fix(mcp): launch parallel children before waiting

evals/mcp-tool-use/cases/orchestration.ndjson

@@ -42,3 +42,4 @@
 {"id": "settle-after-delayed-merge-waits", "area": "orchestration", "kind": "guard", "pattern": "settle before delayed work finishes", "experience": "Asked to merge a PR once its checks pass and then settle this thread, an agent following the #26749 settle bullet can settle in the first turn; a settled thread refuses watch_pull_request and drops PR-watch wakes, so the merge never happens.", "rule": "Asked to settle ... a thread, including this one: call t3_thread_organize. (the request is to settle after the merge, not now)", "privacy": "commit-safe", "notes": "From the CodeRabbit finding on #26765. Settling this thread applies at turn end, and Orchestrator.ts rejects watch wakes on a settled thread. Good: watch #123 and end the turn without settling. gh pr merge --auto plus a settle would still lose the wake that confirms the merge.", "setup": {"role": "top", "priorTurns": [{"role": "user", "text": "Okay this looks good to me. Any risk merging it?"}, {"role": "assistant", "text": "Low risk. [#123](https://github.com/acme/app/pull/123) only adds an accessible title to the HTML preview frame, and the new test covers it. Two checks are still running: Check and Test Web.", "toolCalls": [{"tool": "Bash", "input": {"command": "gh pr view 123 --json title,files --jq '.title, .files[].path'"}, "result": "fix(web): HTML preview frame gets an accessible title\napps/web/src/HtmlPreview.tsx\napps/web/src/HtmlPreview.test.tsx"}, {"tool": "Bash", "input": {"command": "gh pr checks 123"}, "result": "Lint\tpass\t41s\nTypecheck\tpass\t1m2s\nCheck\tpending\t0\nTest Web\tpending\t0"}, {"tool": "link_pull_request", "input": {"url": "https://github.com/acme/app/pull/123"}, "result": {"host": "github.com", "repository": "acme/app", "number": 123, "url": "https://github.com/acme/app/pull/123", "alreadyLinked": false}}]}], "mocks": {"watch_pull_request": "default", "link_pull_request": "default", "t3_thread_organize": {"settlesWhenTurnEnds": true}}, "world": {"branch": "fix/html-preview-title", "commits": [{"sha": "abc1234", "subject": "fix(web): HTML preview frame gets an accessible title"}], "diff": "diff --git a/apps/web/src/HtmlPreview.tsx b/apps/web/src/HtmlPreview.tsx\n--- a/apps/web/src/HtmlPreview.tsx\n+++ b/apps/web/src/HtmlPreview.tsx\n@@ -1,3 +1,3 @@\n export function HtmlPreview({ html }: { html: string }) {\n-  return <iframe sandbox=\"allow-scripts\" srcDoc={html} height={400} />;\n+  return <iframe title=\"HTML preview\" sandbox=\"allow-scripts\" srcDoc={html} height={400} />;\n }\ndiff --git a/apps/web/src/HtmlPreview.test.tsx b/apps/web/src/HtmlPreview.test.tsx\nnew file mode 100644\n--- /dev/null\n+++ b/apps/web/src/HtmlPreview.test.tsx\n+import { expect, it } from 'vitest';\n+import { render, screen } from '@testing-library/react';\n+import { HtmlPreview } from './HtmlPreview';\n+\n+it('gives the preview frame an accessible name', () => {\n+  render(<HtmlPreview html=\"<p>hi</p>\" />);\n+  expect(screen.getByTitle('HTML preview')).toBeTruthy();\n+});\n", "prs": [{"number": 123, "title": "fix(web): HTML preview frame gets an accessible title", "headRefName": "fix/html-preview-title", "checks": [{"name": "Lint", "state": "pass"}, {"name": "Typecheck", "state": "pass"}, {"name": "Check", "state": "pending"}, {"name": "Test Web", "state": "pending"}]}], "files": {"apps/web/src/HtmlPreview.tsx": "export function HtmlPreview({ html }: { html: string }) {\n  return <iframe title=\"HTML preview\" sandbox=\"allow-scripts\" srcDoc={html} height={400} />;\n}\n", "apps/web/src/HtmlPreview.test.tsx": "import { expect, it } from 'vitest';\nimport { render, screen } from '@testing-library/react';\nimport { HtmlPreview } from './HtmlPreview';\n\nit('gives the preview frame an accessible name', () => {\n  render(<HtmlPreview html=\"<p>hi</p>\" />);\n  expect(screen.getByTitle('HTML preview')).toBeTruthy();\n});\n"}}, "shellMocks": [{"match": "gh pr merge", "output": "✓ Squashed and merged pull request acme/app#123 (fix(web): HTML preview frame gets an accessible title)"}]}, "prompt": "Merge it once its checks pass, then settle this thread.", "expect": {"calls": [{"tool": "watch_pull_request", "args": {"url": "~/pull/123"}}], "notCalls": ["t3_thread_organize", "Monitor", "ScheduleWakeup"], "shellMustNot": ["\\bsleep \\d", "gh pr checks[^\\n]*--watch", "gh run watch", "\\buntil\\b[^\\n]*\\bgh (pr|run|api)\\b", "pr-wait", "gh pr merge(?![^\\n]*--auto)"]}}
 {"id": "settle-after-merge-on-wake", "area": "orchestration", "kind": "bad", "pattern": "settle read as plain English for finish", "experience": "Asked to merge a PR once its checks pass and then settle this thread, the agent merged on the checks-passed wake and ended the turn without calling t3_thread_organize (#26749).", "rule": "Asked to settle ... a thread, including this one: call t3_thread_organize.", "privacy": "commit-safe", "notes": "From #26749's delayed pattern. Wake text is copied from pullRequestWatch.ts. Good: merge #123, then settle this thread on the same turn.", "setup": {"role": "top", "priorTurns": [{"role": "user", "text": "Okay this looks good to me. Any risk merging it?"}, {"role": "assistant", "text": "Low risk. [#123](https://github.com/acme/app/pull/123) only adds an accessible title to the HTML preview frame, and the new test covers it. Two checks are still running: Check and Test Web.", "toolCalls": [{"tool": "Bash", "input": {"command": "gh pr view 123 --json title,files --jq '.title, .files[].path'"}, "result": "fix(web): HTML preview frame gets an accessible title\napps/web/src/HtmlPreview.tsx\napps/web/src/HtmlPreview.test.tsx"}, {"tool": "Bash", "input": {"command": "gh pr checks 123"}, "result": "Lint\tpass\t41s\nTypecheck\tpass\t1m2s\nCheck\tpending\t0\nTest Web\tpending\t0"}, {"tool": "link_pull_request", "input": {"url": "https://github.com/acme/app/pull/123"}, "result": {"host": "github.com", "repository": "acme/app", "number": 123, "url": "https://github.com/acme/app/pull/123", "alreadyLinked": false}}]}, {"role": "user", "text": "Merge it once its checks pass, then settle this thread."}, {"role": "assistant", "text": "T3 Code is watching [#123](https://github.com/acme/app/pull/123). I'll merge it once Check and Test Web pass, then settle this thread.", "toolCalls": [{"tool": "watch_pull_request", "input": {"url": "https://github.com/acme/app/pull/123"}, "result": {"host": "github.com", "repository": "acme/app", "number": 123, "url": "https://github.com/acme/app/pull/123", "watching": true, "wasWatching": false}}]}], "mocks": {"watch_pull_request": "default", "link_pull_request": "default", "t3_thread_organize": {"settlesWhenTurnEnds": true}, "unwatch_pull_request": "default"}, "world": {"branch": "fix/html-preview-title", "commits": [{"sha": "abc1234", "subject": "fix(web): HTML preview frame gets an accessible title"}], "diff": "diff --git a/apps/web/src/HtmlPreview.tsx b/apps/web/src/HtmlPreview.tsx\n--- a/apps/web/src/HtmlPreview.tsx\n+++ b/apps/web/src/HtmlPreview.tsx\n@@ -1,3 +1,3 @@\n export function HtmlPreview({ html }: { html: string }) {\n-  return <iframe sandbox=\"allow-scripts\" srcDoc={html} height={400} />;\n+  return <iframe title=\"HTML preview\" sandbox=\"allow-scripts\" srcDoc={html} height={400} />;\n }\ndiff --git a/apps/web/src/HtmlPreview.test.tsx b/apps/web/src/HtmlPreview.test.tsx\nnew file mode 100644\n--- /dev/null\n+++ b/apps/web/src/HtmlPreview.test.tsx\n+import { expect, it } from 'vitest';\n+import { render, screen } from '@testing-library/react';\n+import { HtmlPreview } from './HtmlPreview';\n+\n+it('gives the preview frame an accessible name', () => {\n+  render(<HtmlPreview html=\"<p>hi</p>\" />);\n+  expect(screen.getByTitle('HTML preview')).toBeTruthy();\n+});\n", "prs": [{"number": 123, "title": "fix(web): HTML preview frame gets an accessible title", "headRefName": "fix/html-preview-title", "checks": [{"name": "Lint", "state": "pass"}, {"name": "Typecheck", "state": "pass"}, {"name": "Check", "state": "pass"}, {"name": "Test Web", "state": "pass"}], "mergeStateStatus": "CLEAN"}], "files": {"apps/web/src/HtmlPreview.tsx": "export function HtmlPreview({ html }: { html: string }) {\n  return <iframe title=\"HTML preview\" sandbox=\"allow-scripts\" srcDoc={html} height={400} />;\n}\n", "apps/web/src/HtmlPreview.test.tsx": "import { expect, it } from 'vitest';\nimport { render, screen } from '@testing-library/react';\nimport { HtmlPreview } from './HtmlPreview';\n\nit('gives the preview frame an accessible name', () => {\n  render(<HtmlPreview html=\"<p>hi</p>\" />);\n  expect(screen.getByTitle('HTML preview')).toBeTruthy();\n});\n"}}, "shellMocks": [{"match": "gh pr merge", "output": "✓ Squashed and merged pull request acme/app#123 (fix(web): HTML preview frame gets an accessible title)"}]}, "prompt": "Update on pull request #123 (https://github.com/acme/app/pull/123), which T3 Code is watching for you:\n- All 4 checks passed on abc1234.\n\nLook into each item and act on it as your task requires. This PR stays linked and watched, so do not link, watch, or list it again. End your turn when you are done, and T3 Code wakes you on the next change. When you hand the work back to the user, call unwatch_pull_request first so the thread returns to their inbox.", "expect": {"calls": [{"tool": "Bash", "args": {"command": "~gh pr merge"}}, {"tool": "t3_thread_organize", "args": {"action": "settle"}}], "notCalls": ["watch_pull_request", "t3_thread_update", "Monitor", "ScheduleWakeup"], "shellMustNot": ["\\bsleep \\d", "gh pr checks[^\\n]*--watch", "gh run watch", "\\buntil\\b[^\\n]*\\bgh (pr|run|api)\\b", "pr-wait"]}}
 {"id": "thread-send-fresh-context", "area": "orchestration", "kind": "guard", "pattern": "t3_thread_send that should start a fresh provider session", "experience": "The user wanted a confused long-running thread to start over in the same thread without its old context; a plain send would keep feeding it the history.", "rule": "`freshContext: true` on t3_thread_send starts a new provider session in the same thread, like /clear.", "privacy": "commit-safe", "setup": {"role": "top", "priorTurns": [{"role": "user", "text": "The thread working on the CSV importer keeps reverting to the old column mapping from early in its history."}, {"role": "assistant", "text": "That thread has a long history with three different mappings in it, so the model keeps picking up the stale one."}], "mocks": {"t3_thread_send": {"threadId": "11111111-1111-4111-8111-111111111111", "link": "<t3-thread://v2/eeeeeeee-eeee-4eee-8eee-eeeeeeeeeeee/11111111-1111-4111-8111-111111111111>", "messageId": "msg-1", "runId": "run-1", "status": "starting", "delivery": "started"}}}, "prompt": "Send it the final mapping below and have it start over with a clean context in that same thread, so the old history stops leaking in: thread 11111111-1111-4111-8111-111111111111.\n\nFinal mapping: id -> customer_id, amt -> amount_cents, ts -> created_at.", "expect": {"calls": [{"tool": "t3_thread_send", "args": {"threadId": "11111111-1111-4111-8111-111111111111", "freshContext": true}}], "notCalls": ["delegate_task", "t3_thread_launch", "create_threads"]}, "source": {"request": "juliusmarminge (maintainer) request, 2026-11-03: fresh provider sessions in one T3 thread"}, "notes": "Pairs with thread-send-to-named-top-level-thread, where an ordinary send must not set freshContext."}
+{"id": "parallel-delegates-launch-async", "area": "orchestration", "kind": "bad", "pattern": "parallel delegates launched with batched waits", "experience": "Asked for two delegates in parallel, the agent batched two delegate_task mode:'wait' calls. The provider's MCP client ran them one at a time, so the second child started only after the first wait returned, while the agent told the user both were running.", "rule": "delegate_task mode: Default 'async'. Parallel: start all, then follow `next`. 'wait' only for one child this turn needs.", "privacy": "commit-safe", "setup": {"role": "top", "context": "Repository: /home/user/app (acme/app). This is the local machine.", "world": {"repo": "acme/app", "branch": "main", "status": "", "files": {"src/thread-pool.ts": "export const workerCount = 4;\n", "src/task-queue.ts": "export const queueLimit = 10;\n"}}}, "prompt": "Have two GPT-6.1 Sol delegates in Codex review in parallel: one reviews src/thread-pool.ts, the other src/task-queue.ts. I need both reviews before you answer.", "expect": {"calls": [{"tool": "delegate_task", "args": {"task": "~thread-pool"}}, {"tool": "delegate_task", "args": {"task": "~task-queue"}}], "notCalls": ["t3_thread_launch", "create_threads"], "callsMustNot": [{"tool": "delegate_task", "args": {"mode": "wait"}}]}, "source": {"issue": "pingdotgg/t3code#23175"}, "notes": "Synthetic Acme scenario; no field transcript copied. The simulated MCP client does not serialize calls, so the case checks the launch mode, not dispatch timing."}

packages/contracts/src/orchestratorMcp.ts

@@ -174,13 +174,13 @@ export const OrchestratorMcpDelegateTaskInput = Schema.Struct({
   isolation: Schema.optional(
     Schema.Literals(["shared", "worktree"]).annotate({
       description:
-        "'shared' (default): parent checkout. 'worktree': new prepared checkout from the parent commit, for a separate checkout or PR per child. Uncommitted edits stay out.",
+        "'shared' (default): parent checkout. 'worktree': new prepared checkout from the parent commit. Uncommitted edits stay out.",
     }),
   ),
   mode: Schema.optional(
     Schema.Literals(["async", "wait"]).annotate({
       description:
-        "Default 'async'. 'wait' only if this turn needs the result. A question or approval ends the wait.",
+        "Default 'async'. Parallel: start all, then follow `next`. 'wait' only for one child this turn needs. A question or approval ends the wait.",
     }),
   ),
   timeoutMs: Schema.optional(Schema.Finite).annotate({