Per-quarter share + value history for a single (fund, CUSIP) position — the chronological trail of one security held by one filer across every 13F-HR quarter we have on file.

Returns the full chronological trail of ONE position held by ONE filer — every quarter we have a 13F filing where the (CIK, CUSIP) appeared, the shares held, the reported value, the QoQ share delta, and a transaction-type classification. Used by the FinRadar.ai filer-page transaction-timeline chart on the chevron-expanded position row (replaces the placeholder that used to read 'Transaction-timeline chart coming next — needs per-ticker quarterly history endpoint').

Why CUSIP-keyed (not ticker): tickers change. Mergers (SHEN → CALX 2024), spinoffs (GOOG/GOOGL 2014), ticker reuse, and corporate-action chains (SIRI's 2024 reverse split flipped CUSIP 82968B103 → 829933100 mid-quarter) all break ticker-keyed timelines. CUSIPs are the canonical 13F security identifier — frontend rows from GET /api/v1/form-13f/fund/{cik} already carry both cusip and canonicalCusip, pass either back here.

Filing selection per quarter matches GET /api/v1/form-13f/fund/{cik} and CostBasisService exactly — for each period_of_report we pick the filing with the MOST non-option holdings (#264 amendment-handling). So a fund that filed a 36-holding 13F-HR and then a 4-holding 13F-HR/A 'correction' amendment shows the 36-holding original on this endpoint, NOT the 4-holding amendment.

Closed positions appear in the history up through their last reported quarter — once the fund has zero shares of the security, there is no row for subsequent quarters (no synthetic 0-share emit). Frontends rendering the chart should interpret 'no entry for quarter X' as 'position closed before X'; the chart axis can drop to 0 by interpolating. Share counts are SPLIT-ADJUSTED — forward-adjusted to the latest split basis via the split feed (ticker-keyed) so a stock split is NOT mislabelled as a phantom buy/sell; the timeline is continuous and only real trading moves the line. Each row also carries shares_raw (the literal as-filed count), and the response carries top-level split_adjusted + splits[] for reconciliation. value is left raw (13F value = shares × quarter-end price, already split-invariant). If the ticker can't be resolved or the split-feed read fails, the endpoint degrades to raw (unadjusted) shares rather than erroring.