feat(compiler): run error section on ssr api call failure

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/compiler/src/codegen.ts

@@ -35,6 +35,10 @@ interface RenderBinding {
   path: string;
   body: string;
   helpers: string;
+  // Present only for a sectioned ssr block with a non-empty `error {}` section.
+  // When set, a failed API call runs this body (with `status`/`message`/`data`
+  // bound) instead of propagating. Absent -> failures propagate, unchanged.
+  errorBody?: string;
 }
 
 interface SsrBinding extends RenderBinding {
@@ -873,6 +877,7 @@ function renderBinding(binding: NamedDataBinding): RenderBinding {
     path: binding.path,
     body: binding.body,
     helpers: binding.helpers,
+    ...(binding.errorBody ? { errorBody: binding.errorBody } : {}),
   };
 }
 
@@ -937,6 +942,7 @@ function apiBindingMap(ast: PageAst, sharedHelpers: string): Map<string, NamedDa
       throw new Error(`Duplicate .wrn api binding "${block.name}"`);
     }
     const sectioned = block.sections;
+    const errorSection = sectioned?.error.trim();
     bindings.set(block.name, {
       mode: block.mode,
       method: block.method,
@@ -946,6 +952,10 @@ function apiBindingMap(ast: PageAst, sharedHelpers: string): Map<string, NamedDa
       body: sectioned
         ? `const data = $data; ${sectioned.response.trim() || "return data;"}`
         : dataBody(block.body),
+      // Only a sectioned block with a non-empty `error {}` gets a fallback —
+      // legacy blocks and sectioned blocks without `error` keep failures
+      // propagating exactly as before.
+      ...(errorSection ? { errorBody: errorSection } : {}),
       helpers: modeHelpers(ast, block.mode, sharedHelpers),
     });
   }
@@ -973,6 +983,18 @@ function __wrnexusEvalData(data: unknown, body: string, helpers = "", ctx: __Wrn
   return new Function("$data", "$adapters", "const cookies = $adapters.cookies;\\nconst session = $adapters.session;\\nconst localStorage = $adapters.localStorage;\\nwith ($data ?? {}) {\\n" + helpers + "\\n" + body + "\\n}")(data, adapters);
 }
 
+function __wrnexusEvalError(err: unknown, body: string, helpers = "", ctx: __WrnexusContext): unknown {
+  const adapters = {
+    cookies: ctx.cookies,
+    session: ctx.session,
+    localStorage: ctx.localStorage,
+  };
+  const status = (err as { status?: unknown } | null | undefined)?.status;
+  const data = (err as { data?: unknown } | null | undefined)?.data;
+  const message = err instanceof Error ? err.message : String(err);
+  return new Function("$status", "$message", "$data", "$adapters", "const cookies = $adapters.cookies;\\nconst session = $adapters.session;\\nconst localStorage = $adapters.localStorage;\\nconst status = $status;\\nconst message = $message;\\nconst data = $data;\\n" + helpers + "\\n" + body)(status, message, data, adapters);
+}
+
 function __wrnexusPropAttr(
   value: unknown,
 ): string {
@@ -1002,18 +1024,34 @@ async function __wrnexusCallApi(path: string, method: string, ctx: __WrnexusCont
 
   const url = new URL(path, ctx.req.url);
   const res = await fetch(new Request(url, { method, headers: ctx.req.headers }));
+  const type = res.headers.get("content-type") || "";
   if (!res.ok) {
-    throw new Error(".wrn data API request failed with status " + res.status);
+    const data = type.includes("application/json")
+      ? await res.json().catch(() => undefined)
+      : await res.text().catch(() => undefined);
+    throw Object.assign(new Error(".wrn data API request failed with status " + res.status), {
+      status: res.status,
+      data,
+    });
   }
 
-  const type = res.headers.get("content-type") || "";
   return type.includes("application/json") ? await res.json() : await res.text();
 }
 
 async function __wrnexusRenderSsrBindings(html: string, ctx: __WrnexusContext): Promise<string> {
   for (const binding of __wrnexusSsrBindings) {
-    const data = await __wrnexusCallApi(binding.path, binding.method, ctx);
-    const value = __wrnexusEvalData(data, binding.body, binding.helpers, ctx);
+    let value: unknown;
+    if (binding.errorBody) {
+      try {
+        const data = await __wrnexusCallApi(binding.path, binding.method, ctx);
+        value = __wrnexusEvalData(data, binding.body, binding.helpers, ctx);
+      } catch (err) {
+        value = __wrnexusEvalError(err, binding.errorBody, binding.helpers, ctx);
+      }
+    } else {
+      const data = await __wrnexusCallApi(binding.path, binding.method, ctx);
+      value = __wrnexusEvalData(data, binding.body, binding.helpers, ctx);
+    }
     html = html.replace(binding.marker, __wrnexusEscapeHtml(value));
   }
   return html;
@@ -1531,7 +1569,9 @@ function generateInner(ast: PageAst): string {
   const needsSsrRuntime = ssrBindings.length > 0 || loops.length > 0 || runtimeStateNames.size > 0;
   if (needsSsrRuntime) {
     out.push(ssrRuntimeSource());
-    out.push(`const __wrnexusSsrBindings = ${JSON.stringify(ssrBindings, null, 2)};`);
+    out.push(
+      `const __wrnexusSsrBindings: Array<{ method: string; path: string; body: string; helpers: string; errorBody?: string }> = ${JSON.stringify(ssrBindings, null, 2)};`,
+    );
     const decls = loopConsts.length > 0 ? loopConsts.join("\n") + "\n" : "";
     out.push(
       `export default async function ${ast.name}(ctx: __WrnexusContext) {

packages/compiler/test/api-block-ssr.test.ts

@@ -32,3 +32,31 @@ test("a legacy ssr block is unchanged", () => {
 
   expect(generated).toContain("users.length");
 });
+
+test("an ssr block with an error section emits the error body and binds status/message/data", () => {
+  const generated = serverModule(`    api ssrUsers GET /api/users {
+      response {
+        return data.users.length
+      }
+      error {
+        return message + status + data
+      }
+    }`);
+
+  expect(generated).toContain('"errorBody"');
+  expect(generated).toContain("return message + status + data");
+  expect(generated).toContain("const status = $status");
+  expect(generated).toContain("const message = $message");
+  expect(generated).toContain("const data = $data");
+  expect(generated).toContain("__wrnexusEvalError");
+});
+
+test("an ssr block without an error section emits no catch entry for that binding", () => {
+  const generated = serverModule(`    api ssrUsers GET /api/users {
+      response {
+        return data.users.length
+      }
+    }`);
+
+  expect(generated).not.toContain('"errorBody"');
+});