Replaces two persona-signed direct pushes with CDN-propagated control posts:
a single `VisibilityIntent::Control` post type whose content is a signed
`ControlOp` the receiver verifies and applies. Deletes and visibility updates
now flow through the same neighbor-manifest CDN path as regular content — no
direct recipient push needed for persona-signed ops.
Core pieces:
- `VisibilityIntent::Control` + `VisibilityIntent::Profile` variants.
- `ControlOp::DeletePost` / `ControlOp::UpdateVisibility` (JSON, ed25519-signed
by the target post's author over op-specific byte strings).
- `crypto::{sign,verify}_control_{delete,visibility}` signing primitives.
- `control::build_delete_control_post` + `build_visibility_control_post`
for authors to construct control posts.
- `control::receive_post` — unified incoming-post path used by all 6 receive
sites. Verifies control signatures BEFORE storing, so bogus controls never
enter storage and can't be re-propagated via neighbor-manifest diffs.
- `control::apply_control_post_if_applicable` — executes the op under the
same storage guard as the insert.
Feed filter:
- Feeds (`get_feed`, `get_feed_page`, `list_posts_page`,
`list_posts_reverse_chron`) now exclude `Control` and `Profile` posts so
they propagate + tombstone without surfacing.
- Sync/export path (`list_posts_with_visibility`) keeps its own unfiltered
query so control posts still propagate via CDN.
Wire protocol:
- `SyncPost` carries `intent: Option<VisibilityIntent>` so control posts
arrive with their intent preserved.
- `BlobDeleteNotice` (0x95) removed — orphan blobs on remote holders evict
naturally via LRU rather than via a persona-signed push. Code path,
payload, sender, tests, and `delete_blob_with_cdn_notify` all gone.
Tests: control delete roundtrip (apply + tombstone) and wrong-author
rejection (not stored, not applied). 112/112 core tests pass.
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