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title A8 PATTERNS — choose the synchronization contract
rectangle "01 Critical section\nvery short CPU-local invariant\nnever block" as critical
rectangle "02 Scheduler suspension\ndefer scheduling\ninterrupts still run" as suspend
rectangle "03 Mutex\nownership + priority inheritance\ntask context only" as mutex
rectangle "04 Gatekeeper task\nsingle resource owner\nmessage-based access" as gatekeeper
critical -[hidden]right- suspend
suspend -[hidden]right- mutex
mutex -[hidden]right- gatekeeper
note bottom of mutex
  FC08 selects this contract.
  A binary semaphore would not prove PIP.
end note
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