TUI auto-resolves `display.personality` at session init, unlike the base CLI.
If config contains `agent.personalities: null`, `_resolve_personality_prompt`
called `.get()` on None and failed before model/provider selection.
Normalize null personalities to `{}` and surface a targeted config warning.
Tolerating null top-level keys silently drops user settings (e.g.
`agent.system_prompt` next to a bare `agent:` line is gone). Probe at
session create, log via `logger.warning`, and surface in the boot info
under `config_warning` — rendered in the TUI feed alongside the existing
`credential_warning` banner.
YAML parses bare keys like `agent:` or `display:` as None. `dict.get(key, {})`
returns that None instead of the default (defaults only fire on missing keys),
so every `cfg.get("agent", {}).get(...)` chain in tui_gateway/server.py
crashed agent init with `'NoneType' object has no attribute 'get'`.
Guard all 21 sites with `(cfg.get(X) or {})`. Regression test covers the
null-section init path reported on Twitter against the new TUI.
_make_agent() was not calling resolve_runtime_provider(), so bare-slug
models (e.g. 'claude-opus-4-6' with provider: anthropic) left provider,
base_url, and api_key empty in AIAgent — causing HTTP 404 at
api.anthropic.com.
Now mirrors cli.py: calls resolve_runtime_provider(requested=None) and
forwards all 7 resolved fields to AIAgent.
Adds regression test.
