Function normalize_egress_pattern 

pub fn normalize_egress_pattern(raw: &str) -> Result<String, String>

Canonicalize one egress allowlist entry, or explain why it is rejected.

This is the single grammar for both halves of the egress contract: the signed manifest’s egress.hosts declaration and the operator’s plugins.entries[].egress_hosts grant. Both validate here so a pattern that a publisher can declare is exactly a pattern an operator can grant.

Accepted forms:

• an exact host: a lowercase domain name, IPv4 literal, or IPv6 literal (bare ::1 or bracketed [::1]; both canonicalize to bare). It matches that host and nothing else — a bare domain never implies its subdomains.
• an explicit suffix pattern *.example.com: matches strict subdomains of example.com and not the apex itself. Grant the apex by listing it separately.

Rejected, each with a message naming the reason:

• a bare *. There is no “everything” pattern; deny-by-default has no escape hatch at the grammar level.
• empty or whitespace-bearing entries.
• anything carrying a scheme, path, query, fragment, or userinfo (/, @, ?, #, \), so an entry is never a URL that silently loses its path.
• a * anywhere other than the leading *. (no a*.b, no *.*.c).
• a port (example.com:8443). Ports are deliberately not part of this slice’s grammar: a granted host is granted on every port, all-or-nothing. Rejecting the syntax outright keeps an operator from writing a port and believing it narrowed the grant when it would in fact have been dropped.
• a wildcard over an IP literal (*.10.0.0.1), which has no meaning.
• a single-label wildcard suffix (*.com, *.internal). This is a footgun guard, not a public-suffix check: no public-suffix list is imported here, so *.co.uk is accepted even though it is just as broad. The rule only removes the most obvious way to write an accidental internet-wide grant.
• any entry that is not already canonical (a trailing dot, uppercase, or a form normalize_domain would silently rewrite), so the file an operator audits reads exactly as the policy that is enforced.

Errors

Returns the human-readable reason the entry is not a legal egress pattern.