fix(agents): reject empty media and ignore URL at-signs

tools/skills/validate-agent-guidance.mjs

@@ -41,6 +41,7 @@ async function validateReference(
     if (unresolvedReference !== undefined)
         return `${source}: unresolved Markdown reference "${unresolvedReference}"`;
     if (/^(?:[a-z][a-z\d+.-]*:|\/\/)/iu.test(target)) return;
+    if (image && !target) return `${source}: empty media target`;
     let path;
     let anchor;
     try {
@@ -184,7 +185,10 @@ export async function validateAgentGuidance({ rootDir }) {
                 diagnostics.push(
                     `${source}: at most ${maxBytes} UTF-8 bytes allowed (received ${bytes})`
                 );
-            const prose = guidanceProse(markdown);
+            const prose = guidanceProse(markdown).replace(
+                /(?:\b[a-z][a-z\d+.-]*:\/\/|\/\/)[^\s]+/giu,
+                ' '
+            );
             const imports = guidanceStandaloneImports(markdown);
             const inlineImports = [];
             for (const match of prose.matchAll(

tools/skills/validate-agent-guidance.test.mjs

@@ -1381,3 +1381,21 @@ for (const entity of ['	', '
', '
']) {
         );
     });
 }
+
+for (const markup of ['![logo]()', '<img src="">', '<video src=" "></video>']) {
+    test(`empty media references are rejected: ${markup}`, async (t) => {
+        assert.ok((await diagnostics(t, { 'AGENTS.md': markup })).length > 0);
+    });
+}
+for (const url of [
+    'https://example.com/@docs/guide',
+    'https://example.com/user?next=@docs/guide',
+    '//example.com/@docs/guide',
+]) {
+    test(`external URL at-sign is not an import: ${url}`, async (t) => {
+        assert.deepEqual(
+            await diagnostics(t, { 'AGENTS.md': 'Visit ' + url }),
+            []
+        );
+    });
+}