Greptile Summary

This PR fixes a UI regression on the /agents page where editing a non-default agent and saving config would silently reset the selection back to the default agent. The fix expands the onConfigSave handler in app-render.ts to capture the selected agent ID before the save, explicitly refresh the agents list after the save, and restore the selection if the agent still exists in the refreshed list.

Key changes:

• onConfigSave in app-render.ts is now async, and explicitly calls await loadAgents(state) after await saveConfig(state) — without this, no agents-list refresh was triggered on save, leaving the UI out of sync.
• A post-loadAgents restoration block re-applies state.agentsSelectedId = selectedBefore when the agent still exists. This acts as a safety net against a gateway reconnect triggered mid-saveConfig that could asynchronously null out agentsSelectedId before loadAgents runs — a window that loadAgents's own preservation logic cannot protect against once the reset has already occurred.
• Three new unit tests are added for loadAgents documenting the selection-preservation, reset-to-default, and no-prior-selection behaviours that the fix depends on. The tests correctly exercise the underlying controller function in isolation.

Confidence Score: 5/5

• This PR is safe to merge — the change is narrow, well-motivated, and backed by targeted tests.
• The fix correctly addresses the root cause (missing loadAgents call after saveConfig on the agents page) and mirrors the same pattern used by handleChannelConfigSave. Both saveConfig and loadAgents handle errors internally, so no try/catch is needed in the handler. The post-loadAgents restoration block is technically redundant in the common case (since loadAgents already preserves the selection), but provides legitimate defence against async reconnect-driven state resets. Tests cover all three meaningful loadAgents selection scenarios. No unintended side effects are introduced.
• No files require special attention.

_{Last reviewed commit: cb44463}

Rebased onto the latest main, deep-reviewed, and landed.

What changed on top of the original PR:

• moved the agents-page save/reload/selection-restore path into the agents controller for tighter test coverage
• added controller regressions covering both restore-after-save and fallback-to-default when the edited agent disappears
• updated CHANGELOG.md
• ran pnpm lint, pnpm build, and pnpm test on the rebased landing commit

Landed commit: c0a7c30
Source commit: 0448f39

Thanks @MumuTW.