forge: external forge accounts live in swarm bao; the agent fetches them itself

An operator now links an agent's external forge account (label, base URL,
token) in the swarm UI. swarm-controller stores it at
swarm/agents/<agent>/forge/<label>. There is no index: the store's
listing of the agent's forge/ directory is the set of accounts.

In the agent, hive-agent-forge-accounts (oneshot + 2-minute timer, as
the agent user, under its own store certificate) lists
swarm/agents/<agent>/forge/ with the `list` #4866 grants an agent on its
own metadata subtree, reads each account, and writes
<state>/forge-<label>-token and forge-<label>.json in the names and shape
hive-forge -f already reads. An empty listing (a 404, which `bao kv list
-format=json` answers with `{}` and an empty stderr) is zero accounts; a
denial or an unreachable store fails the unit. It never deletes: files
for labels not listed, including ones the hive wrote, stay as they are.

Removed: the dashboard FORGES tab (credentials.js/html section and its
CSS), hive-c0re's extra_forges.rs and its routes, priv_client's
extra-forge calls, and hive-priv's WriteAgentExtraForgeAccount /
DeleteAgentExtraForgeAccount with their helpers. The GITHUB tab and
WriteAgentGithubToken stay.

Also: persistence.md's matrix avatar note names the exit-75 restart on a
changed account listing, not the dashboard, as what brings a linked
account up.

Refs #4348

hive-priv/src/main.rs

@@ -27,7 +27,6 @@ use hive_priv_sock::{
     PAUSED_MARKER_FILE, PRIV_SOCK, PrivEvent, PrivRequest, PrivResponse, PrivStream,
     PrivStreamLine, SIBLING_CONTAINERS,
 };
-use serde::Serialize;
 use tokio::io::{AsyncWriteExt, BufReader};
 use tokio::net::unix::OwnedWriteHalf;
 use tokio::net::{UnixListener, UnixStream};
@@ -413,18 +412,6 @@ async fn exec(
             ref token,
         } => write_github_token(agent_name, token),
 
-        PrivRequest::WriteAgentExtraForgeAccount {
-            ref agent_name,
-            ref label,
-            ref base_url,
-            ref token,
-        } => write_extra_forge_account(agent_name, label, base_url, token),
-
-        PrivRequest::DeleteAgentExtraForgeAccount {
-            ref agent_name,
-            ref label,
-        } => delete_extra_forge_account(agent_name, label),
-
         PrivRequest::RegisterCiRunner { ref token } => register_ci_runner(token).await,
 
         PrivRequest::ControlInfraContainer { container, action } => {
@@ -523,29 +510,6 @@ async fn exec_forge_admin(args: &[String]) -> Result<(String, String)> {
     run_forge_admin(args).await
 }
 
-/// `WriteAgentExtraForgeAccount`: writes the token, then a
-/// `forge-<label>.json` sidecar carrying the base URL — there's no
-/// host-side nix config for extra forges, so this is the only place it's
-/// persisted.
-fn write_extra_forge_account(
-    agent_name: &str,
-    label: &str,
-    base_url: &str,
-    token: &str,
-) -> Result<(String, String)> {
-    validate_agent_name(agent_name)?;
-    validate_name_chars(label)?;
-    let res = write_agent_state_file(
-        agent_name,
-        &format!("forge-{label}-token"),
-        &format!("{token}\n"),
-    )?;
-    let meta = serde_json::to_string(&ForgeSidecar { base_url })
-        .context("serialize forge account sidecar")?;
-    write_agent_state_file(agent_name, &format!("forge-{label}.json"), &meta)?;
-    Ok(res)
-}
-
 /// `StopContainer`.
 async fn stop_container(name: &str) -> Result<(String, String)> {
     validate_agent_name(name)?;
@@ -589,15 +553,6 @@ fn write_github_token(agent_name: &str, token: &str) -> Result<(String, String)>
     write_agent_state_file(agent_name, "github-token", &format!("{token}\n"))
 }
 
-/// `DeleteAgentExtraForgeAccount`. Missing files are not an error
-/// (idempotent revoke).
-fn delete_extra_forge_account(agent_name: &str, label: &str) -> Result<(String, String)> {
-    validate_agent_name(agent_name)?;
-    validate_name_chars(label)?;
-    delete_agent_state_file(agent_name, &format!("forge-{label}-token"))?;
-    delete_agent_state_file(agent_name, &format!("forge-{label}.json"))
-}
-
 /// `EnsureAgentSubvolume`.
 async fn exec_ensure_agent_subvolume(agent_name: &str) -> Result<(String, String)> {
     validate_agent_name(agent_name)?;
@@ -1531,18 +1486,6 @@ fn publish_file(path: &Path, content: &[u8], mode: u32, owner: Option<(u32, u32)
     staged.publish()
 }
 
-/// Sidecar written alongside a dashboard-provisioned extra forge
-/// account's token (`forge-<label>.json`) so `hive-forge` can resolve
-/// the account's base URL. Read side: `hive-forge/src/client.rs`'s own
-/// (separately defined, deserialize-only) `ForgeSidecar` — same field
-/// name (`base_url`), no shared crate between `hive-priv` and
-/// `hive-forge` to hang a common type off, so the two structs are
-/// pinned to the same JSON key by convention, not by the compiler.
-#[derive(Serialize)]
-struct ForgeSidecar<'a> {
-    base_url: &'a str,
-}
-
 /// Shared helper for the `WriteAgent*Token` requests.
 /// Writes `content` to `AGENT_STATE_ROOT/<agent_name>/state/<filename>`,
 /// chowns to the agent user (derived from the state dir's existing owner),
@@ -1675,28 +1618,6 @@ fn write_agent_dir_file(
     Ok((String::new(), String::new()))
 }
 
-/// Remove `AGENT_STATE_ROOT/<agent_name>/state/<filename>` if present.
-/// Idempotent revoke counterpart to [`write_agent_state_file`] — a
-/// missing file is success, not an error. `filename` must be a single
-/// plain component (no `/`, `.`, `..`); callers pass a pre-validated
-/// label into a fixed `forge-<label>-token` shape, same as the write
-/// side.
-fn delete_agent_state_file(agent_name: &str, filename: &str) -> Result<(String, String)> {
-    ensure_plain_filename("delete_agent_state_file", filename)?;
-    let path = PathBuf::from(AGENT_STATE_ROOT)
-        .join(agent_name)
-        .join("state")
-        .join(filename);
-    match std::fs::remove_file(&path) {
-        Ok(()) => {
-            tracing::info!(agent = %agent_name, file = %filename, "removed agent state file");
-        }
-        Err(e) if e.kind() == std::io::ErrorKind::NotFound => {}
-        Err(e) => return Err(e).with_context(|| format!("remove {}", path.display())),
-    }
-    Ok((String::new(), String::new()))
-}
-
 /// btrfs superblock magic, as reported by `statfs(2)`'s `f_type`.
 const BTRFS_SUPER_MAGIC: i64 = 0x9123_683E;