access: `*` for any one key in a capability's path

A capability's path covered by prefix only, so what is the same at every key of a map
(each node's log filter, say, at `_continuum/local/<id>/log` from the next patch on)
took a capability per key. Now a `*` segment stands for any one key, as it already does
in signed paths and sealed places (`envelope`, `sealed`, which now share one `agree`):

* covering (`Capability::covers`): the pattern no longer than the path, and agreeing
  with it segment by segment;
* listings (`reaches`): pattern and path agreeing on the segments both have, so every
  key on the way shows, nothing past where the pattern differs;
* narrowing (`Capability::holds`, for a token's limit narrowed again and a refresh's):
  at or below, a `*` only under a `*`: a limit naming one key never widens to all.

A `*` first is outside protocol data, so it never covers `_continuum`, as `[]` doesn't.
A key that is `*` itself can't be named alone. Every node judges changes by
capabilities, so all must read them alike: they run the same version.

1 files changed, 1 insertions, 8 deletions

diff --git a/src/access/sealed.rs b/src/access/sealed.rs
index ed5024c..7e48e34 100644
--- a/src/access/sealed.rs
+++ b/src/access/sealed.rs
@@ -24,7 +24,7 @@ use base64::{
 use serde_json::Value as JsonValue;
 use sha2::{Digest, Sha256};
 
-use super::{envelope, registry, sshsig};
+use super::{agree, envelope, registry, sshsig};
 use crate::document::{ReadDoc, meta, store};
 
 /// What every sealed value starts with.
@@ -90,13 +90,6 @@ fn reaches(declared: &[Declared], path: &[String]) -> bool {
     declared.iter().any(|declared| agree(&declared.path, path))
 }
 
-fn agree(pattern: &[String], path: &[String]) -> bool {
-    pattern
-        .iter()
-        .zip(path)
-        .all(|(segment, key)| segment == "*" || segment == key)
-}
-
 /// How an age file names `key` as a recipient: the first four bytes of the SHA-256 of
 /// its SSH encoding, base64, unpadded.
 pub(crate) fn tag(key: &sshsig::PublicKey) -> String {