diff --git a/packages/support/acp-snapshot/src/suite.ts b/packages/support/acp-snapshot/src/suite.ts
index f97cb82c59..27de939d3d 100644
--- a/packages/support/acp-snapshot/src/suite.ts
+++ b/packages/support/acp-snapshot/src/suite.ts
@@ -245,7 +245,7 @@ export function refreshFixtureReplacements(logs: HarvestedLog[], fixtures: strin
 function preserveFixtureVolatiles(record: Record<string, unknown>, existing: Record<string, unknown> | undefined): void {
   if (existing === undefined || existing.type !== record.type) return
   if (record.type === 'session') {
-    for (const field of ['id', 'createdAt', 'cwd', 'parentSession', 'seedLength'] as const) {
+    for (const field of ['id', 'createdAt', 'cwd', 'parentSession'] as const) {
       if (field in record && field in existing) record[field] = existing[field]
     }
     return
diff --git a/packages/support/acp-snapshot/tests/suite.spec.ts b/packages/support/acp-snapshot/tests/suite.spec.ts
index 8e79e367f2..ae01190c01 100644
--- a/packages/support/acp-snapshot/tests/suite.spec.ts
+++ b/packages/support/acp-snapshot/tests/suite.spec.ts
@@ -271,7 +271,7 @@ describe('stabilizeRefreshLog', () => {
       { from: 'new-child', to: 'old-child' },
       { from: '/new', to: '/old' },
     ])).toBe([
-      '{"type":"session","id":"old-child","createdAt":100,"cwd":"/old","parentSession":"old-parent","seedLength":5}',
+      '{"type":"session","id":"old-child","createdAt":100,"cwd":"/old","parentSession":"old-parent","seedLength":1}',
       '{"type":"hook/result","seq":1,"time":11,"data":{"decision":"block","durationMs":99}}',
       '{"type":"turn/end","seq":2,"time":33,"data":{"error":"fresh error"}}',
       '{"type":"tool/result","seq":3,"time":44,"data":{"text":"old-parent in /old"}}',