fix: match http_file directory structure for backward compatibility

The wasm_component_download repository rule now creates files in a
'file/' subdirectory matching the http_file structure, allowing
existing references like @repo//file to work unchanged.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: avrabe

toolchains/wasm_component_download.bzl

@@ -53,17 +53,23 @@ def _wasm_component_download_impl(ctx):
             url_suffix,
         )
 
-    # Download the WASM file
+    # Download the WASM file into 'file/' subdirectory (matches http_file structure)
     filename = ctx.attr.filename or "{}.wasm".format(tool_name)
     ctx.download(
         url = url,
         sha256 = sha256,
-        output = filename,
+        output = "file/" + filename,
     )
 
-    # Create BUILD file exposing the WASM component
-    ctx.file("BUILD.bazel", """
+    # Create root BUILD file (empty, just marks as package)
+    ctx.file("BUILD.bazel", "# Generated by wasm_component_download\n")
+
+    # Create BUILD file in 'file/' subdirectory (matches http_file structure)
+    # This allows referencing as @repo//file or @repo//file:file
+    ctx.file("file/BUILD.bazel", """
 # Generated by wasm_component_download
+# Matches http_file structure for backward compatibility
+
 exports_files(["{filename}"])
 
 filegroup(
@@ -104,6 +110,6 @@ Example:
         filename = "loom.wasm",
     )
 
-Then reference as @loom_wasm//:file in build rules.
+Then reference as @loom_wasm//file in build rules (matches http_file structure).
 """,
 )

wasm/private/wasm_optimize.bzl

@@ -77,7 +77,7 @@ wasm_optimize = rule(
         ),
         "_loom_wasm": attr.label(
             doc = "LOOM WebAssembly component",
-            default = "@loom_wasm//file",
+            default = "@loom_wasm//file:file",
             allow_single_file = True,
         ),
     },