Adds a TDD issue-capture test for bug #10395. The
_estimate_token_usage() method in LangChainChatProvider contains a
bare except Exception: return 0 block that silently swallows any
exception raised by the LLM's get_num_tokens() call, returning 0
instead of propagating the error. Downstream cost tracking then
records zero tokens, producing inaccurate cost estimates with no
visible error signal to the caller or operator.
The new Behave scenario in
features/tdd_langchain_token_count_silent_failure.feature is tagged
@tdd_issue, @tdd_issue_10395, and @tdd_expected_fail. The assertion
fails against the current unfixed code (confirming the bug exists),
and the @tdd_expected_fail tag inverts the result so CI reports the
scenario as passed until the fix is merged.
ISSUES CLOSED: #10395
HAL9000