Repair the source-topology recovery E2E fixture

[kostyafarber]

Problem

The source-topology recovery E2E fixture mutates the first metric value by array position. That value is now the baseline, whose position must remain zero, so fixture setup fails before recovery behavior is exercised.

Expected outcome

The recovery scenario varies a legal metric selected by semantic identity and continues to prove source topology across undo, redo, crash recovery, save, and reopen.

Acceptance criteria

• The fixture selects the ascender metric by metric kind rather than array position.
• The baseline metric remains at position zero.
• The source-topology recovery scenario passes without weakening metric validation.