fix(#2391): drop "." entirely from credential/snapshot name charset

Per mara: "i would have even disallowed ., we are making up the rules
here lets go strict". validate_credential_name now restricts to
[A-Za-z0-9_-] (no dot at all) instead of [A-Za-z0-9_.-] + a separate
".." substring check — simpler rule, and there's no legitimate need
for a dot in either a systemd credential id or a hive- prefixed
snapshot label. Matching hivectl client-side check + wire-proto doc
comments updated.

hive-c0re/src/bin/hivectl.rs

@@ -1740,10 +1740,11 @@ async fn subvol_upgrade(socket: &Path, name: &str, yes: bool) -> Result<()> {
 /// `subvol snapshot create <agent> --label <label>` — create a read-only
 /// btrfs snapshot of an agent's state subvolume. Unlike `upgrade`, this does
 /// NOT stop the agent: btrfs snapshots are atomic + consistent to take
-/// against a live subvolume. `label` is mandatory and must start with
-/// `hive-` — hive-priv enforces the same prefix as an allow-list, so this
-/// check is belt-and-suspenders (fail fast client-side with a clear
-/// message).
+/// against a live subvolume. `label` is mandatory, must start with
+/// `hive-`, and is otherwise restricted to `[A-Za-z0-9_-]` (no `.` at all
+/// — mara: "we are making up the rules here, lets go strict"). hive-priv
+/// enforces the same rules server-side, so this check is
+/// belt-and-suspenders (fail fast client-side with a clear message).
 async fn subvol_snapshot_create(name: &str, label: String) -> Result<()> {
     if !agent_exists(name)? {
         bail!("no agent named {name:?} (no state dir under the agents root)");
@@ -1751,8 +1752,13 @@ async fn subvol_snapshot_create(name: &str, label: String) -> Result<()> {
     if !label.starts_with("hive-") {
         bail!("snapshot label {label:?} must start with \"hive-\"");
     }
-    if label.contains("..") {
-        bail!("snapshot label {label:?} must not contain \"..\"");
+    if !label
+        .bytes()
+        .all(|b| b.is_ascii_alphanumeric() || matches!(b, b'_' | b'-'))
+    {
+        bail!(
+            "snapshot label {label:?} must be [A-Za-z0-9_-] only (no \".\" — hive-priv rejects it)"
+        );
     }
     let path = hive_c0re::priv_client::snapshot_agent_subvolume(name, &label)
         .await

hive-priv/src/main.rs

@@ -445,25 +445,21 @@ fn validate_snapshot_name(name: &str) -> Result<()> {
 }
 
 /// A systemd credential id must be a short token — restrict to
-/// `[A-Za-z0-9_.-]` so it can't inject extra `--load-credential` argv or
-/// break the `name:path` shape.
+/// `[A-Za-z0-9_-]` (no `.`) so it can't inject extra `--load-credential`
+/// argv or break the `name:path` shape. `.` is deliberately excluded, not
+/// just a bare `..`: this name gets interpolated into filesystem paths
+/// (snapshot labels) and there's no legitimate need for a dot in either a
+/// systemd credential id or a `hive-`-prefixed snapshot label — we're
+/// defining this token format from scratch, so keep it maximally strict
+/// rather than allow-then-patch each traversal-adjacent character
+/// (mara: "we are making up the rules here, lets go strict").
 fn validate_credential_name(name: &str) -> Result<()> {
     if name.is_empty()
         || !name
             .bytes()
-            .all(|b| b.is_ascii_alphanumeric() || matches!(b, b'_' | b'.' | b'-'))
+            .all(|b| b.is_ascii_alphanumeric() || matches!(b, b'_' | b'-'))
     {
-        bail!("invalid credential name {name:?}: must be non-empty [A-Za-z0-9_.-]");
-    }
-    // `.` is in the allowed charset (systemd credential ids and snapshot
-    // labels both legitimately use dots), but a bare `..` reads as a
-    // directory-traversal token to anyone auditing this path — and a
-    // caller that builds a path via `PathBuf::from(name)` instead of the
-    // current `format!("...{name}...")` embedding would actually be
-    // exploitable. Reject it outright rather than relying on every future
-    // caller getting the embedding right.
-    if name.contains("..") {
-        bail!("invalid credential name {name:?}: must not contain \"..\"");
+        bail!("invalid credential name {name:?}: must be non-empty [A-Za-z0-9_-]");
     }
     Ok(())
 }

hive-sh4re/src/priv_proto.rs

@@ -199,7 +199,7 @@ pub struct BindMount {
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct CredentialMount {
     /// systemd credential id (e.g. `otel-headers`); inner units inherit
-    /// it by this name. Restricted to `[A-Za-z0-9_.-]` by hive-priv.
+    /// it by this name. Restricted to `[A-Za-z0-9_-]` (no `.`) by hive-priv.
     pub name: String,
     /// Host path to the secret file, forwarded via nspawn
     /// `--load-credential=<name>:<host_path>`.
@@ -599,7 +599,8 @@ pub enum PrivRequest {
         /// an allow-list hive-priv enforces so only hivectl-issued names
         /// can reach the `btrfs subvolume snapshot` shellout — and
         /// otherwise follows the same charset as a credential name
-        /// (non-empty `[A-Za-z0-9_.-]`); becomes part of the snapshot path.
+        /// (non-empty `[A-Za-z0-9_-]`, no `.`); becomes part of the
+        /// snapshot path.
         snapshot_name: String,
     },