The automation-only ACP refactor (#586) removed the bridge's pendingSwitches
idle-preset anchoring the inheritance note cited as precedent. Replace the
dangling analogy with the load-bearing fact a reviewer actually needs: an
injection-triggered first turn (a SessionStart hook racing the prompt)
dispatches no prompt-submit and no model request, so the one-shot stamp
listener still lands before the child's first model request.
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