fix(agent): stop tool thrash after writes and log rounds

Cap get_api_docs, break duplicate tool rounds, force a reply after
successful writes, and log each tool call so limit hits are diagnosable.

tests/unit/agent-loop-guards.test.ts

@@ -0,0 +1,152 @@
+import assert from "node:assert/strict";
+import { describe, it } from "node:test";
+import {
+  fingerprintToolCalls,
+  isSuccessfulWrite,
+  summarizeToolTrace,
+  truncateToolResult,
+} from "../../src/modules/agent/server/loop-guards";
+import { runAgentChat } from "../../src/modules/agent/server/run";
+import type {
+  ChatCompletionRequest,
+  ChatCompletionResult,
+  LlmClient,
+} from "../../src/lib/llm/types";
+
+describe("loop-guards", () => {
+  it("fingerprints tool calls stably regardless of key order", () => {
+    const a = fingerprintToolCalls([
+      { name: "create_event", arguments: '{"title":"Dentist","calendarName":"Family"}' },
+    ]);
+    const b = fingerprintToolCalls([
+      { name: "create_event", arguments: '{"calendarName":"Family","title":"Dentist"}' },
+    ]);
+    assert.equal(a, b);
+  });
+
+  it("treats create_event 201 as a successful write", () => {
+    assert.equal(isSuccessfulWrite("create_event", 201), true);
+    assert.equal(isSuccessfulWrite("list_calendars", 200), false);
+    assert.equal(
+      isSuccessfulWrite("call_api", 201, '{"method":"POST","path":"/api/v1/events"}'),
+      true,
+    );
+    assert.equal(
+      isSuccessfulWrite("call_api", 200, '{"method":"GET","path":"/api/v1/events"}'),
+      false,
+    );
+  });
+
+  it("truncates oversized tool results", () => {
+    const result = truncateToolResult("x".repeat(7000), 100);
+    assert.ok(result.length < 200);
+    assert.match(result, /truncated/);
+  });
+
+  it("summarizes tool traces", () => {
+    assert.equal(
+      summarizeToolTrace([
+        { name: "list_calendars", status: 200 },
+        { name: "create_event", status: 201 },
+      ]),
+      "list_calendars→200, create_event→201",
+    );
+  });
+});
+
+describe("runAgentChat loop guards", () => {
+  it("stops after a successful write instead of looping", async () => {
+    let calls = 0;
+    const llm: LlmClient = {
+      async chatCompletion(request: ChatCompletionRequest): Promise<ChatCompletionResult> {
+        calls += 1;
+        if (calls === 1) {
+          return {
+            message: {
+              role: "assistant",
+              content: null,
+              tool_calls: [
+                {
+                  id: "1",
+                  type: "function",
+                  function: {
+                    name: "create_event",
+                    arguments: JSON.stringify({
+                      title: "Dentist",
+                      startAt: "2026-07-10T15:00:00.000Z",
+                      endAt: "2026-07-10T16:00:00.000Z",
+                    }),
+                  },
+                },
+              ],
+            },
+            finishReason: "tool_calls",
+          };
+        }
+
+        assert.equal(request.tools, undefined);
+        return {
+          message: { role: "assistant", content: "Added Dentist to your calendar." },
+          finishReason: "stop",
+        };
+      },
+    };
+
+    const result = await runAgentChat({
+      messages: [{ role: "user", content: "add dentist tomorrow at 10" }],
+      request: new Request("http://localhost:3000/api/agent/chat"),
+      llm,
+      executeTool: async () =>
+        JSON.stringify({ status: 201, body: { id: "evt-1", title: "Dentist" } }),
+    });
+
+    assert.equal(calls, 2);
+    assert.equal(result.toolCalls.length, 1);
+    assert.equal(result.toolCalls[0]?.name, "create_event");
+    assert.match(result.message.content, /Dentist/);
+  });
+
+  it("breaks duplicate identical tool rounds", async () => {
+    let calls = 0;
+    const llm: LlmClient = {
+      async chatCompletion(): Promise<ChatCompletionResult> {
+        calls += 1;
+        if (calls <= 2) {
+          return {
+            message: {
+              role: "assistant",
+              content: null,
+              tool_calls: [
+                {
+                  id: String(calls),
+                  type: "function",
+                  function: {
+                    name: "list_calendars",
+                    arguments: "{}",
+                  },
+                },
+              ],
+            },
+            finishReason: "tool_calls",
+          };
+        }
+        return {
+          message: { role: "assistant", content: "You have one Family calendar." },
+          finishReason: "stop",
+        };
+      },
+    };
+
+    const result = await runAgentChat({
+      messages: [{ role: "user", content: "what calendars do I have?" }],
+      request: new Request("http://localhost:3000/api/agent/chat"),
+      llm,
+      executeTool: async () =>
+        JSON.stringify({ status: 200, body: [{ id: "cal-1", name: "Family" }] }),
+    });
+
+    assert.equal(calls, 3);
+    assert.equal(result.toolCalls.length, 1);
+    assert.match(result.message.content, /Family/);
+  });
+});