When the "busy" flag for the __wti_evict_app_assist_worker function is set, it's supposed to ensure that some minimal eviction is done so that there is cache space for a read operation.

1. This condition should also exit if (busy && pct_full < 100.0).

        /* See if eviction is still needed. */
        if (!__wt_evict_needed(session, busy, readonly, &pct_full) ||
          (pct_full < 100.0 &&
            (__wt_atomic_loadv64(&evict->eviction_progress) > initial_progress + max_progress)))
            break;

Rationale: if we're busy, it's fine to deem the work done as soon as there is any free space available.

2. This should make sure that pct_full < 100.0.

        /* Evict a page. */
        ret = __evict_page(session, false);
        if (ret == 0) {
            /* If the caller holds resources, we can stop after a successful eviction. */
            if (busy)
                break;

Rationale: the space freed up by a single page eviction may not bring pct_full below 100.

In fact, the "if (busy) break;" thing in (2) might not even be required if (1) is done since this check will be done in the next loop iteration.

Note that this change will require a thorough testing to ensure that it doesn't introduce any regressions.