fix(chat): count a subagent's edits in the turn's Edited N files card (#86)

A skill that hands its work to subagents (vp-auto) showed "Edited 1 file"
for a turn that changed 4: a subagent's Write/Edit calls are in its own
agent-<id>.jsonl, so the card only saw the parent's.

- server/lib/agent-edits.js reads a subagent's transcript (readLines, a
  member's only as theirs) for the files it wrote or edited with their +/-
  lines, nested subagents folded in (3 levels), cached by size + mtime.
- The transcript route puts them on each Claude Agent/Task result as
  `edits`; the card adds them to the turn's own edits. A file only a
  subagent wrote is listed, never an artifact card (its versions are
  rebuilt from this transcript's inputs, which a subagent's are not).

server/__tests__/agent-edits.test.js

@@ -0,0 +1,112 @@
+/**
+ * @file Tests for server/lib/agent-edits.js (issue #86): the files a
+ * subagent wrote or edited are read from its own transcript — +/- lines from
+ * `structuredPatch` or a created file's content, a failed call left out, a
+ * nested subagent folded in — and put on the parent's Agent result as `edits`.
+ * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+ */
+
+const { describe, it, before, after } = require("node:test");
+const assert = require("node:assert/strict");
+const fs = require("node:fs");
+const os = require("node:os");
+const path = require("node:path");
+
+const HOME = fs.mkdtempSync(path.join(os.tmpdir(), "agent-edits-"));
+process.env.CLAUDE_HOME = HOME;
+
+const { encodeCwd } = require("../lib/claude-home");
+const { agentEdits, attachAgentEdits, _cache } = require("../lib/agent-edits");
+
+const CWD = "/work/repo";
+const SID = "11111111-2222-3333-4444-555555555555";
+const subDir = path.join(HOME, "projects", encodeCwd(CWD), SID, "subagents");
+
+const call = (id, name, input) => ({
+  type: "assistant",
+  message: { content: [{ type: "tool_use", id, name, input }] },
+});
+const result = (id, toolUseResult, isError = false) => ({
+  type: "user",
+  message: { content: [{ type: "tool_result", tool_use_id: id, is_error: isError }] },
+  toolUseResult,
+});
+const write = (agentId, lines) =>
+  fs.writeFileSync(
+    path.join(subDir, `agent-${agentId}.jsonl`),
+    lines.map((l) => JSON.stringify(l)).join("\n")
+  );
+
+before(() => {
+  fs.mkdirSync(subDir, { recursive: true });
+  write("a1", [
+    call("t1", "Edit", { file_path: "/work/repo/main.go" }),
+    result("t1", { structuredPatch: [{ lines: [" x", "-old", "+new", "+more"] }] }),
+    call("t2", "Write", { file_path: "/work/repo/new_test.go" }),
+    result("t2", { type: "create", content: "a\nb\nc\n" }),
+    call("t3", "Edit", { file_path: "/work/repo/broken.go" }),
+    result("t3", "String to replace not found", true),
+    call("t4", "Agent", { prompt: "go deeper" }),
+    result("t4", { agentId: "a2", status: "completed" }),
+  ]);
+  write("a2", [
+    call("u1", "Edit", { file_path: "/work/repo/main.go" }),
+    result("u1", { structuredPatch: [{ lines: ["+x"] }] }),
+    call("u2", "Bash", { command: "go test ./..." }),
+    result("u2", { stdout: "ok" }),
+  ]);
+});
+after(() => fs.rmSync(HOME, { recursive: true, force: true }));
+
+describe("agentEdits", () => {
+  it("lists a subagent's files with their lines, nested subagents folded in", async () => {
+    const edits = await agentEdits(SID, CWD, "a1");
+    assert.deepEqual(edits, [
+      { path: "/work/repo/main.go", added: 3, removed: 1, counted: true },
+      { path: "/work/repo/new_test.go", added: 3, removed: 0, counted: true },
+    ]);
+  });
+
+  it("answers an empty list for a subagent with no transcript", async () => {
+    assert.deepEqual(await agentEdits(SID, CWD, "nope"), []);
+  });
+
+  it("reads a transcript again only after it changed", async () => {
+    await agentEdits(SID, CWD, "a2");
+    const file = path.join(subDir, "agent-a2.jsonl");
+    const before = _cache.get(file);
+    await agentEdits(SID, CWD, "a2");
+    assert.equal(_cache.get(file), before);
+    fs.appendFileSync(
+      file,
+      "\n" +
+        [
+          call("u3", "Write", { file_path: "/work/repo/late.go" }),
+          result("u3", { type: "create", content: "z\n" }),
+        ]
+          .map((l) => JSON.stringify(l))
+          .join("\n")
+    );
+    const edits = await agentEdits(SID, CWD, "a2");
+    assert.ok(edits.some((e) => e.path === "/work/repo/late.go"));
+  });
+});
+
+describe("attachAgentEdits", () => {
+  it("puts edits on an Agent result only", async () => {
+    const messages = [
+      {
+        content: [
+          { type: "tool_result", id: "t9", agent: { id: "a1" } },
+          { type: "tool_result", id: "t8", diff: { added: 1, removed: 0 } },
+          { type: "tool_result", id: "t7", agent: { id: "a1" }, is_error: true },
+        ],
+      },
+    ];
+    await attachAgentEdits(messages, SID, CWD);
+    const [ok, plain, failed] = messages[0].content;
+    assert.ok(ok.edits.some((e) => e.path === "/work/repo/new_test.go"));
+    assert.equal(plain.edits, undefined);
+    assert.equal(failed.edits, undefined);
+  });
+});