fix(agent): sanitize invalid tool-call history

pkg/agent/context.go

@@ -615,18 +615,26 @@ func sanitizeHistoryForProvider(history []providers.Message) []providers.Message
 
 		case "assistant":
 			if len(msg.ToolCalls) > 0 {
-				if len(sanitized) == 0 {
+				var keep bool
-					logger.DebugCF("agent", "Dropping assistant tool-call turn at history start", map[string]any{})
+				msg, keep = sanitizeAssistantToolCalls(msg)
+				if !keep {
 					continue
 				}
-				prev := sanitized[len(sanitized)-1]
+
-				if prev.Role != "user" && prev.Role != "tool" {
+				if len(msg.ToolCalls) > 0 {
-					logger.DebugCF(
+					if len(sanitized) == 0 {
-						"agent",
+						logger.DebugCF("agent", "Dropping assistant tool-call turn at history start", map[string]any{})
-						"Dropping assistant tool-call turn with invalid predecessor",
+						continue
-						map[string]any{"prev_role": prev.Role},
+					}
-					)
+					prev := sanitized[len(sanitized)-1]
-					continue
+					if prev.Role != "user" && prev.Role != "tool" {
+						logger.DebugCF(
+							"agent",
+							"Dropping assistant tool-call turn with invalid predecessor",
+							map[string]any{"prev_role": prev.Role},
+						)
+						continue
+					}
 				}
 			}
 			sanitized = append(sanitized, msg)
@@ -650,8 +658,10 @@ func sanitizeHistoryForProvider(history []providers.Message) []providers.Message
 				expected[tc.ID] = false
 			}
 
-			// Check following messages for matching tool results
+			// Collect following tool results, keeping only those that still
+			// match a valid tool_call from the assistant message.
 			toolMsgCount := 0
+			matchingToolResults := make([]providers.Message, 0, len(expected))
 			for j := i + 1; j < len(sanitized); j++ {
 				if sanitized[j].Role != "tool" {
 					break
@@ -659,7 +669,12 @@ func sanitizeHistoryForProvider(history []providers.Message) []providers.Message
 				toolMsgCount++
 				if _, exists := expected[sanitized[j].ToolCallID]; exists {
 					expected[sanitized[j].ToolCallID] = true
+					matchingToolResults = append(matchingToolResults, sanitized[j])
+					continue
 				}
+				logger.DebugCF("agent", "Dropping unexpected tool result from history", map[string]any{
+					"tool_call_id": sanitized[j].ToolCallID,
+				})
 			}
 
 			// If any tool_call_id is missing, drop this assistant message and its partial tool messages
@@ -685,6 +700,11 @@ func sanitizeHistoryForProvider(history []providers.Message) []providers.Message
 				i += toolMsgCount
 				continue
 			}
+
+			final = append(final, msg)
+			final = append(final, matchingToolResults...)
+			i += toolMsgCount
+			continue
 		}
 		final = append(final, msg)
 	}
@@ -692,6 +712,33 @@ func sanitizeHistoryForProvider(history []providers.Message) []providers.Message
 	return final
 }
 
+func sanitizeAssistantToolCalls(msg providers.Message) (providers.Message, bool) {
+	filtered := make([]providers.ToolCall, 0, len(msg.ToolCalls))
+	for _, tc := range msg.ToolCalls {
+		normalized := providers.NormalizeToolCall(tc)
+		if strings.TrimSpace(normalized.ID) == "" || strings.TrimSpace(normalized.Name) == "" {
+			logger.DebugCF("agent", "Dropping invalid tool call from history", map[string]any{
+				"tool_call_id": normalized.ID,
+				"tool_name":    normalized.Name,
+			})
+			continue
+		}
+		filtered = append(filtered, normalized)
+	}
+
+	msg.ToolCalls = filtered
+	if len(filtered) > 0 {
+		return msg, true
+	}
+
+	if strings.TrimSpace(msg.Content) != "" || strings.TrimSpace(msg.ReasoningContent) != "" {
+		return msg, true
+	}
+
+	logger.DebugCF("agent", "Dropping assistant message with only invalid tool calls", map[string]any{})
+	return providers.Message{}, false
+}
+
 func (cb *ContextBuilder) AddToolResult(
 	messages []providers.Message,
 	toolCallID, toolName, result string,

pkg/agent/context_test.go

@@ -13,7 +13,7 @@ func msg(role, content string) providers.Message {
 func assistantWithTools(toolIDs ...string) providers.Message {
 	calls := make([]providers.ToolCall, len(toolIDs))
 	for i, id := range toolIDs {
-		calls[i] = providers.ToolCall{ID: id, Type: "function"}
+		calls[i] = providers.ToolCall{ID: id, Type: "function", Name: "tool_" + id}
 	}
 	return providers.Message{Role: "assistant", ToolCalls: calls}
 }
@@ -188,6 +188,61 @@ func TestSanitizeHistoryForProvider_PlainConversation(t *testing.T) {
 	assertRoles(t, result, "user", "assistant", "user", "assistant")
 }
 
+func TestSanitizeHistoryForProvider_DropsInvalidToolCallsAndUnexpectedToolResults(t *testing.T) {
+	history := []providers.Message{
+		msg("user", "check"),
+		{
+			Role: "assistant",
+			ToolCalls: []providers.ToolCall{
+				{ID: "call_ok", Name: "read_file"},
+				{ID: "call_blank_name", Name: "   "},
+				{ID: "", Name: "exec"},
+			},
+		},
+		toolResult("call_ok"),
+		toolResult("call_blank_name"),
+		toolResult(""),
+		msg("assistant", "done"),
+	}
+
+	result := sanitizeHistoryForProvider(history)
+	if len(result) != 4 {
+		t.Fatalf("expected 4 messages, got %d: %+v", len(result), result)
+	}
+	assertRoles(t, result, "user", "assistant", "tool", "assistant")
+	if got := len(result[1].ToolCalls); got != 1 {
+		t.Fatalf("assistant tool call count = %d, want 1", got)
+	}
+	if result[1].ToolCalls[0].ID != "call_ok" {
+		t.Fatalf("assistant tool call id = %q, want %q", result[1].ToolCalls[0].ID, "call_ok")
+	}
+	if result[2].ToolCallID != "call_ok" {
+		t.Fatalf("tool result id = %q, want %q", result[2].ToolCallID, "call_ok")
+	}
+}
+
+func TestSanitizeHistoryForProvider_DropsAssistantWithOnlyInvalidToolCalls(t *testing.T) {
+	history := []providers.Message{
+		msg("user", "check"),
+		{
+			Role: "assistant",
+			ToolCalls: []providers.ToolCall{
+				{ID: "call_blank_name", Name: "   "},
+				{ID: "", Name: "exec"},
+			},
+		},
+		toolResult("call_blank_name"),
+		msg("user", "next"),
+		msg("assistant", "ok"),
+	}
+
+	result := sanitizeHistoryForProvider(history)
+	if len(result) != 3 {
+		t.Fatalf("expected 3 messages, got %d: %+v", len(result), result)
+	}
+	assertRoles(t, result, "user", "user", "assistant")
+}
+
 func roles(msgs []providers.Message) []string {
 	r := make([]string, len(msgs))
 	for i, m := range msgs {