fix(desktop): lift right auxiliary pane above shared header backdrop

[wpfleger96]

Summary

The sidebar close (X) and Edit controls disappeared for in-channel side panels on main. They stayed clickable but were visually washed out.

#6901 added isolate to RightAuxiliaryPane so project workspace sheets slide over an open thread cleanly. The pane carries no z-index, so isolating it makes the whole pane subtree paint at stacking level 0 — below the channel's sibling z-30 shared-header backdrop in split layout. That translucent blur strip then washes out the pane's own z-40 header chrome, where X/Edit live. The backdrop is pointer-events-none, so the controls remained clickable but invisible (matching the reported videos). Threads, channel settings, and in-channel agent panels all route through this wrapper, so all three were affected; the standalone Agents-nav panel does not render inside ChannelPane, so it had no backdrop and worked.

Fix

Add z-31 to the pane's aside — above the z-30 backdrop, still below the z-41 thread drawer/sheet overlays. isolate stays, so #6901's sheet-over-thread layering is preserved and both behaviors coexist.

Regression coverage

tests/e2e/auxiliary-pane-close-visibility.spec.ts opens a split-layout thread from inside a channel and asserts the pane establishes its isolate stacking context and that its z-index outranks the shared-header backdrop. It fails on the pre-fix tree (pane z-index is auto) and passes with z-31. #6901's project workspace sheet stays independent from an open thread spec still passes.

[github-actions]

🔐 Codex Security Review

Note: This is an automated, security-focused review generated by Codex.
Use it as a supplement to human review; false positives are possible.

Scope

• Exact PR diff: 80177e4c8e97e7bf1f1a3760c4e3503aace22860...cb559b36c76e04490624523689d2c52ca974d71a
• Model: gpt-5.6-sol

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Review Summary

Overall Risk: NONE

No concrete security, correctness, or reliability findings. The z-index change restores the intended paint order while remaining below focus drawers, global chrome, and modal layers.

Findings

No concrete security, correctness, or reliability findings were identified.

Notes

• Review used read-only inspection; builds and tests were not executed as requested.

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Requested by: @wpfleger96 |
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