Fix underflow in _updateSubgraphRewards

[RembrandtK]

fix(rewards): reorder subtraction in _updateSubgraphRewards to avoid underflow
The old code's two hooks wrote to different fields with inverted semantics:

• onSubgraphSignalUpdate set accRewardsForSubgraph (A) from storage
• onSubgraphAllocationUpdate set accRewardsForSubgraphSnapshot (S) from
  a view (storage + pending), so S leads and A lags after allocation updates

After the proxy upgrade, _updateSubgraphRewards computed A.sub(S).add(P)
which underflows on the intermediate A - S when A < S. Rearranging to
A.add(P).sub(S) adds pending rewards first, avoiding the intermediate
underflow. S <= A + P always holds because P covers T1→now (a superset
of the T1→T2 gap S - A).

Observed on Arbitrum Sepolia: A < S by ~7,235 GRT for subgraphs whose
last pre-upgrade interaction was onSubgraphAllocationUpdate. All reward
operations (signal, allocation, claim) reverted permanently.

[Copilot]

Pull request overview

This PR fixes a SafeMath underflow in _updateSubgraphRewards that caused all reward operations to permanently revert for subgraphs on Arbitrum Sepolia whose last pre-upgrade interaction was onSubgraphAllocationUpdate. The old hook wrote accRewardsForSubgraphSnapshot (S) from a view function (storage + pending), leaving accRewardsForSubgraph (A) at its stored value, so A < S after those calls. The new code's A.sub(S).add(P) underflowed on the intermediate A - S. The fix reorders to A.add(P).sub(S), which is always non-negative since P covers a superset of the gap.

Changes:

• Reorder SafeMath operations in _updateSubgraphRewards to compute (A + P) - S instead of (A - S) + P, avoiding intermediate underflow.
• Add comprehensive test file covering inverted storage state via hardhat_setStorageAt, accounting correctness, normal operation, and a realistic Arbitrum Sepolia scenario.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
packages/contracts/contracts/rewards/RewardsManager.sol	Core fix: reorders the undistributedRewards subtraction to avoid SafeMath underflow when A < S (pre-upgrade state)
packages/contracts-test/tests/unit/rewards/rewards-snapshot-inversion.test.ts	New test suite validating the fix using direct storage manipulation to reproduce the pre-upgrade inverted state

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[openzeppelin-code]

Fix underflow in _updateSubgraphRewards

Generated at commit: 8d7e2425e0e6d9c032a91e7b17ce4b1c6fea66ec

🚨 Report Summary

	Severity Level	Results
Contracts	Critical High Medium Low Note Total	3 5 0 14 37 59
Dependencies	Critical High Medium Low Note Total	0 0 0 0 0 0

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.55%. Comparing base (ddee12b) to head (8d7e242).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1302   +/-   ##
=======================================
  Coverage   88.55%   88.55%           
=======================================
  Files          75       75           
  Lines        4615     4615           
  Branches      981      981           
=======================================
  Hits         4087     4087           
  Misses        507      507           
  Partials       21       21           

Flag	Coverage Δ
unittests	88.55% <100.00%> (ø)

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