Collection-axis paging: columnar reads are unusable on a disable_lists server

The remote client's columnar collection reads all render as { list { … } }, so a server with concurrency.disable_lists set rejects them — and the client exposes no page alternative for collections. Verified end to end against a disable_lists server:

disable_lists exists precisely to stop unbounded reads, so this is a supported configuration the client cannot work against.

Three axes — do not confuse them

Paging shows up in three different places, and only one is implemented:

1. Within one entity — node.history.page(3). Implemented (HistoryPage/SubPage).
2. Across a collection's membership — nodes.page(100). Server has it (GqlNodes::page); the client does not expose it.
3. A column across a collection — nodes.degree(), nodes.id. Renders as list { degree }; no paged form exists on either side.

The history paging code (axis 1) cannot be reused for axis 3: it pages inside a single entity's event list, whereas a columnar read spans entities. Axis 2 returns node handles, not columns, so exposing it does not fix axis 3 either.

Options

(a) Chunk client-side. Columnar terminals loop over pages internally. Cost: breaks the "one RPC per terminal" invariant that test_parity_rpc_counts.py::test_terminal_fires_exactly_one_rpc asserts across 258 cases; also picks a chunk size on the user's behalf and risks torn reads across pages on a mutating graph.

(b) Paged columnar fields server-side (recommended). Add paged variants of the columnar fields (e.g. pagedDegree(limit:, offset:, pageIndex:)) on the collection types, so each call stays one RPC and disable_lists servers work properly. Cost: ~15 fields × 5 collection types, plus a schema change.

(c) Expose nodes.page(...) only. Half a day, mirrors the existing history paging exactly, gives users on a hardened server a way to read entity-by-entity. Does not fix columnar reads; documents the limit instead.

Recommendation: (b) as the real fix; (c) is a reasonable stop-gap if someone needs a hardened server working before (b) lands.

Related

• #2725 — nested edge collections (the nested axis of the same story)
• #2726 — remote history paging iterator (axis 1)

Start by reading the existing GqlNodes::page implementation and the HistoryPage/SubPage paging code, keeping the three paging axes separate. Review test_parity_rpc_counts.py::test_terminal_fires_exactly_one_rpc to understand the current RPC invariant. Done means columnar collection reads have a paged form that works with disable_lists without breaking the one-RPC terminal behavior.