docs(spec): a missing master row of a controlled_by_parent master is the master_chain leg, on the first hop or above it

The record_not_found bullet of ControlledByParentWriteUnresolvedReason said the
legs judge a missing master row on the first hop and only above it is it the
master_chain leg. The walk reads a controlled_by_parent master's row after the
legs on every iteration, the first included, so an absent row there answers
master_chain. The changeset names the sentence.

Claude-Session: https://claude.ai/code/session_01KNKBCRDJCu5tGy3TEbvtrF
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

.changeset/22497-master-chain-docblock.md

@@ -3,11 +3,11 @@
 '@objectstack/plugin-sharing': patch
 ---
 
-docs: three contract docblocks now describe what the code decides. No type, schema or runtime change.
+docs: four contract docblocks now describe what the code decides. No type, schema or runtime change.
 
 Clause-②: no
 
-- **`ControlledByParentWriteDenialLeg` (`@objectstack/spec`).** The `master_chain` leg has three resolution refusals: no relation to derive from, a row that is not present, and an empty master reference. Each names the master whose own master the walk could not derive. That master is the record's own master, when it is itself `controlled_by_parent`, or any master above it. The docblock said only a master above the record's own master. The next sentence now says "past the record itself" where it said "above the first hop", so the two agree.
+- **`ControlledByParentWriteDenialLeg` (`@objectstack/spec`).** The `master_chain` leg has three resolution refusals: no relation to derive from, a row that is not present, and an empty master reference. Each names the master whose own master the walk could not derive. That master is the record's own master, when it is itself `controlled_by_parent`, or any master above it. The docblock said only a master above the record's own master. The next sentence now says "past the record itself" where it said "above the first hop", so the two agree. The `record_not_found` bullet of `ControlledByParentWriteUnresolvedReason` had the same first-hop gap for a missing master row: it now says an absent row of a master that is itself `controlled_by_parent` is the `master_chain` leg, on the first hop or above it, and the legs judge a missing row only where the master governs its own rows.
 - **`ISharingService.canEdit` (`@objectstack/spec`) and `SharingService.canEdit` (`@objectstack/plugin-sharing`).** The caller lists no longer name the `sys_attachment` and `sys_comment` parent gates. Those gates read `checkEdit` and the master-detail write check. The `ISharingService.canEdit` sentence on how they reach the service now names `checkEdit`.
 
 `ControlledByParentWriteDenialLeg`, `ControlledByParentWriteOutcome`, `canEdit` and `checkEdit` keep their declared shapes, and no verdict, outcome or refusal changes.

packages/spec/src/contracts/security-service.ts

@@ -340,9 +340,11 @@ export type ControlledByParentWriteDenialLeg =
  *   defect (`422 INVALID_METADATA`).
  * - `record_not_found`: the record `(object, recordId)` does not exist
  *   (`404 RECORD_NOT_FOUND`). This is the addressed record, not its master. A
- *   missing master row is not one of these outcomes: on the first hop the legs
- *   judge it as they judge any master row, and above the first hop it is the
- *   `master_chain` leg.
+ *   missing master row is not one of these outcomes: where the master governs
+ *   its own rows the legs judge it as they judge any master row, and where it
+ *   is itself `controlled_by_parent` the walk reads that row to derive the next
+ *   master, so an absent row after the legs is the `master_chain` leg, on the
+ *   first hop or above it.
  * - `master_reference_missing`: the record's stored master reference is empty
  *   (`422 MISSING_REQUIRED_FIELD`).
  */