[Param-Harrison]

Summary

settleUp now settles the whole-dollar part of every balance first, then settles the leftover cents with separate transfers that are each under $1. Cash covers most of the money and every balance still settles to the exact cent.

Closes #193

Plan

Plan comment (rev 1, in the issue thread; .factory/runs/issue-193/plan-comment.md):

• AC-1 issue example (Ben→Asha 3300 + 33, Chen→Asha 3300 + 34), verified by bun test tests/balances.test.ts -t "issue example"
• AC-2 every transfer is a positive multiple of 100 cents or strictly under 100, verified by -t "whole dollars or cents only"
• AC-3 every balance nets to exactly 0, including 2075 / 1050 / -3125 and seeded random groups, verified by -t "settles exactly"
• AC-4 whole-dollar balances give no sub-dollar transfers and match the one-pass result, verified by -t "whole-dollar balances"
• AC-5 existing suite and typecheck still pass, verified by make check

Deliberately left out (non-goals): no change to the Transfer type, /balances JSON shape, computeBalances or schema; no rounding that leaves a balance unsettled; no float money; dollar and cents transfers between the same pair are not merged.

Changed files: src/balances.ts, tests/balances.test.ts (new).

Gate evidence

FACTORY_GATES: status=GREEN passed=3 failed=0 skipped=1 failed_gates=audit

The skipped audit gate is optional and flags existing hono advisories this diff does not cause.

Verify verdict

Verdict comment (in the issue thread; .factory/runs/issue-193/verdict-comment.md): pass, AC-1 to AC-5 all pass, no reviewer findings.

Test that bites: settleUp > issue example: $100 dinner for three gives $33 transfers plus cents-only remainders fails with src/balances.ts reverted (3 assertion failures, no compile error) and passes with the change.

Risk and rollback

Risk: low. One non-protected module, no schema or API-shape change. Note that users now see two transfers between the same pair (a dollar amount and a cents remainder), so a reviewer should confirm this reading of the issue.

Rollback: revert this PR; src/balances.ts returns to the one-pass algorithm and nothing is persisted, so there is no data to migrate.

Factory run

Stage	Agent	Duration	Tool calls	Cost	Outcome
triage	claude	25s	6	$0.09	ok
triage	claude	17s	6	$0.05	ok
plan	claude	1m 33s	9	$0.42	ok
plan	claude	1m 3s	6	$0.22	ok
build	claude	2m 5s	18	$0.59	ok
plan	claude	40s	5	$0.25	ok
build	claude	1m 30s	8	$0.25	ok
verify	claude	1m 20s	9	$0.31	pass
pr	claude	32s	4	$0.08	ok

Proof: the new test fails without the change.

9 stage runs, 9m 25s, $2.26.

Went well

• verify, pr passed on the first attempt
• verify approved on the first round

Needed help

• triage ran 2 times
• plan ran 3 times
• build ran 2 times
• 1 /factory retry