_call_fits_incident measured incident idle with the signed helper while every other recency gate in the file uses the unsigned one. On the re-correlation sweep, `now` is the call's own started_at, which can precede the incident's last activity, so the value went negative. Negative idle made `idle_min >= 15` false, which meant the content-divergence veto never ran and unit overlap was accepted unconditionally -- on a shared dispatch backbone that is the feedback loop that lets one incident absorb a whole talkgroup. It also made `idle_min < 20.0` true at any back-dating, so a tactical channel returned tactical_default for every swept orphan out to the 90-minute bound. One variable feeds all four gates in the function, so this is a one-line change at the source. The signed value is untouched where it belongs: callers still compute corr_incident_idle_min themselves, so debug output keeps its meaning. Direction is toward more splitting, on the sweep path only, which is the point -- the bug was suppressing an over-merge veto. Forward-dated calls and anything inside the thresholds behave exactly as before. Two tests added alongside the existing idle-gate cases; both fail on the old line and pass on the new one. 266 pass, 0 fail. Refs server-26#74, #5, #80. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>