Sums a numeric dotted-path field across events — e.g. opencode emits one
step_finish per agent turn, each carrying that turn's own cost/tokens,
not a running total, so a multi-turn dispatch (any real tool use) needs
every matching line added together. Returns null iff the path itself
is unset, or no event had a numeric value there — distinct from a real
measured 0.
Sums a numeric dotted-path field across events — e.g. opencode emits one
step_finishper agent turn, each carrying that turn's own cost/tokens, not a running total, so a multi-turn dispatch (any real tool use) needs every matching line added together. Returnsnulliff the path itself is unset, or no event had a numeric value there — distinct from a real measured 0.