feat(pi): manage global subagent configuration

hosts/neogaia/default.nix

@@ -68,6 +68,7 @@
   modules.agents.herdr.enable = true;
   modules.agents.tools.gitea-axi.enable = true;
   modules.agents.pi.enable = true;
+  modules.agents.pi.subagents.maxConcurrent = 8;
 
   modules.desktop.enable = true;
   modules.desktop.obsidian.enable = true;

modules/agents/pi/pi.nix

@@ -11,6 +11,40 @@ let
   cfg = config.modules.agents.pi;
   user = config.user.name;
   piDir = "${config.users.users.${user}.home}/.pi/agent";
+  reservedToolProfiles = [
+    "none"
+    "read-only"
+    "read-only-with-safe-bash"
+    "full-tools"
+  ];
+  subagentsConfig =
+    lib.optionalAttrs (cfg.subagents.defaultContext != null) {
+      defaultContext = cfg.subagents.defaultContext;
+    }
+    // lib.optionalAttrs (cfg.subagents.defaultTools != null) {
+      defaultTools = cfg.subagents.defaultTools;
+    }
+    // lib.optionalAttrs (cfg.subagents.maxConcurrent != null) {
+      maxConcurrent = cfg.subagents.maxConcurrent;
+    }
+    // lib.optionalAttrs (cfg.subagents.recentTerminalTtlMs != null) {
+      recentTerminalTtlMs = cfg.subagents.recentTerminalTtlMs;
+    }
+    // lib.optionalAttrs (
+      cfg.subagents.ui.enabled != null || cfg.subagents.ui.defaultExpanded != null
+    ) {
+      ui =
+        lib.optionalAttrs (cfg.subagents.ui.enabled != null) {
+          enabled = cfg.subagents.ui.enabled;
+        }
+        // lib.optionalAttrs (cfg.subagents.ui.defaultExpanded != null) {
+          defaultExpanded = cfg.subagents.ui.defaultExpanded;
+        };
+    }
+    // lib.optionalAttrs (cfg.subagents.toolProfiles != { }) {
+      toolProfiles = cfg.subagents.toolProfiles;
+    };
+  subagentsJson = (pkgs.formats.json { }).generate "pi-subagents.json" subagentsConfig;
   patchedPi = pkgs.pi-coding-agent.overrideAttrs (old: {
     patches = (old.patches or [ ]) ++ [
       ./patches/pi-flex-spacer.patch
@@ -39,10 +73,112 @@ let
   };
 in
 {
-  options.modules.agents.pi.enable = lib.mkEnableOption ''
+  options.modules.agents.pi = {
+    enable = lib.mkEnableOption ''
       Pi, a terminal coding agent, configured via home-manager'';
 
+    subagents = {
+      defaultContext = lib.mkOption {
+        type = lib.types.nullOr (lib.types.enum [
+          "independent"
+          "fork"
+        ]);
+        default = null;
+        description = ''
+          Default context mode for subagents.
+          Left null, the extension keeps its in-code default.
+        '';
+      };
+
+      defaultTools = lib.mkOption {
+        type = lib.types.nullOr lib.types.str;
+        default = null;
+        example = "read-only-with-safe-bash";
+        description = ''
+          Default tool profile for subagents.
+          Left null, the extension keeps its in-code default.
+        '';
+      };
+
+      maxConcurrent = lib.mkOption {
+        type = lib.types.nullOr lib.types.ints.positive;
+        default = null;
+        example = 4;
+        description = ''
+          Maximum number of child processes allowed to run concurrently.
+          Left null, the extension keeps its in-code default.
+        '';
+      };
+
+      recentTerminalTtlMs = lib.mkOption {
+        type = lib.types.nullOr lib.types.ints.unsigned;
+        default = null;
+        example = 600000;
+        description = ''
+          Milliseconds to retain terminal subagents in the recent work set.
+          Zero disables time-based retention.
+          Left null, the extension keeps its in-code default.
+        '';
+      };
+
+      ui = {
+        enabled = lib.mkOption {
+          type = lib.types.nullOr lib.types.bool;
+          default = null;
+          description = ''
+            Whether the extension renders its built-in subagent monitor.
+            Left null, the extension keeps its in-code default.
+          '';
+        };
+
+        defaultExpanded = lib.mkOption {
+          type = lib.types.nullOr lib.types.bool;
+          default = null;
+          description = ''
+            Whether the built-in subagent monitor starts expanded.
+            Left null, the extension keeps its in-code default.
+          '';
+        };
+      };
+
+      toolProfiles = lib.mkOption {
+        type = lib.types.attrsOf (
+          lib.types.submodule {
+            options.activeTools = lib.mkOption {
+              type = lib.types.listOf lib.types.str;
+              description = "Pi tools made available to a child using this profile.";
+            };
+          }
+        );
+        default = { };
+        example = {
+          review = {
+            activeTools = [
+              "read"
+              "grep"
+              "find"
+              "ls"
+            ];
+          };
+        };
+        description = ''
+          Custom named tool profiles for subagents.
+          The extension's reserved built-in profile names cannot be redefined.
+        '';
+      };
+    };
+  };
+
   config = lib.mkIf cfg.enable {
+    assertions = [
+      {
+        assertion = lib.intersectLists reservedToolProfiles (
+          builtins.attrNames cfg.subagents.toolProfiles
+        ) == [ ];
+        message = "modules.agents.pi.subagents.toolProfiles may not redefine the reserved profiles: ${lib.concatStringsSep ", " reservedToolProfiles}.";
+      }
+    ];
+
     home-manager.users.${user} = {
       programs.pi-coding-agent = {
         enable = true;
@@ -58,7 +194,8 @@ in
         };
       };
 
-      home.file = {
+      home.file =
+        {
           # The first declarative rollout replaces the interactive settings file.
           # Login state stays in auth.json, which this module does not manage.
           "${piDir}/settings.json".force = true;
@@ -72,6 +209,13 @@ in
             source = ./prompts;
             recursive = true;
           };
+        }
+        // lib.optionalAttrs (subagentsConfig != { }) {
+          # Declaring any global override makes Nix the owner of the runtime file.
+          "${piDir}/subagents.json" = {
+            source = subagentsJson;
+            force = true;
+          };
         };
     };
   };