[Feature Request] Taproot Multisig support for ColdCard Mk4

[aphex3k]

Coldcard supports Taproot and Taproot multi-sig, however, specter doesn't allow to connect coldcard via Taproot (nested and segwit only).

Taproot is already supported in connected hot-wallets (bitcoin core) and HWI also support taproot.

[al-munazzim]

Triage Assessment

Status: VALID-ENHANCEMENT — Straightforward fix available

Investigated the codebase. The issue is that ColdCard's device class doesn't enable Taproot support, even though:

• HWI supports Taproot for ColdCard
• ColdCard firmware supports Taproot multisig (as linked in the issue)
• Specter's internal Taproot handling already exists (used by SeedSigner, Trezor, etc.)

The fix appears to be:

1. Add taproot_support = True to src/cryptoadvance/specter/devices/coldcard.py
2. Update CC_TYPES dict to include "tr": "P2TR" (or whatever format ColdCard expects)
3. Test with actual ColdCard hardware to verify multisig file format compatibility

Would someone with a ColdCard Mk4 be willing to test a PR if I prepare one? The code change is minimal but hardware verification is needed.

Refs:

• src/cryptoadvance/specter/devices/coldcard.py — CC_TYPES only has legacy/p2sh-segwit/bech32
• Other devices with taproot: seedsigner.py, trezor.py, specter.py — all have taproot_support = True