fix(agent): drop assistant tool_calls turns with incomplete tool results

pkg/agent/context.go

@@ -602,7 +602,52 @@ func sanitizeHistoryForProvider(history []providers.Message) []providers.Message
 		}
 	}
 
-	return sanitized
+	final := make([]providers.Message, 0, len(sanitized))
+	for i := 0; i < len(sanitized); i++ {
+		msg := sanitized[i]
+		if msg.Role != "assistant" || len(msg.ToolCalls) == 0 {
+			final = append(final, msg)
+			continue
+		}
+
+		expected := make(map[string]bool, len(msg.ToolCalls))
+		for _, tc := range msg.ToolCalls {
+			expected[tc.ID] = false
+		}
+
+		for j := i + 1; j < len(sanitized); j++ {
+			next := sanitized[j]
+			if next.Role != "tool" {
+				break
+			}
+			if _, ok := expected[next.ToolCallID]; ok {
+				expected[next.ToolCallID] = true
+			}
+		}
+
+		allFound := true
+		for _, found := range expected {
+			if !found {
+				allFound = false
+				break
+			}
+		}
+		if !allFound {
+			logger.DebugCF(
+				"agent",
+				"Dropping assistant tool-call turn with incomplete tool results",
+				map[string]any{"tool_calls": len(expected)},
+			)
+			for i+1 < len(sanitized) && sanitized[i+1].Role == "tool" {
+				i++
+			}
+			continue
+		}
+
+		final = append(final, msg)
+	}
+
+	return final
 }
 
 func (cb *ContextBuilder) AddToolResult(

pkg/agent/context_test.go

@@ -188,6 +188,54 @@ func TestSanitizeHistoryForProvider_PlainConversation(t *testing.T) {
 	assertRoles(t, result, "user", "assistant", "user", "assistant")
 }
 
+func TestSanitizeHistoryForProvider_AssistantToolCallMissingAllResults(t *testing.T) {
+	history := []providers.Message{
+		msg("user", "run tool"),
+		assistantWithTools("A"),
+		msg("assistant", "fallback text"),
+	}
+
+	result := sanitizeHistoryForProvider(history)
+	if len(result) != 2 {
+		t.Fatalf("expected 2 messages, got %d: %+v", len(result), roles(result))
+	}
+	assertRoles(t, result, "user", "assistant")
+}
+
+func TestSanitizeHistoryForProvider_AssistantToolCallIncompleteResults(t *testing.T) {
+	history := []providers.Message{
+		msg("user", "run two tools"),
+		assistantWithTools("A", "B"),
+		toolResult("A"),
+		msg("assistant", "next"),
+	}
+
+	result := sanitizeHistoryForProvider(history)
+	if len(result) != 2 {
+		t.Fatalf("expected 2 messages, got %d: %+v", len(result), roles(result))
+	}
+	assertRoles(t, result, "user", "assistant")
+}
+
+func TestSanitizeHistoryForProvider_DropsBrokenRoundKeepsCompleteRound(t *testing.T) {
+	history := []providers.Message{
+		msg("user", "first"),
+		assistantWithTools("A", "B"),
+		toolResult("A"),
+		msg("assistant", "after broken round"),
+		msg("user", "second"),
+		assistantWithTools("C"),
+		toolResult("C"),
+		msg("assistant", "done"),
+	}
+
+	result := sanitizeHistoryForProvider(history)
+	if len(result) != 6 {
+		t.Fatalf("expected 6 messages, got %d: %+v", len(result), roles(result))
+	}
+	assertRoles(t, result, "user", "assistant", "user", "assistant", "tool", "assistant")
+}
+
 func roles(msgs []providers.Message) []string {
 	r := make([]string, len(msgs))
 	for i, m := range msgs {