feat(#2035): auto-discover dashboard-provisioned matrix accounts via token+homeserver sidecar

hive-c0re/src/dashboard/matrix_accounts.rs

@@ -244,7 +244,9 @@ pub(super) async fn post_matrix_account_login(Form(f): Form<MatrixLoginForm>) ->
         }
     };
 
-    if let Err(e) = crate::priv_client::write_agent_matrix_token(agent, &token, Some(account)).await
+    if let Err(e) =
+        crate::priv_client::write_agent_matrix_token(agent, &token, Some(account), Some(homeserver))
+            .await
     {
         return error_response(&format!("matrix-account-login: write token failed: {e:#}"));
     }

hive-c0re/src/matrix.rs

@@ -709,7 +709,7 @@ pub async fn ensure_user_for(
     // unprivileged `hive-core` user and cannot write to agent-owned state
     // directories directly. hive-priv writes the file 0600 and chowns it
     // to the agent user so it is readable from inside the container.
-    crate::priv_client::write_agent_matrix_token(name, &access_token, None)
+    crate::priv_client::write_agent_matrix_token(name, &access_token, None, None)
         .await
         .with_context(|| format!("matrix: write matrix-token for {name} via hive-priv"))?;
     tracing::info!(%name, "matrix: provisioned access token");

hive-c0re/src/priv_client.rs

@@ -261,15 +261,22 @@ pub async fn write_agent_forge_token(agent_name: &str, token: &str) -> Result<()
 /// `<state>/matrix-token-<name>` for an extra (external) account. The file
 /// is written 0600 and chowned to the agent user so it is readable from
 /// inside the agent container. hive-priv validates the account suffix.
+///
+/// `homeserver: Some(url)` (only meaningful with `account: Some`) also
+/// writes the sidecar `<state>/matrix-account-<name>.json` so the daemon
+/// can auto-discover the extra account without a `matrixAccounts` config
+/// declaration (see issue tracker "external matrix account auto-discovery").
 pub async fn write_agent_matrix_token(
     agent_name: &str,
     token: &str,
     account: Option<&str>,
+    homeserver: Option<&str>,
 ) -> Result<()> {
     ok(call(&PrivRequest::WriteAgentMatrixToken {
         agent_name: agent_name.to_owned(),
         token: token.to_owned(),
         account: account.map(ToOwned::to_owned),
+        homeserver: homeserver.map(ToOwned::to_owned),
     })
     .await?)
 }