacheable actions with explicit tool dependencies.",
+)

bazel/schema/BUILD.bazel

@@ -0,0 +1,8 @@
+load("//bazel/rules:schema_bundle.bzl", "schema_bundle")
+
+schema_bundle(
+    name = "public-schema-bundle",
+    testonly = True,
+    generator = "//codex-rs/app-server-protocol:schema-generator",
+    tags = ["manual"],
+)

codex-rs/app-server-protocol/BUILD.bazel

@@ -9,3 +9,11 @@ codex_rust_crate(
         allow_empty = True,
     ),
 )
+
+alias(
+    name = "schema-generator",
+    testonly = True,
+    actual = ":app-server-protocol-unit-tests-bin",
+    tags = ["manual"],
+    visibility = ["//bazel/schema:__pkg__"],
+)