fix(codegen): request.security TA expression read at a history offset stays in HTF context - #31

… stays in HTF context

`request.security(tf, ta.<fn>(...)[k], lookahead=...)` — a security expression
that is a TA call read at a history offset — was mis-transpiled. In
security.py::_build_security_expr the `Subscript` branch only handled
`Subscript(Identifier)` (OHLC fields / helper bindings); a `Subscript(FuncCall-TA)`
fell through to the generic chart-context path, which re-lowered the inner TA to
the CHART member and gated a `_hist_call` buffer on `is_first_tick_` (chart tick)
instead of `is_complete` (HTF-bar boundary). Without a magnifier is_first_tick_
is true every bar, so it produced the chart-timeframe TA — the correctly-computed
security value `_secval_*` was discarded.

Mirror the OHLC history-offset machinery (#30) for TA call-sites: declare a
per-(sec, site) `Series<double> {member}_hist`, push the already-committed
`_secval_*` gated on is_complete (so the indicator is not double-stepped), and
read `hist[k-1]` for offset k>=1 (offset 0 reuses the bare `_secval_*`). Handles
scalar, tuple (mixed OHLC+TA), and lower_tf security exprs; cleared in all
clear_security branches. A non-literal TA history index errors loudly.

Regression-safe: when the security tf == chart tf the engine sets is_complete
every bar, so the history advances every bar (identical to chart behaviour);
OHLC `close[1]` stays on the untouched Identifier branch.

officialjackofalltrades-caldera-meridian (htfBasis = ta.ema(close,55)[1] @ "240"):
78.5% -> 97.5% match vs TradingView. 3commas-triple-rsi-dca (ta.rsi(...)[1] in
security): no-trades -> 29% (recovered). quant-synthesis / waranyutrkm unchanged.
Full gate PINEFORGE_ENGINE_INCLUDE=... pytest: 1384 passed, 1 skipped, 0 failed
(incl. 254-strategy corpus compile sweep). New test_request_security_ta_history_offset_uses_htf_gating
has teeth (fails before the fix).

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>