Source-7 constructor omission compatibility

Codex-9e8r6t /root/release_audit, 2026-09-11. This records existing behavior, not a grammar/schema change.

An independent matching-core probe passed 54 accepted explicit/omitted comparisons and 12 missing-required-field refusals across OA and SA source 7. Exact typed body/full Project, canonical reparse, raw stabilization/no-op and name-only source preservation are checked. Nullable occurrence references default to None when omitted. Exchange also defaults message_kind to Asynchronous, values to [], and reply_to/operation to None. ScenarioUse.bindings, Control.kind, Fragment.operator/branches and Branch.guard/occurrences remain required.

Canonical output writes hydrated references and Exchange kind/reply/values, but skips operation=None. Lossless no-op/name editing retains authored omissions. Fresh source-7 Scenario viewpoint omission means MixedLegacy in both layers, equal to explicit MixedLegacy; it does not infer a strict layer viewpoint. Incomplete admitted occurrences may still receive model-check warnings.

The former all-constructor-fields-required/schema-2-only wording contradicted these results. Targeted docs/language.rst paragraphs/table are corrected; root owns HTML regeneration/publication. Other constructor families and older schema versions were not exhaustively audited, and must not inherit defaults from this table by assumption.

Reproducible evidence: harness/experiments/constructor-defaults-20260911/probe.rs, README, results/results.tsv, 120 source/canonical fixtures and provenance.json. Report: harness/release-constructor-defaults-review-20260911.md. Core rlib SHA5018A1FD7286ED9DFEDCBBF5B68B399AD5D143F2A9AAAED3078CFC934C9589C4; probe SHA FAA1A98BEA7A87E24047991D72A54919AE9C66F84B6EB465E24B13FDC82EE040; results TSV SHA2C1BB97234EDFAC386A5DDCA46C28B5B46972CC879B7CC2B1C4179066BAB8AEF. No production Rust, Cargo, native or language semantics changes were made.