Responding to ds-review-bot on #664 (root cause lives here): when a history
window carries a tool/code-dispatch settle without its paired start, the
runtime fabricated callTime = settle time, so downstream duration views
presented a measured 0 ms. Match the native tool-result contract instead —
callTime: null = unknown — and pin it; the trajectory cell already renders
null as the em dash, and the waterfall gains explicit unknown handling in
its own PR.
Tianyi Cui
3e1a22eb2b