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
@@ -360,9 +360,80 @@ impl AnthropicProvider {
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}
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}
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// Defense-in-depth: strip orphaned tool_use blocks that have no matching tool_result
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Self::strip_orphaned_tool_use(&mut anthropic_messages);
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Ok((system_message, anthropic_messages))
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}
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/// Strip orphaned tool_use blocks from assistant messages that have no matching
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/// tool_result in the immediately following user message.
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///
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/// Anthropic API requires: "Each tool_use block must have a corresponding tool_result
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/// block in the next message." This can happen after context compaction when the
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/// last assistant message had tool_calls but the tool_result was summarized away.
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fn strip_orphaned_tool_use(messages: &mut Vec<AnthropicMessage>) {
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// Collect tool_result IDs from each user message, indexed by position
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let tool_result_ids_by_pos: Vec<Option<Vec<String>>> = messages
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.iter()
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.map(|msg| {
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if msg.role == "user" {
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let ids: Vec<String> = msg
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.content
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.iter()
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.filter_map(|c| match c {
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AnthropicContent::ToolResult { tool_use_id, .. } => {
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Some(tool_use_id.clone())
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}
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_ => None,
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})
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.collect();
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if ids.is_empty() { None } else { Some(ids) }
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} else {
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None
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}
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})
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.collect();
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for i in 0..messages.len() {
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if messages[i].role != "assistant" {
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continue;
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}
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let has_tool_use = messages[i].content.iter().any(|c| matches!(c, AnthropicContent::ToolUse { .. }));
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if !has_tool_use {
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continue;
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}
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// Check if next message is a user message with tool_result blocks
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let next_has_results = i + 1 < messages.len()
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&& tool_result_ids_by_pos.get(i + 1).and_then(|v| v.as_ref()).is_some();
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if !next_has_results {
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let tool_use_ids: Vec<String> = messages[i]
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.content
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.iter()
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.filter_map(|c| match c {
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AnthropicContent::ToolUse { id, .. } => Some(id.clone()),
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_ => None,
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})
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.collect();
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tracing::warn!(
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"Stripping {} orphaned tool_use block(s) from assistant message {}: {:?}",
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tool_use_ids.len(), i, tool_use_ids
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);
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messages[i].content.retain(|c| !matches!(c, AnthropicContent::ToolUse { .. }));
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// If stripping left the message empty, add placeholder text
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if messages[i].content.is_empty() {
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messages[i].content.push(AnthropicContent::Text {
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text: "(continued)".to_string(),
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cache_control: None,
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});
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}
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}
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}
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}
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fn create_request_body(
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&self,
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messages: &[Message],
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@@ -1310,4 +1381,146 @@ mod tests {
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assert_eq!(text_content.len(), 1);
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assert_eq!(text_content[0], "Here is my response.");
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}
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// ====================================================================
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// Orphaned tool_use stripping tests
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// ====================================================================
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#[test]
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fn test_strip_orphaned_tool_use_removes_orphaned_blocks() {
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// Simulate: assistant with tool_use, followed by regular user message (no tool_result)
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let mut messages = vec![
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AnthropicMessage {
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role: "user".to_string(),
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content: vec![AnthropicContent::Text {
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text: "Read the file".to_string(),
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cache_control: None,
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}],
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},
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AnthropicMessage {
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role: "assistant".to_string(),
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content: vec![
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AnthropicContent::Text {
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text: "Let me read that.".to_string(),
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cache_control: None,
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},
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AnthropicContent::ToolUse {
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id: "toolu_orphaned".to_string(),
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name: "read_file".to_string(),
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input: serde_json::json!({"file_path": "test.rs"}),
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},
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],
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},
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// Next message is a regular user message, NOT a tool_result
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AnthropicMessage {
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role: "user".to_string(),
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content: vec![AnthropicContent::Text {
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text: "Do something else".to_string(),
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cache_control: None,
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}],
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},
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];
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AnthropicProvider::strip_orphaned_tool_use(&mut messages);
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// The tool_use should be stripped from the assistant message
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let assistant = &messages[1];
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assert!(
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!assistant.content.iter().any(|c| matches!(c, AnthropicContent::ToolUse { .. })),
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"Orphaned tool_use should be stripped"
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);
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// Text content should remain
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assert!(
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assistant.content.iter().any(|c| matches!(c, AnthropicContent::Text { .. })),
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"Text content should be preserved"
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);
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}
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#[test]
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fn test_strip_orphaned_tool_use_preserves_valid_sequence() {
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// Valid: assistant with tool_use, followed by user with matching tool_result
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let mut messages = vec![
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AnthropicMessage {
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role: "user".to_string(),
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content: vec![AnthropicContent::Text {
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text: "Read the file".to_string(),
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cache_control: None,
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}],
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},
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AnthropicMessage {
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role: "assistant".to_string(),
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content: vec![
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AnthropicContent::Text {
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text: "Reading...".to_string(),
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cache_control: None,
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},
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AnthropicContent::ToolUse {
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id: "toolu_valid".to_string(),
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name: "read_file".to_string(),
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input: serde_json::json!({"file_path": "test.rs"}),
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},
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],
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},
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AnthropicMessage {
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role: "user".to_string(),
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content: vec![AnthropicContent::ToolResult {
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tool_use_id: "toolu_valid".to_string(),
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content: "file contents".to_string(),
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cache_control: None,
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}],
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},
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];
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AnthropicProvider::strip_orphaned_tool_use(&mut messages);
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// tool_use should NOT be stripped
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let assistant = &messages[1];
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assert!(
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assistant.content.iter().any(|c| matches!(c, AnthropicContent::ToolUse { .. })),
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"Valid tool_use should be preserved"
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);
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}
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#[test]
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fn test_strip_orphaned_tool_use_adds_placeholder_for_empty_message() {
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// Assistant message with ONLY a tool_use block (no text)
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let mut messages = vec![
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AnthropicMessage {
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role: "user".to_string(),
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content: vec![AnthropicContent::Text {
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text: "Do something".to_string(),
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cache_control: None,
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}],
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},
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AnthropicMessage {
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role: "assistant".to_string(),
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content: vec![AnthropicContent::ToolUse {
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id: "toolu_only".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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},
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AnthropicMessage {
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role: "user".to_string(),
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content: vec![AnthropicContent::Text {
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text: "Never mind".to_string(),
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cache_control: None,
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}],
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},
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];
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AnthropicProvider::strip_orphaned_tool_use(&mut messages);
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// Should have placeholder text instead of empty content
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let assistant = &messages[1];
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assert!(!assistant.content.is_empty(), "Should not have empty content");
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assert!(
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assistant.content.iter().any(|c| matches!(c, AnthropicContent::Text { .. })),
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"Should have placeholder text"
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);
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assert!(
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!assistant.content.iter().any(|c| matches!(c, AnthropicContent::ToolUse { .. })),
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"tool_use should be stripped"
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);
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}
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}
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