docs: clarify the Expand frontier ceiling bounds the initial dispatch frontier

The cap is applied at dispatch on the initial frontier; per-hop fan-out
(union_dense) is not hard-capped. Correct the constants.md and query-language.md
claims: the ceilings bound the initial-dispatch frontier/hops, the cost model
estimates total indexed work as ~hops*frontier*fanout (pricing dense fan-out
toward CSR), and per-hop work is not a hard bound. Drops the overstated 'hard
caps bound indexed work' / 'cost ∝ frontier' wording.

docs/user/constants.md

@@ -33,6 +33,8 @@ hops) plus the index-coverage signal: the indexed path is preferred when its
 frontier-relative work beats building the CSR (≈ when `hops × frontier` is a
 small fraction of the source-vertex set), and CSR is preferred for dense/deep
 traversals or when the BTREE coverage is degraded and a full scan would be paid
-per hop. The two ceilings above are hard caps — beyond them CSR is always used —
-and the override flag forces a path (the `auto` result is identical either way;
+per hop. The two ceilings bound the **initial dispatch** frontier/hops (beyond
+them CSR is always used); they are not a hard per-hop bound — the cost model
+*estimates* total indexed work as ~`hops × frontier × fanout`, so dense fan-out is
+priced toward CSR rather than capped mid-traversal. The override flag forces a path (the `auto` result is identical either way;
 only the path differs).

docs/user/query-language.md

@@ -81,7 +81,7 @@ Reason: under the staged-write rewire (MR-794), inserts and updates accumulate i
 Pipeline operations:
 
 - `NodeScan { variable, type_name, filters }`
-- `Expand { src_var, dst_var, edge_type, direction (Out|In), dst_type, min_hops, max_hops, dst_filters }` — destination filters are pushed *into* the expand so Lance scalar pushdown can prune. Executed one of two ways, chosen per-expand by a cost model over cheap manifest counts (frontier size, |E|, source-vertex count, hops) plus index coverage: selective traversals (small frontier relative to the source set) resolve neighbors from the persisted `src`/`dst` BTREE (one indexed scan per hop, cost ∝ frontier); dense / deep / large-frontier traversals — or those whose BTREE coverage is degraded so a full scan would be paid per hop — use the in-memory CSR adjacency index. Both produce identical results. Bounded by `OMNIGRAPH_EXPAND_INDEXED_MAX_FRONTIER` / `OMNIGRAPH_EXPAND_INDEXED_MAX_HOPS` (hard ceilings, beyond which CSR is always used), with `OMNIGRAPH_TRAVERSAL_MODE=indexed|csr` forcing a mode (see [constants](constants.md)).
+- `Expand { src_var, dst_var, edge_type, direction (Out|In), dst_type, min_hops, max_hops, dst_filters }` — destination filters are pushed *into* the expand so Lance scalar pushdown can prune. Executed one of two ways, chosen per-expand by a cost model over cheap manifest counts (frontier size, |E|, source-vertex count, hops) plus index coverage: selective traversals (small frontier relative to the source set) resolve neighbors from the persisted `src`/`dst` BTREE (one indexed scan per hop); dense / deep / large-frontier traversals — or those whose BTREE coverage is degraded so a full scan would be paid per hop — use the in-memory CSR adjacency index. Both produce identical results. The `OMNIGRAPH_EXPAND_INDEXED_MAX_FRONTIER` / `OMNIGRAPH_EXPAND_INDEXED_MAX_HOPS` ceilings bound the *initial dispatch* frontier/hops (beyond them CSR is always used); the cost model estimates total indexed work as ~`hops × frontier × fanout` and prices dense fan-out toward CSR — they are not a hard per-hop bound. `OMNIGRAPH_TRAVERSAL_MODE=indexed|csr` forces a mode (see [constants](constants.md)).
 - `Filter { left, op, right }`
 - `AntiJoin { outer_var, inner: Vec<IROp> }` — for `not { … }`