feat(desktop): add custom harness inline from agent dialogs

desktop/playwright.config.ts

@@ -126,6 +126,7 @@ export default defineConfig({
         "**/observer-archive-policy.spec.ts",
         "**/harness-management.spec.ts",
         "**/harness-catalog-screenshots.spec.ts",
+        "**/inline-custom-harness.spec.ts",
       ],
       use: {
         ...devices["Desktop Chrome"],

desktop/scripts/check-file-sizes.mjs

@@ -697,12 +697,18 @@ const overrides = new Map([
   // hidden-key projection keeps the top-level secret out of Advanced rows.
   // +6 (1195 -> 1201): rebase onto main — this PR's model-source label wiring
   // lands on top of main's dialog growth. Queued to split.
-  ["src/features/agents/ui/AgentInstanceEditDialog.tsx", 1201],
+  // +28 (1201 -> 1229): inline "Add custom harness…" entry — sentinel option,
+  // modal state, and the AddCustomHarnessDialog mount. The shared routing and
+  // deferred-selection logic lives in addCustomHarness.ts to keep this minimal.
+  ["src/features/agents/ui/AgentInstanceEditDialog.tsx", 1229],
   // AgentDefinitionDialog grew past 1000 with the following load-bearing fixes:
   // isRuntimeAutoSeededRef tracking for edit-mode seeding (Fizz shows models);
   // runtimeSupportsLlmProviderSelection guard on discovery provider (codex fix);
   // hideProviderIds computation for Databricks v1 gate. Queued to split.
-  ["src/features/agents/ui/AgentDefinitionDialog.tsx", 1035],
+  // +28 (1020 -> 1048): inline "Add custom harness…" entry — sentinel option,
+  // modal state, and the AddCustomHarnessDialog mount. The shared routing and
+  // deferred-selection logic lives in addCustomHarness.ts to keep this minimal.
+  ["src/features/agents/ui/AgentDefinitionDialog.tsx", 1048],
   // #2630 emoji picker search: the shadow-root search-input autofocus effect
   // (rAF retry loop) took this file 999 -> 1026 and landed without this entry,
   // so main's Desktop Core went red. Queued to split with the rest of this list.

desktop/src/features/agents/ui/AddCustomHarnessDialog.tsx

@@ -0,0 +1,47 @@
+import { CustomHarnessForm } from "@/features/settings/ui/CustomHarnessForm";
+import { ChooserDialogContent } from "@/shared/ui/chooser-dialog-content";
+import { Dialog } from "@/shared/ui/dialog";
+
+/**
+ * Registers a custom ACP harness from inside an agent dialog, so "New agent"
+ * is a complete entry point and not a dead end that sends the user to
+ * Settings. Hosts the same `CustomHarnessForm` the harness catalog uses.
+ */
+export function AddCustomHarnessDialog({
+  onOpenChange,
+  onSaved,
+  open,
+}: {
+  onOpenChange: (open: boolean) => void;
+  /** Called with the id of the harness that was just registered. */
+  onSaved: (id: string) => void;
+  open: boolean;
+}) {
+  return (
+    <Dialog onOpenChange={onOpenChange} open={open}>
+      <ChooserDialogContent
+        className="h-[42rem] max-w-2xl"
+        contentClassName="flex min-h-0 flex-1 p-0"
+        data-testid="add-custom-harness-dialog"
+        scrollAreaClassName="flex min-h-0 overflow-hidden px-0"
+        title="Add custom harness"
+      >
+        <CustomHarnessForm
+          chromeless
+          header={
+            <p className="text-sm text-muted-foreground">
+              Register any ACP-speaking agent tool as a selectable harness.
+            </p>
+          }
+          onCancel={() => onOpenChange(false)}
+          onSaved={(id) => {
+            // Dismiss on save as well as cancel — both exits belong to this
+            // dialog, so callers only handle the resulting selection.
+            onOpenChange(false);
+            onSaved(id);
+          }}
+        />
+      </ChooserDialogContent>
+    </Dialog>
+  );
+}

desktop/src/features/agents/ui/AgentDefinitionDialog.tsx

@@ -83,6 +83,12 @@ import {
 import { useProviderApiKeyFieldState } from "./providerApiKeyFieldState";
 import { buildRuntimeModelProviderPayload } from "./agentDefinitionSubmitPayload";
 import { AgentDefinitionDialogFooter } from "./AgentDefinitionDialogFooter";
+import { AddCustomHarnessDialog } from "./AddCustomHarnessDialog";
+import {
+  ADD_CUSTOM_HARNESS_OPTION,
+  runtimeDropdownAction,
+  usePendingHarnessSelection,
+} from "./addCustomHarness";
 
 type AgentDefinitionDialogProps = {
   open: boolean;
@@ -167,6 +173,7 @@ export function AgentDefinitionDialog({
   const [isAvatarUploadPending, setIsAvatarUploadPending] =
     React.useState(false);
   const [hasUserChanges, setHasUserChanges] = React.useState(false);
+  const [isAddHarnessOpen, setIsAddHarnessOpen] = React.useState(false);
   const {
     globalConfig,
     inheritedDefaults: {
@@ -308,6 +315,7 @@ export function AgentDefinitionDialog({
       setShowAdvancedFields(false);
       setIsAvatarUploadPending(false);
       setHasUserChanges(false);
+      setIsAddHarnessOpen(false);
       // isRuntimeAutoSeededRef and hasSeededForOpenRef are NOT reset here — the
       // [initialValues, open] effect resets both when the dialog re-opens.
     }
@@ -578,6 +586,7 @@ export function AgentDefinitionDialog({
       runtimes,
       runtimesLoading,
     });
+  runtimeDropdownOptions.push(ADD_CUSTOM_HARNESS_OPTION);
   const runtimeSummaryLabel = selectedRuntime
     ? formatRuntimeOptionLabel(selectedRuntime)
     : runtime.trim() || "Not configured";
@@ -662,9 +671,13 @@ export function AgentDefinitionDialog({
   }
 
   function handleRuntimeDropdownChange(nextValue: string) {
+    const action = runtimeDropdownAction(nextValue);
+    if (action.kind === "add-custom-harness") {
+      setIsAddHarnessOpen(true);
+      return;
+    }
     setHasUserChanges(true);
-    const nextRuntime =
-      nextValue === NO_RUNTIME_DROPDOWN_VALUE ? "" : nextValue;
+    const nextRuntime = action.runtimeId;
     // The user made an explicit choice — no longer auto-seeded.
     isRuntimeAutoSeededRef.current = false;
     setRuntime(nextRuntime);
@@ -680,6 +693,15 @@ export function AgentDefinitionDialog({
     );
   }
 
+  // Routed through the normal change handler so a harness registered inline
+  // resets model/provider exactly as a hand-picked one would. Scoped to `open`
+  // so a pending id can't outlive the dialog that started the registration.
+  const selectSavedHarness = usePendingHarnessSelection(
+    runtimes,
+    handleRuntimeDropdownChange,
+    open,
+  );
+
   function handleProviderDropdownChange(nextValue: string) {
     setHasUserChanges(true);
     const nextProvider =
@@ -944,6 +966,12 @@ export function AgentDefinitionDialog({
               returnFocusRef={aiDefaultsTriggerRef}
             />
 
+            <AddCustomHarnessDialog
+              onOpenChange={setIsAddHarnessOpen}
+              onSaved={selectSavedHarness}
+              open={isAddHarnessOpen}
+            />
+
             {isCreateMode ? createRunSection : null}
 
             <div className="space-y-3">

desktop/src/features/agents/ui/AgentInstanceEditDialog.tsx

@@ -83,6 +83,12 @@ import { useProviderApiKeyFieldState } from "./providerApiKeyFieldState";
 import { resolveModelFieldStatusMessage } from "./agentConfigControls";
 import { AdvancedRequiredBadge } from "./AdvancedRequiredBadge";
 import { showAgentProfileSyncWarning } from "./agentProfileSyncWarning";
+import { AddCustomHarnessDialog } from "./AddCustomHarnessDialog";
+import {
+  ADD_CUSTOM_HARNESS_OPTION,
+  runtimeDropdownAction,
+  usePendingHarnessSelection,
+} from "./addCustomHarness";
 
 const ADVANCED_FIELDS_MOTION_TRANSITION = {
   duration: 0.18,
@@ -157,6 +163,7 @@ export function AgentInstanceEditDialog({
   const [avatarUrl, setAvatarUrl] = React.useState(agent.avatarUrl ?? "");
   const [isAvatarUploadPending, setIsAvatarUploadPending] =
     React.useState(false);
+  const [isAddHarnessOpen, setIsAddHarnessOpen] = React.useState(false);
   const shouldReduceMotion = useReducedMotion();
 
   // Runtime selector: defaults to "custom" until the dialog opens and the
@@ -191,6 +198,7 @@ export function AgentInstanceEditDialog({
       setAvatarUrl(agent.avatarUrl ?? "");
       setShowAdvancedFields(false);
       setIsAvatarUploadPending(false);
+      setIsAddHarnessOpen(false);
       runtimeTouched.current = false;
       const matched =
         runtimes.find((r) => r.command?.trim() === agent.agentCommand.trim()) ??
@@ -244,6 +252,7 @@ export function AgentInstanceEditDialog({
         value: selectedRuntimeId,
       });
     }
+    options.push(ADD_CUSTOM_HARNESS_OPTION);
     return options;
   }, [sortedRuntimes, selectedRuntimeId]);
 
@@ -484,8 +493,12 @@ export function AgentInstanceEditDialog({
   }
 
   function handleRuntimeDropdownChange(nextValue: string) {
-    const nextRuntimeId =
-      nextValue === NO_RUNTIME_DROPDOWN_VALUE ? "" : nextValue;
+    const action = runtimeDropdownAction(nextValue);
+    if (action.kind === "add-custom-harness") {
+      setIsAddHarnessOpen(true);
+      return;
+    }
+    const nextRuntimeId = action.runtimeId;
     const previousRuntimeId = selectedRuntimeId;
     const nextRuntime = runtimes.find((r) => r.id === nextRuntimeId);
 
@@ -532,6 +545,16 @@ export function AgentInstanceEditDialog({
     );
   }
 
+  // Routed through the normal change handler so a harness registered inline
+  // pins its command and resets model/provider like a hand-picked one. Scoped
+  // to `open` so a pending id can't outlive the dialog that started the
+  // registration.
+  const selectSavedHarness = usePendingHarnessSelection(
+    runtimes,
+    handleRuntimeDropdownChange,
+    open,
+  );
+
   function handleProviderDropdownChange(nextValue: string) {
     const nextProvider =
       nextValue === AUTO_PROVIDER_DROPDOWN_VALUE ? "" : nextValue;
@@ -949,6 +972,11 @@ export function AgentInstanceEditDialog({
                   </span>
                 </p>
               ) : null}
+              <AddCustomHarnessDialog
+                onOpenChange={setIsAddHarnessOpen}
+                onSaved={selectSavedHarness}
+                open={isAddHarnessOpen}
+              />
             </div>
             {selectedRuntimeId === "custom" && !inheritHarness ? (
               <div className="space-y-1.5">