Show provider subagents in the subagents track (#2013)

* Add provider-owned subagent stream contract

* OpenCode provider: detect child sessions, attach adopted children to the hosting server, synthesize external turns

- Emit internal provider_child_session_detected / provider_session_deleted stream events from the global event stream (before the no-active-turn gate), including BFS hydration of existing descendants on subscribe
- Track child sessions in a registry mapping child session id -> hosting server url; resumeSession attaches via acquireExisting() so adopted children share the parent's server generation and keep receiving live events
- Synthesize external turns for adopted (externally driven) sessions so timeline, tool calls, and permission requests stream without a Paseo-initiated prompt
- Honor launchContext.env in resumeSession (acquireDedicated parity with createSession)
- Stop folding child tool parts into the parent's sub_agent action log; the parent row stays as a pointer

* Render provider subagents in workspace timelines

* fix provider subagent timeline reliability

* fix provider subagent lifecycle edge cases

* fix provider subagent event fidelity

* Fix provider subagent history fidelity

* Fix restored provider subagent state

* Fix provider subagent visibility edges

* Restore provider subagent timelines

* Page provider subagent history

* Forward subagent questions reliably

* fix(subagents): preserve OpenCode child context

* fix(subagents): harden provider timeline routing

* fix(subagents): preserve provider page continuity

* fix(subagents): retain live child prompts

---------

Co-authored-by: Omer <639682+omercnet@users.noreply.github.com>

packages/app/src/stores/workspace-tabs-store/state.ts

@@ -19,6 +19,7 @@ export interface WorkspaceDraftTabSetup {
 export type WorkspaceTabTarget =
   | { kind: "draft"; draftId: string; setup?: WorkspaceDraftTabSetup }
   | { kind: "agent"; agentId: string }
+  | { kind: "provider_subagent"; parentAgentId: string; subagentId: string }
   | { kind: "terminal"; terminalId: string }
   | { kind: "browser"; browserId: string }
   | WorkspaceFileTabTarget
@@ -508,6 +509,17 @@ function coerceWorkspaceTabTarget(raw: Record<string, unknown>): WorkspaceTabTar
   if (kind === "agent" && typeof raw.agentId === "string") {
     return normalizeWorkspaceTabTarget({ kind: "agent", agentId: raw.agentId });
   }
+  if (
+    kind === "provider_subagent" &&
+    typeof raw.parentAgentId === "string" &&
+    typeof raw.subagentId === "string"
+  ) {
+    return normalizeWorkspaceTabTarget({
+      kind: "provider_subagent",
+      parentAgentId: raw.parentAgentId,
+      subagentId: raw.subagentId,
+    });
+  }
   if (kind === "terminal" && typeof raw.terminalId === "string") {
     return normalizeWorkspaceTabTarget({ kind: "terminal", terminalId: raw.terminalId });
   }