Lydit

Lydite: the black touchstone assayers streak gold across to test it before anyone trusts it.

Lydit is a Binance USDⓈ-M liquidation gauge that counts your other cross positions. Enter a position, see where it liquidates and how the number is built, and share it as a link. No update goes live unless it reproduces Binance's own worked examples, and the answer key lives in TestSprite, outside any pull request.

• Live: https://lydit.vercel.app
• Proof for the commit you are looking at: /proof. Binance's published Example 2 answers (ETH 1,153.26, BTC 26,316.89) and Example 1's maintenance margin reproduce to the cent, and every page shows the TestSprite result for the exact commit it serves.
• The caught mistake: PR #2, a refactor that dropped the other positions. TestSprite went red (16 of 35 failed, ETH showed 1,114.78), merging was blocked, the fix went green and merged.
• TestSprite runs: the red run · the green run on the fix
• Formulas and every term: /sources, from Binance's FAQ
• PRD: prd.md. Design spec: docs/FRONTEND.md

Gauge: Binance's ETH example, with the BTC position counted	Proof: the served commit and its TestSprite result

For judges: two minutes

Keep Binance's FAQ open next to the gauge: its Example 2 is the reference every number below is held to.

1. Open /gauge and click ETH long. The liquidation price is 1,153.26, the number Binance publishes for those inputs. "How this number is built" shows every term.
2. Break it yourself. Click Remove on the BTC position: the price drops to 1,114.78, the mistake TestSprite caught in PR #2. Click ETH long again for 1,153.26.
3. Test the logic. Set the wallet balance to 2000000: a long's price moves down, to 1,013.14. Switch to Isolated: the BTC position stops counting, the page says so, and the price is 1,114.78. Switch to Short: the price jumps above entry, to 1,705.23.
4. Try bad input. Type 120 in Maintenance rate or -1 in Size: an error appears under the field and no number is shown until it is fixed.
5. Share it. Click Copy link and open it in a new tab: the same inputs and the same answer come back.
6. Move the other position. On the landing page, drag the BTC mark in "Same account, two answers": as BTC falls, its loss eats the shared balance and the ETH price moves closer.
7. Check the build you are using. Proof at the top right shows the build's result as an icon; hover it for the commit. /proof lists the 16 golden cases with their Binance sources, and Open the check goes to that commit's TestSprite run. Then search the code: no source, test or fixture file holds an expected liquidation price.

Red on purpose. PR #2 is a coding-agent refactor titled "compute liquidation per position". It sets the other cross positions' margin and PnL to zero, and all 19 in-repo tests still pass. On the PR's Vercel preview, TestSprite saw ETH at 1,114.78 instead of 1,153.26 and BTC at 18,778.73 instead of 26,316.89: 16 of 35 tests failed, the required check went red and GitHub blocked the merge. The fix commit restored the terms, the check went green and the PR merged. Auto-heal did not rewrite the expected numbers to fit the wrong build.

Judging line	Where it shows
Project quality	The live app: a gauge for cross and isolated, long and short, with up to five other positions (or their totals), a step-by-step breakdown, a price strip, presets for Binance's examples and shareable links; a Sources page with every formula and term; a Proof page and a proof line on every screen. Checked at 1440, 768 and 390 px
Tests that run themselves	TestSprite V3 runs 35 UI tests against every PR's Vercel preview and is a required check in the main ruleset (no bypass list), so a red run cannot merge. The golden cases assert one displayed number each, from Binance's published examples or labelled derivations. See Tests that run themselves
Innovation	The maker cannot grade its own work: the answer key sits in TestSprite, never in the PR diff, so a change can rewrite the formula but not the answers. Users see the verification status of the exact build they use, read live from GitHub

Why it exists

A trader in cross margin is long BTC and about to size an ETH long. A calculator that treats each position alone says ETH liquidates at 1,114.78. Binance's own worked example for that account puts it at 1,153.26, because the BTC position's unrealized loss and maintenance margin eat into the shared balance. The trader believes they have about $38 (3.3%) more room than they do. Lydit counts the other positions, shows the working, and is held to Binance's published numbers on every change.

Features

	Feature	Where
F1	Liquidation gauge: one-way mode, cross and isolated, long and short; liquidation price, maintenance margin and distance from mark, with a "no liquidation price" state and the reason	/gauge
F2	Other cross positions: up to five, each with its own unrealized PnL and maintenance margin worked inline, or their totals (TMM1, UPNL1) entered directly; isolated mode ignores them and says so	/gauge
F3	How this number is built: the formula, every term with its value, the numerator and denominator, and the price the position would have alone	/gauge
F4	Binance presets: ETH long, BTC long and Example 1 fill Binance's inputs only; the engine computes every output	/gauge
F5	Scenario links: every input travels in the URL; copying a link and opening it restores the same inputs and outputs	"Copy link", /sources
F6	Validation: field errors for empty, malformed and out-of-range input (size > 0, 0 ≤ MMR < 100%, …), no result until it is fixed	/gauge
F7	Proof: the served commit, environment and branch, and its TestSprite result read from GitHub (commit status or check run, cached 60 s; a merge commit shows its pull request's result); never "passed" unless GitHub says so	/proof, every page, /api/proof
F8	Sources: both formulas, a worked example computed by this build, every variable, the URL parameter reference with a link reader, and what is not covered	/sources
F9	Build identity: { sha, shortSha, pr, ref, env } for the tripwire test, and a health route	/api/build, /api/health

How correctness is established

1. Binance is the source. The formulas and both worked examples come from Binance's FAQ: MM = size × mark × MMR − cumB and LP = (WB − TMM1 + UPNL1 + cumB − Side × Position × EP) / (Position × MMR − Side × Position).
2. Exact decimals. All money math uses decimal.js at 50 significant digits, never floating point. Prices and margins are shown to 2 decimals.
3. The answer key lives outside the repo. Binance's published values are written into TestSprite assertion steps only. The repo holds the formula and Binance's inputs (as presets and links), so a pull request cannot change the formula and the expected answer together.
4. Derived cases are labelled. D-1 to D-5 (isolated long and short, cross short with another position, cross single position, a tier with a maintenance amount) were computed outside the repo, checked by hand, and recorded in TestSprite as "derived", not published.
5. In-repo tests carry no answers. They check properties of the formula (at the liquidation price, equity equals maintenance margin; more wallet balance moves a long's price down and a short's up; isolated mode ignores other positions; the "no liquidation price" states), validation messages and link round trips.

Tests that run themselves

Layer	What runs	When
TestSprite UI (GitHub App)	35 tests. The 16 golden cases: G-0 build identity; G-1 to G-5 Binance's published maintenance margins and liquidation prices; D-1 to D-5 derived prices; D-6 invalid input; D-7 no liquidation; D-8 a copied link restores everything; D-9 the ETH preset; D-10 the Proof page. Plus TestSprite's generated tests for the Sources links, navigation, presets, validation and the how-it-works section	Every push to an open PR, against its Vercel preview; TestSprite V3 is required by the main ruleset, with no bypass
TestSprite exploration	Six agents explored the live site and planned the suite	Once, on production; its first run failed 5 of 35 tests, which led to four fixes (below)
Unit (Vitest)	19 tests: formula properties, other-position sums, validation, link round trips. No expected prices	npm test
Proof	Each deployment reads its own commit's TestSprite result from GitHub and shows it on every page	Every request, cached 60 s

What a green check means: on that exact preview, every Binance example still reproduces to the cent, the derived cases still hold, and bad input still shows an error instead of a number.

The trigger listens for Vercel's status on commits of an open pull request. Vercel builds in under a minute, so a pull request opened after its first preview finished gets no run until its next push.

Mistakes TestSprite caught (red, then green)

Where	Caught by	Mistake	Fixed in
PR #2	TestSprite V3, 16 of 35 failed	A refactor computed each position alone: ETH 1,114.78 instead of 1,153.26, BTC 18,778.73 instead of 26,316.89	bad1dd5
Production, first run	TestSprite UI	Clearing a field from a script (value set, then an input event) was ignored by React, so the old result stayed on screen	ab388b4, 67fa05d
Production, first run	TestSprite UI	The Sources page linked only the ETH example, not BTC or Example 1	87a8521
Production, first run	TestSprite UI	The Proof page listed the golden cases without each one's Binance source or result	89962f4
Production, first run	TestSprite UI	How it works never mentioned the preview the check runs on	fc4aa2d
PR #1	TestSprite V3, 34 of 35	A generated test expected env: production on a PR preview; the test was corrected, not the app. The same run showed TestSprite reports a commit status, which the Proof page did not yet read	eed3137

Develop

npm install
npm run dev     # http://localhost:3000
npm test        # formula properties, validation and link round trips; no expected prices

Variable	Purpose
GITHUB_TOKEN	Read-only token for the GitHub API (raises the rate limit). Server only
NEXT_PUBLIC_REPO_URL	Repository link shown on the site
NEXT_PUBLIC_DEMO_PR_URL	The red-then-green pull request
NEXT_PUBLIC_TESTSPRITE_SUITE_URL	The TestSprite run linked from the site

Vercel needs "Enable access to System Environment Variables" for the proof line, and Vercel Authentication off for previews so TestSprite can reach them.

Stack: Next.js 16 (App Router, Cache Components), React 19, TypeScript, decimal.js, Vitest, Vercel, TestSprite GitHub App.

Not covered: hedge mode, portfolio margin, and venues other than Binance.