feat: add AWS Bedrock as a selectable chat LLM transport

packages/api/src/cell_explorer_api/services/chat_session.py

@@ -201,7 +201,10 @@ async def make_chat_agent(
 
     # 6. Construct LLMClient if not provided
     if llm is None:
-        llm = AnthropicLLMClient(transport=agent_config.llm_transport)
+        llm = AnthropicLLMClient(
+            transport=agent_config.llm_transport,
+            bedrock_region=agent_config.bedrock_region,
+        )
 
     # 7. Return the wired agent
     return ChatAgent(llm=llm, catalog=catalog, dataset_ctx=ctx, config=agent_config)

packages/cell-explorer-agent/pyproject.toml

@@ -4,7 +4,7 @@ version = "0.1.0"
 description = "LLM chat agent library for single-cell zarr datasets"
 requires-python = ">=3.12"
 dependencies = [
-    "anthropic>=0.40",
+    "anthropic[bedrock]>=0.40",
     "pydantic>=2.0",
     "pydantic-settings>=2.8",
     "numpy>=1.26",

packages/cell-explorer-agent/src/cell_explorer_agent/config.py

@@ -13,6 +13,7 @@ class AgentConfig(BaseSettings):
 
     llm_transport: Literal["anthropic", "bedrock", "vertex"] = "anthropic"
     llm_model: str = "claude-sonnet-4-6"
+    bedrock_region: str = "us-east-1"
 
     tool_result_max_bytes: int = Field(default=32_768, ge=1)
     filter_ids_max: int = Field(default=100_000, ge=1)

packages/cell-explorer-agent/src/cell_explorer_agent/llm/anthropic.py

@@ -89,13 +89,15 @@ def neutral_messages_to_anthropic(
 class AnthropicLLMClient(LLMClient):
     """Anthropic SDK adapter. Supports direct/Bedrock/Vertex via transport arg."""
 
-    def __init__(self, *, transport: Transport = "anthropic") -> None:
+    def __init__(
+        self, *, transport: Transport = "anthropic", bedrock_region: str = "us-east-1"
+    ) -> None:
         import anthropic
 
         if transport == "anthropic":
             self._client = anthropic.AsyncAnthropic()
         elif transport == "bedrock":
-            self._client = anthropic.AsyncAnthropicBedrock()
+            self._client = anthropic.AsyncAnthropicBedrock(aws_region=bedrock_region)
         elif transport == "vertex":
             self._client = anthropic.AsyncAnthropicVertex()
         else:

packages/cell-explorer-agent/tests/test_config.py

@@ -8,6 +8,7 @@ def test_defaults():
     cfg = AgentConfig()
     assert cfg.llm_transport == "anthropic"
     assert cfg.llm_model == "claude-sonnet-4-6"
+    assert cfg.bedrock_region == "us-east-1"
     assert cfg.tool_result_max_bytes == 32_768
     assert cfg.filter_ids_max == 100_000
     assert cfg.max_tool_calls_per_turn == 8
@@ -98,3 +99,13 @@ def test_langfuse_base_url_default(monkeypatch):
     from cell_explorer_agent.config import AgentConfig
     cfg = AgentConfig()
     assert cfg.langfuse_base_url == "https://us.cloud.langfuse.com"
+
+
+def test_bedrock_region_default(monkeypatch):
+    monkeypatch.delenv("CHAT_BEDROCK_REGION", raising=False)
+    assert AgentConfig().bedrock_region == "us-east-1"
+
+
+def test_bedrock_region_override(monkeypatch):
+    monkeypatch.setenv("CHAT_BEDROCK_REGION", "us-west-2")
+    assert AgentConfig().bedrock_region == "us-west-2"

packages/cell-explorer-agent/tests/test_llm_client_transport.py

@@ -0,0 +1,31 @@
+"""AnthropicLLMClient transport selection + Bedrock runtime deps."""
+
+import anthropic
+
+from cell_explorer_agent import AnthropicLLMClient
+
+
+def test_bedrock_runtime_dep_importable():
+    # anthropic[bedrock] provides boto3, required for Bedrock SigV4/cred resolution
+    # at request time (construction alone does not import it).
+    import boto3  # noqa: F401
+
+
+def test_bedrock_transport_uses_region():
+    # Non-default region so this fails if aws_region were dropped from the
+    # constructor call (the SDK would otherwise fall back to "us-east-1").
+    client = AnthropicLLMClient(transport="bedrock", bedrock_region="ap-southeast-1")
+    assert isinstance(client._client, anthropic.AsyncAnthropicBedrock)
+    assert client._client.aws_region == "ap-southeast-1"
+
+
+def test_bedrock_transport_region_override():
+    client = AnthropicLLMClient(transport="bedrock", bedrock_region="eu-west-1")
+    assert client._client.aws_region == "eu-west-1"
+
+
+def test_anthropic_transport_is_default(monkeypatch):
+    # AsyncAnthropic() needs an api key present to construct
+    monkeypatch.setenv("ANTHROPIC_API_KEY", "sk-ant-test")
+    client = AnthropicLLMClient()
+    assert isinstance(client._client, anthropic.AsyncAnthropic)