fix(agents): guard prompt cache tool names

vincentkoc · web-flow · commit b16a43597d49 · 2026-06-08T10:36:50.000+09:00
Make prompt-cache observability collect diagnostic tool names through guarded descriptor reads so an unreadable tool-name getter cannot abort cache tracing/debug collection. Preserve readable trimmed names and keep runtime tool registration/schema behavior strict and unchanged.
diff --git a/src/agents/embedded-agent-runner/prompt-cache-observability.test.ts b/src/agents/embedded-agent-runner/prompt-cache-observability.test.ts
@@ -18,6 +18,18 @@ describe("prompt cache observability", () => {
     ).toEqual(["read", "write"]);
   });
 
+  it("collects prompt-cache tool names without aborting on unreadable descriptors", () => {
+    const unreadableTool = {
+      get name(): string {
+        throw new Error("tool name getter exploded");
+      },
+    };
+
+    expect(
+      collectPromptCacheToolNames([{ name: " read " }, unreadableTool, { name: "write" }]),
+    ).toEqual(["read", "write"]);
+  });
+
   it("tracks cache-relevant changes and reports a real cache-read drop", () => {
     // Observability only emits when a material cache-read drop follows a tracked
     // cache-affecting change.
diff --git a/src/agents/embedded-agent-runner/prompt-cache-observability.ts b/src/agents/embedded-agent-runner/prompt-cache-observability.ts
@@ -140,8 +140,19 @@ function diffSnapshots(
   return changes.length > 0 ? changes : null;
 }
 
-export function collectPromptCacheToolNames(tools: Array<{ name?: string }>): string[] {
-  return tools.map((tool) => tool.name?.trim()).filter((name): name is string => Boolean(name));
+export function collectPromptCacheToolNames(tools: readonly { name?: string }[]): string[] {
+  const names: string[] = [];
+  for (const tool of tools) {
+    try {
+      const name = tool.name?.trim();
+      if (name) {
+        names.push(name);
+      }
+    } catch {
+      continue;
+    }
+  }
+  return names;
 }
 
 export function beginPromptCacheObservation(params: {
