What
When another program runs Claude Code through the SDK (the kit for driving Claude Code from code), or in print mode (a single request that prints the answer and exits), the session runner gains new steps at startup. These steps are active:
takeClaimSessionStartHooks: holds backSessionStarthooks, the scripts you configure to run when a session begins or resumes.sdkMcpServersPending: waits for MCP servers supplied through the SDK that are not ready yet. An MCP server is an add-on that gives Claude extra tools.noteSdkEntryWait: records that the session waited at startup.
Why
If you run Claude Code from the SDK with your own MCP servers or SessionStart hooks, startup now waits for those servers and runs the hooks later. Your hooks may therefore fire at a slightly different moment than before.
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The finding does not say how long the session waits or exactly when the held-back hooks run.