feat: zipped packages, target set, checklists, audit fixes and a stress test

Features for the next six months (accessible HTML export, paperpack and
Lode on packages, the personal bundle):

- Zipped packages: the oracle writes and reads `.sct.zip` archives under
  the rules of spec/12 §12.2; validate.py and load.py accept them; a
  byte-identical zip of the tiny package joins the fixtures, and two
  broken archives (traversal, symbolic link) join fixtures/invalid.
- The target set of targeted F3 (spec/08 §8.10) is computed by the
  oracle and pinned by vectors/targets.jsonl under each digit rule; the
  rule now covers cells as well as sentences and the leaves of anchored
  containers, and defines a node's section.
- scienting-checklist/1 (provisional): a conformance check of an export,
  covered by a receipt as ["checklist", id, hash] (spec/08 §8.11), with a
  WCAG 2.1 AA fixture and its receipt.
- QA reports are signed like receipts (spec/08 §8.9).
- A `description` annotation body with role alt or long, so an
  accessible export can find a confirmed figure description; the layer
  fixture carries one, and the store's body-kind constraint allows it.
- scienting-spot-check/1, the seed payload, is registered with a schema.
- exercise, submission and grade are provisional until a course has
  used them.

Audit fixes, each with a vector or a broken package where one was
missing:

- Folder packages: symbolic links are refused on validate and load,
  manifest paths must not collide under case folding, listed files are
  matched by exact name, files are hashed in chunks under a size limit.
- Files are compared byte for byte, so CR LF, a byte order mark, NaN,
  a lone surrogate or invalid UTF-8 is refused instead of translated;
  integers beyond 2^53 are read as doubles, as canonical JSON writes them.
- Receipts: signature.key must equal by and the key must be valid when
  signed; a qa receipt's nodes must be the sample at the original's
  hashes, its scope must name qa.of, its errors must be sampled nodes;
  statuses are computed once, iteratively, so chains of spot-checks
  hundreds deep settle; Base64 and manifest shape errors become refusals
  instead of tracebacks; counts and the fidelity of roster-less packages
  are recomputed.
- The gate enforces rule 11 of spec/11 §11.4: changed nodes are
  validated against the node schema and the references between nodes
  are checked, so a set to a bad value, an insert with unknown
  properties or a delete of a referenced header cell is refused; a
  relabel to null drops the label; a reclassify drops foreign
  attributes; a split strips whitespace across runs; ids.jsonl order
  follows spec/04 §4.4 in every state; a move after itself is refused.
- Anchors: the relabel rule requires that nothing else changed below the
  node; an alias chain ending in a deletion no longer crashes resolve.
- Notation: a script after an empty group applies to the previous atom
  ({}^{14}C); letters are defined by Unicode block in spec/05 §5.4 and
  the oracle; \left) is complex.
- Page fingerprints delete whitespace before folding, so "10 -20" and
  "10-20" fold alike (spec/07 §7.1).
- Grades are summed with exact decimals; the reviewer error bound is
  computed with integer arithmetic.
- receipts and revocations are keyed by (doc_key, id) in SQL, since one
  revocation may be carried by several packages.

Checking:

- tools/stress.py: seeded randomized property tests over canonical JSON,
  normalization, notation, random correction walks, anchor resolution,
  Merkle roots, spot-check samples, error bounds, fingerprints, mutated
  archives and packages, rights and spot-check chains; CI runs it.
- check.py verifies every count and version the prose states against
  the repository, the zipped fixture and crafted archives, the checklist
  coverage, and nine more broken packages.
- CONTRIBUTING.md gains a release checklist.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docs/glossary.md

@@ -32,9 +32,16 @@ Format `scienting-bundle/1`, `provisional`. ([13.5](../spec/13-database.md#135-t
 Changed below
 :   The resolution of an anchor on a container that is unchanged in itself while something inside it changed. ([6.5](../spec/06-anchors.md#65-resolution))
 
+Checklist
+:   A record of checking an export, such as accessible HTML, against a named standard, criterion by criterion; it is covered by the receipt of the person who checked.
+Format `scienting-checklist/1`, `provisional`. ([8.11](../spec/08-fidelity.md#811-checklists))
+
 Correction
 :   An operation on an established document, with its evidence and author; never edited, only appended. ([11](../spec/11-corrections.md))
 
+Description
+:   An annotation that describes a figure, panel or table for readers who cannot see it, as a short text equivalent (`alt`) or a full description (`long`); an accessible export uses confirmed descriptions only. ([18.4](../spec/18-layers.md#184-bodies))
+
 Document
 :   The text established for one version of one work, from one or more witnesses, as a tree of nodes. ([2.1](../spec/02-model.md#21-four-objects), [3](../spec/03-nodes.md))
 
@@ -135,7 +142,7 @@ Suspect
 
 Targeted F3
 :   Proofreading the nodes a team's claims, quotations and datasets rest on, rather than every node.
-The target set also includes every display equation and, under the project's digit rule (`all`, `anchored-sections` or `none`), sentences with a digit in a text or math run (an inline stretch of plain text, or of TeX or Typst math, within the sentence; [3.5](../spec/03-nodes.md#35-inline-runs)). ([8.10](../spec/08-fidelity.md#810-targeted-f3))
+The target set also includes the leaves of every anchored container, every equation and, under the project's digit rule (`all`, `anchored-sections` or `none`), sentences and cells with a digit in a text or math run (an inline stretch of plain text, or of TeX or Typst math, within the node; [3.5](../spec/03-nodes.md#35-inline-runs)). ([8.10](../spec/08-fidelity.md#810-targeted-f3))
 
 Text leaf
 :   A leaf whose text a container's projections are made of: any leaf except an equation line, or an equation inside a sentence, whose text is already part of its equation or its sentence. ([3.6](../spec/03-nodes.md#36-the-plain-projection))