LangChain fixes deepagents parent-state leak into subagents

LangChain fixed a bug in deepagents that let private parent state leak into subagents, in the langchain-quickjs 0.3.7 release posted September 6.

The bug, tracked as issue #3543, sat in how deepagents spawns subagents. Whatever the parent process held back could still pass down to children with no reason to see it.

Teams building parent-to-subagent pipelines in deepagents before this release have no way to know how far back the leak goes. The release notes don't say which earlier versions were affected.

Subagent isolation only works if the boundary between parent and child state actually holds, and this release admits it didn't.

The same release adds native streaming for PTC tool calls, a separate change bundled into the fix.

LangChain didn't publish a security advisory or CVE alongside the release, just a changelog entry. That leaves the exposure scope, how many subagents received data they shouldn't have, unstated.