diff --git a/packages/engine/src/branch-conflicts.ts b/packages/engine/src/branch-conflicts.ts
index adea60350c..b707933928 100644
--- a/packages/engine/src/branch-conflicts.ts
+++ b/packages/engine/src/branch-conflicts.ts
@@ -377,7 +377,6 @@ export async function isBranchAuthoritativeForTask(
   repoDir: string,
   branch: string,
   taskId: string,
-  baseSha?: string,
 ): Promise<{ ok: true } | { ok: false; reason: string }> {
   try {
     await revParse(repoDir, `refs/heads/${branch}`);
diff --git a/packages/engine/src/merger.ts b/packages/engine/src/merger.ts
index 90e97895c4..d76103d78b 100644
--- a/packages/engine/src/merger.ts
+++ b/packages/engine/src/merger.ts
@@ -4668,7 +4668,7 @@ export async function commitOrAmendMergeWithFixes(
     // that this attempt's integration worktree never advanced. Reset rootDir
     // to preAttemptHeadSha so the next merge attempt starts clean, and tag
     // the result so the caller's diagnostic includes that context.
-    const authority = await isBranchAuthoritativeForTask(rootDir, branch, taskId, preAttemptHeadSha).catch(
+    const authority = await isBranchAuthoritativeForTask(rootDir, branch, taskId).catch(
       () => ({ ok: false as const, reason: "authority-probe-failed" }),
     );
     if (authority.ok) {