Backend: Apply per-principal rate limiting

[Cedarich]

Complexity: Medium (150)

Description
apps/backend/src/common/rate-limit/ provides rate limiting infrastructure, but limits are not consistently scoped to the authenticated principal. An authenticated client can consume the shared budget for an entire source address, and expensive endpoints carry the same limit as trivial ones.

Acceptance Criteria

• Limits are keyed by authenticated principal where one exists, falling back to source address otherwise.
• Expensive endpoints — search, export, analytics, contract simulation — carry their own stricter limits.
• Responses include standard rate limit headers and a Retry-After value on rejection.
• Bot and service principals authenticated through bot-auth have separately configurable limits.
• Limit rejections are exported as metrics labelled by endpoint class.

_{Wave 8 · source: backend.md}

[oscar24357]

@oscar24357 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hello boss, good evening, can you please assign this issue to me.

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[drips-wave]

Congratulations, @oscar24357! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on August 31, 2026.

🧑‍💻 @oscar24357: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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[Sensei-Victor]

@Sensei-Victor has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

I'm a developer so I can work on this
I'm very fit for this task

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[Ivenkili]

@Ivenkili has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi Maintainer,
I would to work on this kindly assign

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[devzakari-sketch]

@devzakari-sketch has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi maintainer can i work on this task? Kindly assign

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