fix(condense): preserve lineage across successive condenses and add UI-first rewind hygiene

- Tag prior summaries within the current window with condenseParent (preserve original condenseId/isSummary)
- Propagate condenseParent to the previous UI condense_context for lineage continuity
- Add rewind-aware hygiene (uiOnly) so deletes/rewinds restore API history to exact pre-condense state at the chosen point
- Keep tests green (condense + task suites)

Author: hannesrudolph

src/core/condense/index.ts

@@ -196,16 +196,12 @@ export async function summarizeConversation(
 		condenseId: condenseId,
 	}
 
-	// Tag middle messages from the full middle span, but only set condenseParent
-	// for those that were actually part of the current summarization window and lack a tag.
-	const windowTs = new Set(
-		messagesToSummarize
-			.slice(1) // skip the preserved first
-			.map((m) => m.ts)
-			.filter((ts): ts is number => typeof ts === "number"),
-	)
+	// Tag middle messages from the full middle span, including any previous summaries
+	// that were part of this summarization window. Preserve existing condenseId/isSummary.
+	const windowTs = new Set(messagesToSummarize.map((m) => m.ts).filter((ts): ts is number => typeof ts === "number"))
 	const middleMessages = messages.slice(1, -N_MESSAGES_TO_KEEP).map((msg) => {
-		if (!msg.isSummary && typeof msg.ts === "number" && windowTs.has(msg.ts)) {
+		if (typeof msg.ts === "number" && windowTs.has(msg.ts)) {
+			// Do not alter isSummary or condenseId on prior summaries; only add condenseParent if missing
 			return { ...msg, condenseParent: msg.condenseParent ?? condenseId }
 		}
 		return msg

src/core/task/Task.ts

@@ -1040,6 +1040,29 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 		// Set flag to skip previous_response_id on the next API call after manual condense
 		this.skipPrevResponseIdOnce = true
 
+		// If there was a previous condense_context in the UI, tag it with condenseParent = newCondenseId
+		try {
+			const newCondenseId = messages.find((m) => m.isSummary && m.condenseId)?.condenseId
+			if (newCondenseId) {
+				const lastCondenseIdx = findLastIndex(
+					this.clineMessages,
+					(m) => m.type === "say" && m.say === "condense_context",
+				)
+				if (lastCondenseIdx !== -1) {
+					const lastCondenseMsg = this.clineMessages[lastCondenseIdx] as ClineMessage &
+						ClineMessageWithMetadata
+					lastCondenseMsg.metadata = lastCondenseMsg.metadata ?? {}
+					if (!lastCondenseMsg.metadata.condenseParent) {
+						lastCondenseMsg.metadata.condenseParent = newCondenseId
+						await this.saveClineMessages()
+						await this.updateClineMessage(lastCondenseMsg)
+					}
+				}
+			}
+		} catch {
+			// non-fatal; UI metadata tagging is best-effort
+		}
+
 		const contextCondense: ContextCondense = { summary, cost, newContextTokens, prevContextTokens }
 		await this.say(
 			"condense_context",
@@ -2627,6 +2650,39 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 				// send previous_response_id so the request reflects the fresh condensed context.
 				this.skipPrevResponseIdOnce = true
 
+				// Determine the condenseId of the newly created summary in API history
+				let newCondenseId: string | undefined
+				try {
+					const lastSummary = [...this.apiConversationHistory]
+						.reverse()
+						.find((m) => m.isSummary && m.condenseId)
+					newCondenseId = lastSummary?.condenseId
+				} catch {
+					// non-fatal
+				}
+
+				// Tag the previous UI condense_context (if any) with condenseParent to maintain lineage
+				try {
+					if (newCondenseId) {
+						const lastCondenseIdx = findLastIndex(
+							this.clineMessages,
+							(m) => m.type === "say" && m.say === "condense_context",
+						)
+						if (lastCondenseIdx !== -1) {
+							const lastCondenseMsg = this.clineMessages[lastCondenseIdx] as ClineMessage &
+								ClineMessageWithMetadata
+							lastCondenseMsg.metadata = lastCondenseMsg.metadata ?? {}
+							if (!lastCondenseMsg.metadata.condenseParent) {
+								lastCondenseMsg.metadata.condenseParent = newCondenseId
+								await this.saveClineMessages()
+								await this.updateClineMessage(lastCondenseMsg)
+							}
+						}
+					}
+				} catch {
+					// best-effort
+				}
+
 				const { summary, cost, prevContextTokens, newContextTokens = 0 } = truncateResult
 				const contextCondense: ContextCondense = { summary, cost, newContextTokens, prevContextTokens }
 				await this.say(
@@ -2636,7 +2692,10 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 					false /* partial */,
 					undefined /* checkpoint */,
 					undefined /* progressStatus */,
-					{ isNonInteractive: true } /* options */,
+					{
+						isNonInteractive: true,
+						metadata: newCondenseId ? { condenseId: newCondenseId } : undefined,
+					} /* options */,
 					contextCondense,
 				)
 			}

src/core/webview/webviewMessageHandler.ts

@@ -113,33 +113,51 @@ export const webviewMessageHandler = async (
 			)
 		}
 
-		// Perform hygiene: clean up orphaned condenseParent references
-		await performCondenseHygiene(currentCline)
+		// Perform hygiene: UI is source-of-truth during rewinds (purge API summaries whose UI counterparts were removed)
+		await performCondenseHygiene(currentCline, { uiOnly: true })
 	}
 
 	/**
 	 * Clean up orphaned condenseParent references after truncation
 	 */
-	const performCondenseHygiene = async (currentCline: any) => {
-		// Find all active condenseIds (from remaining summary messages)
+	const performCondenseHygiene = async (currentCline: any, opts?: { uiOnly?: boolean }) => {
+		// Build active condenseIds. If uiOnly, treat UI as source-of-truth (used during rewind/delete).
+		// Otherwise, include API summaries too (general hygiene).
 		const activeCondenseIds = new Set<string>()
 
-		// Check API conversation history for active summaries
-		currentCline.apiConversationHistory.forEach((msg: ApiMessage) => {
-			if (msg.isSummary && msg.condenseId) {
-				activeCondenseIds.add(msg.condenseId)
-			}
-		})
-
-		// Check UI messages for active summaries
+		// Always include UI-derived condenseIds
 		currentCline.clineMessages.forEach((msg: any) => {
 			if (msg.say === "condense_context" && msg.metadata?.condenseId) {
 				activeCondenseIds.add(msg.metadata.condenseId)
 			}
 		})
 
-		// Clean up orphaned condenseParent references in API history
+		// Optionally include API summaries that remain in history (non-delete hygiene)
+		if (!opts?.uiOnly) {
+			currentCline.apiConversationHistory.forEach((msg: ApiMessage) => {
+				if (msg.isSummary && msg.condenseId) {
+					activeCondenseIds.add(msg.condenseId)
+				}
+			})
+		}
+
 		let apiHistoryModified = false
+		let uiMessagesModified = false
+
+		// Purge API summaries that are not represented by UI when uiOnly=true (rewind to pre-condense state).
+		// In general hygiene (uiOnly=false), we only remove summaries with condenseIds not present anywhere.
+		const beforeLen = currentCline.apiConversationHistory.length
+		currentCline.apiConversationHistory = currentCline.apiConversationHistory.filter((msg: ApiMessage) => {
+			if (msg.isSummary && msg.condenseId && !activeCondenseIds.has(msg.condenseId)) {
+				return false
+			}
+			return true
+		})
+		if (currentCline.apiConversationHistory.length !== beforeLen) {
+			apiHistoryModified = true
+		}
+
+		// Clean up orphaned condenseParent references in API history
 		currentCline.apiConversationHistory.forEach((msg: ApiMessage) => {
 			if (msg.condenseParent && !activeCondenseIds.has(msg.condenseParent)) {
 				delete msg.condenseParent
@@ -148,7 +166,6 @@ export const webviewMessageHandler = async (
 		})
 
 		// Clean up orphaned condenseParent references in UI messages
-		let uiMessagesModified = false
 		currentCline.clineMessages.forEach((msg: any) => {
 			if (msg.metadata?.condenseParent && !activeCondenseIds.has(msg.metadata.condenseParent)) {
 				delete msg.metadata.condenseParent