diff --git a/nix/templates/harness-base.nix b/nix/templates/harness-base.nix
index f5efd435..b0361bec 100644
--- a/nix/templates/harness-base.nix
+++ b/nix/templates/harness-base.nix
@@ -299,6 +299,75 @@ in
     '';
   };
 
+  options.hyperhive.matrixAccounts = lib.mkOption {
+    type = lib.types.listOf (
+      lib.types.submodule {
+        options = {
+          name = lib.mkOption {
+            type = lib.types.str;
+            example = "ccc";
+            description = ''
+              Logical account name the agent addresses this account by
+              (the `account` argument on the matrix MCP tools). Must be
+              unique within the agent. The FIRST account in the list is
+              the agent's primary account --- the one selected when a
+              tool call omits `account`.
+            '';
+          };
+          tokenFile = lib.mkOption {
+            type = lib.types.str;
+            example = "/agents/dmatrix/state/matrix-token-ccc";
+            description = ''
+              Path to this account's bearer-token file. The daemon reads
+              the token from here to restore the matrix session; how the
+              file gets populated is the provisioner's concern (hive-c0re
+              for in-hive accounts, an operator-supplied secret for an
+              external account). The daemon skips an account whose token
+              file is absent (the primary account being absent makes the
+              daemon exit cleanly until it appears).
+            '';
+          };
+          sessionDir = lib.mkOption {
+            type = lib.types.str;
+            example = "/agents/dmatrix/state/matrix-sdk-state-ccc";
+            description = ''
+              Per-account matrix-sdk sqlite store directory (crypto keys
+              + event cache). Must differ between accounts so their
+              sessions do not collide.
+            '';
+          };
+          homeserver = lib.mkOption {
+            type = lib.types.nullOr lib.types.str;
+            default = null;
+            example = "https://matrix.example.org";
+            description = ''
+              Homeserver URL for this account. When null (the default),
+              the account falls back to `hyperhive.matrix.url`. Set it for
+              an account on a different homeserver than the agent's
+              default (e.g. an external public-matrix account).
+            '';
+          };
+        };
+      }
+    );
+    default = [ ];
+    description = ''
+      Declare multiple matrix accounts served by a single
+      `hive-matrix-daemon` (one matrix-sdk Client + sync loop each),
+      replacing the wasteful "one MCP server + daemon per account"
+      pattern. Each entry becomes a routable account the matrix MCP
+      tools can target via their `account` argument; omitting `account`
+      on a tool call selects the first (primary) entry.
+
+      Leave empty (the default) for the common single-account case: the
+      daemon then synthesizes one account from `hyperhive.matrix.url` +
+      `<state>/matrix-token` + `<state>/matrix-sdk-state`, so existing
+      agents need no change. When non-empty, this list is serialized to
+      the daemon's `HIVE_MATRIX_ACCOUNTS` environment variable and the
+      legacy single-account fallback is bypassed.
+    '';
+  };
+
   options.hyperhive.frontend.dist = lib.mkOption {
     type = lib.types.package;
     default = pkgs.hyperhive-frontend;
@@ -1239,6 +1308,26 @@ in
         HIVE_MATRIX_URL = config.hyperhive.matrix.url;
         HIVE_MATRIX_SOCKET = "/run/hive-matrix/socket";
         RUST_LOG = "info";
+      }
+      # Multi-account: serialize the declared accounts to the JSON the
+      # daemon parses (`accounts::configured`). Only set when accounts
+      # are declared, so the single-account agents (the common case)
+      # keep hitting the daemon's legacy fallback (which is bypassed the
+      # moment HIVE_MATRIX_ACCOUNTS is present). Keys match the daemon's
+      # `AccountCfg` serde shape: name / token_file / state_dir /
+      # optional homeserver.
+      // lib.optionalAttrs (config.hyperhive.matrixAccounts != [ ]) {
+        HIVE_MATRIX_ACCOUNTS = builtins.toJSON (
+          map (
+            a:
+            {
+              inherit (a) name;
+              token_file = a.tokenFile;
+              state_dir = a.sessionDir;
+            }
+            // lib.optionalAttrs (a.homeserver != null) { inherit (a) homeserver; }
+          ) config.hyperhive.matrixAccounts
+        );
       };
       serviceConfig = {
         ExecStart = "${pkgs.hyperhive}/bin/hive-matrix-daemon";
@@ -1318,9 +1407,12 @@ in
     # would have no backend until next restart. See
     # `docs/persistence.md` (same section as above).
     systemd.paths.hive-matrix-daemon = lib.mkIf config.hyperhive.matrix.enable {
-      description = "trigger hive-matrix-daemon when matrix-token appears";
+      description = "trigger hive-matrix-daemon when a matrix token appears";
       wantedBy = [ "multi-user.target" ];
-      pathConfig.PathExistsGlob = "/agents/*/state/matrix-token";
+      # `matrix-token*` (not just `matrix-token`) so a secondary
+      # multi-account token (e.g. `matrix-token-ccc`) landing also
+      # re-fires the daemon to pick up the freshly-provisioned account.
+      pathConfig.PathExistsGlob = "/agents/*/state/matrix-token*";
     };
 
     # Path-trigger sibling: re-fires matrix-avatar-sync the moment