chore: charge one cent to send USDC

[MicBun]

resolves: https://github.com/trufnetwork/truf-network/issues/1394

What changes

eth_usdc_transfer charges 0.01 USDC instead of 1 USDC, and its testnet counterpart
hoodi_tt2_transfer charges 0.01 TT2 instead of 1 TT2. That is the figure Vin settled on after
revising his first suggestion of a tenth of a cent upward:

log: changed the fee amount for USDC (and TT2) to one cent. We don't want to incentivize
micropayments.

A dollar to move USDC is the larger half of most transfers anyone actually makes with it. A cent
still makes spamming the action pointless, which is the reason the fee exists at all.

$fee := 10000::NUMERIC(78, 0); -- 0.01 USDC with 6 decimals

The two files carry different literals for the same cent. USDC has 6 decimals, so a cent is 10^4.
TT2 stands in for USDC on testnet but is an 18-decimal token, so there it is 10^16. The
insufficient-balance messages move from Requires an extra 1 USDC fee to Requires an extra 0.01 USDC fee, and likewise for TT2.

TRUF transfers are untouched: eth_truf_transfer, ethereum_transfer, sepolia_transfer and
hoodi_tt_transfer all still charge 1 TRUF.

002-public-transfer-actions.prod.sql is a hand-written override rather than one of
generate_prod_migrations.py's targets, so both files are edited in place. Both pass
kwil-cli utils parse.

Tests

hoodi_tt2_transfer had no test at all, so TestHoodiTT2TransferFee is new. It pins the fee
through arithmetic rather than by reading the constant back:

• 1.0 sent out of a 2.0 balance has to leave exactly 0.99, so any other fee fails there
• the recipient receives 1.0 and never the fee
• 0.99 sent out of a 1.0 balance succeeds and leaves 0, which the whole-token fee rejected outright
• an empty wallet's shortfall message has to name Requires an extra 0.01 TT2 fee

Putting the 1 TT2 fee back fails the first assertion (expected: "990000000000000000",
actual: "0"), so the test is wired to the number it claims to guard.

Run and passing: all 8 tests in erc20_bridge_transfer_actions_test.go, which covers the four
TRUF transfer actions this leaves alone.

Rollout notes

1. Mainnet: apply erc20-bridge/002-public-transfer-actions.prod.sql with kwil-cli exec-sql,
   after 000-extension.prod.sql so eth_usdc exists. It is CREATE OR REPLACE ACTION on two
   actions, so no fleet upgrade and no restart.
2. Testnet picks the dev *.sql up on the next scripts/migrate.sh run.
3. Nobody can be newly blocked, because the fee only goes down. Mainnet had seen 7 USDC transfers
   in total as of 2026-07-29, from three USDC-holding wallets.
4. The indexer classifies these rows by the bridge the action stamps into the event metadata
   rather than by the amount, so a 10^4 fee still charts as USDC. Its amount-based fallback
   (a method-4 fee of exactly 1e6 means USDC) applies only to rows written before the node started
   stamping, and those keep their old amounts. Two comments in indexer/types/fee_types.go
   describe the 1 USDC fee in the present tense and go stale with this.
5. All three SDKs document a one-token fee on every bridge, which becomes wrong for USDC —
   sdk-go/docs/api-reference.md:2859, sdk-js/src/client/client.ts:375 and
   src/contracts-api/action.ts:1217, sdk-py/src/trufnetwork_sdk_py/client.py:3267. Each also
   tells the caller the action reverts below amount + 1 token. Separate repos, separate PRs.

Summary by CodeRabbit

• New Features
  • Reduced USDC and TT2 bridge transfer fees to 0.01 tokens.
  • Updated insufficient-balance messages to reflect the new fee amounts.
• Bug Fixes
  • Clarified fee denominations across bridge transfer and ledger information.
• Tests
  • Added coverage verifying TT2 fees, balance deductions, recipient amounts, exact-spend transfers, and insufficient-balance handling.

[holdex]

Time Submission Status

Member	#	Time	Running Total	Status	Last Update
MicBun			3h	✅ Submitted	Aug 4, 2026, 11:59 AM

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[coderabbitai]

📝 Walkthrough

Walkthrough

The ERC20 bridge transfer actions now charge 0.01 USDC and 0.01 TT2. Error messages and fee documentation were updated. Hoodi TT2 tests cover deductions, balances, exact-spend transfers, and insufficient-balance errors.

Changes

ERC20 transfer fee updates

Layer / File(s)	Summary
Update bridge transfer fees internal/migrations/erc20-bridge/002-public-transfer-actions*.sql	The transfer actions now charge 0.01 USDC and 0.01 TT2 in token base units. Insufficient-balance messages use the updated amounts.
Validate fees and ledger descriptions tests/extensions/erc20/erc20_bridge_transfer_actions_test.go, tests/streams/transaction_events_ledger_test.go	Hoodi TT2 tests validate fee deductions, recipient balances, exact spending, wallet balances, and insufficient-balance errors. Ledger documentation distinguishes the 1 TRUF fee from the 0.01 USDC fee.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• trufnetwork/node#1398: Introduced the related Hoodi TT2 transfer action and tests.
• trufnetwork/node#1298: Added the Hoodi TT2 bridge and its transfer actions.
• trufnetwork/node#1163: Modified the same ERC20 bridge transfer actions and tests.

Suggested labels: type: chore

Suggested reviewers: pr-time-tracker, outerlook

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Out of Scope Changes check	⚠️ Warning	The Hoodi TT2 fee changes and tests are not required by linked issue #1394, which only covers USDC transfers.	Move the Hoodi TT2 changes to a separate issue or link an issue that explicitly requires the TT2 fee change.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The USDC fee changes implement issue #1394 by applying a 0.01 USDC fee to reduce spam and denial-of-service risk.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the USDC fee change, which is a primary part of the pull request, but it does not mention the related TT2 fee change.

✨ Finishing Touches

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• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch chore/usdc-transfer-cent-fee

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[MicBun]

@holdex pr submit-time 3h

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@internal/migrations/erc20-bridge/002-public-transfer-actions.prod.sql`:
- Line 79: Update the fee comment in the migration around the ERC-20 transfer
configuration to describe 10^4 USDC as token base units rather than wei, while
preserving the existing fee value and decimal explanation.

🪄 Autofix

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: f8b06d84-b650-40e0-8b4e-d74775d7633b

📥 Commits

Reviewing files that changed from the base of the PR and between 9f04efc and fe11086.

📒 Files selected for processing (4)

• internal/migrations/erc20-bridge/002-public-transfer-actions.prod.sql
• internal/migrations/erc20-bridge/002-public-transfer-actions.sql
• tests/extensions/erc20/erc20_bridge_transfer_actions_test.go
• tests/streams/transaction_events_ledger_test.go