config PRs: each hive removes its own stale config-PR org hook on boot

The hook a hive registered on the agent-configs org points at its
/webhook/config-pr route, which no hive serves any more, so every
config-repo event fails delivery to it. The forge sweep now deletes it.

Only a hook whose URL equals this hive's own exactly is removed. The same
path on another base belongs to another hive and is left alone. A forge
error is logged and boot continues; once the hook is gone the step is a
no-op.

Closes #4850

hive-c0re/src/forge/mod.rs

@@ -251,7 +251,8 @@ pub async fn sync_agent(name: &str, core_token: Option<&str>) -> bool {
 }
 
 /// The `core_token.is_some()` half of [`ensure_all`]: the meta repo, the
-/// local knowledge clone, the core avatar, and CI runner registration —
+/// local knowledge clone, the core avatar, CI runner registration, and
+/// removing this hive's own config-PR hook —
 /// every step that needs an authenticated forge client. The swarm-wide
 /// objects (orgs, the `operators` team, mirrors, `internal/docs`,
 /// `internal/knowledge`, the `agent-configs` avatar) are the
@@ -291,6 +292,63 @@ async fn ensure_all_orgs_and_repos(token: &str) {
     // Register the hive-ci Actions runner (off the container's boot path;
     // no-op when CI is disabled or the runner already holds valid creds).
     ci_runner::ensure_ci_runner_registered(token).await;
+    if let Err(e) = remove_config_pr_webhook(token).await {
+        tracing::warn!(error = ?e, "forge: remove_config_pr_webhook failed");
+    }
+}
+
+/// Delete this hive's own `/webhook/config-pr` hook from the
+/// `agent-configs` org. No hive serves that route, so such a hook fails on
+/// every config-repo event; swarm-controller's hook is the one that acts on
+/// config PRs.
+///
+/// Only a hook whose URL equals this hive's exactly is removed, never one
+/// matching by path: the same path on another base is another hive's hook.
+/// Idempotent, and a no-op when `HYPERHIVE_HIVE_DOMAIN` is unset.
+async fn remove_config_pr_webhook(core_token: &str) -> Result<()> {
+    const HTTP_TIMEOUT: Duration = Duration::from_secs(10);
+
+    let Some(domain) = std::env::var("HYPERHIVE_HIVE_DOMAIN")
+        .ok()
+        .filter(|v| !v.is_empty())
+    else {
+        return Ok(());
+    };
+    let own_url = config_pr_hook_url(&domain);
+    let client = api(core_token)?;
+    let hooks = tokio::time::timeout(HTTP_TIMEOUT, client.org_list_hooks(CONFIG_ORG).send())
+        .await
+        .map_err(anyhow::Error::from)
+        .and_then(|r| r.map_err(anyhow::Error::from))
+        .with_context(|| format!("list webhooks for org {CONFIG_ORG}"))?;
+    for id in hook_ids_at(&hooks, &own_url) {
+        tokio::time::timeout(HTTP_TIMEOUT, client.org_delete_hook(CONFIG_ORG, id).send())
+            .await
+            .map_err(anyhow::Error::from)
+            .and_then(|r| r.map_err(anyhow::Error::from))
+            .with_context(|| format!("delete webhook {id} on org {CONFIG_ORG}"))?;
+        tracing::info!(%own_url, id, "forge: removed this hive's config-pr webhook");
+    }
+    Ok(())
+}
+
+/// The URL this hive's config-PR hook was registered under.
+fn config_pr_hook_url(hive_domain: &str) -> String {
+    format!("https://{hive_domain}/webhook/config-pr")
+}
+
+/// Ids of the hooks whose URL is exactly `url`.
+fn hook_ids_at(hooks: &[forgejo_api::structs::Hook], url: &str) -> Vec<i64> {
+    hooks
+        .iter()
+        .filter(|h| {
+            h.config
+                .as_ref()
+                .and_then(|c| c.get("url"))
+                .is_some_and(|u| u == url)
+        })
+        .filter_map(|h| h.id)
+        .collect()
 }
 
 /// Poll the local Forgejo API until it answers, with a timeout of 1 minute.
@@ -400,7 +458,27 @@ pub async fn ensure_all() {
 
 #[cfg(test)]
 mod tests {
-    use super::{describe_forge_admin, git_url_with_base};
+    use super::{config_pr_hook_url, describe_forge_admin, git_url_with_base, hook_ids_at};
+
+    fn hook(id: i64, url: &str) -> forgejo_api::structs::Hook {
+        serde_json::from_value(serde_json::json!({ "id": id, "config": { "url": url } }))
+            .expect("hook json")
+    }
+
+    /// The same path on another base is another hive's hook, and removing it
+    /// would cut that hive off. Only an exact URL match is this hive's.
+    #[test]
+    fn only_this_hives_own_config_pr_hook_is_removed() {
+        let own = config_pr_hook_url("hive.example");
+        let hooks = [
+            hook(1, &own),
+            hook(2, "https://other-hive.example/webhook/config-pr"),
+            hook(3, "http://127.0.0.1:7000/webhook/config-pr"),
+            hook(4, "https://swarm.example/webhook/forge/config-pr"),
+        ];
+        assert_eq!(hook_ids_at(&hooks, &own), vec![1]);
+        assert!(hook_ids_at(&hooks[1..], &own).is_empty());
+    }
 
     /// The remote carries **no credential**. `argv` is world-readable through
     /// `/proc/<pid>/cmdline`, so a token spliced in here would be published to