fix: prevent overlapping orgs from splitting inferred stints (CM-1143)

[skwowet]

Summary

This PR fixes a stint-inference bug in the email-domain cron flow that could generate many one-day memberOrganizations rows for the same (member, organization).

The root cause was the multi-stint guard: it treated any long overlap from another org as a break, which made the job insert new stints repeatedly instead of extending the existing one.

The logic now treats another org as a separator only when one of its date boundaries falls between the nearest same-org stint and the incoming activity date. Fully overlapping/concurrent rows stay on the normal debounce/extend path. This preserves intended multi-stint behavior (A → B → A) while preventing overlap-driven row explosion.

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Note

Medium Risk
Changes stint-inference splitting logic, which can affect how memberOrganizations rows are inserted/extended and therefore impacts historical data shape. While scoped to a small block, edge cases in date-boundary detection could still alter multi-stint outcomes.

Overview
Prevents inferred memberOrganizations stints from being split just because another organization has a long overlapping stint.

Replaces the previous “gap overlap” conflict check with a stricter separator rule that only starts a new stint when another org’s dateStart/dateEnd falls between the nearest same-org stint and the incoming targetDate; otherwise the existing stint continues to use the normal debounce/extend path.

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[Copilot]

Pull request overview

This PR updates the email-domain member-organization stint inference logic to avoid splitting stints when another organization merely overlaps concurrently, which fits the cron-based affiliation inference flow in common_services and the cron worker that applies those inferred changes.

Changes:

• Replaced the old overlap-based “conflict” check with a narrower “separator” check.
• Kept the existing debounce/extend behavior when no separator is detected.
• Clarified the inline comments around multi-stint splitting behavior.

Findings:

• The new separator predicate is too narrow and misses A → B → A cases where the middle org overlaps the edge of the first/last A stint before occupying the gap. In those cases the code now merges the two A periods instead of starting a new stint.

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