## Why
App-server initialization captures exec-policy parse warnings only once.
Each `thread/start` then reloads config for that thread's cwd and
rereads its `.rules` files, so rules that become malformed after
initialization—or belong to a different project—are dropped without a
fresh warning to the requesting client.
## What changed
- Validate exec-policy rules against the freshly loaded per-thread
config during `thread/start`.
- Send the existing structured `configWarning` only to the connection
that requested the thread.
- Preserve nonfatal startup and avoid repeating an identical warning
already delivered during initialization.
This is intentionally separate from the TUI `legacy_core` cleanup in
#31179 and the managed-requirements fallback fix in #31188.