feat: minted keys, VRF seeds, RFC 9162 proofs, history roots, tag URIs and a transparency log

Keys (spec/02 §2.4), the rule paperstack settled on:
- A work key is a Scholar-style citation key, a hyphen and the first four
  Crockford base32 characters of SHA-256("scienting-key/1:" + identity),
  where the identity is the first of doi, arxiv, isbn, pmid, pmcid and
  openalex in same_as, else the folded title, year and family name. A
  collision lengthens the later key by two characters; a key is minted
  once and never recomputed. A document key adds .si, .v<seq> or .<type>
  for versions other than the version of record.
- Every fixture key is now minted (hale2026harmonic-damb,
  okafor2025solvent-acth, writer2027fixed-ynr7.v3, tiny2026tiny-j4qm), so
  every node and record ID was re-minted and the docs rewritten to match.
  The validator checks the document key against the work key and version
  (doc.key.work) and the hash part against the identifier (doc.key.suffix).
  vectors/keys.jsonl pins the cases paperstack's tests pin.

Review:
- Spot-check seeds are ECVRF-EDWARDS25519-SHA512-TAI proofs (RFC 9381),
  implemented in tools/oracle/vrf.py in plain Python and reproduced
  against the RFC's Example 16; the sample ranks by the VRF output. The
  earlier Ed25519 seed could be ground by a dishonest checker.
- RFC 9162 inclusion and consistency proofs (crypto.inclusion_path,
  verify_inclusion, consistency_proof, verify_consistency) with
  scienting-proof/1, vectors/proofs.jsonl and two fixture records.
- document.json carries `history`, the root over the corrections, with
  the empty-tree hash for none (spec/11 §11.5, rule doc.history).
- A provisional transparency log (spec/23): log entries, signed-note
  checkpoints with key hashes as transparency logs share them, the rule
  that a logged revocation beats a self-asserted time, and vectors.
- Reserved signature schemes cose and ml-dsa-65 (spec/08 §8.4).

Identifiers and text:
- urn:scienting: becomes tag:scient.ing,2026: (RFC 4151), since the URN
  namespace was never registered.
- Unicode 16.0 is pinned for normalization and categories (spec/01 §1.4);
  the checker refuses another version.

Checking:
- check.py: keys, proofs, VRF and checkpoint vectors; the proof and
  checkpoint records; a check that every ID and hash the prose quotes
  exists in the fixtures or vectors; three more broken packages
  (history-wrong, key-suffix, key-work).
- stress.py: key, VRF, proof and checkpoint properties.
- Docs: a keys section in the concepts and FAQ, rationale entries for
  keys, VRF, proofs, tag URIs and the Unicode pin, a "Looking ahead"
  section, media-type registration and OCI distribution notes.

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

tools/oracle/receipts.py

@@ -10,7 +10,7 @@ import math
 from fractions import Fraction
 from math import comb
 
-from . import crypto, jcs
+from . import crypto, jcs, vrf
 from .model import LEVELS
 from .text import record_id, sha256_hex
 
@@ -76,7 +76,8 @@ def seed_payload(receipt):
 
 
 def make_seed(receipt, checker_secret):
-    return crypto.ed25519_sign(checker_secret, seed_payload(receipt))
+    """The seed: the checker's VRF proof (RFC 9381, ECVRF-EDWARDS25519-SHA512-TAI) for the receipt's payload."""
+    return vrf.prove(checker_secret, seed_payload(receipt))
 
 
 def sample_size(n, rate="0.05", minimum=10):
@@ -84,9 +85,13 @@ def sample_size(n, rate="0.05", minimum=10):
 
 
 def sample(receipt, seed, rate="0.05", minimum=10):
+    """The sample a seed selects: ranked by SHA-256 of the proof's VRF output followed by the node ID."""
+    beta = vrf.proof_to_hash(seed)
+    if beta is None:
+        raise ValueError("the seed is not a VRF proof")
     ids = [nid for nid, _ in receipt["nodes"]]
     m = sample_size(len(ids), rate, minimum)
-    ranked = sorted(ids, key=lambda nid: (hashlib.sha256(seed + nid.encode("utf-8")).hexdigest(), nid))
+    ranked = sorted(ids, key=lambda nid: (hashlib.sha256(beta + nid.encode("utf-8")).hexdigest(), nid))
     return sorted(ranked[:m])