fix(server): retain the legacy structured diff payload budget

packages/server/src/server/checkout-diff-manager.ts

@@ -11,7 +11,10 @@ import {
   type DiffBody,
 } from "@getpaseo/protocol/binary-frames/index";
 import type { ParsedDiffFile } from "@getpaseo/protocol/messages";
-import { resolveCheckoutDiffBase } from "../utils/checkout-git.js";
+import {
+  CHECKOUT_DIFF_MAX_STRUCTURED_BYTES,
+  resolveCheckoutDiffBase,
+} from "../utils/checkout-git.js";
 import { expandTilde } from "../utils/path.js";
 import { toCheckoutError } from "./checkout-git-utils.js";
 
@@ -105,7 +108,7 @@ export class CheckoutDiffManager {
           next.set(entry.path, file);
         }
         files = next;
-        payload = { cwd, files: [...next.values()], error: null };
+        payload = legacySnapshot(cwd, [...next.values()]);
       }
       pending = null;
       if (delivered) listener(payload);
@@ -169,3 +172,19 @@ export class CheckoutDiffManager {
     await this.streams.close();
   }
 }
+
+function legacySnapshot(cwd: string, files: ParsedDiffFile[]): CheckoutDiffSnapshotPayload {
+  let bytes = 2;
+  for (let index = 0; index < files.length; index++) {
+    bytes += Buffer.byteLength(JSON.stringify(files[index])) + Number(index > 0);
+    if (bytes > CHECKOUT_DIFF_MAX_STRUCTURED_BYTES) {
+      return {
+        cwd,
+        files: [],
+        diffTooLarge: true,
+        error: toCheckoutError(new Error("Diff too large to display")),
+      };
+    }
+  }
+  return { cwd, files, error: null };
+}

packages/server/src/server/daemon-e2e/checkout-diff-subscription.e2e.test.ts

@@ -142,7 +142,8 @@ test("keeps the socket usable after rejecting an oversized structured diff", asy
     commitFile(cwd, "large-b.js", "const value = 0;\n");
     // Short lines stay eligible for highlighting; a giant single line is skipped
     // before token expansion and cannot exercise the structured-payload limit.
-    const denseExpression = `const value = ${"a+".repeat(100)}a;\n`.repeat(4_000);
+    // Stay below the full-source highlighting budget as well.
+    const denseExpression = `const value = ${"a+".repeat(100)}a;\n`.repeat(3_500);
     writeFileSync(path.join(cwd, "large-a.js"), denseExpression);
     writeFileSync(path.join(cwd, "large-b.js"), denseExpression);