feat(tui): allow backgrounding synchronous subagents (#30488)

packages/opencode/src/server/routes/instance/httpapi/groups/experimental.ts

@@ -2,6 +2,7 @@ import { AccountID, OrgID } from "@/account/schema"
 import { MCP } from "@/mcp"
 
 import { Session } from "@/session/session"
+import { SessionID } from "@/session/schema"
 import { Worktree } from "@/worktree"
 import { NonNegativeInt } from "@opencode-ai/core/schema"
 import { Schema } from "effect"
@@ -91,6 +92,7 @@ export const ExperimentalPaths = {
   worktree: "/experimental/worktree",
   worktreeReset: "/experimental/worktree/reset",
   session: "/experimental/session",
+  sessionBackground: "/experimental/session/:sessionID/background",
   resource: "/experimental/resource",
 } as const
 
@@ -215,6 +217,19 @@ export const ExperimentalApi = HttpApi.make("experimental")
               "Get a list of all OpenCode sessions across projects, sorted by most recently updated. Archived sessions are excluded by default.",
           }),
         ),
+        HttpApiEndpoint.post("sessionBackground", ExperimentalPaths.sessionBackground, {
+          params: { sessionID: SessionID },
+          query: WorkspaceRoutingQuery,
+          success: described(Schema.Boolean, "Backgrounded subagents"),
+          error: HttpApiError.BadRequest,
+        }).annotateMerge(
+          OpenApi.annotations({
+            identifier: "experimental.session.background",
+            summary: "Background subagents",
+            description:
+              "Detach any synchronous subagents currently blocking the session and continue them in the background.",
+          }),
+        ),
         HttpApiEndpoint.get("resource", ExperimentalPaths.resource, {
           query: WorkspaceRoutingQuery,
           success: described(Schema.Record(Schema.String, MCP.Resource), "MCP resources"),