feat: trace annotation body for traced citations; paperspec.traces

A trace follows one citation of a sentence of a citing paper to a passage of the
cited paper (spec/18 section 18.5). Minor change: a new body kind, optional
properties and two rules, with no valid file made invalid.

- annotation schema branch (source, selector, reference, note, verdict, proposer;
  proposer required for a Software creator); body_kind in sql/store.sql; the note
  and proposer terms of the JSON-LD context; rules layer.trace.source and
  layer.trace.target.
- paperspec.traces: resolve(annotation, citing_state, cited_state, same_as) gives
  current, changed, stale, unlinked or misresolved with open and cites; problems,
  disputes, disputed.
- fixtures/records/traces/ on writer2027fixed-ynr7.v3 and vectors/traces.jsonl
  (29 cases); check.py runs the record checks over both layers; counts, glossary,
  examples and CHANGELOG updated.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Uy4ZYbWRoCdUtWLEfigysY

spec/22-conformance.md

@@ -6,7 +6,7 @@
 | --- | --- | --- |
 | `vectors/*.jsonl` | Inputs and expected outputs, one case per line. | Computes every expected output from its input. |
 | `fixtures/packages/` | Valid packages: a converted chemistry paper with corrections, receipts, a multi-level-header table and a dataset; its checks-only export; an open-access paper with two witnesses; a Typst draft; a tiny document, as a folder and as the zip of [12.2](12-package.md#122-paths). | Accepts each, and recomputes every value it contains. |
-| `fixtures/records/` | A valid record of every other format that is a JSON file of its own; the stage requirements and stamp rules are in `registry/`, and a bundle is built by `paperspec load --bundle`. | Accepts each. |
+| `fixtures/records/` | A valid record of every other format that is a JSON file of its own, and a second layer, of traced citations ([18.5](18-layers.md#185-traced-citations)), whose traces resolve as `vectors/traces.jsonl` says; the stage requirements and stamp rules are in `registry/`, and a bundle is built by `paperspec load --bundle`. | Accepts each. |
 | `fixtures/invalid/` | Invalid packages, each with `expect.json` naming the rule it breaks. | Refuses each, and SHOULD name that rule. |
 | `fixtures/keys/` | The test keys that signed the fixtures and the team secret of the checks-only export. | Never uses them for anything else. |
 
@@ -49,6 +49,10 @@ Rule IDs are stable: a rule's meaning never changes, and a retired rule's ID is
 | `doc.receipt.`, `doc.qa.`, `doc.fidelity.` | Receipts, spot-checks and levels. |
 | `doc.witness.`, `doc.page.`, `doc.location.`, `doc.reference.` | Witnesses and geometry. |
 | `grade.` | Grading. |
+| `layer.` | Annotations that refer to documents: `layer.trace.source` and `layer.trace.target` ([18.5](18-layers.md#185-traced-citations)). |
+
+A package is validated by [22.2](#222-validating-a-package), but a layer is not part of one.
+The `layer.` rules are reported for an annotation, in the form `annotation: rule: message`, by a validator that has the annotation and the states of the documents it names; the reference implementation does so for traces in `paperspec.traces.problems`.
 
 ## 22.5 Stability