Claude Code mirrors your working directory in the background so it can compare and sync file states (directory sync, sometimes called checkout mirroring). This update teaches that internal engine to handle a new kind of update: a 'chained' generation, which arrives as a link pointing back to a previous bundle of files rather than sending the full bundle again.
Along with this, the engine now tracks two specific failure states, git_failed and link_stall, for when something goes wrong while following one of these chained links. When a chained update doesn't arrive as expected, the internal not_received diagnostic event now reports whether it was chained and whether it hit a link_stall. There's also a new published: null field recorded when a sync is in its 'armed' (ready but not yet fired) state.
This is internal plumbing for how Claude Code keeps its directory mirror in sync, and it makes failures in the sync process easier to diagnose: instead of a generic timeout, Anthropic can now tell whether a stalled update was following a chain of linked bundles and where exactly it got stuck.
The finding does not say what user-visible problem, if any, chained bundles fix or what triggers them.