fix(browser): interpret agent link relations once per element (#10345)

src/browser/CdpCaptureDocuments.ts

@@ -777,11 +777,15 @@ const domMetadata = (
       destination_scope: destination.scope,
     });
   }
-  const rel = (pairs.get("rel") ?? "")
-    .toLowerCase()
-    // HTML link type tokens are separated by ASCII whitespace only.
-    .split(/[\t\n\f\r ]+/u)
-    .filter((value) => agentRelValues.includes(value));
+  // HTML link types form a set per element, separated by ASCII whitespace.
+  const rel = [
+    ...new Set(
+      (pairs.get("rel") ?? "")
+        .toLowerCase()
+        .split(/[\t\n\f\r ]+/u)
+        .filter((value) => agentRelValues.includes(value)),
+    ),
+  ];
   const href = urls.find(({ attribute }) => attribute === "href")?.url ?? null;
   const agentHints =
     tagName === "link" && rel.length > 0

tests/boundary/cli/browserRelationSets.test.ts

@@ -0,0 +1,106 @@
+import { expect } from "vitest";
+import { parseEvidence } from "../../../src/domain/evidence.js";
+import { webPageInspectionSchema } from "../../../src/domain/browserObservationSchemas.js";
+import { startFakeCdpBrowser } from "../../fixtures/fakeCdpBrowser.js";
+import { connectLocalToolsMcp } from "../../fixtures/localToolsMcp.js";
+import { cliTest } from "../../support/cli/cliFixture.js";
+
+cliTest.for(["CLI", "stdio MCP"] as const)(
+  "owns recognized relation types per link through %s",
+  async (surface, { cli }) => {
+    const browser = await startFakeCdpBrowser({
+      commandResult: (command, origin) =>
+        command.method === "DOMSnapshot.captureSnapshot"
+          ? {
+              strings: [
+                "#document",
+                "html",
+                "head",
+                "link",
+                "",
+                "xmlns",
+                "http://www.w3.org/1999/xhtml",
+                "rel",
+                `${"mcp ".repeat(150_000)}model-context model-context AI-PLUGIN`,
+                "href",
+                "/agent",
+                `${origin}/root/page.xhtml`,
+                "MCP service-desc service-desc mcp unrelated",
+                "/other-agent",
+              ],
+              documents: [
+                {
+                  documentURL: 11,
+                  nodes: {
+                    nodeType: [9, 1, 1, 1, 1],
+                    nodeName: [0, 1, 2, 3, 3],
+                    nodeValue: [4, 4, 4, 4, 4],
+                    parentIndex: [-1, 0, 1, 2, 2],
+                    attributes: [[], [5, 6], [], [7, 8, 9, 10], [7, 12, 9, 13]],
+                  },
+                },
+              ],
+            }
+          : undefined,
+    });
+    try {
+      let document: unknown;
+      if (surface === "CLI") {
+        const reply = await cli.run({
+          arguments: [
+            "inspect-web-page",
+            browser.endpoint,
+            "allowed-page",
+            "--observation-ms",
+            "0",
+            "--json",
+          ],
+        });
+        expect(reply.exitCode, reply.stderr).toBe(0);
+        document = reply.json;
+      } else {
+        const { call } = await connectLocalToolsMcp();
+        const reply = await call("inspect_web_page", {
+          cdp_endpoint: browser.endpoint,
+          target_id: "allowed-page",
+          observation_ms: 0,
+        });
+        expect(reply.isError, JSON.stringify(reply)).not.toBe(true);
+        document = reply.structuredContent;
+      }
+      const evidence = parseEvidence(document);
+      expect(evidence.operation).toBe("inspect_web_page");
+      const inspection = webPageInspectionSchema.parse(
+        evidence.normalized_result,
+      );
+      expect(
+        inspection.metadata.agent_hints.filter(
+          ({ mechanism }) => mechanism === "dom_link_rel",
+        ),
+      ).toEqual(
+        [
+          ["mcp", "/agent"],
+          ["model-context", "/agent"],
+          ["ai-plugin", "/agent"],
+          ["mcp", "/other-agent"],
+          ["service-desc", "/other-agent"],
+        ].map(([declaration, path]) => ({
+          mechanism: "dom_link_rel",
+          declaration,
+          url: `${browser.allowedOrigin}${path}`,
+          trust: "page-declared-untrusted",
+        })),
+      );
+      expect(inspection.metadata.dom_urls).toEqual(
+        ["/agent", "/other-agent"].map((path, index) => ({
+          node_index: index + 3,
+          attribute: "href",
+          url: `${browser.allowedOrigin}${path}`,
+          destination_scope: "approved",
+        })),
+      );
+    } finally {
+      await browser.close();
+    }
+  },
+);