diff --git a/internal/providers/openai_tool_message_name_test.go b/internal/providers/openai_tool_message_name_test.go
new file mode 100644
index 00000000..7a0c7c22
--- /dev/null
+++ b/internal/providers/openai_tool_message_name_test.go
@@ -0,0 +1,111 @@
+package providers
+
+import (
+	"testing"
+)
+
+// TestBuildRequestBody_ToolMessageIncludesName verifies that role="tool" wire
+// messages carry the originating tool's `name` field. Google Gemini's
+// OpenAI-compat shim maps this to native `FunctionResponse.name`; an empty name
+// trips HTTP 400 ("Name cannot be empty"). Trace: 019d8f33-2de1-7ab2-9a32-9df92cd610dd.
+func TestBuildRequestBody_ToolMessageIncludesName(t *testing.T) {
+	p := NewOpenAIProvider("test-gemini", "key",
+		"https://generativelanguage.googleapis.com/v1beta/openai", "gemini-3-flash-preview")
+
+	req := ChatRequest{
+		Messages: []Message{
+			{Role: "user", Content: "hello"},
+			{Role: "assistant", Content: "", ToolCalls: []ToolCall{
+				{
+					ID: "call_1", Name: "write_file",
+					Arguments: map[string]any{"path": "USER.md", "content": "x"},
+					// thought_signature present → not collapsed by Gemini sig-missing collapser.
+					Metadata: map[string]string{"thought_signature": "sig-abc"},
+				},
+			}},
+			{Role: "tool", ToolCallID: "call_1", Content: "ok"},
+		},
+	}
+
+	body := p.buildRequestBody("gemini-3-flash-preview", req, false)
+	msgs, ok := body["messages"].([]map[string]any)
+	if !ok {
+		t.Fatalf("messages not []map[string]any: %T", body["messages"])
+	}
+	if len(msgs) != 3 {
+		t.Fatalf("expected 3 messages, got %d", len(msgs))
+	}
+
+	toolMsg := msgs[2]
+	if toolMsg["role"] != "tool" {
+		t.Fatalf("msg[2] role = %v, want tool", toolMsg["role"])
+	}
+	if toolMsg["tool_call_id"] != "call_1" {
+		t.Fatalf("msg[2] tool_call_id = %v, want call_1", toolMsg["tool_call_id"])
+	}
+	if got := toolMsg["name"]; got != "write_file" {
+		t.Fatalf("msg[2] name = %v, want write_file (Gemini 400 fix)", got)
+	}
+}
+
+// TestBuildRequestBody_ToolMessageNameLookupUsesRawID ensures the lookup map is
+// keyed by the *raw* ToolCallID (pre-wire-truncation) so long IDs still resolve.
+func TestBuildRequestBody_ToolMessageNameLookupUsesRawID(t *testing.T) {
+	longID := "call_0123456789abcdef0123456789abcdef0123456789abcdef" // > maxToolCallIDLen
+	p := NewOpenAIProvider("test-gemini", "key",
+		"https://generativelanguage.googleapis.com/v1beta/openai", "gemini-3-flash-preview")
+
+	req := ChatRequest{
+		Messages: []Message{
+			{Role: "user", Content: "hi"},
+			{Role: "assistant", ToolCalls: []ToolCall{
+				{
+					ID: longID, Name: "read_file",
+					Arguments: map[string]any{"path": "x"},
+					Metadata:  map[string]string{"thought_signature": "sig-xyz"},
+				},
+			}},
+			{Role: "tool", ToolCallID: longID, Content: "data"},
+		},
+	}
+
+	body := p.buildRequestBody("gemini-3-flash-preview", req, false)
+	msgs := body["messages"].([]map[string]any)
+	toolMsg := msgs[2]
+
+	if got := toolMsg["name"]; got != "read_file" {
+		t.Fatalf("name lookup must use raw ID; got %v want read_file", got)
+	}
+	wireID := p.wireToolCallID(longID)
+	if got := toolMsg["tool_call_id"]; got != wireID {
+		t.Fatalf("tool_call_id should be wire-translated; got %v want %v", got, wireID)
+	}
+}
+
+// TestBuildRequestBody_ToolMessageWithoutMatchingCallOmitsName verifies that a
+// stray tool message (no preceding tool_call with matching ID) does NOT emit an
+// empty name field — better to drop the field than send "" which Gemini rejects
+// just the same. Logged via slog.Warn for observability.
+func TestBuildRequestBody_ToolMessageWithoutMatchingCallOmitsName(t *testing.T) {
+	p := NewOpenAIProvider("test-gemini", "key",
+		"https://generativelanguage.googleapis.com/v1beta/openai", "gemini-3-flash-preview")
+
+	req := ChatRequest{
+		Messages: []Message{
+			{Role: "user", Content: "hi"},
+			{Role: "tool", ToolCallID: "orphan_id", Content: "stale"},
+		},
+	}
+
+	body := p.buildRequestBody("gemini-3-flash-preview", req, false)
+	msgs := body["messages"].([]map[string]any)
+	if len(msgs) < 2 {
+		t.Fatalf("expected at least 2 msgs after collapse, got %d", len(msgs))
+	}
+	last := msgs[len(msgs)-1]
+	if last["role"] == "tool" {
+		if _, present := last["name"]; present {
+			t.Fatalf("orphan tool msg should omit name field, got %v", last["name"])
+		}
+	}
+}