Atlas was the only agent that bailed early (returning undefined) when
applyModelResolution returned undefined, even if the user had explicitly
configured agents.atlas.model. The general-agents.ts path already handled
this case by falling back to the user's override; sisyphus has its own
explicit-config check. Atlas had neither, so under edge cases (cold
provider cache, no system default, empty availableModels) Atlas was
silently dropped and OpenCode used its built-in default — surfaced as
the hardcoded claude-sonnet-4-6 in the reported bug.
This aligns atlas-agent.ts with the same defensive pattern used in
general-agents.ts: when resolution fails but the user has an explicit
model override, honor it directly instead of dropping the agent.
Adds a regression test covering the scenario where availableModels is
empty AND systemDefaultModel is undefined AND no provider cache exists.
bellman
7d444eed5e