Retain and diagnose recursive graph references across CAS boundaries

[flyingrobots]

Plan: https://github.com/git-stunts/git-warp/blob/plan/streaming-recursive-materialization/docs/plans/streaming-indexed-recursive-warp.md
Design PR: #813

Outcome

Make pinned and live graph attachments honest about retention, garbage collection, trust, encryption, redaction, and cross-repository ownership.

Required work

• Retain pinned child roots through an owned git-cas witness or explicit external-retention contract.
• Resolve live locators under operation-scoped leases without silently retaining history.
• Traverse reference manifests for retention/doctor with cycle detection and bounded work.
• Report retained, externally retained, missing, expired, dangling, redacted, and inaccessible graph references.
• Prevent one repository from silently retaining, repairing, or mutating another repository.
• Carry capability and encryption posture through recursive reads.

Acceptance

• Recursive retention and doctor terminate on cycles.
• Pinned child roots survive ordinary cache/GC lifecycle while owned.
• Released/expired roots become collectible according to policy.
• Cross-repository references never broaden mutation authority.
• Missing/redacted/inaccessible children remain explicit receipt and doctor facts.
• Existing v19 emergency: delegate all CAS and cache ownership to git-cas #734, Move cursor and replay retention to git-cas expiry collections #740, Delegate WARP doctor, retention repair, and usage evidence to git-cas #741, and Enforce the no-CAS-management boundary and reachability proof #742 boundaries remain intact.

[coderabbitai]

🔗 Related PRs

#93 - Fix recursive tree OID read fanout and release v17.0.1 [merged]
#732 - Fix: anchor state-cache payloads against Git GC [merged]
#751 - feat(materialize): add retained CAS materialization handles [merged]
#771 - feat: resume retained materialization predecessors [merged]
#813 - Define streaming indexed recursive WARP architecture [open]

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