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feat: implement non-destructive sliding window truncation
- Add truncationId, truncationParent, and isTruncationMarker fields to ApiMessage type - Refactor truncateConversation() to tag messages instead of deleting them - Update getEffectiveApiHistory() to filter messages by truncationParent - Enhance cleanupAfterTruncation() to handle orphaned truncation tags - Add sliding_window_truncation ClineMessage type and ContextTruncation schema - Create UI events when truncation occurs - Sync truncation marker removal during rewind operations - Add comprehensive test suite with 45 passing tests This makes sliding window truncation rewindable by preserving messages with tags, mirroring the non-destructive approach used for condensing.
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‎packages/types/src/message.ts‎

Lines changed: 16 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -175,6 +175,7 @@ export const clineSays = [
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"diff_error",
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"condense_context",
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"condense_context_error",
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"sliding_window_truncation",
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"codebase_search_result",
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"user_edit_todos",
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] as const
@@ -208,6 +209,20 @@ export const contextCondenseSchema = z.object({
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export type ContextCondense = z.infer<typeof contextCondenseSchema>
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/**
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* ContextTruncation
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*
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* Used to track sliding window truncation events for the UI.
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*/
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export const contextTruncationSchema = z.object({
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truncationId: z.string(),
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messagesRemoved: z.number(),
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prevContextTokens: z.number(),
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})
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export type ContextTruncation = z.infer<typeof contextTruncationSchema>
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/**
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* ClineMessage
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*/
@@ -225,6 +240,7 @@ export const clineMessageSchema = z.object({
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checkpoint: z.record(z.string(), z.unknown()).optional(),
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progressStatus: toolProgressStatusSchema.optional(),
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contextCondense: contextCondenseSchema.optional(),
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contextTruncation: contextTruncationSchema.optional(),
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isProtected: z.boolean().optional(),
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apiProtocol: z.union([z.literal("openai"), z.literal("anthropic")]).optional(),
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isAnswered: z.boolean().optional(),

‎src/core/condense/index.ts‎

Lines changed: 60 additions & 16 deletions
Original file line numberDiff line numberDiff line change
@@ -370,59 +370,103 @@ export function getMessagesSinceLastSummary(messages: ApiMessage[]): ApiMessage[
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* Filters the API conversation history to get the "effective" messages to send to the API.
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* Messages with a condenseParent that points to an existing summary are filtered out,
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* as they have been replaced by that summary.
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* Messages with a truncationParent that points to an existing truncation marker are also filtered out,
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* as they have been hidden by sliding window truncation.
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*
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* This allows non-destructive condensing where messages are tagged but not deleted,
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* enabling accurate rewind operations while still sending condensed history to the API.
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* This allows non-destructive condensing and truncation where messages are tagged but not deleted,
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* enabling accurate rewind operations while still sending condensed/truncated history to the API.
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*
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* @param messages - The full API conversation history including tagged messages
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* @returns The filtered history that should be sent to the API
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*/
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export function getEffectiveApiHistory(messages: ApiMessage[]): ApiMessage[] {
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// Collect all condenseIds of summaries that exist in the current history
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const existingSummaryIds = new Set<string>()
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// Collect all truncationIds of truncation markers that exist in the current history
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const existingTruncationIds = new Set<string>()
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for (const msg of messages) {
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if (msg.isSummary && msg.condenseId) {
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existingSummaryIds.add(msg.condenseId)
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}
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if (msg.isTruncationMarker && msg.truncationId) {
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existingTruncationIds.add(msg.truncationId)
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}
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}
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// Filter out messages whose condenseParent points to an existing summary
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// Messages with orphaned condenseParent (summary was deleted) are included
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// or whose truncationParent points to an existing truncation marker.
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// Messages with orphaned parents (summary/marker was deleted) are included
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return messages.filter((msg) => {
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if (!msg.condenseParent) {
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return true // No parent, always include
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// Filter out condensed messages if their summary exists
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if (msg.condenseParent && existingSummaryIds.has(msg.condenseParent)) {
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return false
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}
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// Filter out truncated messages if their truncation marker exists
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if (msg.truncationParent && existingTruncationIds.has(msg.truncationParent)) {
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return false
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}
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// Include if the parent summary no longer exists (was deleted by rewind)
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return !existingSummaryIds.has(msg.condenseParent)
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return true
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})
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}
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/**
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* Cleans up orphaned condenseParent references after a truncation operation (rewind/delete).
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* When a summary message is deleted, messages that were tagged with its condenseId
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* should have their condenseParent cleared so they become active again.
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* Cleans up orphaned condenseParent and truncationParent references after a truncation operation (rewind/delete).
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* When a summary message or truncation marker is deleted, messages that were tagged with its ID
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* should have their parent reference cleared so they become active again.
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*
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* This function should be called after any operation that truncates the API history
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* to ensure messages are properly restored when their summary is deleted.
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* to ensure messages are properly restored when their summary or truncation marker is deleted.
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*
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* @param messages - The API conversation history after truncation
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* @returns The cleaned history with orphaned condenseParent fields cleared
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* @returns The cleaned history with orphaned condenseParent and truncationParent fields cleared
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*/
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export function cleanupAfterTruncation(messages: ApiMessage[]): ApiMessage[] {
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// Collect all condenseIds of summaries that still exist
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const existingSummaryIds = new Set<string>()
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// Collect all truncationIds of truncation markers that still exist
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const existingTruncationIds = new Set<string>()
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for (const msg of messages) {
415431
if (msg.isSummary && msg.condenseId) {
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existingSummaryIds.add(msg.condenseId)
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}
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if (msg.isTruncationMarker && msg.truncationId) {
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existingTruncationIds.add(msg.truncationId)
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}
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}
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// Clear condenseParent for messages whose summary was deleted
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// Clear orphaned parent references for messages whose summary or truncation marker was deleted
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return messages.map((msg) => {
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let needsUpdate = false
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const updates: Partial<ApiMessage> = {}
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// Check for orphaned condenseParent
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if (msg.condenseParent && !existingSummaryIds.has(msg.condenseParent)) {
423-
// Summary was deleted, restore this message by clearing the parent reference
424-
const { condenseParent, ...rest } = msg
425-
return rest as ApiMessage
446+
needsUpdate = true
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}
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449+
// Check for orphaned truncationParent
450+
if (msg.truncationParent && !existingTruncationIds.has(msg.truncationParent)) {
451+
needsUpdate = true
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}
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if (needsUpdate) {
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// Create a new object without orphaned parent references
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const { condenseParent, truncationParent, ...rest } = msg
457+
const result: ApiMessage = rest as ApiMessage
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// Keep condenseParent if its summary still exists
460+
if (condenseParent && existingSummaryIds.has(condenseParent)) {
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result.condenseParent = condenseParent
462+
}
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// Keep truncationParent if its truncation marker still exists
465+
if (truncationParent && existingTruncationIds.has(truncationParent)) {
466+
result.truncationParent = truncationParent
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}
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return result
426470
}
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return msg
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})

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