Background

WT-18406 (PR 14561) skips reading a WT_REF_DISK internal page on a disaggregated tree when the address-cell time aggregate shows the whole subtree is deleted and visible. The change lives in _wt_btcur_skip_page() and is used only by cursor next/prev via _wt_tree_walk_custom_skip().

Chenhao asked on that PR whether the same optimisation can be applied elsewhere. WT_READ_SKIP_INTL is not that skip: it only withholds internal pages from the caller. The walk engine still __wt_page_swap}}s an on-disk internal in so it can descend. Without a skip callback that returns {{skipp = true, emptied internals are still read.

This ticket is the evaluation, not an implementation commitment.

What is already covered

• Cursor next/prev (snapshot, not KEY_ONLY / IGNORE_TOMBSTONE): WT-18406.
• RTS __rts_btree_walk_page_skip: already skips on-disk pages whose aggregate is stable past the rollback timestamp. An emptied subtree is a subset of that.
• Prepared discover: already skips on-disk pages with !ta->prepare.

What cannot skip

These walks need the internal page itself, or they never read from disk:

• Checkpoint cleanup — walks internals to mark obsolete children; skipping would miss cleanup. Related to the local-block-manager follow-up.
• Compact — needs internals to decide rewrite.
• Verify page-discard — must collect every live page id for PALI.
• Statistics walk — needs exact internal/leaf/entry counts.
• Checkpoint / eviction file walks — WT_READ_CACHE, no disk read.

Candidates to evaluate

Paths that look for visible records, do not need internal-page contents, and do not go through __wt_btcur_skip_page:

1. __wt_random_descent (src/btree/bt_random.c). Random cursor and eviction sampling treat a WT_REF_DISK internal as a valid descent target and swap it in. An emptied subtree still produces no key.
2. _wti_tree_walk_skip / _tree_walk_skip_count_callback. next_random sample-size walks skip deleted leaves only; an emptied on-disk internal is still read.

_wt_row_search / _wt_col_search look similar but also position inserts. Treat them as out of scope unless the evaluation shows a safe read-only subset.

Expected outcome

• Confirm or reject the two candidates above (and any other non-walk descent found during the review).
• If a path is safe, either implement the skip there or split an implementation ticket.
• If none are worth doing, close this with the analysis.