fix(desktop): pin harness when Custom command selected in EditAgentDialog

Selecting Custom command for an inheriting persona-linked agent left
inheritHarness=true because that branch had no catalog runtime, so Save
silently followed the inherit path and discarded the custom command.
Clear inheritance for any explicit runtime selection so the command
input becomes editable and the pin path persists the choice.

Signed-off-by: npub13fn4ahfnvaa2qwylvegdgeajqs0mph6v4qsw4jcqnw4mjh3hzh2quuucm5 <8a675edd33677aa0389f6650d467b2041fb0df4ca820eacb009babb95e3715d4@sprout-oss.stage.blox.sqprod.co>

Author: npub13fn4ahfnvaa2qwylvegdgeajqs0mph6v4qsw4jcqnw4mjh3hzh2quuucm5

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

@@ -260,19 +260,23 @@ export function EditAgentDialog({
     // effect will no longer overwrite selectedRuntimeId after this point.
     runtimeTouched.current = true;
 
-    setSelectedRuntimeId(nextRuntimeId || "custom");
+    const resolvedRuntimeId = nextRuntimeId || "custom";
+    setSelectedRuntimeId(resolvedRuntimeId);
+
+    // Any explicit runtime selection pins the harness — this is the
+    // authoritative override. Disabling inheritance ensures the choice is
+    // actually persisted (Save follows the pin path, not the inherit path) and
+    // that the Advanced command input becomes editable for the custom case.
+    // "Custom command" has no catalog entry, so it must clear inheritance here
+    // rather than relying on the concrete-runtime branch below.
+    setInheritHarness(false);
 
     // When switching to a catalog-known runtime, update the agent command to
     // its resolved command so the command field stays consistent.
     if (nextRuntime?.command) {
       setAgentCommand(nextRuntime.command);
       const newArgs = nextRuntime.defaultArgs.join(",");
       setAgentArgs(newArgs);
-      // Selecting a concrete catalog runtime pins the harness — this is the
-      // authoritative override. Disabling inheritance ensures the runtime is
-      // actually persisted and prevents a mismatched provider from being saved
-      // against an inherited runtime that will actually run something else.
-      setInheritHarness(false);
     }
 
     // Clear model when switching away from a runtime with a different model scope.

desktop/src/features/agents/ui/editAgentProviderDiscovery.test.mjs

@@ -335,6 +335,63 @@ test("editAgent_runtimeDropdown_pinsHarnessWhenConcreteCatalogRuntimeSelected",
   );
 });
 
+// ── Custom command as a runtime pin ──────────────────────────────────────────
+//
+// "Custom command" has no catalog entry (nextRuntime === undefined), so it must
+// clear inheritance directly in the handler rather than relying on the
+// concrete-runtime branch. Without this, an inheriting persona-linked agent that
+// picks "Custom command" keeps inheritHarness=true, the command input stays
+// gated behind !inheritHarness, and Save silently follows the inherit path —
+// discarding the custom-command intent.
+
+test("editAgent_runtimeDropdown_pinsHarnessWhenCustomCommandSelected", () => {
+  // Simulate handleRuntimeDropdownChange("custom") for an inherited agent.
+  let inheritHarness = true; // starts inherited
+
+  const NO_RUNTIME_DROPDOWN_VALUE = "__none__";
+  const nextValue = "custom";
+  const nextRuntimeId =
+    nextValue === NO_RUNTIME_DROPDOWN_VALUE ? "" : nextValue;
+  const nextRuntime = undefined; // "custom" has no catalog entry
+
+  // The fixed handler clears inheritance for ANY explicit selection, before the
+  // concrete-runtime branch (which never runs for a custom command).
+  inheritHarness = false;
+  if (nextRuntime?.command) {
+    // concrete-runtime branch — not taken for custom command
+  }
+
+  assert.equal(nextRuntimeId, "custom");
+  assert.equal(
+    inheritHarness,
+    false,
+    "selecting 'Custom command' must set inheritHarness=false so the command input is editable and Save takes the pin path",
+  );
+});
+
+test("editAgent_customCommandSelected_savePinsCustomCommandNotInherit", () => {
+  // After the custom-command selection clears inheritance, the submit path must
+  // pin the (edited) custom command rather than following the inherit sentinel.
+  const inheritHarness = false; // cleared by the custom-command selection
+  const agentOriginalCommand = ""; // was inheriting, no command
+  const agentCommandOverride = null;
+  const editedCustomCommand = "/opt/bin/my-custom-agent";
+
+  const agentCommandUpdate = inheritHarness
+    ? agentCommandOverride != null
+      ? ""
+      : undefined
+    : editedCustomCommand.trim() !== agentOriginalCommand
+      ? editedCustomCommand.trim()
+      : undefined;
+
+  assert.equal(
+    agentCommandUpdate,
+    "/opt/bin/my-custom-agent",
+    "custom command must be persisted as a pin, not silently dropped by the inherit path",
+  );
+});
+
 test("editAgent_inheritedAgentRuntimeSwitch_producesConsistentCommandProviderPair", () => {
   // Bad path before fix: inheritHarness stays true, so agentCommandUpdate is
   // undefined (agent still inherits Claude), but provider="databricks_v2" persists.