count_unemitted_tool_calls

Classify buffered tool calls that never emitted a tool.use.

Both surfaces log the same end-of-stream diagnostic for tool calls still in their buffer map when the stream ends: those whose args never parsed, and those whose args parsed but whose tool_id stayed None (so tool.use was gated out). Sharing the classification here keeps the two diagnostics from drifting; each surface still emits its own log lines.

parse_args is safe to re-run: a re-run populates the incremental scan and the join/parse memos but returns the same value, and its one-shot warned latch fires at most once per payload. Only the log line is suppressed on a repeat; the classification below is unaffected either way, since a warned payload counts as unparsed however often it is re-read.