Design recursive owned JSON records

[sanohiro]

Summary

• accept Request 13's closed, acyclic recursive owned-record grammar for json.decode, json.encode, and json.encode_bounded, with a 128-constructor-depth limit and one free-standing ownership model
• replace flat V1 descriptors atomically with the target-bound OwnedJsonGraphDescV2/OwnedJsonInterfaceEnvelopeV2 design and interface format 8, without adding a runtime ABI symbol or parallel route
• pin the complete C6 provenance and authoritative 50-record/543-field Align manifest, including exact field order, owned text mapping, and the seven-field C6b-memory ContextPolicy
• define deterministic validation, allocation, cleanup, cache/interface identity, runtime table use, and the cross-layer implementation closure matrix

Review finding closure

• materialize the complete C6 field/type/order graph locally, add the missing PromptEvaluationTask/RegressionLimits closure, and resolve the sibling specification's two incompatible ContextPolicy forms
• synchronize Request 9's shipped ABI inventory to 294 keyed, 307 base, 311 single-probe, and 315 maximum exports in the ledger and machine owners
• synchronize the native-boundary plan with accepted Request 13 while retaining flat Request 9 behavior until V2 implementation lands

Verification

• git diff --check
• scripts/cargo.sh test -p align_driver --test m5_owned_json
• scripts/cargo.sh test -p align_runtime runtime_export_source_inventory_matches_registry
• scripts/cargo.sh test -p align_codegen_llvm runtime_abi_registry_is_complete_and_unique
• bash scripts/test-runtime-abi-exports.sh
• scripts/pre-pr.sh with the Request 13 owned-JSON compatibility owner, bounded gate, and locked workspace Clippy