Normalize Bedrock tool results

packages/provider/amazon_bedrock.go

@@ -216,6 +216,61 @@ type bedrockRequest struct {
 	} `json:"toolConfig,omitempty"`
 }
 
+func normalizeBedrockToolResults(msgs []Message) []Message {
+	resultByID := map[string]ToolResultBlock{}
+	for _, m := range msgs {
+		for _, c := range m.Content {
+			if tr, ok := c.(ToolResultBlock); ok {
+				if _, exists := resultByID[tr.CallID]; !exists {
+					resultByID[tr.CallID] = tr
+				}
+			}
+		}
+	}
+
+	out := make([]Message, 0, len(msgs))
+	for _, m := range msgs {
+		copy := m
+		copy.Content = nil
+		var toolCalls []ToolCallBlock
+		for _, c := range m.Content {
+			switch v := c.(type) {
+			case ToolResultBlock:
+				// Bedrock requires toolResult blocks immediately after the
+				// assistant toolUse they answer. Reinsert them from the
+				// assistant pass below instead of preserving their original
+				// location, which may be separated by user text in active
+				// sessions.
+				continue
+			case ToolCallBlock:
+				toolCalls = append(toolCalls, v)
+			}
+			copy.Content = append(copy.Content, c)
+		}
+		if len(copy.Content) > 0 {
+			out = append(out, copy)
+		}
+		if m.Role != RoleAssistant || len(toolCalls) == 0 {
+			continue
+		}
+
+		results := make([]Content, 0, len(toolCalls))
+		for _, tc := range toolCalls {
+			if tr, ok := resultByID[tc.ID]; ok {
+				results = append(results, tr)
+				continue
+			}
+			results = append(results, ToolResultBlock{
+				CallID:  tc.ID,
+				IsError: true,
+				Content: []Content{TextBlock{Text: "tool call did not complete before the next user message"}},
+			})
+		}
+		out = append(out, Message{Role: RoleTool, Content: results, Time: m.Time})
+	}
+	return out
+}
+
 func (c *bedrockClient) buildRequest(req Request) (*bedrockRequest, error) {
 	out := &bedrockRequest{}
 	if req.System != "" {
@@ -226,7 +281,7 @@ func (c *bedrockClient) buildRequest(req Request) (*bedrockRequest, error) {
 	if out.InferenceConfig.MaxTokens == 0 {
 		out.InferenceConfig.MaxTokens = 4096
 	}
-	for _, m := range req.Messages {
+	for _, m := range normalizeBedrockToolResults(req.Messages) {
 		role := string(m.Role)
 		if role == "tool" {
 			role = "user"
@@ -267,6 +322,9 @@ func (c *bedrockClient) buildRequest(req Request) (*bedrockRequest, error) {
 				})
 			}
 		}
+		if len(bm.Content) == 0 {
+			continue
+		}
 		out.Messages = append(out.Messages, bm)
 	}
 	if len(req.Tools) > 0 {

packages/provider/amazon_bedrock_test.go

@@ -2,6 +2,7 @@ package provider
 
 import (
 	"bytes"
+	"encoding/json"
 	"net/http"
 	"strings"
 	"testing"
@@ -82,6 +83,71 @@ func TestReadAWSCredentialsFile(t *testing.T) {
 	}
 }
 
+func TestNormalizeBedrockToolResultsMovesResultsAdjacentToToolUse(t *testing.T) {
+	msgs := []Message{
+		{Role: RoleAssistant, Content: []Content{ToolCallBlock{ID: "tool-1", Name: "edit", Arguments: json.RawMessage(`{"path":"a"}`)}}},
+		{Role: RoleUser, Content: []Content{TextBlock{Text: "what's wrong"}}},
+		{Role: RoleTool, Content: []Content{ToolResultBlock{CallID: "tool-1", Content: []Content{TextBlock{Text: "edited"}}}}},
+	}
+
+	out := normalizeBedrockToolResults(msgs)
+	if len(out) != 3 {
+		t.Fatalf("got %d messages, want 3: %+v", len(out), out)
+	}
+	if out[0].Role != RoleAssistant {
+		t.Fatalf("first role = %s, want assistant", out[0].Role)
+	}
+	if out[1].Role != RoleTool {
+		t.Fatalf("second role = %s, want tool", out[1].Role)
+	}
+	tr, ok := out[1].Content[0].(ToolResultBlock)
+	if !ok {
+		t.Fatalf("second message content = %T, want ToolResultBlock", out[1].Content[0])
+	}
+	if tr.CallID != "tool-1" || tr.IsError {
+		t.Fatalf("unexpected tool result: %+v", tr)
+	}
+	if out[2].Role != RoleUser {
+		t.Fatalf("third role = %s, want user", out[2].Role)
+	}
+}
+
+func TestNormalizeBedrockToolResultsInjectsMissingResult(t *testing.T) {
+	msgs := []Message{
+		{Role: RoleAssistant, Content: []Content{ToolCallBlock{ID: "tool-1", Name: "edit", Arguments: json.RawMessage(`{}`)}}},
+		{Role: RoleUser, Content: []Content{TextBlock{Text: "what's wrong"}}},
+	}
+
+	out := normalizeBedrockToolResults(msgs)
+	if len(out) != 3 {
+		t.Fatalf("got %d messages, want 3: %+v", len(out), out)
+	}
+	tr, ok := out[1].Content[0].(ToolResultBlock)
+	if !ok {
+		t.Fatalf("second message content = %T, want ToolResultBlock", out[1].Content[0])
+	}
+	if tr.CallID != "tool-1" || !tr.IsError {
+		t.Fatalf("unexpected synthetic result: %+v", tr)
+	}
+}
+
+func TestBedrockBuildRequestSkipsEmptyToolMessages(t *testing.T) {
+	client := &bedrockClient{}
+	req, err := client.buildRequest(Request{Messages: []Message{
+		{Role: RoleTool, Content: []Content{ToolResultBlock{CallID: "missing", Content: []Content{TextBlock{Text: "orphan"}}}}},
+		{Role: RoleUser, Content: []Content{TextBlock{Text: "hello"}}},
+	}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(req.Messages) != 1 {
+		t.Fatalf("got %d bedrock messages, want 1: %+v", len(req.Messages), req.Messages)
+	}
+	if req.Messages[0].Role != "user" {
+		t.Fatalf("role = %s, want user", req.Messages[0].Role)
+	}
+}
+
 func TestBedrockEventPayloadHelpers(t *testing.T) {
 	wrapped := []byte(`{"contentBlockDelta":{"contentBlockIndex":0,"delta":{"text":"Hello"}}}`)
 	if got := bedrockEventTypeFromPayload(wrapped); got != "contentBlockDelta" {