Implement Parallelized Test Sharding Infrastructure for CI Pipeline Optimization

[temma02]

Description

Implement test sharding infrastructure that splits the test suite across parallel CI workers, reducing total CI runtime while ensuring deterministic, conflict-free test execution.

Requirements and Context

• Testing: Configure Vitest sharding across the monorepo
• Coverage: Affects the root vitest.config.ts and per-app configs
• Documentation: Document the CI sharding strategy

Suggested Execution

Branch: test/issue-042-test-sharding-ci-optimization

Implement Changes

• Configure Vitest --shard support in the root and per-app test configs
• Add CI matrix configuration to run shards in parallel
• Ensure tests do not share mutable global state that would break under sharding
• Document the sharding strategy and shard count rationale

Test and Commit

• Tests must pass identically whether sharded or run as a single suite
• CI runtime must measurably decrease with sharding
• Document the sharding configuration

Example Commit Message

test(ci): implement parallelized test sharding for pipeline optimization

- Configure Vitest shard support across monorepo
- Add parallel CI matrix for shard execution
- Document sharding strategy and shard count

Guidelines

• Ensure no test relies on shared global mutable state
• Balance shards by execution time, not file count
• Verify sharded results aggregate correctly

[Mystery-CLI]

@Mystery-CLI has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

i would like to work on this issue

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[drips-wave]

Congratulations, @Mystery-CLI! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

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