`group_blast_radius`'s `app_chain` up-walk is depth-capped (`ac.depth < 64`,
added by 76926de to stop a should-be-impossible `groups.parent_id` cycle from
spinning the recursive CTE forever), but the sibling `subtree` down-walk in the
same query was left unbounded. A `parent_id` cycle would loop `subtree`
indefinitely and hang the plan — the exact exposure 76926de set out to close,
left half-done on the descendant side.
Add a `depth` column + `WHERE s.depth < 64` to `subtree`, mirroring `app_chain`.
Defense-in-depth: the reparent cycle-guard already prevents `parent_id` cycles,
so this hardens against an unreachable state — but that is precisely the bar
76926de applied. Surfaced by a post-adoption audit of the §7/§6 ownership code.
Verified: 416 manager-core lib tests; 12 ownership/create/divergence/approval
journeys (incl. plan_previews_ownership_and_blast_radius, which drives this
query); clippy -D warnings + fmt clean.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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