807de2cebd wallet: skip R-value grinding for external signers (Sjors Provoost)
72b763e452 wallet: annotate bools in descriptor SPKM FillPSBT() (Sjors Provoost)
Pull request description:
When producing a dummy signature for the purpose of estimating the transaction fee, do not assume an external signer performs R-value grinding on the signature.
In particular, this avoids a scenario where the fee rate is 1 sat / vbyte and a transaction with a 72 byte signature is not accepted into our mempool.
Suggested testing:
1. On master, launch with `-signet` and create an external signer wallet using e.g. a Trezor and HWI, see [guide](https://github.com/bitcoin/bitcoin/blob/master/doc/external-signer.md#example-usage) (with the GUI it should "just work" once you have the HWI path configured).
2. Create a few addresses and fund them from the faucet: https://signet.bc-2.jp/ (wait for confirmation)
3. Create another address, and now send the entire wallet to it, set the fee to 1 sat/byte
4. Most likely this transaction never gets broadcast and you won't see it on the [signet explorer](https://explorer.bc-2.jp)
5. With this PR, try again.
6. Check the explorer and inspect the transaction. Each input witness starts with either `30440220` (R has 32 bytes) or `30440221` (R has 33 bytes). See this explainer for [DER encoding](https://bitcoin.stackexchange.com/questions/92680/what-are-the-der-signature-and-sec-format).
Fixes#26030
ACKs for top commit:
S3RK:
ACK 807de2cebd
achow101:
ACK 807de2cebd
furszy:
ACK 807de2ce
ishaanam:
utACK 807de2cebd
Tree-SHA512: 64f626a3030ef0ab1e43af86d8fba113151512561baf425e6e5182af53df3a64fa9e85c7f67bf4ed15b5ad6e5d5afc7fbba8b6e1f3bad388e48db51cb9446074
710cab1d43