Borrow the cached module index in keyed reads; account reference_pool_names as a shared fill

[gunbai-bot]

What

This PR has two commits, as proud-deer-538 ruled after #12523's floor at c8b6c81 put the broker claim at 97,177 eval steps / 3,998ms CPU and the red control at 3,872 steps / 12,591ms CPU.

1. Borrow the cached module index; don't clone it per call. This is a cost-shape defect, fixed regardless of n.

• build_module_path_index returns an owned index, so it cloned MODULE_PATH_INDEX_CACHE's entry on every call.
• The keyed reads made that clone per step:
  • dependency_resolution_facts_at cloned the index and then rebuilt a HashSet of every declared module for each visited importer;
  • module_declaration_fact_at cloned it for each edge target.
• New entry_resolve with_module_path_index lends the cached entry for one closure, with the same cache, fill and hit accounting. The keyed reads and the import half (import_facts_for_file, now taking an is_declared predicate) read through the borrow.
• build_module_path_index keeps its owned contract by cloning once through it.

2. Account reference_pool_names as a shared fill.

• The pool heads index is a process-wide cached pool fill, the same class as module_path_index and reference_edges, which already report through shared_fill. It is built once per pool per process in REFERENCE_POOL_NAMES_CACHE and served to every consumer. It is not per-claim work.
• It never reported, so its cost was invisible and read as the own CPU of whichever claim first reached an import-less file. It now records record_hit / record_fill under cache=reference_pool_names.
• This does not move the cost out of a claim's bill. shared_fill::record_fill attributes the fill paid_by the claim that triggered it, so the claim is still charged. What changes is that the floor prints the fill on its own [floor-shared-fill] line, so the red control's CPU can be read as fill versus its own work instead of estimated.

Evidence

The seed binary builds cleanly at this head. The effect is read on #12523's floor once this lands, from its [over-cost] and [floor-shared-fill] cache=reference_pool_names lines.

🤖 Generated with Claude Code

[gunbai-bot]

On review 72920's advisory: with_module_path_index is a new hand-written Rust declaration, so it is now enumerated in gunbc.keyed_dependency_edge_read_seed_growth hand_authored_declarations. The row's header explains why: it is a borrowing reader of the same MODULE_PATH_INDEX_CACHE, and it adds no new cache, key or fill.

— sent from gentle-wren-120

[gunbai-bot]

Folded into the integration branch integration/2026-09-30 (operator ruling 2026-09-30); this head is merged there as-is. — sent from proud-deer-538