Thanks for the fix, @LeonSGP43! This change has already landed on main — the commit was applied directly to the branch.

Automated hermes-sweeper review.

• The defensive getattr(self, '_fallback_chain', []) or [] is at run_agent.py:2201 (commit a9fd8d7).
• The regression test test_switch_initializes_missing_fallback_attrs is present in tests/run_agent/test_switch_model_fallback_prune.py lines 81–90, identical to the test in this PR.
• The diff from gh pr diff 14867 matches the committed patch byte-for-byte.

Closing as implemented on main.