Fix split-pane pageXof/pageYof crash on 0-coordinate / native event (BL-16584)

[hatton]

Summary

Sentry BLOOM-DESKTOP-FJ0 (pageY, ~3175 events / 17 users, live 6.3.1), -FPW (pageX, ~646/7,
6.3.2), and -DTS (pageY, ~77/9, 6.2.8) are one bug: dragging a pane splitter (origami page
layout) crashed because pageXof/pageYof used event.pageX || event.originalEvent.pageX.
That treats a legitimate 0 coordinate (dragging to the very edge of the page) as missing,
falls through to event.originalEvent, and originalEvent is undefined for a native
(non-jQuery) event — so it crashes dereferencing .pageX/.pageY on undefined.

Fix: check the coordinate for null/undefined instead of falsiness (so 0 is honored),
guard event.originalEvent before dereferencing, and return 0 as a last resort instead of
throwing.

pageXof/pageYof are module-private inner functions in this legacy jQuery-based split-pane
library with no existing test file or test seam for this module — no unit test was added for
this fix.

Fixed by Claude Opus 4.8; this PR (commit, integration, bot gauntlet) run by Claude Sonnet 5
via the preflight skill.

Ref: BL-16584

Devin review

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This change is 

[greptile-apps]

Greptile Summary

This PR fixes a production crash (Sentry BLOOM-DESKTOP-FJ0/FPW/DTS) in the split-pane drag handler. The root cause was event.pageX || event.originalEvent.pageX treating a legitimate coordinate of 0 as falsy and then dereferencing originalEvent, which is undefined for native (non-jQuery) events.

• pageXof and pageYof now use != null to accept 0 as a valid coordinate and guard event.originalEvent before dereferencing it, returning 0 as a safe fallback.
• The change is narrow and self-contained — two four-line functions in a legacy library with a clear, well-commented rationale.

Important Files Changed

Filename	Overview
src/BloomBrowserUI/lib/split-pane/split-pane.ts	Replaces falsy `

_{Reviews (1): Last reviewed commit: "Merge origin/master into BL-16584-sentry..." | Re-trigger Greptile}

[hatton]

[Claude Sonnet 5] Consulted Devin on 2026-07-20 19:45 UTC up to commit e61bc0e — clean, no Bugs or Investigate flags.