test(params): fence proxy metadata keys out of provider bodies

[shrey-berri]

TLDR

The last two items of the internal-params depth item, after #43221 and #43222

Problem this solves:

• The fence test never checked proxy keys inside metadata
• The _litellm_* naming rule was not written down anywhere

How it solves it:

• Fence test sends metadata={"user_api_key_hash": "h"} to all 6 providers
• It asserts user_api_key_hash never appears in any request body
• AGENTS.md now states the _litellm_* rule and bans internal state in metadata

Linear ticket

Resolves LIT-8316

Pre-Submission checklist

Please complete all items before asking a LiteLLM maintainer to review your PR

• I have added meaningful tests
• The handful of test files covering my change pass locally, e.g. uv run pytest tests/unit/<your_test_file>.py -v. Leave the suites (make test-unit-*, make test-unit) to CI: it finishes in ~15 minutes where a laptop takes an hour or more
• My PR passes all required CI/CD checks (e.g., lint, schema.d.ts sync check, etc.)
• My PR's scope is as isolated as possible; it only solves 1 specific problem
• I have received a Greptile Confidence Score of at least 4/5 before requesting a maintainer review (Greptile reviews automatically once the PR is opened; only comment @greptileai to re-request a review after pushing changes)

Delays in PR merge?

If you're seeing a delay in your PR being merged, ping the LiteLLM Team on Slack (#pr-review).

Screenshots / Proof of Fix

Test and docs only, so nothing a user sees changes. The check that matters is whether the new assertion catches a real leak. Turning on litellm.enable_preview_features makes LiteLLM forward metadata to OpenAI, which leaks user_api_key_hash into the request body

Setup	Old fence test	New fence test
Default settings	24 passed	24 passed
litellm.enable_preview_features = True	24 passed, leak not caught	4 OpenAI cases fail on 'user_api_key_hash' not in keys

Type

✅ Test
📖 Documentation

Caveats (if any)

Medium

• The preview-features leak above is still on main
  • With enable_preview_features on and no requester_metadata, OpenAI receives every string in metadata
  • Not fixed here. The draft fix(proxy): stop forwarding proxy metadata to OpenAI when caller sends none #42753 targets it and should land separately
  • Workaround: leave enable_preview_features off

Final Attestation

• The tests check the right things, including the edge cases, and regressions in the respective real-world customer use-cases are not possible after this PR

---

Generated by Claude Code

[greptile-apps]

Confidence Score: 5/5

[Low risk] Documents internal parameter naming and adds test coverage.

The PR appears safe to merge.

Summary

This PR documents the internal-kwarg naming convention and extends the provider wire test to check that user_api_key_hash inside request metadata does not appear in provider bodies.

• The assertion covers the existing six-provider, sync/async, and streaming/non-streaming matrix.
• No production behavior changes.

_{Reviews (1) · Last reviewed commit: "test(params): fence proxy metadata keys ..."}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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