chore(sync): gate registry_ref materialize (Spec 520 Phase A)

[enricopiovesan]

Summary

Phase A for retire-registry-ref-materialize: gate sync_bundle_materialize_registry_refs behind APP_REFS_MATERIALIZE_REGISTRY_REFS (default on), add a no-Traverse-repo gate test, and document why full deletion is still blocked (Traverse web BundleEmbedder still requires wasm_binary_path; native Spec 107 adopt incomplete). Spec 520 implement (#860) is closed; App-Refs cannot yet drop the rewrite for primary shells.

Governing Spec

• Traverse Spec 520 / ADR-0041 embedded registry cache
• docs/production-packaging.md registry_ref consumer contract
• Project 2 ticket retire-registry-ref-materialize

Project Item

• Ticket ID: retire-registry-ref-materialize
• Item: PVTI_lADOEbiBt84BbzAzzg0cpsg
• Status: In Progress (Cursor) — Phase A only

Definition of Done

• Materialize gated (default on; off preserves registry_ref)
• Gate test without TRAVERSE_REPO example trees
• Docs + AGENTS start-plan updated with honest remaining blockers
• Primary shells load without materialize (blocked on Traverse BundleEmbedder + Spec 107)
• Delete materialize helper entirely (follow-up)

Validation

• bash scripts/ci/repository_checks.sh
• bash scripts/ci/sync_bundle_materialize_registry_refs_gate_test.sh

Checklist

Traceability

• Project 2 ticket updated (Agent + Status); Ticket ID cited above
• Updated AGENTS.md / packaging docs for shipping status
• Blocked remaining work called out (Traverse BundleEmbedder / Spec 107)

Production baseline (platform / runtime-client PRs)

• Embedded mode — unchanged; default materialize keeps current production path
• Digest pin / sync — gate documented in docs/runtime-bundle-sync.md / docs/production-packaging.md
• SDK test doubles — N/A (sync/docs only)
• Docs touchpoints — packaging + sync docs updated
• CI commands — listed under Validation

Architecture

• No business logic added to UI layer
• No private Traverse internals imported
• CI gates pass locally where applicable

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