[0.64.0] Preserve Grok billing defaults

[Finesssee]

Summary

• send Grok's billing RPC as a nonempty gRPC-web request that explicitly encodes exclude_legacy_monthly_usage=false
• preserve fallback from an expired OAuth credential to the configured local Grok token
• add request-contract and fallback regressions

Upstream reference: bb62d35532cc08d7016d7a03605d8adcf67d5ddd (fix(grok): preserve billing defaults in nonempty requests).

Validation

• cargo fmt --all
• cargo test --manifest-path rust/Cargo.toml providers::grok::tests --lib (18 passed)
• cargo clippy --manifest-path rust/Cargo.toml --lib --tests -- -D warnings
• git diff --check

This lane is dependency-free and is based directly on main.

Summary by CodeRabbit

• Bug Fixes
  • Fixed billing requests when credits are not explicitly included, improving usage percentage reporting.
  • Improved billing and usage retrieval when OAuth authentication fails by retrying with the configured local authentication token.
  • Updated billing request handling to ensure compatibility with the service’s expected request format.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Advanced

Run ID: e1c226a7-6214-44dd-9803-b377e4ef68f0

📥 Commits

Reviewing files that changed from the base of the PR and between 8cdd2ca and a3dd63b.

📒 Files selected for processing (2)

• rust/src/providers/grok/mod.rs
• rust/src/providers/grok/tests.rs

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📝 Walkthrough

Walkthrough

The Grok provider now uses a configurable billing endpoint and a non-empty gRPC-web request body. OAuth billing authentication fallback is centralized and retries with the configured local token after an authentication failure. Tests cover both behaviors.

Changes

Grok billing and authentication

Layer / File(s)	Summary
Configurable billing request rust/src/providers/grok/mod.rs, rust/src/providers/grok/tests.rs	GrokProvider stores a configurable billing endpoint. fetch_billing uses the updated gRPC-web body. Tests verify the request bytes and parsed billing percentage.
OAuth billing fallback rust/src/providers/grok/mod.rs, rust/src/providers/grok/tests.rs	fetch_with_oauth_fallback centralizes the OAuth retry with a bearer token from ctx.api_key. fetch_usage uses this method, and a test verifies the local-token retry.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~15 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to a3dd6

The billing request preserves the explicit default, and OAuth billing can fall back to the configured local token after authentication failure. No merge-blocking production risk remains.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 38.46% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 13 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the primary change: preserving Grok billing defaults. It matches the billing request behavior changes in the pull request.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches 💡 1

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[Finesssee]

Thermo-nuclear code-quality review

Verdict: PASS — no actionable maintainability findings.

The change keeps billing behavior inside the Grok provider, extracts OAuth fallback into a focused policy method, and adds a narrow HTTP test seam. Neither touched file crosses 1,000 lines, and the patch adds no scattered provider-specific branching or duplicate implementation path.