From 9dd8d3c6ceea9c8600a6bca6ceb28ed556c78c7f Mon Sep 17 00:00:00 2001
From: usr-bin-roygbiv <roy@davai.fyi>
Date: Tue, 28 Jul 2026 15:27:55 +0000
Subject: [PATCH] fix: preserve native compaction failures

(cherry picked from commit d13e9f30a06cad347226d2fa377cab8c086debc3)
---
 .../src/session/session-maintenance.ts        |  2 +-
 ...issue-986-compaction-auth-fallback.test.ts | 33 +++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/packages/coding-agent/src/session/session-maintenance.ts b/packages/coding-agent/src/session/session-maintenance.ts
index 19cd40efa..dc24d4dfe 100644
--- a/packages/coding-agent/src/session/session-maintenance.ts
+++ b/packages/coding-agent/src/session/session-maintenance.ts
@@ -2542,7 +2542,7 @@ export class SessionMaintenance {
 								candidate.api,
 							);
 							if (AIError.is(id, AIError.Flag.AuthFailed)) {
-								lastError = this.#buildCompactionAuthError();
+								if (!nativeCompactionFailure) lastError = this.#buildCompactionAuthError();
 								break;
 							}
 							if (AIError.is(id, AIError.Flag.Timeout)) {
diff --git a/packages/coding-agent/test/issue-986-compaction-auth-fallback.test.ts b/packages/coding-agent/test/issue-986-compaction-auth-fallback.test.ts
index 1c8f1c51c..b5b0ed692 100644
--- a/packages/coding-agent/test/issue-986-compaction-auth-fallback.test.ts
+++ b/packages/coding-agent/test/issue-986-compaction-auth-fallback.test.ts
@@ -190,6 +190,39 @@ describe("issue #986 compaction auth fallback", () => {
 		]);
 	});
 
+	it("preserves a native transport failure when a later same-provider candidate fails authentication", async () => {
+		const { apiKeySpy, crossProviderModel, currentModel, sameProviderModel, triggerAutoCompaction } =
+			await createAutoNativeFallbackSession();
+		apiKeySpy.mockImplementation(async model =>
+			model.provider === crossProviderModel.provider ? undefined : "test-key",
+		);
+		const attemptedModels: string[] = [];
+		let errorMessage: string | undefined;
+		session.subscribe(event => {
+			if (event.type === "auto_compaction_end") errorMessage = event.errorMessage;
+		});
+		vi.spyOn(compactionModule, "compact").mockImplementation(async (_preparation, model) => {
+			attemptedModels.push(`${model.provider}/${model.id}`);
+			if (model.provider === currentModel.provider && model.id === currentModel.id) {
+				throw new compactionModule.NativeCompactionError(new Error("native compaction transport failed"));
+			}
+			if (model.provider === sameProviderModel.provider && model.id === sameProviderModel.id) {
+				throw new compactionModule.NativeCompactionError(
+					Object.assign(new Error("native compaction authentication failed"), { status: 401 }),
+				);
+			}
+			throw new Error(`Unexpected compaction model ${model.provider}/${model.id}`);
+		});
+
+		await triggerAutoCompaction();
+
+		expect(attemptedModels).toEqual([
+			`${currentModel.provider}/${currentModel.id}`,
+			`${sameProviderModel.provider}/${sameProviderModel.id}`,
+		]);
+		expect(errorMessage).toContain("native compaction transport failed");
+	});
+
 	it("skips unauthenticated cross-provider candidates before enforcing the native boundary", async () => {
 		const { apiKeySpy, crossProviderModel, currentModel, sameProviderModel, triggerAutoCompaction } =
 			await createAutoNativeFallbackSession();