js: coroutine JS step — pre-load spec/coroutines.sx in run_tests.js

All CEK primitives (cek-step-loop/cek-resume/make-cek-state/cek-suspended?/
cek-io-request/cek-terminal?/cek-value) were already registered in sx-browser.js.

Root cause of test failure: (import (sx coroutines)) creates an io-suspended
state when the library isn't pre-loaded; overridden cekRun throws on suspension.
Fix: pre-load spec/signals.sx + spec/coroutines.sx before test files run.

17/17 coroutine tests pass in JS. 1965/2500 total (+25 vs 1940 baseline),
zero new failures.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

hosts/javascript/run_tests.js

@@ -343,6 +343,20 @@ if (fs.existsSync(swapPath)) {
   }
 }
 
+// Load spec library files (define-library modules imported by tests)
+for (const libFile of ["signals.sx", "coroutines.sx"]) {
+  const libPath = path.join(projectDir, "spec", libFile);
+  if (fs.existsSync(libPath)) {
+    const libSrc = fs.readFileSync(libPath, "utf8");
+    const libExprs = Sx.parse(libSrc);
+    for (const expr of libExprs) {
+      try { Sx.eval(expr, env); } catch (e) {
+        console.error(`Error loading spec/${libFile}: ${e.message}`);
+      }
+    }
+  }
+}
+
 // Load tw system (needed by spec/tests/test-tw.sx)
 const twDir = path.join(projectDir, "shared", "sx", "templates");
 for (const twFile of ["tw-type.sx", "tw-layout.sx", "tw.sx"]) {