Move all behavioral instructions out of identity.md into SOUL.md so that
each file has a single clear purpose:
- identity.md: capability facts only (runtime, workspace, format hints,
tool guidance, untrusted content warning)
- SOUL.md: behavioral rules (name, personality, execution rules)
The "Act, don't narrate" rule is refined into layered behavior: act
immediately on single-step tasks, plan first for multi-step tasks. This
eliminates the contradiction where identity said "never end with a plan"
but user SOUL.md said "always plan first".