feat: add Foundry alongside Hardhat

[GitGuru7]

Summary

Adds Foundry next to Hardhat for fuzz and invariant tests. Hardhat still owns the unit tests, deployments, coverage, the storage-layout check and the zkSync build. No existing test is changed.

Changes

• foundry.toml, forge-std v1.16.2 as a submodule in lib/, one-line remappings.txt for editors
• yarn test and yarn clean also run Foundry
• CI: new Forge tests job on Foundry v1.5.1 with the ci profile (2000 fuzz runs, 1000 × 100 invariant)
• Foundry writes to out/ and cache-foundry/, separate from Hardhat's artifacts/ and cache/
• tests/foundry/README.md: layout, what belongs in which toolchain, the 0.5.16 boundary

Tests (tests/foundry)

These tests are added to verify the setup end to end against real contracts. They are a starting point, not full coverage.

Suite	Checks
Comptroller/Diamond	Calls route through the real diamond and its facets
Comptroller/Markets	Listing, enter/exit, risk-parameter bounds (fuzz)
VToken/MintRedeem	Mint and redeem amounts; a round trip never profits, a mint never lowers the exchange rate (fuzz)
VToken/Invariants	Cash matches the token balance, the exchange rate never falls, the market stays solvent

Testing

13/13 passing on Foundry 1.3.5 and v1.5.1, both profiles.

[greptile-apps]

Confidence Score: 3/5

[Medium risk] Adds Foundry test framework alongside Hardhat.

The PR should not merge until the standard local test workflow is usable as documented and the exchange-rate invariant can detect a decrease.

Findings

1.  Standard test setup fails ▶
2.  Exchange rate check always passes ▶

Summary

The PR adds Foundry configuration, a pinned forge-std submodule, a dedicated CI job, and Comptroller and vToken fuzz/invariant suites alongside Hardhat.

• The standard local test command now has prerequisites absent from the main installation instructions.
• The exchange-rate invariant cannot detect a falling rate because its reference value is overwritten after each action.
• The new risk-parameter test, handler, and counterexample guidance have narrower test-quality and documentation issues.

_{Reviews (1) · Last reviewed commit: "chore: drop redundant foundry config, fo..."}

[github-actions]

Package	Line Rate	Branch Rate	Health
contracts	100%	100%	✔
contracts.Admin	88%	41%	✔
contracts.BStock	100%	97%	✔
contracts.Comptroller	100%	90%	✔
contracts.Comptroller.Diamond	95%	66%	✔
contracts.Comptroller.Diamond.facets	88%	74%	✔
contracts.Comptroller.Diamond.interfaces	100%	100%	✔
contracts.Comptroller.Types	100%	100%	✔
contracts.Comptroller.legacy	100%	100%	✔
contracts.Comptroller.legacy.Diamond	0%	0%	❌
contracts.Comptroller.legacy.Diamond.facets	0%	0%	❌
contracts.Comptroller.legacy.Diamond.interfaces	100%	100%	✔
contracts.DelegateBorrowers	100%	89%	✔
contracts.FlashLoan.interfaces	100%	100%	✔
contracts.Governance	68%	45%	➖
contracts.InterestRateModels	74%	59%	➖
contracts.Lens	44%	47%	❌
contracts.Liquidator	83%	60%	✔
contracts.Oracle	100%	100%	✔
contracts.PegStability	88%	84%	✔
contracts.Swap	88%	58%	✔
contracts.Swap.interfaces	100%	100%	✔
contracts.Swap.lib	81%	55%	✔
contracts.Tokens	100%	100%	✔
contracts.Tokens.Prime	97%	81%	✔
contracts.Tokens.Prime.Interfaces	100%	100%	✔
contracts.Tokens.Prime.libs	90%	77%	✔
contracts.Tokens.VAI	82%	52%	✔
contracts.Tokens.VRT	20%	9%	❌
contracts.Tokens.VTokens	71%	53%	➖
contracts.Tokens.VTokens.legacy	0%	0%	❌
contracts.Tokens.VTokens.legacy.Utils	0%	0%	❌
contracts.Tokens.XVS	19%	8%	❌
contracts.Tokens.test	100%	100%	✔
contracts.Utils	52%	31%	➖
contracts.VAIVault	50%	45%	➖
contracts.VRTVault	49%	36%	❌
contracts.XVSVault	63%	50%	➖
contracts.external	100%	100%	✔
contracts.lib	89%	71%	✔
Summary	62% (4519 / 7315)	48% (1753 / 3646)	➖