diff --git a/agent.py b/agent.py
index b975416..1806031 100644
--- a/agent.py
+++ b/agent.py
@@ -190,7 +190,7 @@ class AgentBuilder(A2AAgent[BuilderConfig, NoAuth]):
                     if isinstance(out, dict):
                         final_state = out
         except Exception as exc:  # noqa: BLE001
-            return {"error": f"build graph failed: {type(exc).__name__}: {exc}"}
+            return {"error": _build_failure_error(exc)}
         finally:
             heartbeat_task.cancel()
             with suppress(asyncio.CancelledError):
@@ -278,4 +278,20 @@ def _find_url(value: Any) -> str | None:
         m = _URL_RE.search(value)
         return m.group(0) if m else None
     return None
+
+
+def _build_failure_error(exc: BaseException) -> str:
+    message = str(exc)
+    lowered = message.lower()
+    if (
+        "budget has been exceeded" in lowered
+        or "budget exceeded" in lowered
+        or "ratelimiterror" in type(exc).__name__.lower()
+        or "rate limit" in lowered
+    ):
+        return (
+            "LLM budget exceeded before deployment; retry with a larger budget "
+            "or a smaller build scope"
+        )
+    return f"build graph failed: {type(exc).__name__}: {exc}"
 # rebuild against a2a-pack 0.1.47 for manifest-backed meta-agent defaults
diff --git a/agent_builder/tools.py b/agent_builder/tools.py
index 0908942..3980f4f 100644
--- a/agent_builder/tools.py
+++ b/agent_builder/tools.py
@@ -29,7 +29,7 @@ if TYPE_CHECKING:
     from .config import Settings
 
 
-A2A_PACK_MIN_VERSION = "0.1.47"
+A2A_PACK_MIN_VERSION = "0.1.51"
 
 
 @dataclass(frozen=True)
diff --git a/requirements.txt b/requirements.txt
index dafd889..79e8d2b 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,4 @@
-a2a-pack>=0.1.47
+a2a-pack>=0.1.51
 httpx>=0.27
 boto3>=1.34
 deepagents>=0.5.0
diff --git a/tests/test_builder_prompt.py b/tests/test_builder_prompt.py
index c1cf226..893d26b 100644
--- a/tests/test_builder_prompt.py
+++ b/tests/test_builder_prompt.py
@@ -14,6 +14,7 @@ from agent_builder.builder import (
 from agent_builder.config import Settings
 from agent_builder.tools import A2A_PACK_MIN_VERSION
 from deepagents.backends import StateBackend
+from agent import _build_failure_error
 
 
 class BuilderPromptTests(unittest.TestCase):
@@ -132,6 +133,13 @@ class BuilderPromptTests(unittest.TestCase):
         for skill_name in expected:
             self.assertIn(f"{BUILDER_SKILL_SOURCE}{skill_name}/", paths)
 
+    def test_build_failure_error_classifies_budget_exhaustion(self) -> None:
+        self.assertEqual(
+            _build_failure_error(RuntimeError("Budget has been exceeded! Key=abc")),
+            "LLM budget exceeded before deployment; retry with a larger budget "
+            "or a smaller build scope",
+        )
+
     def test_project_backend_keeps_deepagents_artifacts_inside_project_grant(self) -> None:
         backend = _build_project_backend(
             BuilderContext(