Land T1.24b: part 2, the schema edit semantics in sdm-schema

Part 2 of T1.24b. A core edit_schema operation (contract v17) checks and
applies key, time-column, meaning, column-left-out and relationship
edits as the reference setters do, refusing at the assignment; the
frozen setters only pass an edit to the core and store its answer,
declared allowance under the owner E66(g) approval. schema_edited is the
core own refusal; the bridges refuse no edits. Eight edit cases hold
python-core and rust-host to the reference (fixtures until T1.27 moves
them). A key on a link own foreign key is now refused, as the reference
engine does. E67; P1B-16 and P1B-17 proposed; P1B-14 recommended to the
owner. 2 review rounds (plus part 1), 0 fix rounds.

Candidate run 38259009947 green at
9e3f6c8; this commit changes no file,
so the phase branch moves at once and its own runs are recorded
afterwards (E43 (b)).

Reviewed-by: independent reviewer (fresh agent) and Codex, T1.24b
Protected-paths: contract/case.schema.json; contract/fixtures/edit-cases/README.md; contract/fixtures/edit-cases/edit.accepted-meaning-key-links.json; contract/fixtures/edit-cases/edit.key-missing-column.json; contract/fixtures/edit-cases/edit.key-time-column.json; contract/fixtures/edit-cases/edit.leave-out-the-key.json; contract/fixtures/edit-cases/edit.link-not-the-key.json; contract/fixtures/edit-cases/edit.meaning-not-carried.json; contract/fixtures/edit-cases/edit.meaning-unknown.json; contract/fixtures/edit-cases/edit.time-column-not-a-time.json; contract/fixtures/edit-cases/reference.jsonl; contract/observation.schema.json; contract/pinned/edits.core.json; contract/refusal-maps/keys.json; contract/runners/run_python.py; contract/tests/malformed-cases.json; contract/tests/test_edit_cases.py; contract/tests/test_refusal_map.py; contract/tests/test_runners.py; contract/tests/test_schema_pickles.py; docs/design/rust-core/register.yaml; packages/structured-data-models-client/src/sdm_client/schema.py; packages/structured-data-models-client/tests/test_the_schema_edits.py; rust/crates/sdm-contract/schema/contract.lock; rust/crates/sdm-contract/schema/sdm-contract-16.json; rust/crates/sdm-contract/schema/sdm-contract-17.json; rust/crates/sdm-testkit/src/case.rs; rust/crates/sdm-testkit/src/edits.rs; rust/crates/sdm-testkit/src/host.rs; rust/crates/sdm-testkit/tests/edit_cases.rs; scripts/rust_core/bridge_changes.json; scripts/rust_core/bridge_freeze.json; scripts/rust_core/bridge_freeze.py; scripts/rust_core/compare.py; scripts/rust_core/selftest.py
Base-SHA: 87f1700
Checkpoint-SHA: 87f1700
Signed-off-by: Adi Wadaskar <awadaskar@nvidia.com>

Author: adi-kumo