--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/third_party/emsdk/bazel/emscripten_cache.bzl	Fri Jan 23 22:38:59 2026 -0800
@@ -0,0 +1,113 @@
+BUILD_FILE_CONTENT_TEMPLATE = """
+package(default_visibility = ['//visibility:public'])
+exports_files(['emscripten_config'])
+"""
+
+EMBUILDER_CONFIG_TEMPLATE = """
+CACHE = '{cache}'
+BINARYEN_ROOT = '{binaryen_root}'
+LLVM_ROOT = '{llvm_root}'
+"""
+
+def get_root_and_script_ext(repository_ctx):
+    if repository_ctx.os.name.startswith("linux"):
+        if "amd64" in repository_ctx.os.arch or "x86_64" in repository_ctx.os.arch:
+            return (repository_ctx.path(Label("@emscripten_bin_linux//:BUILD.bazel")).dirname, "")
+        elif "aarch64" in repository_ctx.os.arch:
+            return (repository_ctx.path(Label("@emscripten_bin_linux_arm64//:BUILD.bazel")).dirname, "")
+        else:
+            fail("Unsupported architecture for Linux")
+    elif repository_ctx.os.name.startswith("mac"):
+        if "amd64" in repository_ctx.os.arch or "x86_64" in repository_ctx.os.arch:
+            return (repository_ctx.path(Label("@emscripten_bin_mac//:BUILD.bazel")).dirname, "")
+        elif "aarch64" in repository_ctx.os.arch:
+            return (repository_ctx.path(Label("@emscripten_bin_mac_arm64//:BUILD.bazel")).dirname, "")
+        else:
+            fail("Unsupported architecture for MacOS")
+    elif repository_ctx.os.name.startswith("windows"):
+        return (repository_ctx.path(Label("@emscripten_bin_win//:BUILD.bazel")).dirname, ".bat")
+    else:
+        fail("Unsupported operating system")
+
+def _emscripten_cache_repository_impl(repository_ctx):
+    # Read the default emscripten configuration file
+    default_config = repository_ctx.read(
+        repository_ctx.path(
+            Label("@emsdk//emscripten_toolchain:default_config"),
+        ),
+    )
+
+    if repository_ctx.attr.targets or repository_ctx.attr.configuration:
+        root, script_ext = get_root_and_script_ext(repository_ctx)
+        llvm_root = root.get_child("bin")
+        cache = repository_ctx.path("cache")
+
+        # Create configuration file
+        embuilder_config_content = EMBUILDER_CONFIG_TEMPLATE.format(
+            cache = cache,
+            binaryen_root = root,
+            llvm_root = llvm_root,
+        )
+        repository_ctx.file("embuilder_config", embuilder_config_content)
+        embuilder_config_path = repository_ctx.path("embuilder_config")
+        embuilder_path = "{}{}".format(root.get_child("emscripten").get_child("embuilder"), script_ext)
+
+        # Prepare the command line
+        if repository_ctx.attr.targets:
+            targets = repository_ctx.attr.targets
+        else:
+            # If no targets are requested, build everything
+            targets = ["ALL"]
+        flags = ["--em-config", embuilder_config_path] + repository_ctx.attr.configuration
+        embuilder_args = [embuilder_path] + flags + ["build"] + targets
+
+        # Run embuilder
+        repository_ctx.report_progress("Building secondary cache")
+        result = repository_ctx.execute(
+            embuilder_args,
+            quiet = True,
+            environment = {
+                "EM_IGNORE_SANITY": "1",
+                "EM_NODE_JS": "empty",
+            },
+        )
+        if result.return_code != 0:
+            fail("Embuilder exited with a non-zero return code")
+
+        # Override Emscripten's cache with the secondary cache
+        default_config += "CACHE = '{}'\n".format(cache)
+
+    # Create the configuration file for the toolchain and export
+    repository_ctx.file("emscripten_config", default_config)
+    repository_ctx.file("BUILD.bazel", BUILD_FILE_CONTENT_TEMPLATE)
+
+_emscripten_cache_repository = repository_rule(
+    implementation = _emscripten_cache_repository_impl,
+    attrs = {
+        "configuration": attr.string_list(),
+        "targets": attr.string_list(),
+    },
+)
+
+def _emscripten_cache_impl(ctx):
+    all_configuration = []
+    all_targets = []
+    for mod in ctx.modules:
+        for configuration in mod.tags.configuration:
+            all_configuration += configuration.flags
+        for targets in mod.tags.targets:
+            all_targets += targets.targets
+
+    _emscripten_cache_repository(
+        name = "emscripten_cache",
+        configuration = all_configuration,
+        targets = all_targets,
+    )
+
+emscripten_cache = module_extension(
+    tag_classes = {
+        "configuration": tag_class(attrs = {"flags": attr.string_list()}),
+        "targets": tag_class(attrs = {"targets": attr.string_list()}),
+    },
+    implementation = _emscripten_cache_impl,
+)