fix: restore context when rewinding after condense (#8295) (#9665)

packages/types/src/message.ts

@@ -175,6 +175,7 @@ export const clineSays = [
 	"diff_error",
 	"condense_context",
 	"condense_context_error",
+	"sliding_window_truncation",
 	"codebase_search_result",
 	"user_edit_todos",
 ] as const
@@ -203,10 +204,25 @@ export const contextCondenseSchema = z.object({
 	prevContextTokens: z.number(),
 	newContextTokens: z.number(),
 	summary: z.string(),
+	condenseId: z.string().optional(),
 })
 
 export type ContextCondense = z.infer<typeof contextCondenseSchema>
 
+/**
+ * ContextTruncation
+ *
+ * Used to track sliding window truncation events for the UI.
+ */
+
+export const contextTruncationSchema = z.object({
+	truncationId: z.string(),
+	messagesRemoved: z.number(),
+	prevContextTokens: z.number(),
+})
+
+export type ContextTruncation = z.infer<typeof contextTruncationSchema>
+
 /**
  * ClineMessage
  */
@@ -224,6 +240,7 @@ export const clineMessageSchema = z.object({
 	checkpoint: z.record(z.string(), z.unknown()).optional(),
 	progressStatus: toolProgressStatusSchema.optional(),
 	contextCondense: contextCondenseSchema.optional(),
+	contextTruncation: contextTruncationSchema.optional(),
 	isProtected: z.boolean().optional(),
 	apiProtocol: z.union([z.literal("openai"), z.literal("anthropic")]).optional(),
 	isAnswered: z.boolean().optional(),

src/core/condense/__tests__/condense.spec.ts

@@ -6,7 +6,12 @@ import { TelemetryService } from "@roo-code/telemetry"
 
 import { BaseProvider } from "../../../api/providers/base-provider"
 import { ApiMessage } from "../../task-persistence/apiMessages"
-import { summarizeConversation, getMessagesSinceLastSummary, N_MESSAGES_TO_KEEP } from "../index"
+import {
+	summarizeConversation,
+	getMessagesSinceLastSummary,
+	getEffectiveApiHistory,
+	N_MESSAGES_TO_KEEP,
+} from "../index"
 
 // Create a mock ApiHandler for testing
 class MockApiHandler extends BaseProvider {
@@ -83,11 +88,13 @@ describe("Condense", () => {
 			expect(summaryMessage).toBeTruthy()
 			expect(summaryMessage?.content).toBe("Mock summary of the conversation")
 
-			// Verify we have the expected number of messages
-			// [first message, summary, last N messages]
-			expect(result.messages.length).toBe(1 + 1 + N_MESSAGES_TO_KEEP)
+			// With non-destructive condensing, all messages are retained (tagged but not deleted)
+			// Use getEffectiveApiHistory to verify the effective view matches the old behavior
+			expect(result.messages.length).toBe(messages.length + 1) // All original messages + summary
+			const effectiveHistory = getEffectiveApiHistory(result.messages)
+			expect(effectiveHistory.length).toBe(1 + 1 + N_MESSAGES_TO_KEEP) // first + summary + last N
 
-			// Verify the last N messages are preserved
+			// Verify the last N messages are preserved (same messages by reference)
 			const lastMessages = result.messages.slice(-N_MESSAGES_TO_KEEP)
 			expect(lastMessages).toEqual(messages.slice(-N_MESSAGES_TO_KEEP))
 		})

src/core/condense/__tests__/index.spec.ts

@@ -2,6 +2,7 @@
 
 import type { Mock } from "vitest"
 
+import { Anthropic } from "@anthropic-ai/sdk"
 import { TelemetryService } from "@roo-code/telemetry"
 
 import { ApiHandler } from "../../../api"
@@ -11,6 +12,8 @@ import {
 	summarizeConversation,
 	getMessagesSinceLastSummary,
 	getKeepMessagesWithToolBlocks,
+	getEffectiveApiHistory,
+	cleanupAfterTruncation,
 	N_MESSAGES_TO_KEEP,
 } from "../index"
 
@@ -407,22 +410,28 @@ describe("summarizeConversation", () => {
 		expect(mockApiHandler.createMessage).toHaveBeenCalled()
 		expect(maybeRemoveImageBlocks).toHaveBeenCalled()
 
-		// Verify the structure of the result
-		// The result should be: first message + summary + last N messages
-		expect(result.messages.length).toBe(1 + 1 + N_MESSAGES_TO_KEEP) // First + summary + last N
+		// With non-destructive condensing, the result contains ALL original messages
+		// plus the summary message. Condensed messages are tagged but not deleted.
+		// Use getEffectiveApiHistory to verify the effective API view matches the old behavior.
+		expect(result.messages.length).toBe(messages.length + 1) // All original messages + summary
 
 		// Check that the first message is preserved
 		expect(result.messages[0]).toEqual(messages[0])
 
-		// Check that the summary message was inserted correctly
-		const summaryMessage = result.messages[1]
-		expect(summaryMessage.role).toBe("assistant")
-		expect(summaryMessage.content).toBe("This is a summary")
-		expect(summaryMessage.isSummary).toBe(true)
+		// Find the summary message (it has isSummary: true)
+		const summaryMessage = result.messages.find((m) => m.isSummary)
+		expect(summaryMessage).toBeDefined()
+		expect(summaryMessage!.role).toBe("assistant")
+		expect(summaryMessage!.content).toBe("This is a summary")
+		expect(summaryMessage!.isSummary).toBe(true)
 
-		// Check that the last N_MESSAGES_TO_KEEP messages are preserved
-		const lastMessages = messages.slice(-N_MESSAGES_TO_KEEP)
-		expect(result.messages.slice(-N_MESSAGES_TO_KEEP)).toEqual(lastMessages)
+		// Verify that the effective API history matches expected: first + summary + last N messages
+		const effectiveHistory = getEffectiveApiHistory(result.messages)
+		expect(effectiveHistory.length).toBe(1 + 1 + N_MESSAGES_TO_KEEP) // First + summary + last N
+
+		// Check that condensed messages are properly tagged
+		const condensedMessages = result.messages.filter((m) => m.condenseParent !== undefined)
+		expect(condensedMessages.length).toBeGreaterThan(0)
 
 		// Check the cost and token counts
 		expect(result.cost).toBe(0.05)
@@ -643,9 +652,11 @@ describe("summarizeConversation", () => {
 			prevContextTokens,
 		)
 
-		// Should successfully summarize
-		// Result should be: first message + summary + last N messages
-		expect(result.messages.length).toBe(1 + 1 + N_MESSAGES_TO_KEEP) // First + summary + last N
+		// With non-destructive condensing, result contains all messages plus summary
+		// Use getEffectiveApiHistory to verify the effective API view
+		expect(result.messages.length).toBe(messages.length + 1) // All messages + summary
+		const effectiveHistory = getEffectiveApiHistory(result.messages)
+		expect(effectiveHistory.length).toBe(1 + 1 + N_MESSAGES_TO_KEEP) // First + summary + last N
 		expect(result.cost).toBe(0.03)
 		expect(result.summary).toBe("Concise summary")
 		expect(result.error).toBeUndefined()
@@ -809,23 +820,27 @@ describe("summarizeConversation", () => {
 			true, // useNativeTools - required for tool_use block preservation
 		)
 
-		// Verify the summary message has content array with text and tool_use blocks
-		const summaryMessage = result.messages[1]
-		expect(summaryMessage.role).toBe("assistant")
-		expect(summaryMessage.isSummary).toBe(true)
-		expect(Array.isArray(summaryMessage.content)).toBe(true)
+		// Find the summary message
+		const summaryMessage = result.messages.find((m) => m.isSummary)
+		expect(summaryMessage).toBeDefined()
+		expect(summaryMessage!.role).toBe("assistant")
+		expect(summaryMessage!.isSummary).toBe(true)
+		expect(Array.isArray(summaryMessage!.content)).toBe(true)
 
 		// Content should be [text block, tool_use block]
-		const content = summaryMessage.content as any[]
+		const content = summaryMessage!.content as Anthropic.Messages.ContentBlockParam[]
 		expect(content).toHaveLength(2)
 		expect(content[0].type).toBe("text")
-		expect(content[0].text).toBe("Summary of conversation")
+		expect((content[0] as Anthropic.Messages.TextBlockParam).text).toBe("Summary of conversation")
 		expect(content[1].type).toBe("tool_use")
-		expect(content[1].id).toBe("toolu_123")
-		expect(content[1].name).toBe("read_file")
+		expect((content[1] as Anthropic.Messages.ToolUseBlockParam).id).toBe("toolu_123")
+		expect((content[1] as Anthropic.Messages.ToolUseBlockParam).name).toBe("read_file")
 
-		// Verify the keepMessages are preserved correctly
-		expect(result.messages).toHaveLength(1 + 1 + N_MESSAGES_TO_KEEP) // first + summary + last 3
+		// With non-destructive condensing, all messages are retained plus the summary
+		expect(result.messages.length).toBe(messages.length + 1) // all original + summary
+		// Verify effective history matches expected
+		const effectiveHistory = getEffectiveApiHistory(result.messages)
+		expect(effectiveHistory.length).toBe(1 + 1 + N_MESSAGES_TO_KEEP) // first + summary + last 3
 		expect(result.error).toBeUndefined()
 	})
 
@@ -961,12 +976,16 @@ describe("summarizeConversation", () => {
 			true,
 		)
 
-		const summaryMessage = result.messages[1]
-		expect(Array.isArray(summaryMessage.content)).toBe(true)
-		const summaryContent = summaryMessage.content as any[]
+		// Find the summary message (it has isSummary: true)
+		const summaryMessage = result.messages.find((m) => m.isSummary)
+		expect(summaryMessage).toBeDefined()
+		expect(Array.isArray(summaryMessage!.content)).toBe(true)
+		const summaryContent = summaryMessage!.content as Anthropic.Messages.ContentBlockParam[]
 		expect(summaryContent[0]).toEqual({ type: "text", text: "This is a summary" })
 
-		const preservedToolUses = summaryContent.filter((block) => block.type === "tool_use")
+		const preservedToolUses = summaryContent.filter(
+			(block): block is Anthropic.Messages.ToolUseBlockParam => block.type === "tool_use",
+		)
 		expect(preservedToolUses).toHaveLength(2)
 		expect(preservedToolUses.map((block) => block.id)).toEqual(["toolu_parallel_1", "toolu_parallel_2"])
 	})

src/core/condense/__tests__/rewind-after-condense.spec.ts

@@ -0,0 +1,542 @@
+// npx vitest src/core/condense/__tests__/rewind-after-condense.spec.ts
+
+/**
+ * Regression tests for the issue: "Rewind after Condense is broken"
+ * https://github.com/RooCodeInc/Roo-Code/issues/8295
+ *
+ * These tests verify that when a user rewinds (deletes/truncates) their conversation
+ * after a condense operation, the orphaned condensed messages are properly reactivated
+ * so they can be sent to the API again.
+ */
+
+import { TelemetryService } from "@roo-code/telemetry"
+
+import { getEffectiveApiHistory, cleanupAfterTruncation } from "../index"
+import { ApiMessage } from "../../task-persistence/apiMessages"
+
+describe("Rewind After Condense - Issue #8295", () => {
+	beforeEach(() => {
+		if (!TelemetryService.hasInstance()) {
+			TelemetryService.createInstance([])
+		}
+	})
+
+	describe("getEffectiveApiHistory", () => {
+		it("should filter out messages tagged with condenseParent", () => {
+			const condenseId = "summary-123"
+			const messages: ApiMessage[] = [
+				{ role: "user", content: "First message", ts: 1 },
+				{ role: "assistant", content: "First response", ts: 2, condenseParent: condenseId },
+				{ role: "user", content: "Second message", ts: 3, condenseParent: condenseId },
+				{ role: "assistant", content: "Summary", ts: 4, isSummary: true, condenseId },
+				{ role: "user", content: "Third message", ts: 5 },
+				{ role: "assistant", content: "Third response", ts: 6 },
+			]
+
+			const effective = getEffectiveApiHistory(messages)
+
+			// Effective history should be: first message, summary, third message, third response
+			expect(effective.length).toBe(4)
+			expect(effective[0].content).toBe("First message")
+			expect(effective[1].isSummary).toBe(true)
+			expect(effective[2].content).toBe("Third message")
+			expect(effective[3].content).toBe("Third response")
+		})
+
+		it("should include messages without condenseParent", () => {
+			const messages: ApiMessage[] = [
+				{ role: "user", content: "Hello", ts: 1 },
+				{ role: "assistant", content: "Hi", ts: 2 },
+			]
+
+			const effective = getEffectiveApiHistory(messages)
+
+			expect(effective.length).toBe(2)
+			expect(effective).toEqual(messages)
+		})
+
+		it("should handle empty messages array", () => {
+			const effective = getEffectiveApiHistory([])
+			expect(effective).toEqual([])
+		})
+	})
+
+	describe("cleanupAfterTruncation", () => {
+		it("should clear condenseParent when summary message is deleted", () => {
+			const condenseId = "summary-123"
+			const messages: ApiMessage[] = [
+				{ role: "user", content: "First message", ts: 1 },
+				{ role: "assistant", content: "First response", ts: 2, condenseParent: condenseId },
+				{ role: "user", content: "Second message", ts: 3, condenseParent: condenseId },
+				// Summary is NOT in the array (was truncated/deleted)
+			]
+
+			const cleaned = cleanupAfterTruncation(messages)
+
+			// All condenseParent tags should be cleared since summary is gone
+			expect(cleaned[1].condenseParent).toBeUndefined()
+			expect(cleaned[2].condenseParent).toBeUndefined()
+		})
+
+		it("should preserve condenseParent when summary message still exists", () => {
+			const condenseId = "summary-123"
+			const messages: ApiMessage[] = [
+				{ role: "user", content: "First message", ts: 1 },
+				{ role: "assistant", content: "First response", ts: 2, condenseParent: condenseId },
+				{ role: "assistant", content: "Summary", ts: 3, isSummary: true, condenseId },
+			]
+
+			const cleaned = cleanupAfterTruncation(messages)
+
+			// condenseParent should remain since summary exists
+			expect(cleaned[1].condenseParent).toBe(condenseId)
+		})
+
+		it("should handle multiple condense operations with different IDs", () => {
+			const condenseId1 = "summary-1"
+			const condenseId2 = "summary-2"
+			const messages: ApiMessage[] = [
+				{ role: "user", content: "Message 1", ts: 1, condenseParent: condenseId1 },
+				{ role: "assistant", content: "Summary 1", ts: 2, isSummary: true, condenseId: condenseId1 },
+				{ role: "user", content: "Message 2", ts: 3, condenseParent: condenseId2 },
+				// Summary 2 is NOT present (was truncated)
+			]
+
+			const cleaned = cleanupAfterTruncation(messages)
+
+			// condenseId1 should remain (summary exists)
+			expect(cleaned[0].condenseParent).toBe(condenseId1)
+			// condenseId2 should be cleared (summary deleted)
+			expect(cleaned[2].condenseParent).toBeUndefined()
+		})
+
+		it("should not modify messages without condenseParent", () => {
+			const messages: ApiMessage[] = [
+				{ role: "user", content: "Hello", ts: 1 },
+				{ role: "assistant", content: "Hi", ts: 2 },
+			]
+
+			const cleaned = cleanupAfterTruncation(messages)
+
+			expect(cleaned).toEqual(messages)
+		})
+
+		it("should handle empty messages array", () => {
+			const cleaned = cleanupAfterTruncation([])
+			expect(cleaned).toEqual([])
+		})
+	})
+
+	describe("Rewind scenario: truncate after condense", () => {
+		it("should reactivate condensed messages when their summary is deleted via truncation", () => {
+			const condenseId = "summary-abc"
+
+			// Simulate a conversation after condensing
+			const fullHistory: ApiMessage[] = [
+				{ role: "user", content: "Initial task", ts: 1 },
+				{ role: "assistant", content: "Working on it", ts: 2, condenseParent: condenseId },
+				{ role: "user", content: "Continue", ts: 3, condenseParent: condenseId },
+				{ role: "assistant", content: "Summary of work so far", ts: 4, isSummary: true, condenseId },
+				{ role: "user", content: "Now do this", ts: 5 },
+				{ role: "assistant", content: "Done", ts: 6 },
+				{ role: "user", content: "And this", ts: 7 },
+				{ role: "assistant", content: "Also done", ts: 8 },
+			]
+
+			// Verify effective history before truncation
+			const effectiveBefore = getEffectiveApiHistory(fullHistory)
+			// Should be: first message, summary, last 4 messages
+			expect(effectiveBefore.length).toBe(6)
+
+			// Simulate rewind: user truncates back to message ts=4 (keeping 0-3)
+			const truncatedHistory = fullHistory.slice(0, 4) // Keep first, condensed1, condensed2, summary
+
+			// After truncation, the summary is still there, so condensed messages remain condensed
+			const cleanedAfterKeepingSummary = cleanupAfterTruncation(truncatedHistory)
+			expect(cleanedAfterKeepingSummary[1].condenseParent).toBe(condenseId)
+			expect(cleanedAfterKeepingSummary[2].condenseParent).toBe(condenseId)
+
+			// Now simulate a more aggressive rewind: delete back to message ts=2
+			const aggressiveTruncate = fullHistory.slice(0, 2) // Keep only first message and first response
+
+			// The condensed messages should now be reactivated since summary is gone
+			const cleanedAfterDeletingSummary = cleanupAfterTruncation(aggressiveTruncate)
+			expect(cleanedAfterDeletingSummary[1].condenseParent).toBeUndefined()
+
+			// Verify effective history after cleanup
+			const effectiveAfterCleanup = getEffectiveApiHistory(cleanedAfterDeletingSummary)
+			// Now both messages should be active (no condensed filtering)
+			expect(effectiveAfterCleanup.length).toBe(2)
+			expect(effectiveAfterCleanup[0].content).toBe("Initial task")
+			expect(effectiveAfterCleanup[1].content).toBe("Working on it")
+		})
+
+		it("should properly restore context after rewind when summary was deleted", () => {
+			const condenseId = "summary-xyz"
+
+			// Scenario: Most of the conversation was condensed, but the summary was deleted.
+			// getEffectiveApiHistory already correctly handles orphaned messages (includes them
+			// when their summary doesn't exist). cleanupAfterTruncation cleans up the tags.
+			const messages: ApiMessage[] = [
+				{ role: "user", content: "Start", ts: 1 },
+				{ role: "assistant", content: "Response 1", ts: 2, condenseParent: condenseId },
+				{ role: "user", content: "More", ts: 3, condenseParent: condenseId },
+				{ role: "assistant", content: "Response 2", ts: 4, condenseParent: condenseId },
+				{ role: "user", content: "Even more", ts: 5, condenseParent: condenseId },
+				// Summary was deleted (not present), so these are "orphaned" messages
+			]
+
+			// getEffectiveApiHistory already includes orphaned messages (summary doesn't exist)
+			const effectiveBefore = getEffectiveApiHistory(messages)
+			expect(effectiveBefore.length).toBe(5) // All messages visible since summary was deleted
+			expect(effectiveBefore[0].content).toBe("Start")
+			expect(effectiveBefore[1].content).toBe("Response 1")
+
+			// cleanupAfterTruncation clears the orphaned condenseParent tags for data hygiene
+			const cleaned = cleanupAfterTruncation(messages)
+
+			// Verify condenseParent was cleared for all orphaned messages
+			expect(cleaned[1].condenseParent).toBeUndefined()
+			expect(cleaned[2].condenseParent).toBeUndefined()
+			expect(cleaned[3].condenseParent).toBeUndefined()
+			expect(cleaned[4].condenseParent).toBeUndefined()
+
+			// After cleanup, effective history is the same (all visible)
+			const effectiveAfter = getEffectiveApiHistory(cleaned)
+			expect(effectiveAfter.length).toBe(5) // All messages visible
+		})
+
+		it("should hide condensed messages when their summary still exists", () => {
+			const condenseId = "summary-exists"
+
+			// Scenario: Messages were condensed and summary exists - condensed messages should be hidden
+			const messages: ApiMessage[] = [
+				{ role: "user", content: "Start", ts: 1 },
+				{ role: "assistant", content: "Response 1", ts: 2, condenseParent: condenseId },
+				{ role: "user", content: "More", ts: 3, condenseParent: condenseId },
+				{ role: "assistant", content: "Summary", ts: 4, isSummary: true, condenseId },
+				{ role: "user", content: "After summary", ts: 5 },
+			]
+
+			// Effective history should hide condensed messages since summary exists
+			const effective = getEffectiveApiHistory(messages)
+			expect(effective.length).toBe(3) // Start, Summary, After summary
+			expect(effective[0].content).toBe("Start")
+			expect(effective[1].content).toBe("Summary")
+			expect(effective[2].content).toBe("After summary")
+
+			// cleanupAfterTruncation should NOT clear condenseParent since summary exists
+			const cleaned = cleanupAfterTruncation(messages)
+			expect(cleaned[1].condenseParent).toBe(condenseId)
+			expect(cleaned[2].condenseParent).toBe(condenseId)
+		})
+
+		describe("Summary timestamp collision prevention", () => {
+			it("should give summary a unique timestamp that does not collide with first kept message", () => {
+				// Scenario: After condense, the summary message should have a unique timestamp
+				// (ts - 1 from the first kept message) to prevent lookup collisions.
+				//
+				// This test verifies the expected data structure after condense:
+				// - Summary should have ts = firstKeptMessage.ts - 1
+				// - Summary and first kept message should NOT share the same timestamp
+				//
+				// With real millisecond timestamps, the summary timestamp (firstKeptTs - 1) will
+				// never collide with an existing message since timestamps are always increasing.
+
+				const condenseId = "summary-unique-ts"
+				// Use timestamps that represent a realistic scenario where firstKeptTs - 1
+				// does not collide with any existing message timestamp
+				const firstKeptTs = 1000
+
+				// Simulate post-condense state where summary has unique timestamp (firstKeptTs - 1)
+				// In real usage, condensed messages have timestamps like 100, 200, 300...
+				// and firstKeptTs is much larger, so firstKeptTs - 1 = 999 is unique
+				const messagesAfterCondense: ApiMessage[] = [
+					{ role: "user", content: "Initial task", ts: 100 },
+					{ role: "assistant", content: "Response 1", ts: 200, condenseParent: condenseId },
+					{ role: "user", content: "Continue", ts: 300, condenseParent: condenseId },
+					{ role: "assistant", content: "Response 2", ts: 400, condenseParent: condenseId },
+					{ role: "user", content: "More work", ts: 500, condenseParent: condenseId },
+					{ role: "assistant", content: "Response 3", ts: 600, condenseParent: condenseId },
+					{ role: "user", content: "Even more", ts: 700, condenseParent: condenseId },
+					// Summary gets ts = firstKeptTs - 1 = 999, which is unique
+					{ role: "assistant", content: "Summary", ts: firstKeptTs - 1, isSummary: true, condenseId },
+					// First kept message
+					{ role: "user", content: "First kept message", ts: firstKeptTs },
+					{ role: "assistant", content: "Response to first kept", ts: 1100 },
+					{ role: "user", content: "Last message", ts: 1200 },
+				]
+
+				// Find all messages with the same timestamp as the summary
+				const summaryTs = firstKeptTs - 1
+				const messagesWithSummaryTs = messagesAfterCondense.filter((msg) => msg.ts === summaryTs)
+
+				// There should be exactly one message with the summary timestamp
+				expect(messagesWithSummaryTs.length).toBe(1)
+				expect(messagesWithSummaryTs[0].isSummary).toBe(true)
+
+				// The first kept message should have a different timestamp
+				const firstKeptMessage = messagesAfterCondense.find(
+					(msg) => msg.ts === firstKeptTs && !msg.isSummary && !msg.condenseParent,
+				)
+				expect(firstKeptMessage).toBeDefined()
+				expect(firstKeptMessage?.content).toBe("First kept message")
+				expect(firstKeptMessage?.ts).not.toBe(summaryTs)
+			})
+
+			it("should not target summary message when looking up first kept message by timestamp", () => {
+				// This test verifies that when timestamps are unique (as they should be after the fix),
+				// looking up by the first kept message's timestamp returns that message, not the summary.
+
+				const condenseId = "summary-lookup-test"
+				const firstKeptTs = 8
+
+				const messages: ApiMessage[] = [
+					{ role: "user", content: "Initial", ts: 1 },
+					{ role: "assistant", content: "Summary", ts: firstKeptTs - 1, isSummary: true, condenseId },
+					{ role: "user", content: "First kept message", ts: firstKeptTs },
+					{ role: "assistant", content: "Response", ts: 9 },
+				]
+
+				// Look up by first kept message's timestamp
+				const foundMessage = messages.find((msg) => msg.ts === firstKeptTs)
+				expect(foundMessage).toBeDefined()
+				expect(foundMessage?.content).toBe("First kept message")
+				expect(foundMessage?.isSummary).toBeUndefined()
+
+				// Looking up by summary's timestamp should find the summary
+				const foundSummary = messages.find((msg) => msg.ts === firstKeptTs - 1)
+				expect(foundSummary).toBeDefined()
+				expect(foundSummary?.isSummary).toBe(true)
+			})
+		})
+
+		describe("Message preservation after condense operations", () => {
+			/**
+			 * These tests verify that the correct user and assistant messages are preserved
+			 * and sent to the LLM after condense operations. With N_MESSAGES_TO_KEEP = 3,
+			 * condense should always preserve:
+			 * - The first message (never condensed)
+			 * - The active summary
+			 * - The last 3 kept messages
+			 */
+
+			it("should preserve correct messages after single condense (10 messages)", () => {
+				const condenseId = "summary-single"
+
+				// Simulate storage state after condensing 10 messages with N_MESSAGES_TO_KEEP = 3
+				// Original: [msg1, msg2, msg3, msg4, msg5, msg6, msg7, msg8, msg9, msg10]
+				// After condense:
+				// - msg1 preserved (first message)
+				// - msg2-msg7 tagged with condenseParent
+				// - summary inserted with ts = msg8.ts - 1
+				// - msg8, msg9, msg10 kept
+				const storageAfterCondense: ApiMessage[] = [
+					{ role: "user", content: "Task: Build a feature", ts: 100 },
+					{ role: "assistant", content: "I'll help with that", ts: 200, condenseParent: condenseId },
+					{ role: "user", content: "Start with the API", ts: 300, condenseParent: condenseId },
+					{ role: "assistant", content: "Creating API endpoints", ts: 400, condenseParent: condenseId },
+					{ role: "user", content: "Add validation", ts: 500, condenseParent: condenseId },
+					{ role: "assistant", content: "Added validation logic", ts: 600, condenseParent: condenseId },
+					{ role: "user", content: "Now the tests", ts: 700, condenseParent: condenseId },
+					// Summary inserted before first kept message
+					{
+						role: "assistant",
+						content: "Summary: Built API with validation, working on tests",
+						ts: 799, // msg8.ts - 1
+						isSummary: true,
+						condenseId,
+					},
+					// Last 3 kept messages (N_MESSAGES_TO_KEEP = 3)
+					{ role: "assistant", content: "Writing unit tests now", ts: 800 },
+					{ role: "user", content: "Include edge cases", ts: 900 },
+					{ role: "assistant", content: "Added edge case tests", ts: 1000 },
+				]
+
+				const effective = getEffectiveApiHistory(storageAfterCondense)
+
+				// Should send exactly 5 messages to LLM:
+				// 1. First message (user) - preserved
+				// 2. Summary (assistant)
+				// 3-5. Last 3 kept messages
+				expect(effective.length).toBe(5)
+
+				// Verify exact order and content
+				expect(effective[0].role).toBe("user")
+				expect(effective[0].content).toBe("Task: Build a feature")
+
+				expect(effective[1].role).toBe("assistant")
+				expect(effective[1].isSummary).toBe(true)
+				expect(effective[1].content).toBe("Summary: Built API with validation, working on tests")
+
+				expect(effective[2].role).toBe("assistant")
+				expect(effective[2].content).toBe("Writing unit tests now")
+
+				expect(effective[3].role).toBe("user")
+				expect(effective[3].content).toBe("Include edge cases")
+
+				expect(effective[4].role).toBe("assistant")
+				expect(effective[4].content).toBe("Added edge case tests")
+
+				// Verify condensed messages are NOT in effective history
+				const condensedContents = ["I'll help with that", "Start with the API", "Creating API endpoints"]
+				for (const content of condensedContents) {
+					expect(effective.find((m) => m.content === content)).toBeUndefined()
+				}
+			})
+
+			it("should preserve correct messages after double condense (10 msgs → condense → 10 more msgs → condense)", () => {
+				const condenseId1 = "summary-first"
+				const condenseId2 = "summary-second"
+
+				// Simulate storage state after TWO condense operations
+				// First condense: 10 messages condensed, summary1 created
+				// Then: 10 more messages added (making effective history have 15 messages)
+				// Second condense: summary1 + msg8-msg17 condensed, summary2 created
+				//
+				// Storage after double condense:
+				const storageAfterDoubleCondense: ApiMessage[] = [
+					// First message - never condensed
+					{ role: "user", content: "Initial task: Build a full app", ts: 100 },
+
+					// Messages from first condense (tagged with condenseId1)
+					{ role: "assistant", content: "Starting the project", ts: 200, condenseParent: condenseId1 },
+					{ role: "user", content: "Add authentication", ts: 300, condenseParent: condenseId1 },
+					{ role: "assistant", content: "Added auth module", ts: 400, condenseParent: condenseId1 },
+					{ role: "user", content: "Add database", ts: 500, condenseParent: condenseId1 },
+					{ role: "assistant", content: "Set up database", ts: 600, condenseParent: condenseId1 },
+					{ role: "user", content: "Connect them", ts: 700, condenseParent: condenseId1 },
+
+					// First summary - now ALSO tagged with condenseId2 (from second condense)
+					{
+						role: "assistant",
+						content: "Summary1: Built auth and database",
+						ts: 799,
+						isSummary: true,
+						condenseId: condenseId1,
+						condenseParent: condenseId2, // Tagged during second condense!
+					},
+
+					// Messages after first condense but before second (tagged with condenseId2)
+					{ role: "assistant", content: "Continuing development", ts: 800, condenseParent: condenseId2 },
+					{ role: "user", content: "Add API routes", ts: 900, condenseParent: condenseId2 },
+					{ role: "assistant", content: "Created REST endpoints", ts: 1000, condenseParent: condenseId2 },
+					{ role: "user", content: "Add validation", ts: 1100, condenseParent: condenseId2 },
+					{ role: "assistant", content: "Added input validation", ts: 1200, condenseParent: condenseId2 },
+					{ role: "user", content: "Add error handling", ts: 1300, condenseParent: condenseId2 },
+					{ role: "assistant", content: "Implemented error handlers", ts: 1400, condenseParent: condenseId2 },
+					{ role: "user", content: "Add logging", ts: 1500, condenseParent: condenseId2 },
+					{ role: "assistant", content: "Set up logging system", ts: 1600, condenseParent: condenseId2 },
+					{ role: "user", content: "Now write tests", ts: 1700, condenseParent: condenseId2 },
+
+					// Second summary - inserted before the last 3 kept messages
+					{
+						role: "assistant",
+						content: "Summary2: App complete with auth, DB, API, validation, errors, logging. Now testing.",
+						ts: 1799, // msg18.ts - 1
+						isSummary: true,
+						condenseId: condenseId2,
+					},
+
+					// Last 3 kept messages (N_MESSAGES_TO_KEEP = 3)
+					{ role: "assistant", content: "Writing integration tests", ts: 1800 },
+					{ role: "user", content: "Test the auth flow", ts: 1900 },
+					{ role: "assistant", content: "Auth tests passing", ts: 2000 },
+				]
+
+				const effective = getEffectiveApiHistory(storageAfterDoubleCondense)
+
+				// Should send exactly 5 messages to LLM:
+				// 1. First message (user) - preserved
+				// 2. Summary2 (assistant) - the ACTIVE summary
+				// 3-5. Last 3 kept messages
+				expect(effective.length).toBe(5)
+
+				// Verify exact order and content
+				expect(effective[0].role).toBe("user")
+				expect(effective[0].content).toBe("Initial task: Build a full app")
+
+				expect(effective[1].role).toBe("assistant")
+				expect(effective[1].isSummary).toBe(true)
+				expect(effective[1].condenseId).toBe(condenseId2) // Must be the SECOND summary
+				expect(effective[1].content).toContain("Summary2")
+
+				expect(effective[2].role).toBe("assistant")
+				expect(effective[2].content).toBe("Writing integration tests")
+
+				expect(effective[3].role).toBe("user")
+				expect(effective[3].content).toBe("Test the auth flow")
+
+				expect(effective[4].role).toBe("assistant")
+				expect(effective[4].content).toBe("Auth tests passing")
+
+				// Verify Summary1 is NOT in effective history (it's tagged with condenseParent)
+				const summary1 = effective.find((m) => m.content?.toString().includes("Summary1"))
+				expect(summary1).toBeUndefined()
+
+				// Verify all condensed messages are NOT in effective history
+				const condensedContents = [
+					"Starting the project",
+					"Added auth module",
+					"Continuing development",
+					"Created REST endpoints",
+					"Implemented error handlers",
+				]
+				for (const content of condensedContents) {
+					expect(effective.find((m) => m.content === content)).toBeUndefined()
+				}
+			})
+
+			it("should maintain proper user/assistant alternation in effective history", () => {
+				const condenseId = "summary-alternation"
+
+				// Verify that after condense, the effective history maintains proper
+				// user/assistant message alternation (important for API compatibility)
+				const storage: ApiMessage[] = [
+					{ role: "user", content: "Start task", ts: 100 },
+					{ role: "assistant", content: "Response 1", ts: 200, condenseParent: condenseId },
+					{ role: "user", content: "Continue", ts: 300, condenseParent: condenseId },
+					{ role: "assistant", content: "Summary text", ts: 399, isSummary: true, condenseId },
+					// Kept messages - should alternate properly
+					{ role: "assistant", content: "Response after summary", ts: 400 },
+					{ role: "user", content: "User message", ts: 500 },
+					{ role: "assistant", content: "Final response", ts: 600 },
+				]
+
+				const effective = getEffectiveApiHistory(storage)
+
+				// Verify the sequence: user, assistant(summary), assistant, user, assistant
+				// Note: Having two assistant messages in a row (summary + next response) is valid
+				// because the summary replaces what would have been multiple messages
+				expect(effective[0].role).toBe("user")
+				expect(effective[1].role).toBe("assistant")
+				expect(effective[1].isSummary).toBe(true)
+				expect(effective[2].role).toBe("assistant")
+				expect(effective[3].role).toBe("user")
+				expect(effective[4].role).toBe("assistant")
+			})
+
+			it("should preserve timestamps in chronological order in effective history", () => {
+				const condenseId = "summary-timestamps"
+
+				const storage: ApiMessage[] = [
+					{ role: "user", content: "First", ts: 100 },
+					{ role: "assistant", content: "Condensed", ts: 200, condenseParent: condenseId },
+					{ role: "assistant", content: "Summary", ts: 299, isSummary: true, condenseId },
+					{ role: "user", content: "Kept 1", ts: 300 },
+					{ role: "assistant", content: "Kept 2", ts: 400 },
+					{ role: "user", content: "Kept 3", ts: 500 },
+				]
+
+				const effective = getEffectiveApiHistory(storage)
+
+				// Verify timestamps are in ascending order
+				for (let i = 1; i < effective.length; i++) {
+					const prevTs = effective[i - 1].ts ?? 0
+					const currTs = effective[i].ts ?? 0
+					expect(currTs).toBeGreaterThan(prevTs)
+				}
+			})
+		})
+	})
+})

src/core/condense/index.ts

@@ -1,4 +1,5 @@
 import Anthropic from "@anthropic-ai/sdk"
+import crypto from "crypto"
 
 import { TelemetryService } from "@roo-code/telemetry"
 
@@ -117,6 +118,7 @@ export type SummarizeResponse = {
 	cost: number // The cost of the summarization operation
 	newContextTokens?: number // The number of tokens in the context for the next API request
 	error?: string // Populated iff the operation fails: error message shown to the user on failure (see Task.ts)
+	condenseId?: string // The unique ID of the created Summary message, for linking to condense_context clineMessage
 }
 
 /**
@@ -266,15 +268,51 @@ export async function summarizeConversation(
 		summaryContent = summary
 	}
 
+	// Generate a unique condenseId for this summary
+	const condenseId = crypto.randomUUID()
+
+	// Use first kept message's timestamp minus 1 to ensure unique timestamp for summary.
+	// Fallback to Date.now() if keepMessages is empty (shouldn't happen due to earlier checks).
+	const firstKeptTs = keepMessages[0]?.ts ?? Date.now()
+
 	const summaryMessage: ApiMessage = {
 		role: "assistant",
 		content: summaryContent,
-		ts: keepMessages[0].ts,
+		ts: firstKeptTs - 1, // Unique timestamp before first kept message to avoid collision
 		isSummary: true,
+		condenseId, // Unique ID for this summary, used to track which messages it replaces
 	}
 
-	// Reconstruct messages: [first message, summary, last N messages]
-	const newMessages = [firstMessage, summaryMessage, ...keepMessages]
+	// NON-DESTRUCTIVE CONDENSE:
+	// Instead of deleting middle messages, tag them with condenseParent so they can be
+	// restored if the user rewinds to a point before the summary.
+	//
+	// Storage structure after condense:
+	// [firstMessage, msg2(parent=X), ..., msg8(parent=X), summary(id=X), msg9, msg10, msg11]
+	//
+	// Effective for API (filtered by getEffectiveApiHistory):
+	// [firstMessage, summary, msg9, msg10, msg11]
+
+	// Tag middle messages with condenseParent (skip first message, skip last N messages)
+	const newMessages = messages.map((msg, index) => {
+		// First message stays as-is
+		if (index === 0) {
+			return msg
+		}
+		// Messages in the "keep" range stay as-is
+		if (index >= keepStartIndex) {
+			return msg
+		}
+		// Middle messages get tagged with condenseParent (unless they already have one from a previous condense)
+		// If they already have a condenseParent, we leave it - nested condense is handled by filtering
+		if (!msg.condenseParent) {
+			return { ...msg, condenseParent: condenseId }
+		}
+		return msg
+	})
+
+	// Insert the summary message right before the keep messages
+	newMessages.splice(keepStartIndex, 0, summaryMessage)
 
 	// Count the tokens in the context for the next API request
 	// We only estimate the tokens in summaryMesage if outputTokens is 0, otherwise we use outputTokens
@@ -293,7 +331,7 @@ export async function summarizeConversation(
 		const error = t("common:errors.condense_context_grew")
 		return { ...response, cost, error }
 	}
-	return { messages: newMessages, summary, cost, newContextTokens }
+	return { messages: newMessages, summary, cost, newContextTokens, condenseId }
 }
 
 /* Returns the list of all messages since the last summary message, including the summary. Returns all messages if there is no summary. */
@@ -329,3 +367,108 @@ export function getMessagesSinceLastSummary(messages: ApiMessage[]): ApiMessage[
 
 	return messagesSinceSummary
 }
+
+/**
+ * Filters the API conversation history to get the "effective" messages to send to the API.
+ * Messages with a condenseParent that points to an existing summary are filtered out,
+ * as they have been replaced by that summary.
+ * Messages with a truncationParent that points to an existing truncation marker are also filtered out,
+ * as they have been hidden by sliding window truncation.
+ *
+ * This allows non-destructive condensing and truncation where messages are tagged but not deleted,
+ * enabling accurate rewind operations while still sending condensed/truncated history to the API.
+ *
+ * @param messages - The full API conversation history including tagged messages
+ * @returns The filtered history that should be sent to the API
+ */
+export function getEffectiveApiHistory(messages: ApiMessage[]): ApiMessage[] {
+	// Collect all condenseIds of summaries that exist in the current history
+	const existingSummaryIds = new Set<string>()
+	// Collect all truncationIds of truncation markers that exist in the current history
+	const existingTruncationIds = new Set<string>()
+
+	for (const msg of messages) {
+		if (msg.isSummary && msg.condenseId) {
+			existingSummaryIds.add(msg.condenseId)
+		}
+		if (msg.isTruncationMarker && msg.truncationId) {
+			existingTruncationIds.add(msg.truncationId)
+		}
+	}
+
+	// Filter out messages whose condenseParent points to an existing summary
+	// or whose truncationParent points to an existing truncation marker.
+	// Messages with orphaned parents (summary/marker was deleted) are included
+	return messages.filter((msg) => {
+		// Filter out condensed messages if their summary exists
+		if (msg.condenseParent && existingSummaryIds.has(msg.condenseParent)) {
+			return false
+		}
+		// Filter out truncated messages if their truncation marker exists
+		if (msg.truncationParent && existingTruncationIds.has(msg.truncationParent)) {
+			return false
+		}
+		return true
+	})
+}
+
+/**
+ * Cleans up orphaned condenseParent and truncationParent references after a truncation operation (rewind/delete).
+ * When a summary message or truncation marker is deleted, messages that were tagged with its ID
+ * should have their parent reference cleared so they become active again.
+ *
+ * This function should be called after any operation that truncates the API history
+ * to ensure messages are properly restored when their summary or truncation marker is deleted.
+ *
+ * @param messages - The API conversation history after truncation
+ * @returns The cleaned history with orphaned condenseParent and truncationParent fields cleared
+ */
+export function cleanupAfterTruncation(messages: ApiMessage[]): ApiMessage[] {
+	// Collect all condenseIds of summaries that still exist
+	const existingSummaryIds = new Set<string>()
+	// Collect all truncationIds of truncation markers that still exist
+	const existingTruncationIds = new Set<string>()
+
+	for (const msg of messages) {
+		if (msg.isSummary && msg.condenseId) {
+			existingSummaryIds.add(msg.condenseId)
+		}
+		if (msg.isTruncationMarker && msg.truncationId) {
+			existingTruncationIds.add(msg.truncationId)
+		}
+	}
+
+	// Clear orphaned parent references for messages whose summary or truncation marker was deleted
+	return messages.map((msg) => {
+		let needsUpdate = false
+
+		// Check for orphaned condenseParent
+		if (msg.condenseParent && !existingSummaryIds.has(msg.condenseParent)) {
+			needsUpdate = true
+		}
+
+		// Check for orphaned truncationParent
+		if (msg.truncationParent && !existingTruncationIds.has(msg.truncationParent)) {
+			needsUpdate = true
+		}
+
+		if (needsUpdate) {
+			// Create a new object without orphaned parent references
+			const { condenseParent, truncationParent, ...rest } = msg
+			const result: ApiMessage = rest as ApiMessage
+
+			// Keep condenseParent if its summary still exists
+			if (condenseParent && existingSummaryIds.has(condenseParent)) {
+				result.condenseParent = condenseParent
+			}
+
+			// Keep truncationParent if its truncation marker still exists
+			if (truncationParent && existingTruncationIds.has(truncationParent)) {
+				result.truncationParent = truncationParent
+			}
+
+			return result
+		}
+		return msg
+	})
+}

src/core/context-management/__tests__/context-management.spec.ts

@@ -65,10 +65,14 @@ describe("Context Management", () => {
 
 			// With 2 messages after the first, 0.5 fraction means remove 1 message
 			// But 1 is odd, so it rounds down to 0 (to make it even)
-			expect(result.length).toBe(3) // First message + 2 remaining messages
-			expect(result[0]).toEqual(messages[0])
-			expect(result[1]).toEqual(messages[1])
-			expect(result[2]).toEqual(messages[2])
+			// Result should have messages + truncation marker
+			expect(result.messages.length).toBe(4) // First message + truncation marker + 2 remaining messages
+			expect(result.messages[0]).toEqual(messages[0])
+			// messages[1] is the truncation marker
+			expect(result.messages[1].isTruncationMarker).toBe(true)
+			// Original messages[1] and messages[2] are at indices 2 and 3 now
+			expect(result.messages[2].content).toEqual(messages[1].content)
+			expect(result.messages[3].content).toEqual(messages[2].content)
 		})
 
 		it("should remove the specified fraction of messages (rounded to even number)", () => {
@@ -84,10 +88,17 @@ describe("Context Management", () => {
 			// 2 is already even, so no rounding needed
 			const result = truncateConversation(messages, 0.5, taskId)
 
-			expect(result.length).toBe(3)
-			expect(result[0]).toEqual(messages[0])
-			expect(result[1]).toEqual(messages[3])
-			expect(result[2]).toEqual(messages[4])
+			// Should have all original messages + truncation marker
+			expect(result.messages.length).toBe(6) // 5 original + 1 marker
+			expect(result.messagesRemoved).toBe(2)
+			expect(result.messages[0]).toEqual(messages[0])
+			expect(result.messages[1].isTruncationMarker).toBe(true)
+			// Messages 2 and 3 (indices 1 and 2 from original) should be tagged
+			expect(result.messages[2].truncationParent).toBe(result.truncationId)
+			expect(result.messages[3].truncationParent).toBe(result.truncationId)
+			// Messages 4 and 5 (indices 3 and 4 from original) should NOT be tagged
+			expect(result.messages[4].truncationParent).toBeUndefined()
+			expect(result.messages[5].truncationParent).toBeUndefined()
 		})
 
 		it("should round to an even number of messages to remove", () => {
@@ -105,8 +116,10 @@ describe("Context Management", () => {
 			// 1.8 rounds down to 1, then to 0 to make it even
 			const result = truncateConversation(messages, 0.3, taskId)
 
-			expect(result.length).toBe(7) // No messages removed
-			expect(result).toEqual(messages)
+			expect(result.messagesRemoved).toBe(0) // No messages removed
+			// Should still have truncation marker inserted
+			expect(result.messages.length).toBe(8) // 7 original + 1 marker
+			expect(result.messages[1].isTruncationMarker).toBe(true)
 		})
 
 		it("should handle edge case with fracToRemove = 0", () => {
@@ -118,7 +131,10 @@ describe("Context Management", () => {
 
 			const result = truncateConversation(messages, 0, taskId)
 
-			expect(result).toEqual(messages)
+			expect(result.messagesRemoved).toBe(0)
+			// Should have original messages + truncation marker
+			expect(result.messages.length).toBe(4)
+			expect(result.messages[1].isTruncationMarker).toBe(true)
 		})
 
 		it("should handle edge case with fracToRemove = 1", () => {
@@ -133,9 +149,16 @@ describe("Context Management", () => {
 			// But 3 is odd, so it rounds down to 2 to make it even
 			const result = truncateConversation(messages, 1, taskId)
 
-			expect(result.length).toBe(2)
-			expect(result[0]).toEqual(messages[0])
-			expect(result[1]).toEqual(messages[3])
+			expect(result.messagesRemoved).toBe(2)
+			// Should have all original messages + truncation marker
+			expect(result.messages.length).toBe(5) // 4 original + 1 marker
+			expect(result.messages[0]).toEqual(messages[0])
+			expect(result.messages[1].isTruncationMarker).toBe(true)
+			// Messages at indices 2 and 3 should be tagged (original indices 1 and 2)
+			expect(result.messages[2].truncationParent).toBe(result.truncationId)
+			expect(result.messages[3].truncationParent).toBe(result.truncationId)
+			// Last message should NOT be tagged
+			expect(result.messages[4].truncationParent).toBeUndefined()
 		})
 	})
 
@@ -289,14 +312,6 @@ describe("Context Management", () => {
 				{ ...messages[messages.length - 1], content: "" },
 			]
 
-			// When truncating, always uses 0.5 fraction
-			// With 4 messages after the first, 0.5 fraction means remove 2 messages
-			const expectedMessages = [
-				messagesWithSmallContent[0],
-				messagesWithSmallContent[3],
-				messagesWithSmallContent[4],
-			]
-
 			const result = await manageContext({
 				messages: messagesWithSmallContent,
 				totalTokens,
@@ -311,12 +326,14 @@ describe("Context Management", () => {
 				currentProfileId: "default",
 			})
 
-			expect(result).toEqual({
-				messages: expectedMessages,
-				summary: "",
-				cost: 0,
-				prevContextTokens: totalTokens,
-			})
+			// Should have truncation
+			expect(result.truncationId).toBeDefined()
+			expect(result.messagesRemoved).toBe(2) // With 4 messages after first, 0.5 fraction = 2 to remove
+			expect(result.summary).toBe("")
+			expect(result.cost).toBe(0)
+			expect(result.prevContextTokens).toBe(totalTokens)
+			// Should have all original messages + truncation marker (non-destructive)
+			expect(result.messages.length).toBe(6) // 5 original + 1 marker
 		})
 
 		it("should work with non-prompt caching models the same as prompt caching models", async () => {
@@ -360,10 +377,14 @@ describe("Context Management", () => {
 				currentProfileId: "default",
 			})
 
-			expect(result1.messages).toEqual(result2.messages)
+			// For truncation results, we can't compare messages directly because
+			// truncationId is randomly generated. Compare structure instead.
+			expect(result1.messages.length).toEqual(result2.messages.length)
 			expect(result1.summary).toEqual(result2.summary)
 			expect(result1.cost).toEqual(result2.cost)
 			expect(result1.prevContextTokens).toEqual(result2.prevContextTokens)
+			expect(result1.truncationId).toBeDefined()
+			expect(result2.truncationId).toBeDefined()
 
 			// Test above threshold
 			const aboveThreshold = 70001
@@ -395,10 +416,14 @@ describe("Context Management", () => {
 				currentProfileId: "default",
 			})
 
-			expect(result3.messages).toEqual(result4.messages)
+			// For truncation results, we can't compare messages directly because
+			// truncationId is randomly generated. Compare structure instead.
+			expect(result3.messages.length).toEqual(result4.messages.length)
 			expect(result3.summary).toEqual(result4.summary)
 			expect(result3.cost).toEqual(result4.cost)
 			expect(result3.prevContextTokens).toEqual(result4.prevContextTokens)
+			expect(result3.truncationId).toBeDefined()
+			expect(result4.truncationId).toBeDefined()
 		})
 
 		it("should consider incoming content when deciding to truncate", async () => {
@@ -510,14 +535,6 @@ describe("Context Management", () => {
 				{ ...messages[messages.length - 1], content: "" },
 			]
 
-			// When truncating, always uses 0.5 fraction
-			// With 4 messages after the first, 0.5 fraction means remove 2 messages
-			const expectedResult = [
-				messagesWithSmallContent[0],
-				messagesWithSmallContent[3],
-				messagesWithSmallContent[4],
-			]
-
 			const result = await manageContext({
 				messages: messagesWithSmallContent,
 				totalTokens,
@@ -531,12 +548,15 @@ describe("Context Management", () => {
 				profileThresholds: {},
 				currentProfileId: "default",
 			})
-			expect(result).toEqual({
-				messages: expectedResult,
-				summary: "",
-				cost: 0,
-				prevContextTokens: totalTokens,
-			})
+
+			// Should have truncation
+			expect(result.truncationId).toBeDefined()
+			expect(result.messagesRemoved).toBe(2) // With 4 messages after first, 0.5 fraction = 2 to remove
+			expect(result.summary).toBe("")
+			expect(result.cost).toBe(0)
+			expect(result.prevContextTokens).toBe(totalTokens)
+			// Should have all original messages + truncation marker (non-destructive)
+			expect(result.messages.length).toBe(6) // 5 original + 1 marker
 		})
 
 		it("should use summarizeConversation when autoCondenseContext is true and tokens exceed threshold", async () => {
@@ -650,10 +670,13 @@ describe("Context Management", () => {
 			// Verify summarizeConversation was called
 			expect(summarizeSpy).toHaveBeenCalled()
 
-			// Verify it fell back to truncation
-			expect(result.messages).toEqual(expectedMessages)
+			// Verify it fell back to truncation (non-destructive)
+			expect(result.truncationId).toBeDefined()
+			expect(result.messagesRemoved).toBe(2)
 			expect(result.summary).toBe("")
 			expect(result.prevContextTokens).toBe(totalTokens)
+			// Should have all original messages + truncation marker
+			expect(result.messages.length).toBe(6) // 5 original + 1 marker
 			// The cost might be different than expected, so we don't check it
 
 			// Clean up
@@ -697,13 +720,14 @@ describe("Context Management", () => {
 			// Verify summarizeConversation was not called
 			expect(summarizeSpy).not.toHaveBeenCalled()
 
-			// Verify it used truncation
-			expect(result).toEqual({
-				messages: expectedMessages,
-				summary: "",
-				cost: 0,
-				prevContextTokens: totalTokens,
-			})
+			// Verify it used truncation (non-destructive)
+			expect(result.truncationId).toBeDefined()
+			expect(result.messagesRemoved).toBe(2)
+			expect(result.summary).toBe("")
+			expect(result.cost).toBe(0)
+			expect(result.prevContextTokens).toBe(totalTokens)
+			// Should have all original messages + truncation marker
+			expect(result.messages.length).toBe(6) // 5 original + 1 marker
 
 			// Clean up
 			summarizeSpy.mockRestore()
@@ -1093,7 +1117,10 @@ describe("Context Management", () => {
 				currentProfileId: "default",
 			})
 			expect(result2.messages).not.toEqual(messagesWithSmallContent)
-			expect(result2.messages.length).toBe(3) // Truncated with 0.5 fraction
+			// Should have all original messages + truncation marker (non-destructive)
+			expect(result2.messages.length).toBe(6) // 5 original + 1 marker
+			expect(result2.truncationId).toBeDefined()
+			expect(result2.messagesRemoved).toBe(2)
 			expect(result2.summary).toBe("")
 			expect(result2.cost).toBe(0)
 			expect(result2.prevContextTokens).toBe(50001)
@@ -1146,7 +1173,9 @@ describe("Context Management", () => {
 				currentProfileId: "default",
 			})
 			expect(result2.messages).not.toEqual(messagesWithSmallContent)
-			expect(result2.messages.length).toBe(3) // Truncated with 0.5 fraction
+			// Should have all original messages + truncation marker (non-destructive)
+			expect(result2.messages.length).toBe(6) // 5 original + 1 marker
+			expect(result2.truncationId).toBeDefined()
 			expect(result2.summary).toBe("")
 			expect(result2.cost).toBe(0)
 			expect(result2.prevContextTokens).toBe(81809)
@@ -1192,8 +1221,10 @@ describe("Context Management", () => {
 				profileThresholds: {},
 				currentProfileId: "default",
 			})
-			expect(result2).not.toEqual(messagesWithSmallContent)
-			expect(result2.messages.length).toBe(3) // Truncated with 0.5 fraction
+			expect(result2.messages).not.toEqual(messagesWithSmallContent)
+			// Should have all original messages + truncation marker (non-destructive)
+			expect(result2.messages.length).toBe(6) // 5 original + 1 marker
+			expect(result2.truncationId).toBeDefined()
 		})
 
 		it("should handle large context windows appropriately", async () => {
@@ -1237,8 +1268,10 @@ describe("Context Management", () => {
 				profileThresholds: {},
 				currentProfileId: "default",
 			})
-			expect(result2).not.toEqual(messagesWithSmallContent)
-			expect(result2.messages.length).toBe(3) // Truncated with 0.5 fraction
+			expect(result2.messages).not.toEqual(messagesWithSmallContent)
+			// Should have all original messages + truncation marker (non-destructive)
+			expect(result2.messages.length).toBe(6) // 5 original + 1 marker
+			expect(result2.truncationId).toBeDefined()
 		})
 	})
 })

src/core/context-management/__tests__/truncation.spec.ts

@@ -0,0 +1,402 @@
+import { describe, it, expect, beforeEach } from "vitest"
+import { TelemetryService } from "@roo-code/telemetry"
+import { truncateConversation } from "../index"
+import { getEffectiveApiHistory, cleanupAfterTruncation } from "../../condense"
+import { ApiMessage } from "../../task-persistence/apiMessages"
+
+describe("Non-Destructive Sliding Window Truncation", () => {
+	let messages: ApiMessage[]
+
+	beforeEach(() => {
+		// Initialize TelemetryService for tests
+		if (!TelemetryService.hasInstance()) {
+			TelemetryService.createInstance([])
+		}
+
+		// Create a sample conversation with 11 messages (1 initial + 10 conversation messages)
+		messages = [
+			{ role: "user", content: "Initial task", ts: 1000 },
+			{ role: "assistant", content: "Response 1", ts: 1100 },
+			{ role: "user", content: "Message 2", ts: 1200 },
+			{ role: "assistant", content: "Response 2", ts: 1300 },
+			{ role: "user", content: "Message 3", ts: 1400 },
+			{ role: "assistant", content: "Response 3", ts: 1500 },
+			{ role: "user", content: "Message 4", ts: 1600 },
+			{ role: "assistant", content: "Response 4", ts: 1700 },
+			{ role: "user", content: "Message 5", ts: 1800 },
+			{ role: "assistant", content: "Response 5", ts: 1900 },
+			{ role: "user", content: "Message 6", ts: 2000 },
+		]
+	})
+
+	describe("truncateConversation()", () => {
+		it("should tag messages with truncationParent instead of deleting", () => {
+			const result = truncateConversation(messages, 0.5, "test-task-id")
+
+			// All messages should still be present
+			expect(result.messages.length).toBe(messages.length + 1) // +1 for truncation marker
+
+			// Calculate expected messages to remove: floor((11-1) * 0.5) = 5, rounded to even = 4
+			const expectedMessagesToRemove = 4
+
+			// Messages 1-4 should be tagged with truncationParent
+			for (let i = 1; i <= expectedMessagesToRemove; i++) {
+				// Account for truncation marker inserted at position 1
+				const msgIndex = i < 1 ? i : i + 1
+				expect(result.messages[msgIndex].truncationParent).toBeDefined()
+				expect(result.messages[msgIndex].truncationParent).toBe(result.truncationId)
+			}
+
+			// First message should not be tagged
+			expect(result.messages[0].truncationParent).toBeUndefined()
+
+			// Remaining messages should not be tagged
+			for (let i = expectedMessagesToRemove + 2; i < result.messages.length; i++) {
+				expect(result.messages[i].truncationParent).toBeUndefined()
+			}
+		})
+
+		it("should insert truncation marker with truncationId", () => {
+			const result = truncateConversation(messages, 0.5, "test-task-id")
+
+			// Truncation marker should be at index 1 (after first message)
+			const marker = result.messages[1]
+			expect(marker.isTruncationMarker).toBe(true)
+			expect(marker.truncationId).toBeDefined()
+			expect(marker.truncationId).toBe(result.truncationId)
+			expect(marker.role).toBe("assistant")
+			expect(marker.content).toContain("Sliding window truncation")
+		})
+
+		it("should return truncationId and messagesRemoved", () => {
+			const result = truncateConversation(messages, 0.5, "test-task-id")
+
+			expect(result.truncationId).toBeDefined()
+			expect(typeof result.truncationId).toBe("string")
+			expect(result.messagesRemoved).toBe(4) // floor((11-1) * 0.5) rounded to even
+		})
+
+		it("should round messagesToRemove to an even number", () => {
+			// Test with 12 messages (1 initial + 11 conversation)
+			const manyMessages: ApiMessage[] = [
+				{ role: "user", content: "Initial", ts: 1000 },
+				...Array.from({ length: 11 }, (_, i) => ({
+					role: (i % 2 === 0 ? "assistant" : "user") as "assistant" | "user",
+					content: `Message ${i + 1}`,
+					ts: 1100 + i * 100,
+				})),
+			]
+
+			// fracToRemove=0.5 -> rawMessagesToRemove = floor(11 * 0.5) = 5
+			// messagesToRemove = 5 - (5 % 2) = 4 (rounded down to even)
+			const result = truncateConversation(manyMessages, 0.5, "test-task-id")
+			expect(result.messagesRemoved).toBe(4)
+		})
+	})
+
+	describe("getEffectiveApiHistory()", () => {
+		it("should filter out truncated messages when truncation marker exists", () => {
+			const truncationResult = truncateConversation(messages, 0.5, "test-task-id")
+			const effective = getEffectiveApiHistory(truncationResult.messages)
+
+			// Should exclude 4 truncated messages but keep the first message and truncation marker
+			// Original: 11 messages
+			// After truncation: 11 + 1 marker = 12
+			// Effective: 11 - 4 (hidden) + 1 (marker) = 8
+			expect(effective.length).toBe(8)
+
+			// First message should be present
+			expect(effective[0].content).toBe("Initial task")
+
+			// Truncation marker should be present
+			expect(effective[1].isTruncationMarker).toBe(true)
+
+			// Messages with truncationParent should be filtered out
+			for (const msg of effective) {
+				if (msg.truncationParent) {
+					throw new Error("Message with truncationParent should be filtered out")
+				}
+			}
+		})
+
+		it("should include truncated messages when truncation marker is removed", () => {
+			const truncationResult = truncateConversation(messages, 0.5, "test-task-id")
+
+			// Remove the truncation marker (simulate rewind past truncation)
+			const messagesWithoutMarker = truncationResult.messages.filter((msg) => !msg.isTruncationMarker)
+
+			const effective = getEffectiveApiHistory(messagesWithoutMarker)
+
+			// All messages should be visible now
+			expect(effective.length).toBe(messages.length)
+
+			// Verify first and last messages are present
+			expect(effective[0].content).toBe("Initial task")
+			expect(effective[effective.length - 1].content).toBe("Message 6")
+		})
+
+		it("should handle both condenseParent and truncationParent filtering", () => {
+			// Create a scenario with both condensing and truncation
+			const messagesWithCondense: ApiMessage[] = [
+				{ role: "user", content: "Initial", ts: 1000 },
+				{ role: "assistant", content: "Msg 1", ts: 1100, condenseParent: "condense-1" },
+				{ role: "user", content: "Msg 2", ts: 1200, condenseParent: "condense-1" },
+				{
+					role: "assistant",
+					content: "Summary 1",
+					ts: 1250,
+					isSummary: true,
+					condenseId: "condense-1",
+				},
+				{ role: "user", content: "Msg 3", ts: 1300 },
+				{ role: "assistant", content: "Msg 4", ts: 1400 },
+			]
+
+			const truncationResult = truncateConversation(messagesWithCondense, 0.5, "test-task-id")
+			const effective = getEffectiveApiHistory(truncationResult.messages)
+
+			// Should filter both condensed messages and truncated messages
+			// Messages with condenseParent="condense-1" should be filtered (summary exists)
+			// Messages with truncationParent should be filtered (marker exists)
+			const hasCondensedMessage = effective.some((msg) => msg.condenseParent === "condense-1")
+			const hasTruncatedMessage = effective.some((msg) => msg.truncationParent)
+
+			expect(hasCondensedMessage).toBe(false)
+			expect(hasTruncatedMessage).toBe(false)
+		})
+	})
+
+	describe("cleanupAfterTruncation()", () => {
+		it("should clear orphaned truncationParent tags when marker is deleted", () => {
+			const truncationResult = truncateConversation(messages, 0.5, "test-task-id")
+
+			// Remove the truncation marker (simulate rewind)
+			const messagesWithoutMarker = truncationResult.messages.filter((msg) => !msg.isTruncationMarker)
+
+			const cleaned = cleanupAfterTruncation(messagesWithoutMarker)
+
+			// All truncationParent tags should be cleared
+			for (const msg of cleaned) {
+				expect(msg.truncationParent).toBeUndefined()
+			}
+		})
+
+		it("should preserve truncationParent tags when marker still exists", () => {
+			const truncationResult = truncateConversation(messages, 0.5, "test-task-id")
+
+			const cleaned = cleanupAfterTruncation(truncationResult.messages)
+
+			// truncationParent tags should be preserved (marker still exists)
+			const taggedMessages = cleaned.filter((msg) => msg.truncationParent)
+			expect(taggedMessages.length).toBeGreaterThan(0)
+
+			// All tagged messages should point to the existing marker
+			for (const msg of taggedMessages) {
+				expect(msg.truncationParent).toBe(truncationResult.truncationId)
+			}
+		})
+
+		it("should handle both condenseParent and truncationParent cleanup", () => {
+			const messagesWithBoth: ApiMessage[] = [
+				{ role: "user", content: "Initial", ts: 1000 },
+				{ role: "assistant", content: "Msg 1", ts: 1100, condenseParent: "orphan-condense" },
+				{ role: "user", content: "Msg 2", ts: 1200, truncationParent: "orphan-truncation" },
+				{ role: "assistant", content: "Msg 3", ts: 1300 },
+			]
+
+			const cleaned = cleanupAfterTruncation(messagesWithBoth)
+
+			// Both orphaned parent references should be cleared
+			expect(cleaned[1].condenseParent).toBeUndefined()
+			expect(cleaned[2].truncationParent).toBeUndefined()
+		})
+
+		it("should preserve valid parent references", () => {
+			const messagesWithValidParents: ApiMessage[] = [
+				{ role: "user", content: "Initial", ts: 1000 },
+				{ role: "assistant", content: "Msg 1", ts: 1100, condenseParent: "valid-condense" },
+				{
+					role: "assistant",
+					content: "Summary",
+					ts: 1150,
+					isSummary: true,
+					condenseId: "valid-condense",
+				},
+				{ role: "user", content: "Msg 2", ts: 1200, truncationParent: "valid-truncation" },
+				{
+					role: "assistant",
+					content: "Truncation marker",
+					ts: 1250,
+					isTruncationMarker: true,
+					truncationId: "valid-truncation",
+				},
+			]
+
+			const cleaned = cleanupAfterTruncation(messagesWithValidParents)
+
+			// Valid parent references should be preserved
+			expect(cleaned[1].condenseParent).toBe("valid-condense")
+			expect(cleaned[3].truncationParent).toBe("valid-truncation")
+		})
+	})
+
+	describe("Rewind past truncation integration", () => {
+		it("should restore hidden messages when rewinding past truncation point", () => {
+			// Step 1: Perform truncation
+			const truncationResult = truncateConversation(messages, 0.5, "test-task-id")
+
+			// Step 2: Verify messages are hidden initially
+			const effectiveBeforeRewind = getEffectiveApiHistory(truncationResult.messages)
+			expect(effectiveBeforeRewind.length).toBeLessThan(messages.length)
+
+			// Step 3: Simulate rewind by removing truncation marker and subsequent messages
+			// In practice this would be done via removeMessagesThisAndSubsequent
+			const markerIndex = truncationResult.messages.findIndex((msg) => msg.isTruncationMarker)
+			const messagesAfterRewind = truncationResult.messages.slice(0, markerIndex)
+
+			// Step 4: Clean up orphaned parent references
+			const cleanedAfterRewind = cleanupAfterTruncation(messagesAfterRewind)
+
+			// Step 5: Get effective history after cleanup
+			const effectiveAfterRewind = getEffectiveApiHistory(cleanedAfterRewind)
+
+			// All original messages before the marker should be restored
+			expect(effectiveAfterRewind.length).toBe(markerIndex)
+
+			// No messages should have truncationParent
+			for (const msg of effectiveAfterRewind) {
+				expect(msg.truncationParent).toBeUndefined()
+			}
+		})
+
+		it("should handle multiple truncations correctly", () => {
+			// Step 1: First truncation
+			const firstTruncation = truncateConversation(messages, 0.5, "task-1")
+
+			// Step 2: Get effective history and simulate more messages being added
+			const effectiveAfterFirst = getEffectiveApiHistory(firstTruncation.messages)
+			const moreMessages: ApiMessage[] = [
+				...firstTruncation.messages,
+				{ role: "user", content: "New message 1", ts: 3000 },
+				{ role: "assistant", content: "New response 1", ts: 3100 },
+				{ role: "user", content: "New message 2", ts: 3200 },
+				{ role: "assistant", content: "New response 2", ts: 3300 },
+			]
+
+			// Step 3: Second truncation
+			const secondTruncation = truncateConversation(moreMessages, 0.5, "task-1")
+
+			// Step 4: Get effective history after second truncation
+			const effectiveAfterSecond = getEffectiveApiHistory(secondTruncation.messages)
+
+			// Should have messages hidden by both truncations filtered out
+			const firstMarker = secondTruncation.messages.find(
+				(msg) => msg.isTruncationMarker && msg.truncationId === firstTruncation.truncationId,
+			)
+			const secondMarker = secondTruncation.messages.find(
+				(msg) => msg.isTruncationMarker && msg.truncationId === secondTruncation.truncationId,
+			)
+
+			expect(firstMarker).toBeDefined()
+			expect(secondMarker).toBeDefined()
+
+			// Messages tagged with either truncationId should be filtered
+			for (const msg of effectiveAfterSecond) {
+				if (msg.truncationParent === firstTruncation.truncationId) {
+					throw new Error("First truncation messages should be filtered")
+				}
+				if (msg.truncationParent === secondTruncation.truncationId) {
+					throw new Error("Second truncation messages should be filtered")
+				}
+			}
+		})
+
+		it("should handle rewinding when second truncation affects first truncation marker", () => {
+			// Step 1: First truncation
+			const firstTruncation = truncateConversation(messages, 0.5, "task-1")
+
+			// Step 2: Add more messages AFTER getting effective history
+			// This simulates real usage where we only send effective messages to API
+			const effectiveAfterFirst = getEffectiveApiHistory(firstTruncation.messages)
+			const moreMessages: ApiMessage[] = [
+				...firstTruncation.messages, // Keep full history with tagged messages
+				{ role: "user", content: "New message 1", ts: 3000 },
+				{ role: "assistant", content: "New response 1", ts: 3100 },
+				{ role: "user", content: "New message 2", ts: 3200 },
+				{ role: "assistant", content: "New response 2", ts: 3300 },
+			]
+
+			// Step 3: Second truncation - this will tag some messages including possibly the first marker
+			const secondTruncation = truncateConversation(moreMessages, 0.5, "task-1")
+
+			// Step 4: Simulate rewind past second truncation marker
+			const secondMarkerIndex = secondTruncation.messages.findIndex(
+				(msg) => msg.isTruncationMarker && msg.truncationId === secondTruncation.truncationId,
+			)
+			const afterSecondRewind = secondTruncation.messages.slice(0, secondMarkerIndex)
+
+			// Step 5: Clean up orphaned references
+			const cleaned = cleanupAfterTruncation(afterSecondRewind)
+
+			// Step 6: Get effective history
+			const effective = getEffectiveApiHistory(cleaned)
+
+			// The second truncation marker should be removed
+			const hasSecondTruncationMarker = effective.some(
+				(msg) => msg.isTruncationMarker && msg.truncationId === secondTruncation.truncationId,
+			)
+			expect(hasSecondTruncationMarker).toBe(false)
+
+			// Messages that were tagged by the second truncation should have those tags cleared
+			const hasSecondTruncationParent = cleaned.some(
+				(msg) => msg.truncationParent === secondTruncation.truncationId,
+			)
+			expect(hasSecondTruncationParent).toBe(false)
+
+			// First truncation marker and its tagged messages may or may not be present
+			// depending on whether the second truncation affected them
+			// The important thing is that cleanup works correctly
+			expect(cleaned.length).toBeGreaterThan(0)
+		})
+	})
+
+	describe("Edge cases", () => {
+		it("should handle truncateConversation with fracToRemove=0", () => {
+			const result = truncateConversation(messages, 0, "test-task-id")
+
+			// No messages should be tagged (messagesToRemove = 0)
+			const taggedMessages = result.messages.filter((msg) => msg.truncationParent)
+			expect(taggedMessages.length).toBe(0)
+
+			// Should still have truncation marker
+			const marker = result.messages.find((msg) => msg.isTruncationMarker)
+			expect(marker).toBeDefined()
+		})
+
+		it("should handle truncateConversation with very few messages", () => {
+			const fewMessages: ApiMessage[] = [
+				{ role: "user", content: "Initial", ts: 1000 },
+				{ role: "assistant", content: "Response", ts: 1100 },
+			]
+
+			const result = truncateConversation(fewMessages, 0.5, "test-task-id")
+
+			// Should not crash and should still create marker
+			expect(result.messages.length).toBeGreaterThan(0)
+			const marker = result.messages.find((msg) => msg.isTruncationMarker)
+			expect(marker).toBeDefined()
+		})
+
+		it("should handle empty condenseParent and truncationParent gracefully", () => {
+			const messagesWithoutTags: ApiMessage[] = [
+				{ role: "user", content: "Message 1", ts: 1000 },
+				{ role: "assistant", content: "Response 1", ts: 1100 },
+			]
+
+			const cleaned = cleanupAfterTruncation(messagesWithoutTags)
+
+			// Should return same messages unchanged
+			expect(cleaned).toEqual(messagesWithoutTags)
+		})
+	})
+})

src/core/context-management/index.ts

@@ -1,4 +1,5 @@
 import { Anthropic } from "@anthropic-ai/sdk"
+import crypto from "crypto"
 
 import { TelemetryService } from "@roo-code/telemetry"
 
@@ -39,27 +40,62 @@ export async function estimateTokenCount(
 }
 
 /**
- * Truncates a conversation by removing a fraction of the messages.
+ * Result of truncation operation, includes the truncation ID for UI events.
+ */
+export type TruncationResult = {
+	messages: ApiMessage[]
+	truncationId: string
+	messagesRemoved: number
+}
+
+/**
+ * Truncates a conversation by tagging messages as hidden instead of removing them.
  *
  * The first message is always retained, and a specified fraction (rounded to an even number)
- * of messages from the beginning (excluding the first) is removed.
+ * of messages from the beginning (excluding the first) is tagged with truncationParent.
+ * A truncation marker is inserted to track where truncation occurred.
  *
- * This implements the sliding window truncation behavior.
+ * This implements non-destructive sliding window truncation, allowing messages to be
+ * restored if the user rewinds past the truncation point.
  *
  * @param {ApiMessage[]} messages - The conversation messages.
- * @param {number} fracToRemove - The fraction (between 0 and 1) of messages (excluding the first) to remove.
+ * @param {number} fracToRemove - The fraction (between 0 and 1) of messages (excluding the first) to hide.
  * @param {string} taskId - The task ID for the conversation, used for telemetry
- * @returns {ApiMessage[]} The truncated conversation messages.
+ * @returns {TruncationResult} Object containing the tagged messages, truncation ID, and count of messages removed.
  */
-export function truncateConversation(messages: ApiMessage[], fracToRemove: number, taskId: string): ApiMessage[] {
+export function truncateConversation(messages: ApiMessage[], fracToRemove: number, taskId: string): TruncationResult {
 	TelemetryService.instance.captureSlidingWindowTruncation(taskId)
-	const truncatedMessages = [messages[0]]
+
+	const truncationId = crypto.randomUUID()
 	const rawMessagesToRemove = Math.floor((messages.length - 1) * fracToRemove)
 	const messagesToRemove = rawMessagesToRemove - (rawMessagesToRemove % 2)
-	const remainingMessages = messages.slice(messagesToRemove + 1)
-	truncatedMessages.push(...remainingMessages)
 
-	return truncatedMessages
+	// Tag messages that are being "truncated" (hidden from API calls)
+	const taggedMessages = messages.map((msg, index) => {
+		if (index > 0 && index <= messagesToRemove) {
+			return { ...msg, truncationParent: truncationId }
+		}
+		return msg
+	})
+
+	// Insert truncation marker after first message (so we know a truncation happened)
+	const firstKeptTs = messages[messagesToRemove + 1]?.ts ?? Date.now()
+	const truncationMarker: ApiMessage = {
+		role: "assistant",
+		content: `[Sliding window truncation: ${messagesToRemove} messages hidden to reduce context]`,
+		ts: firstKeptTs - 1,
+		isTruncationMarker: true,
+		truncationId,
+	}
+
+	// Insert marker after first message
+	const result = [taggedMessages[0], truncationMarker, ...taggedMessages.slice(1)]
+
+	return {
+		messages: result,
+		truncationId,
+		messagesRemoved: messagesToRemove,
+	}
 }
 
 /**
@@ -89,7 +125,11 @@ export type ContextManagementOptions = {
 	useNativeTools?: boolean
 }
 
-export type ContextManagementResult = SummarizeResponse & { prevContextTokens: number }
+export type ContextManagementResult = SummarizeResponse & {
+	prevContextTokens: number
+	truncationId?: string
+	messagesRemoved?: number
+}
 
 /**
  * Conditionally manages conversation context (condense and fallback truncation).
@@ -178,8 +218,16 @@ export async function manageContext({
 
 	// Fall back to sliding window truncation if needed
 	if (prevContextTokens > allowedTokens) {
-		const truncatedMessages = truncateConversation(messages, 0.5, taskId)
-		return { messages: truncatedMessages, prevContextTokens, summary: "", cost, error }
+		const truncationResult = truncateConversation(messages, 0.5, taskId)
+		return {
+			messages: truncationResult.messages,
+			prevContextTokens,
+			summary: "",
+			cost,
+			error,
+			truncationId: truncationResult.truncationId,
+			messagesRemoved: truncationResult.messagesRemoved,
+		}
 	}
 	// No truncation or condensation needed
 	return { messages, summary: "", cost, prevContextTokens, error }

src/core/task-persistence/apiMessages.ts

@@ -20,6 +20,18 @@ export type ApiMessage = Anthropic.MessageParam & {
 	text?: string
 	// For OpenRouter reasoning_details array format (used by Gemini 3, etc.)
 	reasoning_details?: any[]
+	// For non-destructive condense: unique identifier for summary messages
+	condenseId?: string
+	// For non-destructive condense: points to the condenseId of the summary that replaces this message
+	// Messages with condenseParent are filtered out when sending to API if the summary exists
+	condenseParent?: string
+	// For non-destructive truncation: unique identifier for truncation marker messages
+	truncationId?: string
+	// For non-destructive truncation: points to the truncationId of the marker that hides this message
+	// Messages with truncationParent are filtered out when sending to API if the marker exists
+	truncationParent?: string
+	// Identifies a message as a truncation boundary marker
+	isTruncationMarker?: boolean
 }
 
 export async function readApiMessages({

src/core/task/Task.ts

@@ -21,6 +21,7 @@ import {
 	type ToolUsage,
 	type ToolName,
 	type ContextCondense,
+	type ContextTruncation,
 	type ClineMessage,
 	type ClineSay,
 	type ClineAsk,
@@ -121,7 +122,7 @@ import {
 	checkpointDiff,
 } from "../checkpoints"
 import { processUserContentMentions } from "../mentions/processUserContentMentions"
-import { getMessagesSinceLastSummary, summarizeConversation } from "../condense"
+import { getMessagesSinceLastSummary, summarizeConversation, getEffectiveApiHistory } from "../condense"
 import { MessageQueueService } from "../message-queue/MessageQueueService"
 import { AutoApprovalHandler, checkAutoApproval } from "../auto-approval"
 
@@ -1327,6 +1328,7 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 			cost,
 			newContextTokens = 0,
 			error,
+			condenseId,
 		} = await summarizeConversation(
 			this.apiConversationHistory,
 			this.api, // Main API handler (fallback)
@@ -1352,7 +1354,13 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 		}
 		await this.overwriteApiConversationHistory(messages)
 
-		const contextCondense: ContextCondense = { summary, cost, newContextTokens, prevContextTokens }
+		const contextCondense: ContextCondense = {
+			summary,
+			cost,
+			newContextTokens,
+			prevContextTokens,
+			condenseId: condenseId!,
+		}
 		await this.say(
 			"condense_context",
 			undefined /* text */,
@@ -1379,6 +1387,7 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 			isNonInteractive?: boolean
 		} = {},
 		contextCondense?: ContextCondense,
+		contextTruncation?: ContextTruncation,
 	): Promise<undefined> {
 		if (this.abort) {
 			throw new Error(`[RooCode#say] task ${this.taskId}.${this.instanceId} aborted`)
@@ -1414,6 +1423,7 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 						images,
 						partial,
 						contextCondense,
+						contextTruncation,
 					})
 				}
 			} else {
@@ -1451,6 +1461,7 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 						text,
 						images,
 						contextCondense,
+						contextTruncation,
 					})
 				}
 			}
@@ -1474,6 +1485,7 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 				images,
 				checkpoint,
 				contextCondense,
+				contextTruncation,
 			})
 		}
 
@@ -3383,6 +3395,24 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 				{ isNonInteractive: true } /* options */,
 				contextCondense,
 			)
+		} else if (truncateResult.truncationId) {
+			// Sliding window truncation occurred (fallback when condensing fails or is disabled)
+			const contextTruncation: ContextTruncation = {
+				truncationId: truncateResult.truncationId,
+				messagesRemoved: truncateResult.messagesRemoved ?? 0,
+				prevContextTokens: truncateResult.prevContextTokens,
+			}
+			await this.say(
+				"sliding_window_truncation",
+				undefined /* text */,
+				undefined /* images */,
+				false /* partial */,
+				undefined /* checkpoint */,
+				undefined /* progressStatus */,
+				{ isNonInteractive: true } /* options */,
+				undefined /* contextCondense */,
+				contextTruncation,
+			)
 		}
 	}
 
@@ -3493,8 +3523,14 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 			if (truncateResult.error) {
 				await this.say("condense_context_error", truncateResult.error)
 			} else if (truncateResult.summary) {
-				const { summary, cost, prevContextTokens, newContextTokens = 0 } = truncateResult
-				const contextCondense: ContextCondense = { summary, cost, newContextTokens, prevContextTokens }
+				const { summary, cost, prevContextTokens, newContextTokens = 0, condenseId } = truncateResult
+				const contextCondense: ContextCondense = {
+					summary,
+					cost,
+					newContextTokens,
+					prevContextTokens,
+					condenseId,
+				}
 				await this.say(
 					"condense_context",
 					undefined /* text */,
@@ -3505,10 +3541,32 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 					{ isNonInteractive: true } /* options */,
 					contextCondense,
 				)
+			} else if (truncateResult.truncationId) {
+				// Sliding window truncation occurred (fallback when condensing fails or is disabled)
+				const contextTruncation: ContextTruncation = {
+					truncationId: truncateResult.truncationId,
+					messagesRemoved: truncateResult.messagesRemoved ?? 0,
+					prevContextTokens: truncateResult.prevContextTokens,
+				}
+				await this.say(
+					"sliding_window_truncation",
+					undefined /* text */,
+					undefined /* images */,
+					false /* partial */,
+					undefined /* checkpoint */,
+					undefined /* progressStatus */,
+					{ isNonInteractive: true } /* options */,
+					undefined /* contextCondense */,
+					contextTruncation,
+				)
 			}
 		}
 
-		const messagesSinceLastSummary = getMessagesSinceLastSummary(this.apiConversationHistory)
+		// Get the effective API history by filtering out condensed messages
+		// This allows non-destructive condensing where messages are tagged but not deleted,
+		// enabling accurate rewind operations while still sending condensed history to the API.
+		const effectiveHistory = getEffectiveApiHistory(this.apiConversationHistory)
+		const messagesSinceLastSummary = getMessagesSinceLastSummary(effectiveHistory)
 		const messagesWithoutImages = maybeRemoveImageBlocks(messagesSinceLastSummary, this.api)
 		const cleanConversationHistory = this.buildCleanConversationHistory(messagesWithoutImages as ApiMessage[])
 

src/core/webview/__tests__/webviewMessageHandler.delete.spec.ts

@@ -241,5 +241,322 @@ describe("webviewMessageHandler delete functionality", () => {
 				{ ts: 1500, role: "assistant", content: { type: "text", text: "First response" } },
 			])
 		})
+
+		describe("condense preservation behavior", () => {
+			it("should preserve summary and condensed messages when deleting after the summary", async () => {
+				// Design: Rewind/delete preserves summaries that were created BEFORE the rewind point.
+				// Only summaries removed by truncation have their associated condenseParent tags cleared.
+				const condenseId = "summary-abc"
+
+				getCurrentTaskMock.clineMessages = [
+					{ ts: 100, say: "user", text: "First message" },
+					{ ts: 200, say: "assistant", text: "Response 1" },
+					{ ts: 300, say: "user", text: "Second message" },
+					{ ts: 799, say: "assistant", text: "Summary" },
+					{ ts: 800, say: "assistant", text: "Kept message 1" },
+					{ ts: 900, say: "user", text: "Kept message 2" },
+					{ ts: 1000, say: "assistant", text: "Kept message 3" },
+				]
+
+				// API history after condense: msg1, msg2(tagged), msg3(tagged), summary, kept1, kept2, kept3
+				getCurrentTaskMock.apiConversationHistory = [
+					{ ts: 100, role: "user", content: "First message" },
+					{ ts: 200, role: "assistant", content: "Response 1", condenseParent: condenseId },
+					{ ts: 300, role: "user", content: "Second message", condenseParent: condenseId },
+					{ ts: 799, role: "assistant", content: "Summary", isSummary: true, condenseId },
+					{ ts: 800, role: "assistant", content: "Kept message 1" },
+					{ ts: 900, role: "user", content: "Kept message 2" },
+					{ ts: 1000, role: "assistant", content: "Kept message 3" },
+				]
+
+				// Delete kept message 2 (ts=900) - summary is BEFORE truncation point so should be preserved
+				await webviewMessageHandler(provider, {
+					type: "deleteMessageConfirm",
+					messageTs: 900,
+				})
+
+				expect(getCurrentTaskMock.overwriteApiConversationHistory).toHaveBeenCalled()
+				const result = getCurrentTaskMock.overwriteApiConversationHistory.mock.calls[0][0]
+
+				// Summary should be PRESERVED, condensed messages should KEEP their tags
+				// Expected: [msg1, msg2(tagged), msg3(tagged), summary, kept1]
+				expect(result.length).toBe(5)
+				expect(result[0].content).toBe("First message")
+				expect(result[1].content).toBe("Response 1")
+				expect(result[1].condenseParent).toBe(condenseId) // Tag preserved
+				expect(result[2].content).toBe("Second message")
+				expect(result[2].condenseParent).toBe(condenseId) // Tag preserved
+				expect(result[3].content).toBe("Summary")
+				expect(result[3].isSummary).toBe(true) // Summary preserved
+				expect(result[4].content).toBe("Kept message 1")
+			})
+
+			it("should restore condensed messages when summary is removed by truncation", async () => {
+				// Scenario: Condensed messages exist, user deletes in a way that removes the summary
+				// The orphaned condenseParent tags should be cleared
+				const condenseId = "summary-xyz"
+
+				getCurrentTaskMock.clineMessages = [
+					{ ts: 100, say: "user", text: "Task start" },
+					{ ts: 200, say: "assistant", text: "Response 1" },
+					{ ts: 300, say: "user", text: "Message 2" },
+					{ ts: 999, say: "assistant", text: "Summary displayed" },
+					{ ts: 1000, say: "user", text: "First kept" },
+				]
+
+				// API history with condensed messages and summary
+				getCurrentTaskMock.apiConversationHistory = [
+					{ ts: 100, role: "user", content: "Task start" },
+					{ ts: 200, role: "assistant", content: "Response 1", condenseParent: condenseId },
+					{ ts: 300, role: "user", content: "Message 2", condenseParent: condenseId },
+					{ ts: 999, role: "assistant", content: "Summary", isSummary: true, condenseId },
+					{ ts: 1000, role: "user", content: "First kept" },
+				]
+
+				// Delete "Message 2" (ts=300) - this removes summary too, so orphaned tags should be cleared
+				await webviewMessageHandler(provider, {
+					type: "deleteMessageConfirm",
+					messageTs: 300,
+				})
+
+				expect(getCurrentTaskMock.overwriteApiConversationHistory).toHaveBeenCalled()
+				const result = getCurrentTaskMock.overwriteApiConversationHistory.mock.calls[0][0]
+
+				// Summary was removed, so orphaned tags should be cleared
+				expect(result.length).toBe(2)
+				expect(result[0].content).toBe("Task start")
+				expect(result[1].content).toBe("Response 1")
+				expect(result[1].condenseParent).toBeUndefined() // Tag cleared since summary is gone
+			})
+
+			it("should preserve first condense but undo second when rewinding past second condense only", async () => {
+				// Scenario: Double condense, user deletes a message that removes the second summary
+				// but keeps the first summary. First condense should remain intact.
+				const condenseId1 = "summary-first"
+				const condenseId2 = "summary-second"
+
+				getCurrentTaskMock.clineMessages = [
+					{ ts: 100, say: "user", text: "First message" },
+					{ ts: 799, say: "assistant", text: "Summary1" },
+					{ ts: 1799, say: "assistant", text: "Summary2" },
+					{ ts: 1800, say: "user", text: "Kept1" },
+					{ ts: 1900, say: "assistant", text: "Kept2" },
+					{ ts: 2000, say: "user", text: "To delete" },
+				]
+
+				getCurrentTaskMock.apiConversationHistory = [
+					{ ts: 100, role: "user", content: "First message" },
+					// Messages from first condense (tagged with condenseId1)
+					{ ts: 200, role: "assistant", content: "Msg2", condenseParent: condenseId1 },
+					{ ts: 300, role: "user", content: "Msg3", condenseParent: condenseId1 },
+					// First summary - ALSO tagged with condenseId2 from second condense
+					{
+						ts: 799,
+						role: "assistant",
+						content: "Summary1",
+						isSummary: true,
+						condenseId: condenseId1,
+						condenseParent: condenseId2,
+					},
+					// Messages from second condense (tagged with condenseId2)
+					{ ts: 1000, role: "assistant", content: "Msg after summary1", condenseParent: condenseId2 },
+					{ ts: 1100, role: "user", content: "More msgs", condenseParent: condenseId2 },
+					// Second summary
+					{ ts: 1799, role: "assistant", content: "Summary2", isSummary: true, condenseId: condenseId2 },
+					// Kept messages
+					{ ts: 1800, role: "user", content: "Kept1" },
+					{ ts: 1900, role: "assistant", content: "Kept2" },
+					{ ts: 2000, role: "user", content: "To delete" },
+				]
+
+				// Delete "Kept2" (ts=1900) - summary2 is BEFORE truncation, so it's preserved
+				await webviewMessageHandler(provider, {
+					type: "deleteMessageConfirm",
+					messageTs: 1900,
+				})
+
+				expect(getCurrentTaskMock.overwriteApiConversationHistory).toHaveBeenCalled()
+				const result = getCurrentTaskMock.overwriteApiConversationHistory.mock.calls[0][0]
+
+				// Both summaries should be preserved since they're before the truncation point
+				const summaries = result.filter((msg: any) => msg.isSummary)
+				expect(summaries.length).toBe(2)
+
+				// Verify tags are preserved
+				const summary1 = result.find((msg: any) => msg.content === "Summary1")
+				expect(summary1.condenseParent).toBe(condenseId2) // Still tagged
+			})
+
+			it("should prefer non-summary message when timestamps collide for deletion target", async () => {
+				// When multiple messages share the same timestamp, prefer non-summary for targeting
+				const sharedTs = 1000
+
+				getCurrentTaskMock.clineMessages = [
+					{ ts: 900, say: "user", text: "Previous message" },
+					{ ts: sharedTs, say: "user", text: "First kept message" },
+					{ ts: 1100, say: "assistant", text: "Response" },
+				]
+
+				// Summary and regular message share timestamp (edge case)
+				getCurrentTaskMock.apiConversationHistory = [
+					{ ts: 900, role: "user", content: "Previous message" },
+					{ ts: sharedTs, role: "assistant", content: "Summary", isSummary: true, condenseId: "abc" },
+					{ ts: sharedTs, role: "user", content: "First kept message" },
+					{ ts: 1100, role: "assistant", content: "Response" },
+				]
+
+				// Delete at shared timestamp - should target non-summary message (index 2)
+				await webviewMessageHandler(provider, {
+					type: "deleteMessageConfirm",
+					messageTs: sharedTs,
+				})
+
+				expect(getCurrentTaskMock.overwriteApiConversationHistory).toHaveBeenCalled()
+				const result = getCurrentTaskMock.overwriteApiConversationHistory.mock.calls[0][0]
+
+				// Truncation at index 2 means we keep indices 0-1: previous message and summary
+				expect(result.length).toBe(2)
+				expect(result[0].content).toBe("Previous message")
+				// The summary is kept since it's before truncation point
+				expect(result[1].content).toBe("Summary")
+				expect(result[1].isSummary).toBe(true)
+			})
+
+			it("should remove Summary when its condense_context clineMessage is deleted", async () => {
+				// Scenario: Summary has timestamp BEFORE the deletion point (so it survives truncation),
+				// BUT the condense_context UI message has timestamp AFTER the deletion point (so it gets removed).
+				// The fix links them via condenseId so the Summary is explicitly removed.
+				const condenseId = "summary-sync-test"
+
+				getCurrentTaskMock.clineMessages = [
+					{ ts: 100, say: "user", text: "Task start" },
+					{ ts: 200, say: "assistant", text: "Response 1" },
+					{ ts: 300, say: "user", text: "Message to delete this and after" },
+					{ ts: 400, say: "assistant", text: "Response 2" },
+					// condense_context is created AFTER the condense operation
+					{ ts: 500, say: "condense_context", contextCondense: { condenseId, summary: "Summary text" } },
+					{ ts: 600, say: "user", text: "Post-condense message" },
+				]
+
+				// Summary has ts=299 (before first kept message), so it would survive basic truncation
+				// But since condense_context (ts=500) is being removed, Summary should be removed too
+				getCurrentTaskMock.apiConversationHistory = [
+					{ ts: 100, role: "user", content: "Task start" },
+					{ ts: 200, role: "assistant", content: "Response 1", condenseParent: condenseId },
+					// Summary timestamp is BEFORE the kept messages (this is the bug scenario)
+					{ ts: 299, role: "assistant", content: "Summary text", isSummary: true, condenseId },
+					{ ts: 300, role: "user", content: "Message to delete this and after" },
+					{ ts: 400, role: "assistant", content: "Response 2" },
+					{ ts: 600, role: "user", content: "Post-condense message" },
+				]
+
+				// Delete at ts=300 - this removes condense_context (ts=500), so Summary should be removed too
+				await webviewMessageHandler(provider, {
+					type: "deleteMessageConfirm",
+					messageTs: 300,
+				})
+
+				expect(getCurrentTaskMock.overwriteApiConversationHistory).toHaveBeenCalled()
+				const result = getCurrentTaskMock.overwriteApiConversationHistory.mock.calls[0][0]
+
+				// Summary should be REMOVED even though its timestamp (299) is before truncation point (300)
+				// because its corresponding condense_context message is being removed
+				expect(result.length).toBe(2)
+				expect(result[0].content).toBe("Task start")
+				expect(result[1].content).toBe("Response 1")
+				// condenseParent should be cleared since the Summary is gone
+				expect(result[1].condenseParent).toBeUndefined()
+			})
+
+			it("should preserve first Summary when only second condense_context is deleted (nested condense)", async () => {
+				// Scenario: Two condense operations occurred. User deletes a message that removes
+				// the second condense_context but keeps the first. First summary should stay intact.
+				const condenseId1 = "summary-first"
+				const condenseId2 = "summary-second"
+
+				getCurrentTaskMock.clineMessages = [
+					{ ts: 100, say: "user", text: "First message" },
+					{ ts: 200, say: "assistant", text: "Response 1" },
+					// First condense_context created after first condense
+					{
+						ts: 800,
+						say: "condense_context",
+						contextCondense: { condenseId: condenseId1, summary: "First summary" },
+					},
+					{ ts: 900, say: "user", text: "After first condense" },
+					{ ts: 1000, say: "assistant", text: "Response after 1st condense" },
+					// Delete target - deleting this will remove the second condense_context below
+					{ ts: 1100, say: "user", text: "Message to delete this and after" },
+					// Second condense_context created after second condense (AFTER delete target)
+					{
+						ts: 1800,
+						say: "condense_context",
+						contextCondense: { condenseId: condenseId2, summary: "Second summary" },
+					},
+					{ ts: 1900, say: "user", text: "Post second condense" },
+					{ ts: 2000, say: "assistant", text: "Final response" },
+				]
+
+				getCurrentTaskMock.apiConversationHistory = [
+					{ ts: 100, role: "user", content: "First message" },
+					// Messages from first condense (tagged with condenseId1)
+					{ ts: 200, role: "assistant", content: "Response 1", condenseParent: condenseId1 },
+					// First summary (also tagged with condenseId2 from second condense)
+					{
+						ts: 799,
+						role: "assistant",
+						content: "First summary",
+						isSummary: true,
+						condenseId: condenseId1,
+						condenseParent: condenseId2,
+					},
+					{ ts: 900, role: "user", content: "After first condense", condenseParent: condenseId2 },
+					{
+						ts: 1000,
+						role: "assistant",
+						content: "Response after 1st condense",
+						condenseParent: condenseId2,
+					},
+					{ ts: 1100, role: "user", content: "Message to delete this and after" },
+					// Second summary (timestamp is BEFORE the messages it summarized for sort purposes)
+					{
+						ts: 1799,
+						role: "assistant",
+						content: "Second summary",
+						isSummary: true,
+						condenseId: condenseId2,
+					},
+					{ ts: 1900, role: "user", content: "Post second condense" },
+					{ ts: 2000, role: "assistant", content: "Final response" },
+				]
+
+				// Delete at ts=1100 - this removes second condense_context (ts=1800) but keeps first (ts=800)
+				await webviewMessageHandler(provider, {
+					type: "deleteMessageConfirm",
+					messageTs: 1100,
+				})
+
+				expect(getCurrentTaskMock.overwriteApiConversationHistory).toHaveBeenCalled()
+				const result = getCurrentTaskMock.overwriteApiConversationHistory.mock.calls[0][0]
+
+				// First summary should be PRESERVED (its condense_context is not being removed)
+				const firstSummary = result.find((msg: any) => msg.condenseId === condenseId1)
+				expect(firstSummary).toBeDefined()
+				expect(firstSummary.content).toBe("First summary")
+				expect(firstSummary.isSummary).toBe(true)
+
+				// Second summary should be REMOVED (its condense_context is being removed)
+				const secondSummary = result.find((msg: any) => msg.condenseId === condenseId2)
+				expect(secondSummary).toBeUndefined()
+
+				// Messages that were tagged with condenseId2 should have their tags cleared
+				const afterFirstCondense = result.find((msg: any) => msg.content === "After first condense")
+				expect(afterFirstCondense?.condenseParent).toBeUndefined() // Tag cleared
+
+				// Messages tagged with condenseId1 should KEEP their tags
+				const response1 = result.find((msg: any) => msg.content === "Response 1")
+				expect(response1?.condenseParent).toBe(condenseId1) // Tag preserved
+			})
+		})
 	})
 })

src/core/webview/webviewMessageHandler.ts

@@ -21,6 +21,7 @@ import { TelemetryService } from "@roo-code/telemetry"
 
 import { type ApiMessage } from "../task-persistence/apiMessages"
 import { saveTaskMessages } from "../task-persistence"
+import { cleanupAfterTruncation } from "../condense"
 
 import { ClineProvider } from "./ClineProvider"
 import { BrowserSessionPanelManager } from "./BrowserSessionPanelManager"
@@ -78,14 +79,24 @@ export const webviewMessageHandler = async (
 		return provider.getCurrentTask()?.cwd || provider.cwd
 	}
 	/**
-	 * Shared utility to find message indices based on timestamp
+	 * Shared utility to find message indices based on timestamp.
+	 * When multiple messages share the same timestamp (e.g., after condense),
+	 * this function prefers non-summary messages to ensure user operations
+	 * target the intended message rather than the summary.
 	 */
 	const findMessageIndices = (messageTs: number, currentCline: any) => {
 		// Find the exact message by timestamp, not the first one after a cutoff
 		const messageIndex = currentCline.clineMessages.findIndex((msg: ClineMessage) => msg.ts === messageTs)
-		const apiConversationHistoryIndex = currentCline.apiConversationHistory.findIndex(
-			(msg: ApiMessage) => msg.ts === messageTs,
-		)
+
+		// Find all matching API messages by timestamp
+		const allApiMatches = currentCline.apiConversationHistory
+			.map((msg: ApiMessage, idx: number) => ({ msg, idx }))
+			.filter(({ msg }: { msg: ApiMessage }) => msg.ts === messageTs)
+
+		// Prefer non-summary message if multiple matches exist (handles timestamp collision after condense)
+		const preferred = allApiMatches.find(({ msg }: { msg: ApiMessage }) => !msg.isSummary) || allApiMatches[0]
+		const apiConversationHistoryIndex = preferred?.idx ?? -1
+
 		return { messageIndex, apiConversationHistoryIndex }
 	}
 
@@ -101,20 +112,81 @@ export const webviewMessageHandler = async (
 	}
 
 	/**
-	 * Removes the target message and all subsequent messages
+	 * Removes the target message and all subsequent messages.
+	 * After truncation, cleans up orphaned condenseParent and truncationParent references for any
+	 * summaries or truncation markers that were removed by the truncation.
+	 *
+	 * Design: Rewind/delete operations preserve earlier condense and truncation states.
+	 * Only summaries and truncation markers that are removed by the truncation (i.e., were created
+	 * after the rewind point) have their associated tags cleared.
+	 * This allows nested condensing and multiple truncations to work correctly - rewinding past the
+	 * second condense restores visibility of messages condensed by it, while keeping the first condense intact.
+	 * Same applies to truncation markers.
 	 */
 	const removeMessagesThisAndSubsequent = async (
 		currentCline: any,
 		messageIndex: number,
 		apiConversationHistoryIndex: number,
 	) => {
-		// Delete this message and all that follow
+		// Step 1: Collect condenseIds from condense_context messages being removed.
+		// These IDs link clineMessages to their corresponding Summaries in apiConversationHistory.
+		const removedCondenseIds = new Set<string>()
+		// Step 1b: Collect truncationIds from sliding_window_truncation messages being removed.
+		// These IDs link clineMessages to their corresponding truncation markers in apiConversationHistory.
+		const removedTruncationIds = new Set<string>()
+
+		for (let i = messageIndex; i < currentCline.clineMessages.length; i++) {
+			const msg = currentCline.clineMessages[i]
+			if (msg.say === "condense_context" && msg.contextCondense?.condenseId) {
+				removedCondenseIds.add(msg.contextCondense.condenseId)
+			}
+			if (msg.say === "sliding_window_truncation" && msg.contextTruncation?.truncationId) {
+				removedTruncationIds.add(msg.contextTruncation.truncationId)
+			}
+		}
+
+		// Step 2: Delete this message and all that follow
 		await currentCline.overwriteClineMessages(currentCline.clineMessages.slice(0, messageIndex))
 
 		if (apiConversationHistoryIndex !== -1) {
-			await currentCline.overwriteApiConversationHistory(
-				currentCline.apiConversationHistory.slice(0, apiConversationHistoryIndex),
-			)
+			// Step 3: Truncate API history by timestamp/index
+			let truncatedApiHistory = currentCline.apiConversationHistory.slice(0, apiConversationHistoryIndex)
+
+			// Step 4: Remove Summaries whose condenseId was in a removed condense_context message.
+			// This handles the case where Summary.ts < truncation point but condense_context.ts > truncation point.
+			// Without this, the Summary would survive truncation but its corresponding UI event would be gone.
+			if (removedCondenseIds.size > 0) {
+				truncatedApiHistory = truncatedApiHistory.filter((msg: ApiMessage) => {
+					if (msg.isSummary && msg.condenseId && removedCondenseIds.has(msg.condenseId)) {
+						console.log(
+							`[removeMessagesThisAndSubsequent] Removing orphaned Summary with condenseId=${msg.condenseId}`,
+						)
+						return false
+					}
+					return true
+				})
+			}
+
+			// Step 4b: Remove truncation markers whose truncationId was in a removed sliding_window_truncation message.
+			// Same logic as condense - without this, the marker would survive but its UI event would be gone.
+			if (removedTruncationIds.size > 0) {
+				truncatedApiHistory = truncatedApiHistory.filter((msg: ApiMessage) => {
+					if (msg.isTruncationMarker && msg.truncationId && removedTruncationIds.has(msg.truncationId)) {
+						console.log(
+							`[removeMessagesThisAndSubsequent] Removing orphaned truncation marker with truncationId=${msg.truncationId}`,
+						)
+						return false
+					}
+					return true
+				})
+			}
+
+			// Step 5: Clean up orphaned condenseParent and truncationParent references for messages whose
+			// summary or truncation marker was removed by the truncation. Summaries, truncation markers, and messages
+			// from earlier condense/truncation operations are preserved.
+			const cleanedApiHistory = cleanupAfterTruncation(truncatedApiHistory)
+
+			await currentCline.overwriteApiConversationHistory(cleanedApiHistory)
 		}
 	}