Background (run_in_background) subagents run detached from the main query loop, so their tool_use/tool_result never reached the desktop and their cards stayed on "no tool activity" even after completion. Route the activity through the SDK event queue as agent_tool_activity, re-emitted by the ws handler as tool_use_complete/tool_result tagged with the parent Agent tool_use id, so the UI groups them under the agent card like synchronous subagents.
/agent should behave like a normal session prompt that tells the main model to use the selected Agent tool. The previous forked command path buffered the subagent run behind local command output and forced desktop clients to wait for command completion instead of seeing the normal Agent interaction stream.
Constraint: Desktop /agent must preserve ordinary chat/session semantics and still require /agent <agent> <prompt>.
Rejected: Keep slash_agent SDK event bridging | it preserves the separate forked execution path instead of fixing the product flow.
Confidence: high
Scope-risk: moderate
Directive: Do not move /agent back to context: fork without proving the desktop normal Agent tool stream still works.
Tested: bun test src/commands/agent.test.ts src/utils/processUserInput/processSlashCommand.test.ts src/server/__tests__/ws-memory-events.test.ts
Tested: cd desktop && bun run test -- --run src/stores/chatStore.test.ts src/components/chat/MessageList.test.tsx
Tested: git diff --check
Not-tested: bun run check:server is blocked before source checks by expired quarantine entries: server:cron-scheduler, server:providers-real, server:tasks, server:e2e:business-flow, server:e2e:full-flow
The desktop /agent slash path runs before the normal query loop, so the old implementation waited for the forked command to finish and only surfaced the final local-command stdout. Emit foreground slash-agent task events from /agent, drain SDK events while QueryEngine waits for pre-query slash processing, and allow those current-turn events through the WebSocket pre-send mute gate.
Constraint: /agent is a forked slash command that does not produce ordinary assistant deltas until its final stdout is synthesized.
Rejected: Frontend-only loading state | would not expose real forked-agent progress or tool/tool-result updates.
Confidence: high
Scope-risk: moderate
Directive: Keep slash_agent task events scoped to /agent; ordinary slash command stdout and /goal event handling should remain on the existing local-command paths.
Tested: bun test src/QueryEngine.test.ts src/utils/processUserInput/processSlashCommand.test.ts src/server/__tests__/ws-memory-events.test.ts
Tested: cd desktop && bun run test -- --run src/stores/chatStore.test.ts src/components/chat/MessageList.test.tsx
Not-tested: bun run check:server is blocked by expired quarantine review entries: server:cron-scheduler, server:providers-real, server:tasks, server:e2e:business-flow, server:e2e:full-flow
Desktop sessions can receive task tools, background-agent lifecycle events, and child tool stream events in the same turn. The UI now keeps root Agent cards separate from task-management tools, preserves parent links when later stream events omit them, and surfaces completed background-agent result text from task notifications.
Constraint: Existing desktop session history can contain task-notification XML and live WS events with incomplete parent metadata.
Rejected: Render local_agent lifecycle messages as standalone cards | duplicates the Agent tool card and makes ownership unclear.
Confidence: high
Scope-risk: moderate
Directive: Do not collapse Agent and TaskCreate/TaskUpdate root tools into one generic group without checking multi-agent screenshots.
Tested: SKIP_INSTALL=1 PRESERVE_TAURI_TARGET=1 ./desktop/scripts/build-macos-arm64.sh
Tested: Real gpt-5.5 desktop E2E sessions under /tmp/cc-haha-subagent-e2e-20260519-025454 for 3 subagents, child tools, result dialog, and background Bash completion.
Not-tested: Full bun run verify gate.
