fix(bedrock): preserve regional runtime on model switch

agent/agent_runtime_helpers.py

@@ -1413,6 +1413,7 @@ def switch_model(agent, new_model, new_provider, api_key='', base_url='', api_mo
             "_anthropic_base_url",
             "_is_anthropic_oauth",
             "_config_context_length",
+            "_bedrock_region",
         )
     }
     # _client_kwargs is a dict — snapshot a shallow copy so mutating the
@@ -1443,7 +1444,28 @@ def switch_model(agent, new_model, new_provider, api_key='', base_url='', api_mo
             agent.api_key = api_key
 
         # ── Build new client ──
-        if api_mode == "anthropic_messages":
+        if new_provider == "bedrock" and api_mode in {"anthropic_messages", "bedrock_converse"}:
+            _br_match = re.search(
+                r"bedrock-runtime\.([a-z0-9-]+)\.",
+                (base_url or agent.base_url or ""),
+            )
+            _br_region = _br_match.group(1) if _br_match else "us-east-1"
+            agent._bedrock_region = _br_region
+            agent.api_key = "aws-sdk"
+            agent.client = None
+            agent._client_kwargs = {}
+            if api_mode == "anthropic_messages":
+                from agent.anthropic_adapter import build_anthropic_bedrock_client
+                agent._anthropic_client = build_anthropic_bedrock_client(_br_region)
+                agent._anthropic_api_key = "aws-sdk"
+                agent._anthropic_base_url = base_url or agent.base_url
+                agent._is_anthropic_oauth = False
+            else:
+                agent._anthropic_client = None
+                agent._anthropic_api_key = None
+                agent._anthropic_base_url = None
+                agent._is_anthropic_oauth = False
+        elif api_mode == "anthropic_messages":
             from agent.anthropic_adapter import (
                 build_anthropic_client,
                 resolve_anthropic_token,

hermes_cli/runtime_provider.py

@@ -1596,7 +1596,9 @@ def resolve_runtime_provider(
         # Dual-path routing: Claude models use AnthropicBedrock SDK for full
         # feature parity (prompt caching, thinking budgets, adaptive thinking).
         # Non-Claude models use the Converse API for multi-model support.
-        _current_model = str(model_cfg.get("default") or "").strip()
+        # Prefer target_model for in-session /model switches; using the stale
+        # config default misroutes Claude-on-Bedrock switches to Converse.
+        _current_model = str(target_model or model_cfg.get("default") or "").strip()
         if is_anthropic_bedrock_model(_current_model):
             # Claude on Bedrock → AnthropicBedrock SDK → anthropic_messages path
             runtime = {

tests/hermes_cli/test_runtime_provider_resolution.py

@@ -2705,3 +2705,61 @@ def test_host_derived_key_helper_basic_cases():
     for k in ("DEEPSEEK_API_KEY", "GROQ_API_KEY", "MISTRAL_API_KEY",
               "OPENAI_API_KEY", "OPENROUTER_API_KEY"):
         _os.environ.pop(k, None)
+
+
+def test_bedrock_runtime_provider_uses_target_model_for_switch(monkeypatch):
+    """Bedrock /model switches should route from the target model, not stale config."""
+    monkeypatch.setattr(rp, "resolve_provider", lambda *a, **k: "bedrock")
+    monkeypatch.setattr(
+        rp,
+        "_get_model_config",
+        lambda: {"provider": "openrouter", "default": "openai/gpt-5.5"},
+    )
+    monkeypatch.setattr(
+        rp,
+        "load_config",
+        lambda: {"bedrock": {"region": "ap-northeast-1"}},
+    )
+    monkeypatch.setattr(
+        "agent.bedrock_adapter.resolve_aws_auth_env_var",
+        lambda: "aws-sdk-default-chain",
+    )
+
+    resolved = rp.resolve_runtime_provider(
+        requested="bedrock",
+        target_model="jp.anthropic.claude-opus-4-8",
+    )
+
+    assert resolved["provider"] == "bedrock"
+    assert resolved["api_mode"] == "anthropic_messages"
+    assert resolved["bedrock_anthropic"] is True
+    assert resolved["region"] == "ap-northeast-1"
+    assert resolved["base_url"] == "https://bedrock-runtime.ap-northeast-1.amazonaws.com"
+
+
+def test_bedrock_runtime_provider_keeps_converse_for_non_anthropic_target(monkeypatch):
+    monkeypatch.setattr(rp, "resolve_provider", lambda *a, **k: "bedrock")
+    monkeypatch.setattr(
+        rp,
+        "_get_model_config",
+        lambda: {"provider": "anthropic", "default": "anthropic/claude-sonnet-4"},
+    )
+    monkeypatch.setattr(
+        rp,
+        "load_config",
+        lambda: {"bedrock": {"region": "eu-west-1"}},
+    )
+    monkeypatch.setattr(
+        "agent.bedrock_adapter.resolve_aws_auth_env_var",
+        lambda: "aws-sdk-default-chain",
+    )
+
+    resolved = rp.resolve_runtime_provider(
+        requested="bedrock",
+        target_model="amazon.nova-pro-v1:0",
+    )
+
+    assert resolved["provider"] == "bedrock"
+    assert resolved["api_mode"] == "bedrock_converse"
+    assert "bedrock_anthropic" not in resolved
+    assert resolved["region"] == "eu-west-1"

tests/run_agent/test_switch_model_context.py

@@ -73,3 +73,50 @@ def test_switch_model_without_config_context_length():
         mock_ctx_len.assert_called_once()
         call_kwargs = mock_ctx_len.call_args.kwargs
         assert call_kwargs.get("config_context_length") is None
+
+
+def test_switch_model_builds_bedrock_anthropic_client_with_resolved_region():
+    agent = _make_agent_with_compressor(config_context_length=None)
+    built = object()
+
+    with patch("agent.anthropic_adapter.build_anthropic_bedrock_client", return_value=built) as mock_build:
+        with patch("agent.model_metadata.get_model_context_length", return_value=200_000):
+            agent.switch_model(
+                "jp.anthropic.claude-opus-4-8",
+                "bedrock",
+                api_key="aws-sdk",
+                base_url="https://bedrock-runtime.ap-northeast-1.amazonaws.com",
+                api_mode="anthropic_messages",
+            )
+
+    mock_build.assert_called_once_with("ap-northeast-1")
+    assert agent.provider == "bedrock"
+    assert agent.api_mode == "anthropic_messages"
+    assert agent.api_key == "aws-sdk"
+    assert agent._bedrock_region == "ap-northeast-1"
+    assert agent._anthropic_client is built
+    assert agent._anthropic_api_key == "aws-sdk"
+    assert agent.client is None
+    assert agent._client_kwargs == {}
+
+
+def test_switch_model_builds_bedrock_converse_without_openai_client():
+    agent = _make_agent_with_compressor(config_context_length=None)
+    agent._create_openai_client = MagicMock(side_effect=AssertionError("bedrock should not build OpenAI client"))
+
+    with patch("agent.model_metadata.get_model_context_length", return_value=128_000):
+        agent.switch_model(
+            "amazon.nova-pro-v1:0",
+            "bedrock",
+            api_key="aws-sdk",
+            base_url="https://bedrock-runtime.eu-west-1.amazonaws.com",
+            api_mode="bedrock_converse",
+        )
+
+    assert agent.provider == "bedrock"
+    assert agent.api_mode == "bedrock_converse"
+    assert agent.api_key == "aws-sdk"
+    assert agent._bedrock_region == "eu-west-1"
+    assert agent.client is None
+    assert agent._anthropic_client is None
+    assert agent._client_kwargs == {}