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POST /transactions/:id/cosign

Completes a user-proposed screening-off SafeTx queued below the threshold: the backup key signs the transaction’s safeTxHash, the server verifies the signature recovers to a distinct non-agent owner of that Safe, appends it, and triggers execution — relay-only, since the user’s signatures now meet the threshold and the agent signs nothing it didn’t screen. This is the mirror image of POST /transactions/:id/sign, which completes an agent-proposed (pre-signed) transaction with the user’s primary signature. The same transaction can always be completed in the Safe app instead — confirm with the backup key at app.safe.global and Zhentan’s sync worker reconciles the execution.

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Request

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Validation

  • The transaction must be a queued SafeTx with a proposer signature and no terminal state
  • The signature must recover to an owner of the Safe that is not the agent and has not already signed
  • Ownership: authenticated calls must belong to the transaction’s Safe

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Response