§6/§7 M2: a project's attach point is its ceiling — applies are refused for
any node not strictly within the declared subtree, so a repo can't reach (or
claim) above its local root even with the RBAC to do so.
- `[project] parent_group = "<slug>"` (ManifestProject + ProjectDecl); absent
= instance root = no ceiling (the default, backward-compatible).
- `check_within_attach`: the attach group must be a PROPER ancestor of a group
node (you can't apply the attach point itself) or an ancestor (inclusive) of
an app node's group; resolved via `groups.ancestors`. Enforced read-only in
apply_owner (prologue) + apply_tree (per node), before the claim.
- `ApplyError::OutsideAttachPoint` → 422 (a scope error, like Invalid).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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