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Background sessions run with session allow-rules cleared and a narrower set of working directories, and always snapshot the system prompt.
A new permission-context snapshot publisher zeroes out session allow-rules and restricts additional working directories to session-sourced ones specifically for background sessions, giving them a narrower permission footprint than foreground sessions. System prompt snapshotting is also now forced on whenever the session kind is bg (CLAUDE_CODE_SESSION_KIND=bg), in addition to being triggered by the existing explicit systemPromptSnapshot flag.
Names in the bundleCLAUDE_CODE_SESSION_KINDsystemPromptSnapshot