diff --git a/plugins/platforms/a2a/adapter.py b/plugins/platforms/a2a/adapter.py
index 79842c88c676..e1fafa815730 100644
--- a/plugins/platforms/a2a/adapter.py
+++ b/plugins/platforms/a2a/adapter.py
@@ -60,7 +60,7 @@
 logger = logging.getLogger(__name__)
 
 _DEFAULT_PORT = 9900
-_ORPHAN_TIMEOUT = 300  # seconds before a pending task is considered orphaned
+_MIN_ORPHAN_TIMEOUT = 300  # preserve the existing five-minute floor
 _WATCHDOG_INTERVAL = 60  # seconds between orphaned task watchdog runs
 _MAX_BODY = 1_048_576  # 1MB max request body — prevents DoS via memory exhaustion
 _SSE_KEEPALIVE = 5  # seconds between SSE keepalive comments
@@ -74,6 +74,16 @@ def _reply_timeout() -> float:
         return 300.0
 
 
+def _orphan_timeout() -> float:
+    """Keep pending tasks alive through the configured reply deadline.
+
+    The watchdog runs independently from request waiters, so add one watchdog
+    interval of grace. Otherwise a reply timeout above five minutes is
+    ineffective because the task is marked failed at the old fixed deadline.
+    """
+    return max(float(_MIN_ORPHAN_TIMEOUT), _reply_timeout() + _WATCHDOG_INTERVAL)
+
+
 def _default_agent_name() -> str:
     name = os.getenv("A2A_AGENT_NAME", "").strip()
     if name:
@@ -473,8 +483,9 @@ def _watchdog_loop(self) -> None:
         """Background thread that fails orphaned tasks (keeps them queryable)."""
         while not self._watchdog_stop.wait(_WATCHDOG_INTERVAL):
             try:
-                for tid in self.tasks.fail_orphans(_ORPHAN_TIMEOUT):
-                    logger.warning("A2A: orphaned task %s marked failed (timeout %ds)", tid, _ORPHAN_TIMEOUT)
+                orphan_timeout = _orphan_timeout()
+                for tid in self.tasks.fail_orphans(orphan_timeout):
+                    logger.warning("A2A: orphaned task %s marked failed (timeout %.0fs)", tid, orphan_timeout)
                     protocol.metrics.tasks_failed += 1
             except Exception:
                 logger.debug("A2A: watchdog error", exc_info=True)
diff --git a/tests/plugins/test_a2a_plugin.py b/tests/plugins/test_a2a_plugin.py
index 346284b27796..e66d2e54df5f 100644
--- a/tests/plugins/test_a2a_plugin.py
+++ b/tests/plugins/test_a2a_plugin.py
@@ -35,6 +35,26 @@ def _free_port() -> int:
     return port
 
 
+# --------------------------------------------------------------------------
+# Timeouts
+# --------------------------------------------------------------------------
+
+class TestA2ATimeouts:
+    def test_orphan_timeout_never_preempts_configured_reply_timeout(self, monkeypatch):
+        from plugins.platforms.a2a import adapter
+
+        monkeypatch.setenv("A2A_REPLY_TIMEOUT", "900")
+        assert adapter._orphan_timeout() >= (
+            adapter._reply_timeout() + adapter._WATCHDOG_INTERVAL
+        )
+
+    def test_orphan_timeout_keeps_existing_five_minute_floor(self, monkeypatch):
+        from plugins.platforms.a2a import adapter
+
+        monkeypatch.setenv("A2A_REPLY_TIMEOUT", "1")
+        assert adapter._orphan_timeout() >= adapter._MIN_ORPHAN_TIMEOUT
+
+
 # --------------------------------------------------------------------------
 # Security
 # --------------------------------------------------------------------------