fix(chat): keep a long turn's Edited N files card whole across the page cut (#86)

The reported turn (/vp-auto, ~120 messages) showed "Edited 1 file": the
chat loads the newest 50 messages, and the turn's other Write
(rbac_routes_test.go, +176) was in the part before the page.

- turnCarry (agent-edits.js): every message the route's sliding window
  drops goes through it; it keeps the file changes since the last prompt it
  dropped (a dropped call whose result is on the page, and dropped
  subagents, included).
- A Claude page that starts mid-turn answers them as `turn_edits`; the
  chat keeps the one from the page that holds its oldest message and adds
  it to that turn's card.

Files a turn changed through Bash (python/sed writing a file) are still not
listed: nothing in the transcript says which files a command wrote.

server/__tests__/agent-edits.test.js

@@ -2,7 +2,9 @@
  * @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`.
+ * nested subagent folded in — and put on the parent's Agent result as `edits`;
+ * and `turnCarry` hands a page of the chat the edits its cut-off first turn
+ * made before the page began.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
@@ -16,7 +18,7 @@ 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 { agentEdits, attachAgentEdits, turnCarry, _cache } = require("../lib/agent-edits");
 
 const CWD = "/work/repo";
 const SID = "11111111-2222-3333-4444-555555555555";
@@ -110,3 +112,56 @@ describe("attachAgentEdits", () => {
     assert.equal(failed.edits, undefined);
   });
 });
+
+describe("turnCarry", () => {
+  const prompt = (text) => ({ type: "user", sender: "user", content: [{ type: "text", text }] });
+  const use = (id, name, file_path) => ({
+    type: "assistant",
+    sender: "assistant",
+    content: [{ type: "tool_use", id, name, input: file_path ? { file_path } : {} }],
+  });
+  const res = (id, extra = {}) => ({
+    type: "user",
+    sender: "tool",
+    content: [{ type: "tool_result", id, ...extra }],
+  });
+
+  it("answers the files the cut-off turn changed before the page", async () => {
+    const c = turnCarry();
+    for (const m of [
+      prompt("old turn"),
+      use("o1", "Write", "/w/old.go"),
+      res("o1", { diff: { added: 9, removed: 0 } }),
+      prompt("this turn"),
+      use("1", "Write", "/w/a_test.go"),
+      res("1", { diff: { added: 176, removed: 0 } }),
+      use("2", "Edit", "/w/bad.go"),
+      res("2", { is_error: true }),
+      use("3", "Edit", "/w/b.go"),
+    ])
+      c.drop(m);
+    // The page: the result of a dropped call, then more of the same turn.
+    const page = [res("3", { diff: { added: 2, removed: 1 } }), use("4", "Write", "/w/c.go")];
+    assert.deepEqual(await c.result(page, SID, CWD), [
+      { path: "/w/a_test.go", added: 176, removed: 0, counted: true },
+      { path: "/w/b.go", added: 2, removed: 1, counted: true },
+    ]);
+  });
+
+  it("answers null when the page starts on a prompt", async () => {
+    const c = turnCarry();
+    c.drop(prompt("p"));
+    c.drop(use("1", "Write", "/w/a.go"));
+    c.drop(res("1", { diff: { added: 1, removed: 0 } }));
+    assert.equal(await c.result([prompt("next")], SID, CWD), null);
+  });
+
+  it("folds in a dropped subagent's own edits", async () => {
+    const c = turnCarry();
+    c.drop(prompt("p"));
+    c.drop(use("9", "Agent"));
+    c.drop(res("9", { agent: { id: "a1" } }));
+    const got = await c.result([use("10", "Bash")], SID, CWD);
+    assert.ok(got.some((e) => e.path === "/work/repo/new_test.go"));
+  });
+});