Replaces manual isinstance/<=0 checks in calculate_spread_ratio() and
determine_order_limits() with _valid_tick_price(), ensuring NaN, inf,
-inf, zero, negative, bool, and invalid-string tick values are
consistently rejected across all trading helpers.
Adds regression tests covering numeric-string acceptance and every
invalid-value category for both functions.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Add _valid_tick_price() internal helper that returns a positive finite float
from a tick dict or None for any invalid value (missing, None, NaN, infinite,
zero, negative, or unsupported type). Refactor five existing bid/ask validation
sites in trading.py to use it, removing duplicated isinstance/isfinite checks.
Add calculate_positions_margin_by_symbol() which computes margin per unique
symbol independently using the existing strict calculate_positions_margin(),
with first-seen deduplication and configurable error suppression
(Mt5TradingError, Mt5RuntimeError, AttributeError) via suppress_errors=.
Add calculate_positions_margin_safe() as a thin sum wrapper with
suppress_errors=True, returning 0.0 on empty or fully-failed inputs.
Both new helpers are exported from mt5cli, added to STABLE_SDK_EXPORTS, and
documented in docs/api/public-contract.md. Existing strict behavior of
calculate_positions_margin() is unchanged.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
