gnd: Validate WASM handler exports after compilation

After compiling AssemblyScript mappings to WASM, parse the compiled
binary with wasmparser and verify that all handler names declared in
the manifest (event, call, and block handlers) exist as exported
functions. This catches mismatches between the manifest and the
actual WASM code early, during `gnd build`, rather than at
deployment time.

Author: lutter

Cargo.lock

@@ -63,6 +63,7 @@ semver = { workspace = true }
 
 # Build command
 sha1 = "0.10"
+wasmparser = { workspace = true }
 
 # Test command
 which = "7"

gnd/Cargo.toml

@@ -20,7 +20,8 @@ use crate::migrations;
 use crate::output::{step, Step};
 use crate::services::IpfsClient;
 use crate::validation::{
-    format_manifest_errors, format_schema_errors, validate_manifest, validate_schema,
+    collect_handler_names, collect_template_handler_names, format_manifest_errors,
+    format_schema_errors, validate_manifest, validate_schema, validate_wasm_handlers,
 };
 use crate::watch::watch_and_run;
 
@@ -234,6 +235,55 @@ async fn build_subgraph(opt: &BuildOpt) -> Result<BuildResult> {
         }
     }
 
+    // Validate compiled WASM handler exports (only for binary WASM output)
+    if opt.output_format == "wasm" {
+        let mut wasm_errors = Vec::new();
+
+        for ds in &manifest.data_sources {
+            let handler_names = collect_handler_names(ds);
+            if handler_names.is_empty() {
+                continue;
+            }
+            let wasm_path = opt
+                .output_dir
+                .join(&ds.name)
+                .join(format!("{}.wasm", ds.name));
+            if wasm_path.exists() {
+                wasm_errors.extend(validate_wasm_handlers(&wasm_path, &ds.name, &handler_names));
+            }
+        }
+
+        for template in &manifest.templates {
+            let handler_names = collect_template_handler_names(template);
+            if handler_names.is_empty() {
+                continue;
+            }
+            let wasm_path = opt
+                .output_dir
+                .join("templates")
+                .join(&template.name)
+                .join(format!("{}.wasm", template.name));
+            if wasm_path.exists() {
+                wasm_errors.extend(validate_wasm_handlers(
+                    &wasm_path,
+                    &template.name,
+                    &handler_names,
+                ));
+            }
+        }
+
+        if !wasm_errors.is_empty() {
+            eprintln!(
+                "WASM handler validation errors:\n{}",
+                format_manifest_errors(&wasm_errors)
+            );
+            return Err(anyhow!(
+                "WASM handler validation failed with {} error(s)",
+                wasm_errors.len()
+            ));
+        }
+    }
+
     // Copy schema file
     if let Some(schema_path) = &manifest.schema {
         let schema_path = resolve_path(&opt.manifest, schema_path);