diff --git a/app/modules/documents/agent_package.py b/app/modules/documents/agent_package.py
index 2e520c4..ffae7c6 100644
--- a/app/modules/documents/agent_package.py
+++ b/app/modules/documents/agent_package.py
@@ -8,6 +8,12 @@ ERP_LOCAL_AGENT_VERSION = "1.3.0"
 ERP_LOCAL_AGENT_NAME = "ERP Local Agent"
 RUNTIME_ROOT = Path(__file__).resolve().parent / "local_agent_runtime"
 
+# ZIP metadata is part of the ZIP byte stream. If writestr() is allowed to use
+# the current clock time, two packages built from identical source files have
+# different SHA256 hashes. Keep update packages reproducible so the SHA256
+# returned by update-manifest is exactly the SHA256 of update-package.
+_DETERMINISTIC_ZIP_TIMESTAMP = (2026, 1, 1, 0, 0, 0)
+
 
 def build_agent_env(*, erp_base_url: str, node_code: str, node_secret: str, storage_root: str, tenant_id=None, branch_id=None, sync_interval_seconds: int = 30, request_timeout_seconds: int = 60, tunnel_enabled: bool = True, tunnel_reconnect_seconds: int = 10) -> str:
     erp_base_url = (erp_base_url or "").strip().rstrip("/")
@@ -38,34 +44,67 @@ def build_agent_env(*, erp_base_url: str, node_code: str, node_secret: str, stor
     )
 
 
+def _zip_info(name: str) -> zipfile.ZipInfo:
+    info = zipfile.ZipInfo(filename=name, date_time=_DETERMINISTIC_ZIP_TIMESTAMP)
+    info.compress_type = zipfile.ZIP_DEFLATED
+    info.create_system = 3
+    # Regular file with rw-r--r-- permissions. Stable metadata keeps ZIP bytes
+    # reproducible on every request and across Linux deployments.
+    info.external_attr = (0o100644 & 0xFFFF) << 16
+    return info
+
+
+def _write_zip_bytes(dst: zipfile.ZipFile, name: str, payload: bytes) -> None:
+    dst.writestr(_zip_info(name), payload)
+
+
 def _build_zip(*, env_text: str | None, include_env: bool, include_admin_readme: bool) -> bytes:
     if not RUNTIME_ROOT.exists():
         raise RuntimeError(f"ERP Local Agent runtime is missing: {RUNTIME_ROOT}")
+
     buffer = io.BytesIO()
-    with zipfile.ZipFile(buffer, "w", compression=zipfile.ZIP_DEFLATED) as dst:
-        for path in sorted(RUNTIME_ROOT.rglob("*")):
+    with zipfile.ZipFile(
+        buffer,
+        "w",
+        compression=zipfile.ZIP_DEFLATED,
+        compresslevel=9,
+    ) as dst:
+        for path in sorted(RUNTIME_ROOT.rglob("*"), key=lambda item: item.as_posix()):
             if not path.is_file() or "__pycache__" in path.parts:
                 continue
             name = path.relative_to(RUNTIME_ROOT).as_posix()
-            dst.writestr(name, path.read_bytes())
+            _write_zip_bytes(dst, name, path.read_bytes())
+
         if include_env and env_text is not None:
-            dst.writestr(".env", env_text)
+            _write_zip_bytes(dst, ".env", env_text.encode("utf-8"))
+
         if include_admin_readme:
-            dst.writestr(
-                "README_ERP_LOCAL_AGENT.txt",
+            readme = (
                 f"ERP Local Agent {ERP_LOCAL_AGENT_VERSION}\n"
                 "Existing storage, WebSocket tunnel, Tally, accounting .act and local dashboard functionality are preserved.\n"
                 "Local dashboard: http://127.0.0.1:8788\n"
                 "The agent checks for updates automatically but installation is always initiated by the local user.\n"
-                "The existing .env, data, logs, .venv and client storage are preserved during updates.\n",
+                "The existing .env, data, logs, .venv and client storage are preserved during updates.\n"
             )
+            _write_zip_bytes(dst, "README_ERP_LOCAL_AGENT.txt", readme.encode("utf-8"))
+
     return buffer.getvalue()
 
 
 def build_preconfigured_agent_zip(*, env_text: str, include_admin_readme: bool = False) -> bytes:
-    return _build_zip(env_text=env_text, include_env=True, include_admin_readme=include_admin_readme)
+    return _build_zip(
+        env_text=env_text,
+        include_env=True,
+        include_admin_readme=include_admin_readme,
+    )
 
 
 def build_agent_update_zip() -> bytes:
     # Update package deliberately excludes .env, .venv, data, logs and client files.
-    return _build_zip(env_text=None, include_env=False, include_admin_readme=False)
+    # The ZIP is deterministic so update-manifest and update-package always agree
+    # on SHA256 for the same deployed runtime/version.
+    return _build_zip(
+        env_text=None,
+        include_env=False,
+        include_admin_readme=False,
+    )