SRD Casting Time: a spell that takes 1 round is a full-round action
that comes into effect just before the caster's turn in the next round;
the caster then acts normally. _cast_spell now spends the slot and runs
the start-of-casting gates, then records a PendingCast (spell, target,
center, metamagic, slot level, hp at cast); delivery (touch attack, SR,
saves, effects) resolves at the start of the caster's next turn, before
the policy runs. Net hp lost in between forces the injured-while-casting
concentration check (DC 10 + damage + spell level, no Combat Casting) or
the spell fizzles; a caster knocked out of the fight loses it. Exposed
in the observation via pending_cast. Bounded model documented: net-hp
measurement instead of a per-damage-site hook; long (1 minute+) casting
stays out of scope.
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
