Tests that mock an AgentFactory were using an `as AgentFactory` cast
and a separate mutation of `mockFactory.mode` to satisfy the type.
Replace with Object.assign so the factory type is constructed correctly
without casts. Also type the empty discoveredSkills fixture so its
element type is inferred from the function signature instead of
collapsing to never[].
OpenCode Desktop 1.14.x filters agents by `mode` field. The `mode` was
only present on the factory function as a static property, but not copied
to the generated AgentConfig object.
This fix copies `source.mode` to `base.mode` in `buildAgent()` when:
- source is a factory function (has `mode` static property)
- the generated config doesn't already define `mode`
Test: agent-builder.test.ts (4 pass)
Closes: #3835
Related: #3762, #3812, #3794, #3475, #3474, #3829, #3831, #3824, #3826, #3721, #3806, #3188
YeonGyu-Kim