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feat(core): run subagents in the background by default - #62035
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This was referenced Nov 5, 2026
Foreground becomes background plus a wait: an explicit background=false starts the same job and blocks on it, returning the child result inline. The tool description and docs now lead with background.
…uation A foreground follow-up that continues a child whose job is already backgrounded joined it through jobs.block, which returns a running handle immediately. Claim the backgrounded generation instead: silence the subagent.notify preference before the prompt is admitted, wait on the job's done with jobs.wait, and return the final answer inline. A prompt that never reaches the child releases the claim so the original launch still reports. A joined backgrounded job holds no block registration, so the user's move-to-background cannot detach this explicit foreground wait.
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The subagent tool now runs subagents in the background by default.
The parent gets the child's session ID right away and keeps working; the child's answer arrives later as a message. Pass
background: falseto wait for the answer inline, as before.Stacked on #61833, which makes those later reports reliable. Part 2 of 3.
💡 Why
Most subagent work is independent. Waiting by default blocks the parent for minutes, and models rarely ask for background on their own. With #61833, a background child always reports back once it and its own background work are done, so waiting is no longer the safe choice.
🆕 Now you can
background: falsewhen the next step needs it.notify: falseand read its session yourself later.The tool description and the tools docs page now say background is the default and when to use
background: false.background: falseon a child that is already running in the background waits for that run and returns its answer inline, and an interrupted foreground prompt releases its claim so the child can report again.📊 Proof: 38 tests pass in
subagent-lifetimeandtool-subagent. The tests that relied on the old default now passbackground: falseexplicitly.👀 Read:
packages/core/src/tool/plugin/subagent.ts, the tool description. It's what tells the model to end its turn or keep working instead of waiting. The rest is routine.From a team design discussion · no user reports · reviewed before push
Checks run
bun test test/subagent-lifetime.test.ts test/tool-subagent.test.ts(packages/core): 38 passbun typecheck(packages/core): no type errors