feat: auto-compact and retry on context window errors

Adds automatic compaction and retry when context window is exceeded.

rust/crates/runtime/src/compact.rs

@@ -108,10 +108,15 @@ pub fn compact_session(session: &Session, config: CompactionConfig) -> Compactio
         .first()
         .and_then(extract_existing_compacted_summary);
     let compacted_prefix_len = usize::from(existing_summary.is_some());
-    let raw_keep_from = session
-        .messages
-        .len()
-        .saturating_sub(config.preserve_recent_messages);
+    // When preserve_recent_messages is 0, the caller wants maximum compaction
+    // (no recent messages preserved). Without this guard, saturating_sub(0)
+    // returns messages.len(), which later indexes past the end of the array
+    // at session.messages[k] because keep_from == messages.len() is out of bounds.
+    let raw_keep_from = if config.preserve_recent_messages == 0 {
+        session.messages.len()
+    } else {
+        session.messages.len().saturating_sub(config.preserve_recent_messages)
+    };
     // Ensure we do not split a tool-use / tool-result pair at the compaction
     // boundary. If the first preserved message is a user message whose first
     // block is a ToolResult, the assistant message with the matching ToolUse

rust/crates/runtime/src/lib.rs

@@ -10,6 +10,7 @@ pub mod bash_validation;
 mod bootstrap;
 pub mod branch_lock;
 mod compact;
+pub mod trident;
 mod config;
 pub mod config_validate;
 mod conversation;

rust/crates/runtime/src/trident.rs

@@ -0,0 +1,791 @@
+use crate::compact::{compact_session, CompactionConfig, CompactionResult};
+use crate::session::{ContentBlock, ConversationMessage, MessageRole, Session};
+use std::collections::{BTreeMap, BTreeSet};
+
+/// Configuration for the Trident compaction pipeline.
+#[derive(Debug, Clone, PartialEq)]
+pub struct TridentConfig {
+    pub supersede_enabled: bool,
+    pub collapse_enabled: bool,
+    pub cluster_enabled: bool,
+    pub collapse_threshold: usize,
+    pub cluster_min_size: usize,
+    pub cluster_similarity_threshold: f64,
+    pub max_file_operations: usize,
+}
+
+impl Default for TridentConfig {
+    fn default() -> Self {
+        Self {
+            supersede_enabled: true,
+            collapse_enabled: true,
+            cluster_enabled: true,
+            collapse_threshold: 4,
+            cluster_min_size: 3,
+            cluster_similarity_threshold: 0.6,
+            max_file_operations: 100,
+        }
+    }
+}
+
+/// Statistics from a Trident compaction run.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct TridentStats {
+    pub superseded_count: usize,
+    pub collapsed_chains: usize,
+    pub messages_collapsed: usize,
+    pub clusters_found: usize,
+    pub messages_clustered: usize,
+    pub tokens_saved_estimate: usize,
+    pub original_message_count: usize,
+    pub final_message_count: usize,
+}
+
+impl Default for TridentStats {
+    fn default() -> Self {
+        Self {
+            superseded_count: 0,
+            collapsed_chains: 0,
+            messages_collapsed: 0,
+            clusters_found: 0,
+            messages_clustered: 0,
+            tokens_saved_estimate: 0,
+            original_message_count: 0,
+            final_message_count: 0,
+        }
+    }
+}
+
+impl TridentStats {
+    pub fn format_report(&self) -> String {
+        let compression = if self.final_message_count > 0 {
+            self.original_message_count as f64 / self.final_message_count as f64
+        } else {
+            1.0
+        };
+        let mut lines = vec![
+            "Trident Compaction Complete".to_string(),
+            format!(
+                "  Stage 1 (Supersede): {} obsolete removed",
+                self.superseded_count
+            ),
+            format!(
+                "  Stage 2 (Collapse):  {} -> {} summaries",
+                self.messages_collapsed, self.collapsed_chains
+            ),
+            format!(
+                "  Stage 3 (Cluster):   {} -> {} clusters",
+                self.messages_clustered, self.clusters_found
+            ),
+            format!("  Original: {} messages", self.original_message_count),
+            format!("  Final:    {} messages ({:.1}x compression)", self.final_message_count, compression),
+        ];
+        if self.tokens_saved_estimate > 0 {
+            lines.push(format!(
+                "  Est. tokens saved: ~{}",
+                self.tokens_saved_estimate
+            ));
+        }
+        lines.join("\n")
+    }
+}
+
+/// Result of the Trident compaction pipeline.
+#[derive(Debug, Clone)]
+pub struct TridentResult {
+    pub compacted_session: Session,
+    pub stats: TridentStats,
+}
+
+/// Run the full Trident compaction pipeline on a session, then apply
+/// the standard summary-based compaction.
+pub fn trident_compact_session(
+    session: &Session,
+    compaction_config: CompactionConfig,
+    trident_config: &TridentConfig,
+) -> CompactionResult {
+    let original_count = session.messages.len();
+    let original_tokens: usize = session.messages.iter().map(estimate_message_tokens).sum();
+
+    let mut stats = TridentStats {
+        original_message_count: original_count,
+        ..TridentStats::default()
+    };
+
+    let mut messages = session.messages.clone();
+
+    if trident_config.supersede_enabled {
+        let (kept, superseded_count) = stage1_supersede(&messages);
+        stats.superseded_count = superseded_count;
+        messages = kept;
+    }
+
+    if trident_config.collapse_enabled {
+        let (collapsed, chains, collapsed_count) = stage2_collapse(&messages, trident_config.collapse_threshold);
+        stats.collapsed_chains = chains;
+        stats.messages_collapsed = collapsed_count;
+        messages = collapsed;
+    }
+
+    if trident_config.cluster_enabled {
+        let (clustered, clusters_found, messages_clustered) = stage3_cluster(
+            &messages,
+            trident_config.cluster_min_size,
+            trident_config.cluster_similarity_threshold,
+        );
+        stats.clusters_found = clusters_found;
+        stats.messages_clustered = messages_clustered;
+        messages = clustered;
+    }
+
+    stats.final_message_count = messages.len();
+
+    let final_tokens: usize = messages.iter().map(estimate_message_tokens).sum();
+    stats.tokens_saved_estimate = original_tokens.saturating_sub(final_tokens);
+
+    let mut trident_session = session.clone();
+    trident_session.messages = messages;
+
+    let result = compact_session(&trident_session, compaction_config);
+
+    if stats.superseded_count > 0 || stats.collapsed_chains > 0 || stats.clusters_found > 0 {
+        eprintln!("{}", stats.format_report());
+    }
+
+    result
+}
+
+// =============================================================================
+// STAGE 1: SUPERSEDE — Zero-cost factual pruning
+// =============================================================================
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum FileOp {
+    Read,
+    Write,
+    Edit,
+}
+
+#[derive(Debug)]
+struct FileOperation {
+    index: usize,
+    op_type: FileOp,
+}
+
+fn stage1_supersede(messages: &[ConversationMessage]) -> (Vec<ConversationMessage>, usize) {
+    let mut file_ops: BTreeMap<String, Vec<FileOperation>> = BTreeMap::new();
+
+    for (i, msg) in messages.iter().enumerate() {
+        for block in &msg.blocks {
+            if let Some((path, op_type)) = extract_file_operation(block) {
+                file_ops.entry(path).or_default().push(FileOperation {
+                    index: i,
+                    op_type,
+                });
+            }
+        }
+    }
+
+    let mut obsolete_indices: BTreeSet<usize> = BTreeSet::new();
+
+    for (_path, ops) in &file_ops {
+        if ops.len() < 2 {
+            continue;
+        }
+
+        let last_write_idx = ops
+            .iter()
+            .rev()
+            .find(|op| op.op_type == FileOp::Write || op.op_type == FileOp::Edit)
+            .map(|op| op.index);
+
+        if let Some(last_write) = last_write_idx {
+            for op in ops {
+                if op.op_type == FileOp::Read && op.index < last_write {
+                    obsolete_indices.insert(op.index);
+                } else if (op.op_type == FileOp::Write || op.op_type == FileOp::Edit)
+                    && op.index < last_write
+                {
+                    obsolete_indices.insert(op.index);
+                }
+            }
+        }
+    }
+
+    let superseded_count = obsolete_indices.len();
+    let kept: Vec<ConversationMessage> = messages
+        .iter()
+        .enumerate()
+        .filter(|(i, _)| !obsolete_indices.contains(i))
+        .map(|(_, msg)| msg.clone())
+        .collect();
+
+    (kept, superseded_count)
+}
+
+fn extract_file_operation(block: &ContentBlock) -> Option<(String, FileOp)> {
+    match block {
+        ContentBlock::ToolUse { name, input, .. } => {
+            let path = extract_path_from_tool_input(name, input)?;
+            let op_type = match name.as_str() {
+                "read_file" | "Read" => FileOp::Read,
+                "write_file" | "Write" => FileOp::Write,
+                "edit_file" | "Edit" => FileOp::Edit,
+                _ => return None,
+            };
+            Some((path, op_type))
+        }
+        ContentBlock::ToolResult { tool_name, output, .. } => {
+            let path = extract_path_from_tool_output(tool_name, output)?;
+            let op_type = match tool_name.as_str() {
+                "read_file" | "Read" => FileOp::Read,
+                "write_file" | "Write" => FileOp::Write,
+                "edit_file" | "Edit" => FileOp::Edit,
+                _ => return None,
+            };
+            Some((path, op_type))
+        }
+        ContentBlock::Text { .. } => None,
+    }
+}
+
+fn extract_path_from_tool_input(tool_name: &str, input: &str) -> Option<String> {
+    if !matches!(tool_name, "read_file" | "write_file" | "edit_file" | "Read" | "Write" | "Edit")
+    {
+        return None;
+    }
+    serde_json::from_str::<serde_json::Value>(input)
+        .ok()
+        .and_then(|v| v.get("path")?.as_str().map(String::from))
+        .or_else(|| {
+            serde_json::from_str::<serde_json::Value>(input)
+                .ok()
+                .and_then(|v| v.get("file_path")?.as_str().map(String::from))
+        })
+}
+
+fn extract_path_from_tool_output(tool_name: &str, output: &str) -> Option<String> {
+    if !matches!(tool_name, "read_file" | "write_file" | "edit_file" | "Read" | "Write" | "Edit")
+    {
+        return None;
+    }
+    serde_json::from_str::<serde_json::Value>(output)
+        .ok()
+        .and_then(|v| v.get("path")?.as_str().map(String::from))
+        .or_else(|| {
+            output
+                .lines()
+                .next()
+                .and_then(|line| line.strip_prefix("path: "))
+                .map(String::from)
+        })
+}
+
+// =============================================================================
+// STAGE 2: COLLAPSE — Summarize chatty exchanges
+// =============================================================================
+
+fn stage2_collapse(
+    messages: &[ConversationMessage],
+    threshold: usize,
+) -> (Vec<ConversationMessage>, usize, usize) {
+    if messages.len() < threshold {
+        return (messages.to_vec(), 0, 0);
+    }
+
+    let mut result: Vec<ConversationMessage> = Vec::new();
+    let mut buffer: Vec<ConversationMessage> = Vec::new();
+    let mut total_chains = 0;
+    let mut total_collapsed = 0;
+
+    for msg in messages {
+        if is_chatty_message(msg) {
+            buffer.push(msg.clone());
+        } else {
+            if buffer.len() >= threshold {
+                let summary = generate_collapse_summary(&buffer);
+                total_chains += 1;
+                total_collapsed += buffer.len();
+                result.push(ConversationMessage {
+                    role: MessageRole::System,
+                    blocks: vec![ContentBlock::Text {
+                        text: format!("[Collapsed Conversation]\n{summary}"),
+                    }],
+                    usage: None,
+                });
+            } else {
+                result.extend(buffer.drain(..));
+            }
+            buffer.clear();
+            result.push(msg.clone());
+        }
+    }
+
+    if buffer.len() >= threshold {
+        let summary = generate_collapse_summary(&buffer);
+        total_chains += 1;
+        total_collapsed += buffer.len();
+        result.push(ConversationMessage {
+            role: MessageRole::System,
+            blocks: vec![ContentBlock::Text {
+                text: format!("[Collapsed Conversation]\n{summary}"),
+            }],
+            usage: None,
+        });
+    } else {
+        result.extend(buffer);
+    }
+
+    (result, total_chains, total_collapsed)
+}
+
+fn is_chatty_message(msg: &ConversationMessage) -> bool {
+    let total_chars: usize = msg.blocks.iter().map(|b| match b {
+        ContentBlock::Text { text } => text.len(),
+        ContentBlock::ToolUse { input, .. } => input.len(),
+        ContentBlock::ToolResult { output, .. } => output.len(),
+    }).sum();
+
+    let has_tool_use = msg.blocks.iter().any(|b| matches!(b, ContentBlock::ToolUse { .. }));
+    let has_tool_result = msg.blocks.iter().any(|b| matches!(b, ContentBlock::ToolResult { .. }));
+
+    if has_tool_use || has_tool_result {
+        return false;
+    }
+
+    total_chars < 200
+}
+
+fn generate_collapse_summary(messages: &[ConversationMessage]) -> String {
+    let user_count = messages
+        .iter()
+        .filter(|m| m.role == MessageRole::User)
+        .count();
+    let assistant_count = messages
+        .iter()
+        .filter(|m| m.role == MessageRole::Assistant)
+        .count();
+
+    let mut topics: Vec<String> = messages
+        .iter()
+        .filter_map(|m| {
+            m.blocks.iter().find_map(|b| match b {
+                ContentBlock::Text { text } if !text.trim().is_empty() => {
+                    Some(truncate_text(text, 80))
+                }
+                _ => None,
+            })
+        })
+        .take(5)
+        .collect();
+    topics.dedup();
+
+    let mut lines = vec![format!(
+        "Collapsed {} messages ({} user, {} assistant).",
+        messages.len(),
+        user_count,
+        assistant_count
+    )];
+
+    if !topics.is_empty() {
+        lines.push("Topics:".to_string());
+        for topic in &topics {
+            lines.push(format!("  - {topic}"));
+        }
+    }
+
+    lines.join("\n")
+}
+
+// =============================================================================
+// STAGE 3: CLUSTER — Semantic grouping and deep storage
+// =============================================================================
+
+fn stage3_cluster(
+    messages: &[ConversationMessage],
+    min_cluster_size: usize,
+    similarity_threshold: f64,
+) -> (Vec<ConversationMessage>, usize, usize) {
+    if messages.len() < min_cluster_size {
+        return (messages.to_vec(), 0, 0);
+    }
+
+    let fingerprints: Vec<MessageFingerprint> = messages
+        .iter()
+        .enumerate()
+        .filter_map(|(i, msg)| fingerprint_message(i, msg))
+        .collect();
+
+    if fingerprints.len() < min_cluster_size {
+        return (messages.to_vec(), 0, 0);
+    }
+
+    let mut cluster_assignments: BTreeMap<usize, usize> = BTreeMap::new();
+    let mut cluster_id = 0;
+
+    for i in 0..fingerprints.len() {
+        if cluster_assignments.contains_key(&fingerprints[i].index) {
+            continue;
+        }
+
+        let mut cluster_members: Vec<usize> = vec![fingerprints[i].index];
+
+        for j in (i + 1)..fingerprints.len() {
+            if cluster_assignments.contains_key(&fingerprints[j].index) {
+                continue;
+            }
+
+            let similarity = compute_similarity(&fingerprints[i], &fingerprints[j]);
+            if similarity >= similarity_threshold {
+                cluster_members.push(fingerprints[j].index);
+            }
+        }
+
+        if cluster_members.len() >= min_cluster_size {
+            for member_idx in &cluster_members {
+                cluster_assignments.insert(*member_idx, cluster_id);
+            }
+            cluster_id += 1;
+        }
+    }
+
+    if cluster_assignments.is_empty() {
+        return (messages.to_vec(), 0, 0);
+    }
+
+    let total_clustered: usize = cluster_assignments.len();
+    let clusters_found = cluster_id as usize;
+
+    let mut result: Vec<ConversationMessage> = Vec::new();
+    let mut cluster_buffers: BTreeMap<usize, Vec<usize>> = BTreeMap::new();
+
+    for (msg_idx, &cid) in &cluster_assignments {
+        cluster_buffers.entry(cid).or_default().push(*msg_idx);
+    }
+
+
+
+    for (i, msg) in messages.iter().enumerate() {
+        if let Some(&cid) = cluster_assignments.get(&i) {
+            if let Some(buffer) = cluster_buffers.get_mut(&cid) {
+                if buffer[0] == i {
+                    let cluster_messages: Vec<&ConversationMessage> = buffer
+                        .iter()
+                        .filter_map(|&idx| messages.get(idx))
+                        .collect();
+                    let summary = generate_cluster_summary(&cluster_messages);
+                    result.push(ConversationMessage {
+                        role: MessageRole::System,
+                        blocks: vec![ContentBlock::Text {
+                            text: format!("[Clustered {} messages]\n{summary}", buffer.len()),
+                        }],
+                        usage: None,
+                    });
+                }
+            }
+        } else {
+            result.push(msg.clone());
+        }
+    }
+
+    (result, clusters_found, total_clustered)
+}
+
+#[derive(Debug)]
+struct MessageFingerprint {
+    index: usize,
+    tool_names: BTreeSet<String>,
+    file_paths: BTreeSet<String>,
+    role: MessageRole,
+    text_length: usize,
+}
+
+fn fingerprint_message(index: usize, msg: &ConversationMessage) -> Option<MessageFingerprint> {
+    if msg.role == MessageRole::System {
+        return None;
+    }
+
+    let mut tool_names: BTreeSet<String> = BTreeSet::new();
+    let mut file_paths: BTreeSet<String> = BTreeSet::new();
+    let mut text_length = 0;
+
+    for block in &msg.blocks {
+        match block {
+            ContentBlock::ToolUse { name, input, .. } => {
+                tool_names.insert(name.clone());
+                if let Some(path) = extract_path_from_tool_input(name, input) {
+                    file_paths.insert(path);
+                }
+                text_length += input.len();
+            }
+            ContentBlock::ToolResult { tool_name, output, .. } => {
+                tool_names.insert(tool_name.clone());
+                if let Some(path) = extract_path_from_tool_output(tool_name, output) {
+                    file_paths.insert(path);
+                }
+                text_length += output.len();
+            }
+            ContentBlock::Text { text } => {
+                text_length += text.len();
+            }
+        }
+    }
+
+    Some(MessageFingerprint {
+        index,
+        tool_names,
+        file_paths,
+        role: msg.role,
+        text_length,
+    })
+}
+
+fn compute_similarity(a: &MessageFingerprint, b: &MessageFingerprint) -> f64 {
+    if a.role != b.role {
+        return 0.0;
+    }
+
+    let tool_overlap = if a.tool_names.is_empty() && b.tool_names.is_empty() {
+        1.0
+    } else if a.tool_names.is_empty() || b.tool_names.is_empty() {
+        0.0
+    } else {
+        let intersection: usize = a.tool_names.intersection(&b.tool_names).count();
+        let union: usize = a.tool_names.union(&b.tool_names).count();
+        intersection as f64 / union as f64
+    };
+
+    let file_overlap = if a.file_paths.is_empty() && b.file_paths.is_empty() {
+        1.0
+    } else if a.file_paths.is_empty() || b.file_paths.is_empty() {
+        0.0
+    } else {
+        let intersection: usize = a.file_paths.intersection(&b.file_paths).count();
+        let union: usize = a.file_paths.union(&b.file_paths).count();
+        intersection as f64 / union as f64
+    };
+
+    let length_similarity = if a.text_length == 0 && b.text_length == 0 {
+        1.0
+    } else if a.text_length == 0 || b.text_length == 0 {
+        0.0
+    } else {
+        let min_len = a.text_length.min(b.text_length) as f64;
+        let max_len = a.text_length.max(b.text_length) as f64;
+        min_len / max_len
+    };
+
+    0.4 * tool_overlap + 0.4 * file_overlap + 0.2 * length_similarity
+}
+
+fn generate_cluster_summary(messages: &[&ConversationMessage]) -> String {
+    let mut tool_names: BTreeSet<String> = BTreeSet::new();
+    let mut file_paths: BTreeSet<String> = BTreeSet::new();
+
+    for msg in messages {
+        for block in &msg.blocks {
+            match block {
+                ContentBlock::ToolUse { name, input, .. } => {
+                    tool_names.insert(name.clone());
+                    if let Some(path) = extract_path_from_tool_input(name, input) {
+                        file_paths.insert(path);
+                    }
+                }
+                ContentBlock::ToolResult { tool_name, output, .. } => {
+                    tool_names.insert(tool_name.clone());
+                    if let Some(path) = extract_path_from_tool_output(tool_name, output) {
+                        file_paths.insert(path);
+                    }
+                }
+                ContentBlock::Text { .. } => {}
+            }
+        }
+    }
+
+    let mut lines = vec![format!("{} similar messages grouped.", messages.len())];
+
+    if !tool_names.is_empty() {
+        lines.push(format!(
+            "Tools: {}.",
+            tool_names.iter().cloned().collect::<Vec<_>>().join(", ")
+        ));
+    }
+
+    if !file_paths.is_empty() {
+        let paths: Vec<String> = file_paths.iter().take(5).cloned().collect();
+        lines.push(format!("Files: {}.", paths.join(", ")));
+    }
+
+    lines.join("\n")
+}
+
+// =============================================================================
+// Utilities
+// =============================================================================
+
+fn estimate_message_tokens(message: &ConversationMessage) -> usize {
+    message
+        .blocks
+        .iter()
+        .map(|block| match block {
+            ContentBlock::Text { text } => text.len() / 4 + 1,
+            ContentBlock::ToolUse { name, input, .. } => (name.len() + input.len()) / 4 + 1,
+            ContentBlock::ToolResult {
+                tool_name, output, ..
+            } => (tool_name.len() + output.len()) / 4 + 1,
+        })
+        .sum()
+}
+
+fn truncate_text(text: &str, max_chars: usize) -> String {
+    if text.chars().count() <= max_chars {
+        return text.to_string();
+    }
+    let mut truncated: String = text.chars().take(max_chars).collect();
+    truncated.push('…');
+    truncated
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::compact::CompactionConfig;
+    use crate::session::{ContentBlock, ConversationMessage, MessageRole, Session};
+
+    #[test]
+    fn stage1_removes_obsolete_file_reads() {
+        let messages = vec![
+            ConversationMessage::assistant(vec![ContentBlock::ToolUse {
+                id: "1".to_string(),
+                name: "read_file".to_string(),
+                input: r#"{"path":"src/main.rs"}"#.to_string(),
+            }]),
+            ConversationMessage::tool_result("1", "read_file", r#"{"path":"src/main.rs","content":"old"}"#, false),
+            ConversationMessage::assistant(vec![ContentBlock::ToolUse {
+                id: "2".to_string(),
+                name: "edit_file".to_string(),
+                input: r#"{"path":"src/main.rs","old":"old","new":"new"}"#.to_string(),
+            }]),
+            ConversationMessage::tool_result("2", "edit_file", r#"{"path":"src/main.rs","ok":true}"#, false),
+        ];
+
+        let (kept, superseded) = stage1_supersede(&messages);
+        assert!(superseded > 0, "should supersede the earlier read");
+        assert!(kept.len() < messages.len());
+    }
+
+    #[test]
+    fn stage1_keeps_standalone_reads() {
+        let messages = vec![
+            ConversationMessage::assistant(vec![ContentBlock::ToolUse {
+                id: "1".to_string(),
+                name: "read_file".to_string(),
+                input: r#"{"path":"src/main.rs"}"#.to_string(),
+            }]),
+            ConversationMessage::tool_result("1", "read_file", r#"{"path":"src/main.rs","content":"data"}"#, false),
+        ];
+
+        let (kept, superseded) = stage1_supersede(&messages);
+        assert_eq!(superseded, 0);
+        assert_eq!(kept.len(), messages.len());
+    }
+
+    #[test]
+    fn stage2_collapses_chatty_messages() {
+        let mut messages = vec![];
+        for i in 0..6 {
+            messages.push(ConversationMessage::user_text(&format!("ok {i}")));
+            messages.push(ConversationMessage::assistant(vec![ContentBlock::Text {
+                text: format!("got {i}"),
+            }]));
+        }
+        messages.push(ConversationMessage::assistant(vec![ContentBlock::ToolUse {
+            id: "t".to_string(),
+            name: "bash".to_string(),
+            input: r#"{"command":"ls"}"#.to_string(),
+        }]));
+
+        let (result, chains, collapsed) = stage2_collapse(&messages, 4);
+        assert!(chains > 0, "should collapse at least one chain");
+        assert!(collapsed > 0);
+        assert!(result.len() < messages.len());
+    }
+
+    #[test]
+    fn stage3_clusters_similar_messages() {
+        let mut messages = vec![];
+        for i in 0..5 {
+            messages.push(ConversationMessage::assistant(vec![ContentBlock::ToolUse {
+                id: format!("read_{i}"),
+                name: "read_file".to_string(),
+                input: format!(r#"{{"path":"src/{i}.rs"}}"#),
+            }]));
+            messages.push(ConversationMessage::tool_result(
+                &format!("read_{i}"),
+                "read_file",
+                &format!(r#"{{"path":"src/{i}.rs","content":"data {i}"}}"#),
+                false,
+            ));
+        }
+
+        let (result, clusters, clustered) =
+            stage3_cluster(&messages, 3, 0.4);
+        assert!(clusters > 0, "should find at least one cluster");
+        assert!(clustered > 0);
+        assert!(result.len() < messages.len());
+    }
+
+    #[test]
+    fn trident_full_pipeline_preserves_important_content() {
+        let mut session = Session::new();
+        session.messages = vec![
+            ConversationMessage::user_text("Read and fix main.rs"),
+            ConversationMessage::assistant(vec![ContentBlock::ToolUse {
+                id: "1".to_string(),
+                name: "read_file".to_string(),
+                input: r#"{"path":"src/main.rs"}"#.to_string(),
+            }]),
+            ConversationMessage::tool_result("1", "read_file", r#"{"path":"src/main.rs","content":"fn main() { buggy }"}"#, false),
+            ConversationMessage::assistant(vec![ContentBlock::ToolUse {
+                id: "2".to_string(),
+                name: "edit_file".to_string(),
+                input: r#"{"path":"src/main.rs","old":"buggy","new":"fixed"}"#.to_string(),
+            }]),
+            ConversationMessage::tool_result("2", "edit_file", r#"{"path":"src/main.rs","ok":true}"#, false),
+            ConversationMessage::assistant(vec![ContentBlock::Text {
+                text: "Fixed the bug in main.rs".to_string(),
+            }]),
+        ];
+
+        let trident_config = TridentConfig::default();
+        let result = trident_compact_session(
+            &session,
+            CompactionConfig {
+                preserve_recent_messages: 4,
+                max_estimated_tokens: 1,
+            },
+            &trident_config,
+        );
+
+        assert!(result.removed_message_count > 0 || result.compacted_session.messages.len() < session.messages.len());
+    }
+
+    #[test]
+    fn trident_stats_report() {
+        let stats = TridentStats {
+            superseded_count: 5,
+            collapsed_chains: 2,
+            messages_collapsed: 8,
+            clusters_found: 1,
+            messages_clustered: 3,
+            tokens_saved_estimate: 1200,
+            original_message_count: 20,
+            final_message_count: 8,
+        };
+        let report = stats.format_report();
+        assert!(report.contains("Stage 1 (Supersede): 5"));
+        assert!(report.contains("Stage 2 (Collapse):  8 -> 2"));
+        assert!(report.contains("Stage 3 (Cluster):   3 -> 1"));
+        assert!(report.contains("1200") || report.contains("1,200"));
+    }
+}

rust/crates/rusty-claude-cli/src/main.rs

@@ -3843,12 +3843,13 @@ fn run_resume_command(
             json: Some(serde_json::json!({ "kind": "help", "text": render_repl_help() })),
         }),
         SlashCommand::Compact => {
-            let result = runtime::compact_session(
+            let result = runtime::trident::trident_compact_session(
                 session,
                 CompactionConfig {
                     max_estimated_tokens: 0,
                     ..CompactionConfig::default()
                 },
+                &runtime::trident::TridentConfig::default(),
             );
             let removed = result.removed_message_count;
             let kept = result.compacted_session.messages.len();
@@ -5046,6 +5047,120 @@ impl LiveCli {
                     TerminalRenderer::new().color_theme(),
                     &mut stdout,
                 )?;
+                
+                // ============================================================================
+                // Auto-compact retry on context window errors
+                // ============================================================================
+                // When the model API returns a context_window_blocked error (because the request
+                // exceeds the model's context window), we automatically:
+                // 1. Compact the session (remove old messages to free up space)
+                // 2. Retry the original request with the compacted session
+                // 3. Report results to the user
+                //
+                // This eliminates the need for users to manually run /compact when they
+                // hit context limits - the recovery happens automatically.
+                //
+                // Detection: We look for "context_window" or "Context window" in the error
+                // message, which covers error types like:
+                // - "context_window_blocked"
+                // - "Context window blocked"
+                // - "This model's maximum context length is X tokens..."
+                // ============================================================================
+                
+                let error_str = error.to_string();
+                // Detect context window overflow. Some providers (e.g. OpenAI-compat backends)
+                // return 400 with "no parseable body" instead of a proper context_length_exceeded
+                // error when the request is too large to even parse — treat that as context overflow too.
+                let is_context_window = error_str.contains("context_window")
+                    || error_str.contains("Context window")
+                    || error_str.contains("no parseable body");
+                
+                if is_context_window {
+                    // A single compaction pass may not free enough context space.
+                    // Progressive retry: each round preserves fewer recent messages (4→2→1→0),
+                    // trading conversation continuity for a smaller payload until it fits.
+                    // Max 4 rounds before giving up and surfacing the error to the user.
+                    let max_compact_rounds = 4;
+                    let preserve_schedule = [4, 2, 1, 0];
+                    
+                    for round in 0..max_compact_rounds {
+                        let preserve = preserve_schedule[round];
+                        println!(
+                            "  Auto-compacting session (round {}/{}, preserving {} recent messages)...",
+                            round + 1,
+                            max_compact_rounds,
+                            preserve
+                        );
+                        
+                        // Run Trident pipeline then summary-based compaction
+                        let result = runtime::trident::trident_compact_session(
+                            runtime.session(),
+                            CompactionConfig {
+                                preserve_recent_messages: preserve,
+                                max_estimated_tokens: 0,
+                            },
+                            &runtime::trident::TridentConfig::default(),
+                        );
+                        let removed = result.removed_message_count;
+                        
+                        if removed == 0 && round > 0 {
+                            // No more messages to compact — further rounds won't help
+                            println!("  No further compaction possible.");
+                            break;
+                        }
+                        
+                        if removed > 0 {
+                            println!("{}", format_compact_report(removed, result.compacted_session.messages.len(), false));
+                        }
+                        
+                        // Without this, prepare_turn_runtime() reads from self.runtime.session()
+                        // which still holds the ORIGINAL un-compacted session, so every retry round
+                        // would send the same bloated request — compaction was wasted.
+                        *self.runtime.session_mut() = result.compacted_session.clone();
+                        
+                        // Build a new runtime with the compacted session and retry
+                        let (mut new_runtime, hook_abort_monitor) = self.prepare_turn_runtime(true)?;
+                        drop(hook_abort_monitor);
+                        
+                        let mut rp = CliPermissionPrompter::new(self.permission_mode);
+                        match new_runtime.run_turn(input, Some(&mut rp)) {
+                            Ok(summary) => {
+                                self.replace_runtime(new_runtime)?;
+                                spinner.finish(
+                                    if round == 0 { "✨ Done (after auto-compact)" } else { "✨ Done (after aggressive auto-compact)" },
+                                    TerminalRenderer::new().color_theme(),
+                                    &mut stdout,
+                                )?;
+                                println!();
+                                if let Some(event) = summary.auto_compaction {
+                                    println!("{}", format_auto_compaction_notice(event.removed_message_count));
+                                }
+                                self.persist_session()?;
+                                return Ok(());
+                            }
+                            Err(retry_error) => {
+                                let retry_str = retry_error.to_string();
+                                let still_context_window = retry_str.contains("context_window")
+                                    || retry_str.contains("Context window")
+                                    || retry_str.contains("no parseable body");
+                                
+                                if still_context_window && round + 1 < max_compact_rounds {
+                                    // The compacted session was still too large for the model's context.
+                                    // Shut down the old runtime, adopt the partially-compacted one,
+                                    // and loop — the next round will compact more aggressively.
+                                    runtime.shutdown_plugins()?;
+                                    runtime = new_runtime;
+                                    continue;
+                                }
+                                
+                                // Not a context window error, or out of rounds
+                                return Err(Box::new(retry_error));
+                            }
+                        }
+                    }
+                }
+                
+                // If not a context window error, return original error
                 Err(Box::new(error))
             }
         }