Adds an optional supersedes_post_id pointer to Post for the
"re-issue with narrower access" path. Author publishes a new post
that references an earlier one; receivers can render "this is a
re-issued version of an earlier post" + offer to view the original.
Covered by PostId = BLAKE3(Post) — receivers can verify it wasn't
forged by anyone but the author.
#[serde(default)] for back-compat; existing posts deserialize with
None. All existing Post construction sites bulk-updated to set the
field to None.
Storage::get_post returns None for the field today; a follow-up can
add a dedicated column if/when receivers need to render the
pointer. The author-side re-issue helper that creates posts with
this field set comes in the Tauri/UI slice — the wire shape is in
place now.
148 tests pass (no regressions).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
fdbf97f2d7