- core-data-structures/core.md: the `agent/*` taxonomy said "turn/step
boundaries", but the step-boundary mirror emits were dropped — `agent/*`
mirrors only turn boundaries; step boundaries are durable `step/start`/
`step/end` session events. Narrow the catalog so plugin authors aren't pointed
at nonexistent `agent/*` step events.
- interception-seams RFC: replace stack-position phrasing ("a later stack PR",
"the stack's first change", "the PR that makes...") with durable mechanism/RFC
names (the hook bridge packages, the event-domain-semantics RFC).
- tools/post-execute snapshot: `dispatched.content` was the same array reference
as `result.content`, so a listener's in-place `push`/`splice` leaked into the
returned content while a reassignment was masked — the "protect from tampering"
comment over-claimed. Copy content into a fresh array so the snapshot guards
the array structure; comment now states it is not deep immutability. Regression
extended to push a block in-place and assert it does not leak (proven red
without the copy).