Record the SHA-256 of spec v0.9 for its tag

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

spec/README.md

@@ -12,14 +12,15 @@
   must respect, the serialization of GT in the tlock H2, and a single code
   for any failure of a release source), all recorded with their
   reproducible cases in the specification's §76.
-- `DateKeys_Protocol_Specification_v0.9.md`: the normative draft v0.9 (29
+- `DateKeys_Protocol_Specification_v0.9.md`: frozen copy of the normative
-  September 2026) implemented by this module, approved by its author on that
+  draft v0.9 (29 September 2026), approved by its author on that date and
-  date. It adds capsule format 2, which hides until the unlock date the exact
+  tagged `spec-v0.9`; this module implements it. SHA-256:
+  `36189e1e62f0f835b7665219aa63df7200cd89ac4e4e924f2705f970fa7c40a9`.
+  It adds capsule format 2, which hides until the unlock date the exact
   length of the content (the payload is padded) and the number of
   credentials (always 16 X25519 stanzas), and it makes the writer rules
   normative. A v0.9 reader still opens format 1, the format of v0.8.2. Its
-  §76 records each change with its reproducible case. Its SHA-256 will be
+  §76 records each change with its reproducible case.
-  recorded here when it is tagged.
 - `datekeys.cddl`: the CBOR schemas of v0.9, both control versions included,
   with the encoding rules CDDL cannot express. Those of v0.8.2 are at the tag
   `spec-v0.8.2`.