Codex gate on #6312 found the extracted helper caught only (TypeError, ValueError)
while the inline code it replaced caught Exception; float(10**400) raises
OverflowError, escaping the helper and aborting terminal-error cleanup before the
error message is persisted / apperror is emitted. Widen _terminal_turn_duration's
float() guard to (TypeError, ValueError, OverflowError) — the exact exceptions
float() can raise. Adds 10**400 to the existing invalid-origin parametrize
(red-before-green verified).
Extract _build_partial_message() shared by cancel_stream() and the new
_snapshot_and_append_partial_on_error(); the two provider/exception error paths
in _run_agent_streaming now snapshot accumulated text/reasoning/tool_calls under
STREAMS_LOCK and append a _partial assistant message instead of discarding it.
Closes#3929.
Co-authored-by: b3nw <150195942+b3nw@users.noreply.github.com>
