fix(agents): guard system prompt tool schema stats

src/agents/system-prompt-report.test.ts

@@ -216,4 +216,83 @@ describe("buildSystemPromptReport", () => {
     });
     expect(report.tools.entries[0]?.schemaHash).toMatch(/^[a-f0-9]{64}$/u);
   });
+
+  it("keeps reporting when a tool schema getter throws", () => {
+    const file = makeBootstrapFile({ path: "/tmp/workspace/AGENTS.md" });
+    const brokenTool = {
+      name: "broken",
+      description: "Broken schema",
+    };
+    Object.defineProperty(brokenTool, "parameters", {
+      get() {
+        throw new Error("schema getter exploded");
+      },
+    });
+
+    const report = buildSystemPromptReport({
+      source: "run",
+      generatedAt: 0,
+      bootstrapMaxChars: 20_000,
+      systemPrompt: "system",
+      bootstrapFiles: [file],
+      injectedFiles: [],
+      skillsPrompt: "",
+      tools: [
+        brokenTool,
+        {
+          name: "healthy",
+          description: "Healthy schema",
+          parameters: {
+            type: "object",
+            properties: { path: { type: "string" } },
+          },
+        },
+      ] as never,
+    });
+
+    expect(report.tools.entries).toHaveLength(2);
+    expect(report.tools.entries[0]).toMatchObject({
+      name: "broken",
+      schemaChars: 0,
+      propertiesCount: null,
+    });
+    expect(report.tools.entries[1]).toMatchObject({
+      name: "healthy",
+      propertiesCount: 1,
+    });
+  });
+
+  it("keeps reporting when a tool schema properties getter throws", () => {
+    const file = makeBootstrapFile({ path: "/tmp/workspace/AGENTS.md" });
+    const schema = { type: "object" };
+    Object.defineProperty(schema, "properties", {
+      get() {
+        throw new Error("properties getter exploded");
+      },
+      enumerable: true,
+    });
+
+    const report = buildSystemPromptReport({
+      source: "run",
+      generatedAt: 0,
+      bootstrapMaxChars: 20_000,
+      systemPrompt: "system",
+      bootstrapFiles: [file],
+      injectedFiles: [],
+      skillsPrompt: "",
+      tools: [
+        {
+          name: "broken",
+          description: "Broken schema",
+          parameters: schema,
+        },
+      ] as never,
+    });
+
+    expect(report.tools.entries[0]).toMatchObject({
+      name: "broken",
+      schemaChars: 0,
+      propertiesCount: null,
+    });
+  });
 });

src/agents/system-prompt-report.ts

@@ -49,7 +49,7 @@ function parseSkillBlocks(skillsPrompt: string): Array<{ name: string; blockChar
 }
 
 function buildToolSchemaStats(
-  parameters: AgentTool["parameters"],
+  parameters: AgentTool["parameters"] | undefined,
 ): Pick<ToolReportEntry, "propertiesCount" | "schemaChars" | "schemaHash"> {
   if (!parameters || typeof parameters !== "object") {
     return { schemaChars: 0, schemaHash: sha256(""), propertiesCount: null };
@@ -67,14 +67,7 @@ function buildToolSchemaStats(
   const stats = {
     schemaChars: schemaJson.length,
     schemaHash: sha256(schemaJson),
-    propertiesCount: (() => {
-      const schema = parameters as Record<string, unknown>;
-      const props = typeof schema.properties === "object" ? schema.properties : null;
-      if (!props || typeof props !== "object") {
-        return null;
-      }
-      return Object.keys(props as Record<string, unknown>).length;
-    })(),
+    propertiesCount: countToolSchemaProperties(parameters),
   };
   // Tool parameter objects are reused across runs; cache their stable size/hash
   // so report generation stays cheap during frequent prompt rebuilds.
@@ -82,6 +75,27 @@ function buildToolSchemaStats(
   return stats;
 }
 
+function countToolSchemaProperties(parameters: object): number | null {
+  try {
+    const schema = parameters as Record<string, unknown>;
+    const props = typeof schema.properties === "object" ? schema.properties : null;
+    if (!props || typeof props !== "object") {
+      return null;
+    }
+    return Object.keys(props as Record<string, unknown>).length;
+  } catch {
+    return null;
+  }
+}
+
+function readToolParameters(tool: AgentTool): AgentTool["parameters"] | undefined {
+  try {
+    return tool.parameters;
+  } catch {
+    return undefined;
+  }
+}
+
 function buildToolsEntries(tools: AgentTool[]): SessionSystemPromptReport["tools"]["entries"] {
   return tools.map((tool) => {
     const cached = toolReportEntryCache.get(tool);
@@ -91,7 +105,7 @@ function buildToolsEntries(tools: AgentTool[]): SessionSystemPromptReport["tools
     const name = tool.name;
     const summary = tool.description?.trim() || tool.label?.trim() || "";
     const summaryChars = summary.length;
-    const schemaStats = buildToolSchemaStats(tool.parameters);
+    const schemaStats = buildToolSchemaStats(readToolParameters(tool));
     const entry = { name, summaryChars, summaryHash: sha256(summary), ...schemaStats };
     toolReportEntryCache.set(tool, entry);
     return entry;