fix: apply moa switches to live tui agent

[itsflownium]

Problem
TUI/Desktop /moa updated the session model override, but it did not switch the already-running session agent. That meant /moa could show the queued notice while the next turn still ran on the previous single provider.

Summary

• Add a MoA live-switch helper for the known virtual-provider runtime values.
• Apply the helper for preset switches and one-shot MoA prompts.
• Restore both the session override and the live agent after one-shot prompts, including cleanup paths.
• Extend command-dispatch tests to assert the live agent actually switches and restores.

Validation

• $HOME/.hermes/hermes-agent/venv/bin/python -m pytest -q tests/tui_gateway/test_goal_command.py
• $HOME/.hermes/hermes-agent/venv/bin/python -m pytest -q tests/tui_gateway/test_goal_command.py -k moa
• $HOME/.hermes/hermes-agent/venv/bin/ruff check tui_gateway/server.py tests/tui_gateway/test_goal_command.py
• git diff --check

Fixes #53444

[tonydwb]

Code Review Summary

Verdict: Approved

Applies MoA (Mixture of Agents) model switches live to the TUI agent via _apply_live_model_override(). Includes proper restore logic for one-shot MoA via _restore_moa_one_shot() with fallback on failure. Well-tested with _FakeAgent mock and dedicated tests for both preset and one-shot paths.

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Reviewed by Hermes Agent

[teknium1]

Superseded by #53548 (merged to main as 50f68552), which fixes the same #53444 bug — the TUI /moa one-shot set session["model_override"] but never switched the already-built cached agent, so the turn silently ran on the previous model. #53548 now does a real in-place agent.switch_model() via _apply_model_switch() for the one-shot (with restore after the turn), and falls back to a model_override for lazy/unbuilt sessions.

One deliberate difference: your PR also keeps the sticky preset-switch path (/moa <preset> switches the session). We removed that on purpose in #53548 — /moa is now one-shot-only sugar, and switching to a MoA preset for the session is done through the model picker, where presets surface under a virtual Mixture of Agents provider. So re-adding the live switch for the sticky path would reintroduce behavior we just retired.

Thanks for the fix and the clear root-cause writeup — you diagnosed the cached-agent issue exactly right, same as the merged change. Closing as superseded.