Brummel
ac4a8c68cf
The rustdoc claimed 'None if the symbol has no data in [from_ms, to_ms]', implying a bar-level None. Empirically (cycle-0011 fieldtest) None is file-level: it propagates data-server's own None, returned only when no archived file overlaps the window (far-future window or unknown symbol). A window that overlaps a loaded file but holds zero bars returns Some(M1Columns) with empty columns, not None. Document the distinction precisely (chosen over collapsing in-coverage- empty into None): None propagates data-server's one file-level meaning unchanged -- 'no data source to read from' -- rather than overloading it with a second aura-level 'source present but empty here' meaning. So Some/None means 'data source present' vs 'nothing to read from', not 'has bars' vs 'has none'; a consumer testing for an empty window must check cols.close.is_empty(). Doc-only, no behaviour change; ledger untouched (the contract is not referenced there). closes #18