fix(agents): sync agent_name across context/configurable and reject empty soul (#3549) (#3553)

* fix(agents): sync agent_name across context/configurable and reject empty soul (#3549)

Two independent issues caused custom agent creation to silently fail:

1. build_run_config only wrote agent_name into one container (configurable
   or context), so setup_agent — which reads ToolRuntime.context exclusively
   since LangGraph >=1.1.9 — saw agent_name=None and wrote SOUL.md to the
   global base_dir instead of users/{user_id}/agents/{name}/. Mirror the
   dual-write pattern already used by merge_run_context_overrides and
   naming.py so both containers always carry the same value.

2. setup_agent persisted whatever soul string it received, including empty
   or whitespace-only content, and still reported success. The frontend
   then surfaced an unusable agent and the global default SOUL.md could be
   silently overwritten with empty content. Reject empty soul before any
   filesystem operation so the model can retry.

Tests:
- test_gateway_services.py: dual-write regressions for both configurable
  and context entry paths, explicit-agent-name precedence on both sides,
  and a shape-parity test against merge_run_context_overrides.
- test_setup_agent_tool.py: empty/whitespace soul rejection, plus
  no-overwrite guarantees for existing global and per-agent SOUL.md.

* Update services.py

backend/tests/test_gateway_services.py

@@ -252,11 +252,17 @@ def test_build_run_config_explicit_agent_name_not_overwritten():
         assistant_id="other-agent",
     )
     assert config["configurable"]["agent_name"] == "explicit-agent"
+    assert config["context"]["agent_name"] == "explicit-agent"
     assert config["run_name"] == "explicit-agent"
 
 
 def test_build_run_config_context_custom_agent_injects_agent_name():
-    """Custom assistant_id must be forwarded as context['agent_name'] in context mode."""
+    """Custom assistant_id must be forwarded as ``agent_name`` in both
+    ``context`` and ``configurable`` (issue #3549). Previously only the
+    active container was populated, so when the caller sent context-only the
+    setup_agent tool — which reads ``ToolRuntime.context`` — saw
+    ``agent_name=None`` and wrote SOUL.md to the global base_dir.
+    """
     from app.gateway.services import build_run_config
 
     config = build_run_config(
@@ -267,7 +273,7 @@ def test_build_run_config_context_custom_agent_injects_agent_name():
     )
 
     assert config["context"]["agent_name"] == "finalis"
-    assert "configurable" not in config
+    assert config["configurable"]["agent_name"] == "finalis"
 
 
 def test_resolve_agent_factory_returns_make_lead_agent():
@@ -281,6 +287,56 @@ def test_resolve_agent_factory_returns_make_lead_agent():
     assert resolve_agent_factory("custom-agent-123") is make_lead_agent
 
 
+def test_build_run_config_configurable_custom_agent_dual_writes_agent_name():
+    """Regression for issue #3549: even when the caller uses the legacy
+    ``configurable`` path, ``agent_name`` must also land in
+    ``config['context']`` so LangGraph >=1.1.9 ``ToolRuntime.context`` consumers
+    (e.g. ``setup_agent``) observe the same value.
+    """
+    from app.gateway.services import build_run_config
+
+    config = build_run_config("thread-1", None, None, assistant_id="finalis")
+
+    assert config["configurable"]["agent_name"] == "finalis"
+    assert config["context"]["agent_name"] == "finalis"
+
+
+def test_build_run_config_context_explicit_agent_name_not_overwritten():
+    """An explicit ``context['agent_name']`` from the request must take
+    precedence over the value derived from ``assistant_id`` and be mirrored
+    to ``configurable`` so the two containers never diverge.
+    """
+    from app.gateway.services import build_run_config
+
+    config = build_run_config(
+        "thread-1",
+        {"context": {"agent_name": "explicit-agent"}},
+        None,
+        assistant_id="other-agent",
+    )
+
+    assert config["context"]["agent_name"] == "explicit-agent"
+    assert config["configurable"]["agent_name"] == "explicit-agent"
+    assert config["run_name"] == "explicit-agent"
+
+
+def test_build_run_config_dual_write_matches_merge_run_context_overrides_shape():
+    """The shape produced by ``build_run_config`` for a custom agent must be
+    indistinguishable from what ``merge_run_context_overrides`` would produce
+    when ``agent_name`` is supplied via ``body.context`` — guarding against
+    the two code paths drifting apart again (issue #3549).
+    """
+    from app.gateway.services import build_run_config, merge_run_context_overrides
+
+    via_assistant_id = build_run_config("thread-1", None, None, assistant_id="finalis")
+
+    via_context = build_run_config("thread-1", None, None)
+    merge_run_context_overrides(via_context, {"agent_name": "finalis"})
+
+    assert via_assistant_id["configurable"]["agent_name"] == via_context["configurable"]["agent_name"]
+    assert via_assistant_id["context"]["agent_name"] == via_context["context"]["agent_name"]
+
+
 # ---------------------------------------------------------------------------
 
 # ---------------------------------------------------------------------------
@@ -610,13 +666,15 @@ def test_build_run_config_rejects_non_mapping_context():
 
 
 def test_build_run_config_null_context_custom_agent_injects_agent_name():
-    """Custom assistant_id can still be injected when context=null starts context mode."""
+    """Custom assistant_id must be injected into both containers even when the
+    request started in context-only mode with ``context=null`` .
+    """
     from app.gateway.services import build_run_config
 
     config = build_run_config("thread-1", {"context": None}, None, assistant_id="finalis")
 
-    assert config["context"] == {"agent_name": "finalis"}
-    assert "configurable" not in config
+    assert config["context"]["agent_name"] == "finalis"
+    assert config["configurable"]["agent_name"] == "finalis"
 
 
 def test_build_run_config_context_plus_configurable_warns(caplog):