diff --git a/packages/agent/src/compaction/compaction.ts b/packages/agent/src/compaction/compaction.ts
index 02a632e25..21768be49 100644
--- a/packages/agent/src/compaction/compaction.ts
+++ b/packages/agent/src/compaction/compaction.ts
@@ -680,14 +680,6 @@ function createSnapcompactArchiveMigrationMessage(archiveText: string): Message
 	};
 }
 
-function stripSnapcompactPreserveData(
-	preserveData: Record<string, unknown> | undefined,
-): Record<string, unknown> | undefined {
-	if (!preserveData || !(snapcompact.PRESERVE_KEY in preserveData)) return preserveData;
-	const { [snapcompact.PRESERVE_KEY]: _removed, ...rest } = preserveData;
-	return Object.keys(rest).length > 0 ? rest : undefined;
-}
-
 export async function generateSummary(
 	currentMessages: AgentMessage[],
 	model: Model,
@@ -1261,7 +1253,11 @@ export async function compact(
 		throw new Error("First kept entry has no ID - session may need migration");
 	}
 
-	const finalPreserveData = previousSnapcompactArchive ? stripSnapcompactPreserveData(preserveData) : preserveData;
+	// This LLM-summary path migrated any prior snapcompact frames into the summary
+	// text above; strip the now-stale frame archive from preserveData so it cannot
+	// re-attach to the rebuilt context. Only the legacy-frame case needs stripping —
+	// when there was no previous archive, preserveData carries no frames to drop.
+	const finalPreserveData = previousSnapcompactArchive ? snapcompact.stripPreservedArchive(preserveData) : preserveData;
 
 	return {
 		summary,
diff --git a/packages/coding-agent/src/session/agent-session.ts b/packages/coding-agent/src/session/agent-session.ts
index cc2e75a94..6badee866 100644
--- a/packages/coding-agent/src/session/agent-session.ts
+++ b/packages/coding-agent/src/session/agent-session.ts
@@ -1117,20 +1117,12 @@ function toRestoredQueuedMessage(message: AgentMessage): RestoredQueuedMessage {
 	return { text: queueChipText(message), images: queuedImageContent(message) };
 }
 
-function stripSnapcompactPreserveData(
-	preserveData: Record<string, unknown> | undefined,
-): Record<string, unknown> | undefined {
-	if (!preserveData || !(snapcompact.PRESERVE_KEY in preserveData)) return preserveData;
-	const { [snapcompact.PRESERVE_KEY]: _removed, ...rest } = preserveData;
-	return Object.keys(rest).length > 0 ? rest : undefined;
-}
-
 function mergeLlmCompactionPreserveData(
 	hookPreserveData: Record<string, unknown> | undefined,
 	resultPreserveData: Record<string, unknown> | undefined,
 ): Record<string, unknown> | undefined {
 	const preserveData = { ...(hookPreserveData ?? {}), ...(resultPreserveData ?? {}) };
-	return stripSnapcompactPreserveData(Object.keys(preserveData).length > 0 ? preserveData : undefined);
+	return snapcompact.stripPreservedArchive(Object.keys(preserveData).length > 0 ? preserveData : undefined);
 }
 
 export class AgentSession {
diff --git a/packages/snapcompact/src/snapcompact.ts b/packages/snapcompact/src/snapcompact.ts
index 4c49df334..ba84dd266 100644
--- a/packages/snapcompact/src/snapcompact.ts
+++ b/packages/snapcompact/src/snapcompact.ts
@@ -1290,6 +1290,19 @@ export function getPreservedArchive(preserveData: Record<string, unknown> | unde
 	};
 }
 
+/** Drop the persisted frame archive ({@link PRESERVE_KEY}) from `preserveData`,
+ *  returning the remaining state — or `undefined` when nothing else remains, so
+ *  an empty `{}` is never persisted. Callers strip the archive once its frames
+ *  have been migrated into a new compaction's text, preventing the stale frames
+ *  from leaking back into the rebuilt context. */
+export function stripPreservedArchive(
+	preserveData: Record<string, unknown> | undefined,
+): Record<string, unknown> | undefined {
+	if (!preserveData || !(PRESERVE_KEY in preserveData)) return preserveData;
+	const { [PRESERVE_KEY]: _removed, ...rest } = preserveData;
+	return Object.keys(rest).length > 0 ? rest : undefined;
+}
+
 /** Extract persisted archive source text as plain text for LLM summarization. */
 export function archiveSourceText(archive: Archive): string | undefined {
 	const text =
diff --git a/packages/snapcompact/test/snapcompact.test.ts b/packages/snapcompact/test/snapcompact.test.ts
index 957d64e0b..7f20a41cf 100644
--- a/packages/snapcompact/test/snapcompact.test.ts
+++ b/packages/snapcompact/test/snapcompact.test.ts
@@ -926,6 +926,25 @@ describe("archive helpers", () => {
 		expect(snapcompact.getPreservedArchive({ [snapcompact.PRESERVE_KEY]: archive })).toEqual(archive);
 	});
 
+	it("stripPreservedArchive drops the frame archive and collapses to undefined when empty", () => {
+		expect(snapcompact.stripPreservedArchive(undefined)).toBeUndefined();
+		// No archive key: pass through unchanged.
+		expect(snapcompact.stripPreservedArchive({ other: "keep-me" })).toEqual({ other: "keep-me" });
+		// Archive key alongside unrelated state: strip only the archive.
+		expect(
+			snapcompact.stripPreservedArchive({
+				other: "keep-me",
+				[snapcompact.PRESERVE_KEY]: { frames: [], totalChars: 0, truncatedChars: 0 },
+			}),
+		).toEqual({ other: "keep-me" });
+		// Archive key was the only state: collapse to undefined, never persist `{}`.
+		expect(
+			snapcompact.stripPreservedArchive({
+				[snapcompact.PRESERVE_KEY]: { frames: [], totalChars: 0, truncatedChars: 0 },
+			}),
+		).toBeUndefined();
+	});
+
 	it("historyBlocks orders text head, imaged middle, then text tail", () => {
 		const archive: snapcompact.Archive = {
 			frames: [{ data: btoa("middle"), mimeType: "image/png", cols: 8, rows: 8, chars: 4 }],