fix: Use wit-bindgen-rt crate instead of wit-bindgen for runtime support

The wit-bindgen crate (v0.47.0) is for procedural macros (generate!()).
For CLI-generated bindings, we need wit-bindgen-rt (v0.39.0) which provides:
  - export! macro for component exports
  - wit_bindgen::rt module with proper allocator integration

Changes:
  - tools/checksum_updater/Cargo.toml: Added wit-bindgen-rt = "0.39.0"
  - rust/rust_wasm_component_bindgen.bzl: Changed wrapper to use wit_bindgen_rt
  - rust/rust_wasm_component_bindgen.bzl: Changed deps to @crates//:wit-bindgen-rt
  - MODULE.bazel: Updated comment to reflect wit-bindgen-rt usage
  - docs/embedded_runtime_fix.md: Updated documentation

Fixes error: could not find `export` in bindings crate

Author: claude

MODULE.bazel

@@ -282,8 +282,11 @@ crate.from_cargo(
     ],
 )
 
-# Note: wit-bindgen crate is available from checksum_updater/Cargo.toml (version 0.47.0)
-# It provides the proper wit_bindgen::rt module for generated bindings instead of embedded stubs
+# Note: wit-bindgen-rt crate is available from checksum_updater/Cargo.toml (version 0.39.0)
+# It provides the proper runtime support for CLI-generated bindings:
+#   - export! macro for component exports
+#   - wit_bindgen::rt module with correct allocator integration
+# This replaces the previously embedded runtime stubs
 
 use_repo(crate, "crates", "ssh_keygen_crates", "wasm_embed_aot_crates", "wasmsign2_crates", "wizer_crates")
 

docs/embedded_runtime_fix.md

@@ -25,34 +25,42 @@ The `rust_wasm_component_bindgen` rule had embedded **broken runtime stubs** for
 
 ### Changes Made
 
-#### 1. Used Existing wit-bindgen Crate Dependency
+#### 1. Added wit-bindgen-rt Runtime Crate
 
-The `wit-bindgen` crate (version 0.47.0) is already available from `tools/checksum_updater/Cargo.toml`:
+The `wit-bindgen-rt` crate provides runtime support for CLI-generated bindings. Added to `tools/checksum_updater/Cargo.toml`:
 
 ```toml
 [dependencies]
-wit-bindgen = "0.47.0"
+wit-bindgen = "0.47.0"       # For proc macro usage
+wit-bindgen-rt = "0.39.0"    # Runtime support (export macro, allocator, etc)
 ```
 
-This is automatically available as `@crates//:wit-bindgen` through the crates repository.
+This is automatically available as `@crates//:wit-bindgen-rt` through the crates repository.
 
-#### 2. Simplified Runtime Wrapper (rust/rust_wasm_component_bindgen.bzl:58-76)
+**Key distinction**:
+- `wit-bindgen` = Procedural macro crate for `generate!()` macro
+- `wit-bindgen-rt` = Runtime crate for CLI-generated bindings (what we need)
+
+#### 2. Simplified Runtime Wrapper (rust/rust_wasm_component_bindgen.bzl:58-79)
 
 **Before**: 114 lines of embedded runtime stubs
-**After**: 4 lines of simple re-export
+**After**: 6 lines of simple re-exports
 
 ```rust
-// Re-export the real wit-bindgen crate to provide proper runtime implementation
+// Re-export wit-bindgen-rt as wit_bindgen to provide proper runtime implementation
 // The wit-bindgen CLI generates code that expects: crate::wit_bindgen::rt
-pub use wit_bindgen;
+pub use wit_bindgen_rt as wit_bindgen;
+
+// Re-export the export macro at crate level for convenience
+pub use wit_bindgen_rt::export;
 ```
 
-#### 3. Added Dependencies to Bindings Libraries (lines 315, 326)
+#### 3. Added Dependencies to Bindings Libraries (lines 326, 337)
 
-Both host and WASM bindings libraries now depend on the real crate:
+Both host and WASM bindings libraries now depend on the runtime crate:
 
 ```starlark
-deps = ["@crates//:wit-bindgen"],  # Provide real wit-bindgen runtime
+deps = ["@crates//:wit-bindgen-rt"],  # Provide wit-bindgen runtime (export macro, allocator)
 ```
 
 #### 4. Removed Complex Filtering Logic

rust/rust_wasm_component_bindgen.bzl

@@ -55,22 +55,25 @@ def _generate_wrapper_impl(ctx):
     """Generate a wrapper that includes both bindings and runtime shim"""
     out_file = ctx.actions.declare_file(ctx.label.name + ".rs")
 
-    # Create wrapper content - re-export the real wit-bindgen crate
+    # Create wrapper content - re-export wit-bindgen-rt as wit_bindgen
     # The wit-bindgen CLI generates code that expects: crate::wit_bindgen::rt
-    # Instead of embedding broken runtime stubs, we use the real wit-bindgen crate
+    # wit-bindgen-rt provides the runtime support (export macro, allocator, etc)
     wrapper_content = """// Generated wrapper for WIT bindings
 //
-// This wrapper re-exports the wit-bindgen crate to provide the runtime
+// This wrapper re-exports wit-bindgen-rt as wit_bindgen to provide the runtime
 // at the path expected by wit-bindgen CLI (--runtime-path crate::wit_bindgen::rt)
 
 // Suppress clippy warnings for generated code
 #![allow(clippy::all)]
 #![allow(unused_imports)]
 #![allow(dead_code)]
 
-// Re-export the real wit-bindgen crate to provide proper runtime implementation
-// This provides wit_bindgen::rt with correct allocator integration
-pub use wit_bindgen;
+// Re-export wit-bindgen-rt as wit_bindgen to provide proper runtime implementation
+// This provides the export! macro, rt module with correct allocator integration
+pub use wit_bindgen_rt as wit_bindgen;
+
+// Re-export the export macro at crate level for convenience
+pub use wit_bindgen_rt::export;
 
 // Generated bindings follow:
 """
@@ -320,7 +323,7 @@ def rust_wasm_component_bindgen(
         crate_name = name.replace("-", "_") + "_bindings",
         edition = "2021",
         visibility = visibility,  # Make native bindings publicly available
-        deps = ["@crates//:wit-bindgen"],  # Provide real wit-bindgen runtime
+        deps = ["@crates//:wit-bindgen-rt"],  # Provide wit-bindgen runtime (export macro, allocator)
     )
 
     # Create a separate WASM bindings library using guest wrapper
@@ -331,7 +334,7 @@ def rust_wasm_component_bindgen(
         crate_name = name.replace("-", "_") + "_bindings",
         edition = "2021",
         visibility = ["//visibility:private"],
-        deps = ["@crates//:wit-bindgen"],  # Provide real wit-bindgen runtime
+        deps = ["@crates//:wit-bindgen-rt"],  # Provide wit-bindgen runtime (export macro, allocator)
     )
 
     # Create a WASM-transitioned version of the WASM bindings library

tools/checksum_updater/Cargo.toml

@@ -32,6 +32,7 @@ tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 tempfile = "3.23"
 async-trait = "0.1"
 wit-bindgen = "0.47.0"  # WIT binding generation for macro usage
+wit-bindgen-rt = "0.39.0"  # Runtime support for CLI-generated bindings (export macro, allocator, etc)
 uuid = { version = "1.18", default-features = false }  # UUID generation for user service (deterministic, no getrandom dependency)
 
 [dev-dependencies]