Introduce targeted cache invalidation tags

[hman38705]

Issue 014: Introduce targeted cache invalidation tags

Area: Backend
Priority: Medium
Files: services/api/src/cache/mod.rs, services/api/src/handlers.rs

Problem

Invalidations are broad and potentially expensive. A single write invalidates unrelated cache entries.

Acceptance Criteria

• Invalidation scope is narrowed to affected entities\n- Blast radius is measured and reduced\n- Docs explain key and tag strategy\n- Benchmark shows reduced invalidation overhead

[Darkdante9]

@Darkdante9 has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

Can I be assigned?? ETA: 1hr

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Congratulations, @Darkdante9! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on April 29, 2026.

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[drips-wave]

This issue has been completed by @Darkdante9 as part of the Stellar Wave Program's 4th Wave 🥳

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