fix: strip orphaned tool_calls from preserved assistant message during compaction
After context compaction, the preserved last assistant message retained its structured tool_calls field, but the corresponding tool_result was summarized away. This created orphaned tool_use blocks that violated the Anthropic API constraint: 'Each tool_use block must have a corresponding tool_result block in the next message', causing 400 errors. Primary fix: clear tool_calls from the preserved assistant message in extract_preserved_messages(). The tool call was already executed and its result is captured in the summary. Defense-in-depth: added strip_orphaned_tool_use() post-processing in Anthropic convert_messages() to detect and strip any orphaned tool_use blocks before they reach the API. Added 7 tests: 3 unit tests for compaction stripping, 3 unit tests for Anthropic orphan detection, 1 integration test reproducing the exact bug scenario from the h3 session.
This commit is contained in:
Dhanji R. Prasanna
@@ -334,13 +334,24 @@ Format this as a detailed but concise summary that can be used to resume the con
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}
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});
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// Find the last assistant message in the conversation
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// Find the last assistant message in the conversation.
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// IMPORTANT: Strip tool_calls from the preserved message. After compaction,
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// the tool_result messages are summarized away, so keeping tool_calls would
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// create orphaned tool_use blocks that violate the Anthropic API constraint:
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// "Each tool_use block must have a corresponding tool_result block in the next message."
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let last_assistant_message = self
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.conversation_history
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.iter()
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.rev()
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.find(|m| matches!(m.role, MessageRole::Assistant))
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.cloned();
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.map(|m| {
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let mut msg = m.clone();
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if !msg.tool_calls.is_empty() {
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debug!("Stripping {} tool_calls from preserved assistant message during compaction", msg.tool_calls.len());
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msg.tool_calls.clear();
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}
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msg
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});
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PreservedMessages {
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system_prompt,
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@@ -767,6 +778,7 @@ impl ThinResult {
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#[cfg(test)]
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mod tests {
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use super::*;
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use g3_providers::MessageToolCall;
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#[test]
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fn test_new_context_window() {
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@@ -858,4 +870,136 @@ mod tests {
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assert_eq!(ThinScope::FirstThird.error_action(), "thinning");
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assert_eq!(ThinScope::All.error_action(), "skinnifying");
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}
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// ====================================================================
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// Compaction: tool_call stripping tests
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// ====================================================================
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/// Helper to create a Message with tool_calls
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fn assistant_msg_with_tool_calls(content: &str, tool_call_ids: &[&str]) -> Message {
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let mut msg = Message::new(MessageRole::Assistant, content.to_string());
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msg.tool_calls = tool_call_ids
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.iter()
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.map(|id| MessageToolCall {
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id: id.to_string(),
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name: "read_file".to_string(),
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input: serde_json::json!({"file_path": "/tmp/test.rs"}),
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})
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.collect();
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msg
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}
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#[test]
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fn test_compaction_strips_tool_calls_from_last_assistant() {
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// Reproduce the exact bug: assistant message with tool_calls gets preserved
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// across compaction, creating orphaned tool_use blocks.
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let mut cw = ContextWindow::new(100_000);
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// Build a conversation: system, user, assistant(with tool_call), user(tool_result), user(new input)
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cw.add_message(Message::new(MessageRole::System, "You are a helpful assistant.".to_string()));
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cw.add_message(Message::new(MessageRole::User, "Read the file please.".to_string()));
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cw.add_message(assistant_msg_with_tool_calls(
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"Let me read that file for you.",
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&["toolu_01QRFL8vGKDjZZkfHR586Srb"],
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));
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let mut tool_result = Message::new(MessageRole::User, "Tool result: file contents here...".to_string());
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tool_result.tool_result_id = Some("toolu_01QRFL8vGKDjZZkfHR586Srb".to_string());
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cw.add_message(tool_result);
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// Now compact
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cw.reset_with_summary(
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"Summary: user asked to read a file, assistant read it.".to_string(),
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Some("Now do something else.".to_string()),
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);
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// Find the preserved assistant message
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let assistant_msgs: Vec<&Message> = cw
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.conversation_history
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.iter()
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.filter(|m| matches!(m.role, MessageRole::Assistant))
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.collect();
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assert_eq!(assistant_msgs.len(), 1, "Should have exactly one assistant message");
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let preserved = assistant_msgs[0];
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// The key assertion: tool_calls must be stripped
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assert!(
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preserved.tool_calls.is_empty(),
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"tool_calls should be stripped from preserved assistant message, but found: {:?}",
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preserved.tool_calls
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);
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// Text content should be preserved
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assert!(preserved.content.contains("Let me read that file"));
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}
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#[test]
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fn test_compaction_drops_assistant_with_only_tool_calls_no_text() {
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// Edge case: assistant message has tool_calls but empty content.
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// After stripping tool_calls, the message is empty and should be dropped.
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let mut cw = ContextWindow::new(100_000);
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cw.add_message(Message::new(MessageRole::System, "You are a helpful assistant.".to_string()));
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cw.add_message(Message::new(MessageRole::User, "Do something.".to_string()));
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// Assistant message with tool_calls but empty text content
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let mut assistant = Message::new(MessageRole::Assistant, "".to_string());
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assistant.tool_calls = vec![MessageToolCall {
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id: "toolu_abc123".to_string(),
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name: "shell".to_string(),
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input: serde_json::json!({"command": "ls"}),
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}];
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// Force-add it (bypassing the empty check since it has tool_calls)
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cw.conversation_history.push(assistant);
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let mut tool_result = Message::new(MessageRole::User, "Tool result: file1 file2".to_string());
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tool_result.tool_result_id = Some("toolu_abc123".to_string());
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cw.add_message(tool_result);
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// Compact
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cw.reset_with_summary(
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"Summary: ran ls command.".to_string(),
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Some("What next?".to_string()),
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);
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// The empty assistant message (after tool_call stripping) should be dropped
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let assistant_msgs: Vec<&Message> = cw
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.conversation_history
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.iter()
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.filter(|m| matches!(m.role, MessageRole::Assistant))
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.collect();
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assert_eq!(
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assistant_msgs.len(), 0,
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"Empty assistant message (after tool_call stripping) should be dropped"
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);
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}
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#[test]
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fn test_compaction_preserves_normal_assistant_message() {
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// Normal case: assistant message without tool_calls should be preserved as-is.
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let mut cw = ContextWindow::new(100_000);
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cw.add_message(Message::new(MessageRole::System, "You are a helpful assistant.".to_string()));
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cw.add_message(Message::new(MessageRole::User, "Hello!".to_string()));
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cw.add_message(Message::new(
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MessageRole::Assistant,
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"Hello! How can I help you today?".to_string(),
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));
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cw.reset_with_summary(
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"Summary: greeting exchange.".to_string(),
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Some("Tell me a joke.".to_string()),
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);
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let assistant_msgs: Vec<&Message> = cw
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.conversation_history
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.iter()
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.filter(|m| matches!(m.role, MessageRole::Assistant))
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.collect();
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assert_eq!(assistant_msgs.len(), 1);
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assert!(assistant_msgs[0].tool_calls.is_empty());
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assert!(assistant_msgs[0].content.contains("Hello! How can I help you today?"));
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}
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}
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