test: pay a winner when an index-change market settles

[MicBun]

A market on index_change_in_range (action id 12) had never been traded and settled.

index_change_settlement_test.go covers how such a market resolves: the YES/NO answer, the
agreement between the market hash and the attestation hash, and the half-open [min, max) bucket
rule. Every market in that file settles against an empty order book, so no position is ever paid.
Nothing anywhere put two traders on opposite sides of one and let it settle, which leaves payout,
the LP reward cut, and the fee split unexercised for this action.

They are expected to work. Migrations 032, 033 and 034 contain no reference to action_id and
branch on query_id alone, so an index-change market should pay exactly as a value market does.
This checks that rather than assuming it.

The winner mints 100 YES/NO pairs and offers the NO side at 40 cents. The loser lifts it. That is a
real match between two wallets rather than one wallet holding both sides, so settlement has someone
to pay and someone to pass over. The market then settles on the [1%, 3%) bucket the 2% move lands
inside.

What it asserts:

• each trader holds 100 of their own side before settlement
• balances move by −60 and −40 first, so a wrong payout later cannot be mistaken for a wrong trade
• every position is cleared after settlement
• the winner ends +38 USDC: 100 out to mint, 40 back from the sale, 98 returned after the 2%
  settlement fee that funds LP rewards
• the loser ends −40, paid nothing and charged nothing further

Notes

• Verified by mutation. Claiming the winner gains nothing fails with
  expected "0", actual "38000000000000000000", so the figure is read from the chain rather than
  an assertion agreeing with itself. Moving the bucket to [3%, 5%) so the 2% falls outside makes
  the market settle NO and collapses the payout assertion, so the money tracks the settlement
  outcome.
• The fixture reuses the 2% move and the anchor timings index_change_settlement_test.go already
  establishes, so the two files cannot drift on what the stream did.
• settle_market runs with a proposer set here, unlike the settlement tests. This market holds
  positions, so process_settlement runs and needs one to attribute the validator share of the
  fees to.
• Test only. No production code changes.

Related:

• https://github.com/truflation/website/issues/4266

Summary by CodeRabbit

• Tests
  • Added coverage for index-change market settlement when positions are held.
  • Verifies winning positions are paid, losing positions are cleared, and trader balances reflect the expected payouts.
  • Confirms settlement behavior for movements within the applicable index-change range.

[holdex]

Time Submission Status

Member	#	Time	Running Total	Status	Last Update
MicBun			4h	✅ Submitted	Aug 31, 2026, 1:46 PM

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• tests/streams/order_book/index_change_payout_test.go

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• tests/streams/order_book/index_change_payout_test.go

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📝 Walkthrough

Walkthrough

Adds an integration test for action 12 index-change markets. The test seeds a two-percent movement, trades YES and NO positions, settles to YES, and verifies participant holdings, USDC deltas, and cleared positions.

Changes

Index-change payout validation

Layer / File(s)	Summary
Test harness and stream fixture tests/streams/order_book/index_change_payout_test.go	Registers the test and seeds stream records that produce a two-percent change.
Market lifecycle and argument encoding tests/streams/order_book/index_change_payout_test.go	Encodes action 12 arguments, creates the market, requests attestation, and settles the market.
Payout and position assertions tests/streams/order_book/index_change_payout_test.go	Trades 100 YES/NO pairs, confirms that each trader holds the intended side, and verifies pre- and post-settlement USDC deltas and cleared positions.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to 2185e

This test-only change adds coverage for winner payouts when an index-change market settles; it does not alter production behavior, and no actionable merge-blocking risk remains beyond normal checks and review.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: adding a test for winner payouts during index-change market settlement.
Docstring Coverage	✅ Passed	Docstring coverage is 80.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 5 functions across 1 files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Actionable comments posted: 1

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Inline comments:
In `@tests/streams/order_book/index_change_payout_test.go`:
- Around line 120-121: Update the holding assertions around requireHolding to
validate ownership as well as share amounts: resolve the participant IDs for
winner and loser, then assert winner holds YES and loser holds NO before
settlement. Ensure requireHolding or its invocation checks
Position.ParticipantID so opposite ownership cannot satisfy the test.

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Run ID: ac11b6c2-f0e8-4b94-800c-afdd8fa163a8

📥 Commits

Reviewing files that changed from the base of the PR and between 05be78a and 33f8847.

📒 Files selected for processing (1)

• tests/streams/order_book/index_change_payout_test.go

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[MicBun]

@holdex pr submit-time 4h

[vinarmani]

@MicBun is this good to be merged?