Add create endpoint for PartnerRequest and make publish/cancel idempotent#5

Draft

Copilot wants to merge 7 commits intofastapifrom

copilot/add-create-partner-request-endpoint

Commits on Dec 19, 2025

Initial plan
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Implement create partner request endpoint and make publish/cancel idempotent

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xiaoland
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Use discriminated union for PartnerRequestCreate to support different types

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Make manager publish/cancel methods idempotent as well

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Address code review feedback: remove redundant checks and fix defaults

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Final code review improvements: organize imports and improve error messages

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Use constant for supported create types to avoid maintenance burden

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xiaoland
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