Clear the deferred full-repo lint backlog so the whole tree passes the strict
ruff select (E,W,F,I,B,UP,C4,SIM). Mechanical fixes dominate: import sorting,
pep585/604 annotations, dropped dead imports, and whitespace. The few semantic
changes are behavior-preserving: declare __all__ on the agent_utils and
alpha_vantage re-export hubs; expand 'from x import *' to explicit names; use
immutable tuple defaults instead of mutable list defaults; contextlib.suppress
for try/except/pass; and narrow an over-broad assertRaises.
The yfinance news date filter only ran when an article had a parsed date, so
flat-format and undated articles bypassed it and leaked future news into
historical/backtest runs. Parse the flat providerPublishTime, apply one
look-ahead-safe window rule across ticker and global news (undated kept only
when the window reaches the present), and return an informative message when
everything is filtered out.
