descriptor: reject OP_IF/OP_NOTIF in Taproot miniscript under reduced-data

[kwsantiago]

Reduced-data (RDTS) invalidates tapscripts that execute OP_IF/OP_NOTIF, so a Taproot output whose leaf uses them can't be spent. The wallet could still create such descriptors via miniscript (or_c, or_d, or_i, andor, and the d:/j:/l:/u: wrappers).

This rejects those fragments at descriptor parse time in Tapscript context, the same layer and style as the existing tr() nesting-depth cap. It applies to create, import and watch alike, matching how deep taptrees are already handled. P2WSH is unaffected (OP_IF is valid there); inference is unaffected.

Tests: adds a guard test to wallet_miniscript.py; updates two descriptor_tests.cpp vectors that used l:pk (an or_i) tapscript leaf, now invalid, to non-branching leaves with recomputed scriptPubKeys.

[pdath]

ACK d97ca9d

I reviewed the code with Code Rabbit, and it only had this nit in wallet_miniscript.py (lines 345-358):
"The test exercises OR_C/OR_D and OR_I, but not ANDOR, WRAP_D, or WRAP_J, despite all being rejected by the parser guard. Add valid Taproot fixtures for those forms so switch-case omissions cannot re-enable conditional leaves."

I tested using the following commands on Ubuntu 24.04 running on ARM:

git clone https://github.com/bitcoinknots/bitcoin.git pr320
cd pr320
git fetch origin pull/320/head:pr320
git switch pr320

cmake -B build \
  -DRDTS_CONSENT=IMPLICIT \
  -DBUILD_GUI=OFF \
  -DCMAKE_BUILD_TYPE=Release
nice cmake --build build -j4

cd build
ctest -R descriptor_tests --output-on-failure
python3 test/functional/wallet_miniscript.py

[pdath]

ACK c8fae19

I reviewed the code with CodeRabbit and found no issues.

I tested using the following commands on Ubuntu 24.04 running on ARMv8-A (64-bit):

git clone https://github.com/bitcoinknots/bitcoin.git pr320
cd pr320
git fetch origin pull/320/head:pr320
git switch pr320

cmake -B build \\
-DRDTS_CONSENT=IMPLICIT \\
-DBUILD_GUI=OFF \\
-DCMAKE_BUILD_TYPE=Release \\
nice cmake --build build -j4

cd build
ctest -R descriptor_tests --output-on-failure
python3 test/functional/test_runner.py wallet_miniscript.py