Fix vehicle unseating on region crossings by ignoring outgoing sim kills

[Shadowolf7]

Description

This PR resolves the long-standing bug where avatars are forcibly unseated from vehicles during region crossings.

Root Cause

During a region crossing:

1. The avatar and vehicle cross into the receiving simulator, and the viewer sets its active agent region to the new simulator.
2. The outgoing simulator (lagging by 0–1s) cleans up its local physics representation of the vehicle and sends a UDP KillObject packet to the client.
3. Because the client did not differentiate between an active-region object deletion and an outgoing-simulator crossing cleanup, process_kill_object called markDead() on the vehicle prim.
4. In LLViewerObject::markDead(), lines 480-489 detected the seated avatar and executed ((LLVOAvatar*)childp)->getOffObject(), prematurely severing the sit link on the client side before the receiving simulator's ObjectUpdate took over.

Solution

In process_kill_object (indra/newview/llviewermessage.cpp), we check if a kill packet for the avatar's seated root object originates from a non-active (outgoing) region (regionp != gAgent.getRegion()). If so, the cleanup packet is ignored, keeping the vehicle and seated avatar intact across the boundary handoff.

Actual vehicle deletions (e.g. parcel auto-return, hard banlines, llDie()) sent by the active simulator (regionp == gAgent.getRegion()) continue to execute normally.

Verification

• Tested in-world across 16+ region crossings with multiple vehicles.
• Confirmed zero markDead() unseat ejections.
• Maintained continuous, uninterrupted seating through multiple consecutive border crossings.

[github-actions]

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[Copilot]

Pull request overview

This PR addresses viewer-side unseating during region crossings by ignoring KillObject packets coming from the outgoing (non-active) simulator when they target the seated vehicle root, preventing premature markDead() unseat behavior during the handoff.

Changes:

• Add a guard in process_kill_object to ignore KillObject messages from non-active regions when they target the agent’s seated root object.
• Emit an informational log when such a kill is ignored.

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[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 1 comment.

Suppressed comments (1)

indra/newview/llviewermessage.cpp:3685

• This compares the sender with gAgent.getRegion(), but the ordinary crossing path does not update that pointer: process_crossed_region() only adds the destination region, and the crossing branch of process_agent_movement_complete() does not call gAgent.setRegion(). After the seated linkset has been updated into the destination, a legitimate KillObject from that active simulator can therefore satisfy this condition and be skipped, leaving the object (and its cache/selection state) alive. Compare against the seated root's current object region, or update the agent region as part of the crossing before applying this filter.

            if ( regionp && (regionp != gAgent.getRegion()) &&
                 isAgentAvatarValid() && gAgentAvatarp->isSitting() )
            {
                LLViewerObject* rootp = objectp->getRootEdit();
                if (rootp && (gAgentAvatarp->getRoot() == rootp))