diff --git a/packages/host/apiproxy/src/api-proxy.ts b/packages/host/apiproxy/src/api-proxy.ts
index 26bc2d7f6b..2474a05df0 100644
--- a/packages/host/apiproxy/src/api-proxy.ts
+++ b/packages/host/apiproxy/src/api-proxy.ts
@@ -3515,9 +3515,9 @@ export function createApiProxy(ctx: Context, defaults: ApiProxyDefaults): ApiPro
           signal.throwIfAborted()
         } catch {
           signal.throwIfAborted()
-          // Backend read failure: answer 500 without echoing the error, which
-          // may carry absolute host paths into the browser error bar.
-          return new Response('session log export failed to read the stored artifact', { status: 500 })
+          // Root preparation failure: answer 500 without echoing the error,
+          // which may carry absolute host paths into the browser error bar.
+          return new Response('session log export failed to prepare the stored artifact', { status: 500 })
         }
         if (root === undefined) {
           return new Response('session not found', { status: 404 })
diff --git a/packages/host/apiproxy/tests/session-export.spec.ts b/packages/host/apiproxy/tests/session-export.spec.ts
index 1932b54501..92cdaa4db2 100644
--- a/packages/host/apiproxy/tests/session-export.spec.ts
+++ b/packages/host/apiproxy/tests/session-export.spec.ts
@@ -392,7 +392,23 @@ describe('session.export download endpoint', () => {
     )
     expect(response.status).toBe(500)
     const body = await response.text()
-    expect(body).toBe('session log export failed to read the stored artifact')
+    expect(body).toBe('session log export failed to prepare the stored artifact')
+    expect(body).not.toContain('/host/private/')
+  })
+
+  it('answers the private-error-safe 500 when the live root flush fails', async () => {
+    const api = await buildApi({ 'session-root': artifact('session-root') }, [], {
+      sessions: {
+        get: id => ({ id }),
+        flush: async () => { throw new Error('/host/private/flush-state') },
+      },
+    })
+    const response = await toFetchHandler(api).fetch(
+      new Request('http://host/api/session.export?sessionId=session-root'),
+    )
+    expect(response.status).toBe(500)
+    const body = await response.text()
+    expect(body).toBe('session log export failed to prepare the stored artifact')
     expect(body).not.toContain('/host/private/')
   })