Engine crash: index out of bounds: the len is 0 but the index is 0

[grizzlybrodams]

What happened
briefly describe what you were doing

Diagnostic

Build: v0.48.0 (aa970cc)
Diagnostic tag: submitAction-panic
Game id: 2429a939-89a9-4719-8007-bf6a4ce02d76
Game mode: ai
User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/151.0.0.0 Safari/537.36

Panic:
panicked at crates/engine/src/ai_support/combat_withdrawal.rs:191:36: index out of bounds: the len is 0 but the index is 0

[mike-theDude]

Triage analysis

Clarified summary
AI combat withdrawal panics when its candidate member list is empty.

Expected behavior
An empty candidate list returns no single member and is handled without indexing.

Observed behavior
The helper evaluates members[0] even when len() == 0, causing the reported bounds panic.

Reproduction status
The diagnostic names the exact source location. Current origin/main uses eager then_some(members[0]), which proves the empty-list panic is reachable from that call.

Investigation findings
This is a localized Rust evaluation-order bug rather than insufficient reporter detail.

Likely scope
Engine AI combat-withdrawal candidate handling.

Acceptance criteria

• Empty and multi-member inputs return None without indexing.
• A one-member input returns that member.
• The reported AI action path no longer panics.

Related issues
No exact duplicate was found.

[matthewevans]

Fixed on main by #7270 (c22f9c08c6): the helper now pattern-matches [member], so empty and multi-member slices return None without indexing; its regression covers all three cardinalities.