Count each reference script UTxO once toward the fee

[theeldermillenial]

Summary

TransactionBuilder counted a reference script once per redeemer that used it, not once per reference input. A transaction that spends a script UTxO and also withdraws through the same script, both resolved from one reference UTxO, got that script's size added to _ref_script_size() twice. reference_inputs is a set, so the UTxO appears in the transaction once, and the ledger charges each input's and reference input's script once. The builder overpaid the fee by the full tiered reference-script fee for every extra use, and max_tx_fee (which sizes the collateral) was inflated the same way.

_add_reference_script(utxo) now records each UTxO's script once, keyed by its input, at every site that appends one: add_input, add_script_input, add_minting_script, add_withdrawal_script and add_certificate_script. The same script held by two different UTxOs still counts twice, matching the ledger.

Example

A mainnet transaction with a 9,851-byte Plutus V3 reference script shared by a spend and a withdrawal:

	before	after
reference-script bytes counted	19,702	9,851
fee (with fee_buffer=100)	603,681	455,916
ledger minimum fee	455,816	455,816

Replaying the transaction through TransactionBuilder before the fix reproduces its on-chain fee, collateral, change and script data hash exactly. After the fix, the fee is the ledger minimum plus the buffer.

Tests

• test_reference_script_shared_by_spend_and_withdrawal_counted_once: one reference UTxO used by a spend and a withdrawal counts once (failed before the fix: 38 vs 19)
• test_same_script_in_two_reference_utxos_counted_per_utxo: the same script in two reference UTxOs counts twice
• pytest test: 643 passed, 5 xfailed; flake8, mypy and black clean

🤖 Generated with Claude Code

https://claude.ai/code/session_01VAhmCntFmrPj5dnjaBBFeG

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.80%. Comparing base (877be3a) to head (7904ea5).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #505      +/-   ##
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+ Coverage   90.79%   90.80%   +0.01%     
==========================================
  Files          37       37              
  Lines        5422     5429       +7     
  Branches      825      826       +1     
==========================================
+ Hits         4923     4930       +7     
  Misses        309      309              
  Partials      190      190              

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