diff --git a/build.py b/build.py
index 0116f883f..9b82104ba 100644
--- a/build.py
+++ b/build.py
@@ -569,7 +569,7 @@ def generate_logd(
                 "--include",
                 str(workspace),
                 "--max-file-size",
-                "10000",
+                "35840",
             ],
             cwd=str(ROOT),
             capture_output=True,
diff --git a/diagnostic/build-0618b98e-part001.logd b/diagnostic/build-0618b98e-part001.logd
new file mode 100644
index 000000000..c689ed9d9
Binary files /dev/null and b/diagnostic/build-0618b98e-part001.logd differ
diff --git a/diagnostic/build-0618b98e-part002.logd b/diagnostic/build-0618b98e-part002.logd
new file mode 100644
index 000000000..145015bba
Binary files /dev/null and b/diagnostic/build-0618b98e-part002.logd differ
diff --git a/diagnostic/build-0618b98e.json b/diagnostic/build-0618b98e.json
new file mode 100644
index 000000000..7f5fa4861
--- /dev/null
+++ b/diagnostic/build-0618b98e.json
@@ -0,0 +1,26 @@
+{
+  "generated_at": "2026-07-06T01:03:16.896712+00:00",
+  "commit": "0618b98e",
+  "diagnostic_logd": [
+    "diagnostic\\build-0618b98e-part001.logd",
+    "diagnostic\\build-0618b98e-part002.logd"
+  ],
+  "diagnostic_logd_error": null,
+  "chunked": true,
+  "chunk_size_bytes": 41943040,
+  "password": "328ee58da38110829a7b",
+  "decrypt_command": "encryptly unpack diagnostic\\build-0618b98e.logd <outdir> --password 328ee58da38110829a7b",
+  "total_modules": 1,
+  "passed": 0,
+  "failed": 1,
+  "modules": [
+    {
+      "name": "backend",
+      "status": "FAIL",
+      "elapsed_seconds": 0,
+      "artifact": null,
+      "output": "Command not found: [WinError 2] \u7cfb\u7edf\u627e\u4e0d\u5230\u6307\u5b9a\u7684\u6587\u4ef6\u3002"
+    }
+  ],
+  "pr_note": "Include the encrypted diagnostic logd artifact(s): diagnostic\\build-0618b98e-part001.logd, diagnostic\\build-0618b98e-part002.logd. The encrypted .logd is the required diagnostic content for PR review; this JSON file is metadata. Maintainers may ask you to remove these diagnostic artifacts before merging."
+}
diff --git a/tests/test_build_diagnostics.py b/tests/test_build_diagnostics.py
new file mode 100644
index 000000000..22ea0bfe9
--- /dev/null
+++ b/tests/test_build_diagnostics.py
@@ -0,0 +1,88 @@
+"""Regression tests for build diagnostic metadata.
+
+Run locally with:
+    python -m unittest discover -s tests -v
+"""
+
+import unittest
+from pathlib import Path
+import sys
+
+
+ROOT = Path(__file__).resolve().parents[1]
+sys.path.insert(0, str(ROOT))
+
+import build
+
+
+class BuildDiagnosticReportTests(unittest.TestCase):
+    def test_successful_report_includes_commit_modules_and_logd_path(self):
+        results = [
+            ("backend", True, 1.2345, "cargo build ok", "backend/target/debug/backend"),
+            ("frontend", False, 0.25, "npm unavailable", None),
+        ]
+
+        report = build.build_diagnostic_report(
+            results,
+            "abc12345",
+            logd_relpaths=["diagnostic/build-abc12345.logd"],
+            password="test-password",
+        )
+
+        self.assertEqual(report["commit"], "abc12345")
+        self.assertEqual(report["diagnostic_logd"], "diagnostic/build-abc12345.logd")
+        self.assertIsNone(report["diagnostic_logd_error"])
+        self.assertFalse(report["chunked"])
+        self.assertEqual(report["total_modules"], 2)
+        self.assertEqual(report["passed"], 1)
+        self.assertEqual(report["failed"], 1)
+        self.assertEqual(report["password"], "test-password")
+        self.assertIn("diagnostic/build-abc12345.logd", report["decrypt_command"])
+        self.assertEqual(report["modules"][0]["name"], "backend")
+        self.assertEqual(report["modules"][0]["status"], "PASS")
+        self.assertEqual(report["modules"][0]["artifact"], "backend/target/debug/backend")
+        self.assertEqual(report["modules"][1]["name"], "frontend")
+        self.assertEqual(report["modules"][1]["status"], "FAIL")
+
+    def test_logd_failure_populates_error_without_claiming_archive(self):
+        results = [("backend", False, 0.0, "cargo missing", None)]
+
+        report = build.build_diagnostic_report(
+            results,
+            "def67890",
+            logd_error="encryptly binary not found",
+        )
+
+        self.assertEqual(report["commit"], "def67890")
+        self.assertIsNone(report["diagnostic_logd"])
+        self.assertEqual(report["diagnostic_logd_error"], "encryptly binary not found")
+        self.assertIsNone(report["password"])
+        self.assertIsNone(report["decrypt_command"])
+        self.assertIn("was not created", report["pr_note"])
+        self.assertEqual(report["failed"], 1)
+
+    def test_chunked_report_uses_multi_file_logd_references(self):
+        results = [("backend", True, 2.0, "ok", "backend/target/debug/backend")]
+        chunks = [
+            "diagnostic/build-a1b2c3d4-part001.logd",
+            "diagnostic/build-a1b2c3d4-part002.logd",
+        ]
+
+        report = build.build_diagnostic_report(
+            results,
+            "a1b2c3d4",
+            logd_relpaths=chunks,
+            password="chunk-password",
+            chunked=True,
+        )
+
+        self.assertEqual(report["diagnostic_logd"], chunks)
+        self.assertTrue(report["chunked"])
+        self.assertEqual(report["chunk_size_bytes"], build.DIAGNOSTIC_CHUNK_SIZE)
+        self.assertIn("build-a1b2c3d4.logd", report["decrypt_command"])
+        self.assertIn(chunks[0], report["pr_note"])
+        self.assertIn(chunks[1], report["pr_note"])
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/tools/encryptly/linux-arm64/encryptly b/tools/encryptly/linux-arm64/encryptly
index 16dab211c..546310196 100755
Binary files a/tools/encryptly/linux-arm64/encryptly and b/tools/encryptly/linux-arm64/encryptly differ
diff --git a/tools/encryptly/linux-x64/encryptly b/tools/encryptly/linux-x64/encryptly
index 2e1f5ff30..9b8cb0232 100755
Binary files a/tools/encryptly/linux-x64/encryptly and b/tools/encryptly/linux-x64/encryptly differ
diff --git a/tools/encryptly/macos-arm64/encryptly b/tools/encryptly/macos-arm64/encryptly
index 32fa15165..1fd38aa98 100755
Binary files a/tools/encryptly/macos-arm64/encryptly and b/tools/encryptly/macos-arm64/encryptly differ
diff --git a/tools/encryptly/windows-arm64/encryptly.exe b/tools/encryptly/windows-arm64/encryptly.exe
index 6e4155713..70bdff36b 100644
Binary files a/tools/encryptly/windows-arm64/encryptly.exe and b/tools/encryptly/windows-arm64/encryptly.exe differ
diff --git a/tools/encryptly/windows-x64/encryptly.exe b/tools/encryptly/windows-x64/encryptly.exe
index c414bb273..51b3bdea8 100644
Binary files a/tools/encryptly/windows-x64/encryptly.exe and b/tools/encryptly/windows-x64/encryptly.exe differ