refactor(gateway): remove redundant connection_mode special-case for external providers

[CatherineSue]

Description

Problem

The connection_mode detection in main.rs had a special-case match arm that hardcoded RoutingMode::OpenAI to ConnectionMode::Http, bypassing determine_connection_mode(). This was a safety measure from the original OpenAI backend PR, but after Simo's cleanup in #9999 (simplified gRPC detection to scheme-only checking), it became redundant. Each new external provider (Anthropic, now Gemini in #679) was forced to either add its own match arm or fall through to URL detection accidentally.

Solution

Remove the RoutingMode match and call determine_connection_mode() unconditionally. External provider URLs (https://...) never start with grpc://, so they always resolve to ConnectionMode::Http through the normal path. The factory already has error guards for invalid gRPC + external provider combinations as a safety net.

Changes

• Remove the RoutingMode::OpenAI special-case match in CliArgs::to_server_config(), replacing it with a direct call to Self::determine_connection_mode(&all_urls)

Test Plan

• cargo check -p smg passes
• No behavioral change: external provider URLs are always https://, which determine_connection_mode() already resolves to ConnectionMode::Http
• The factory's gRPC rejection errors for OpenAI/Anthropic remain as a safety net

Checklist

• cargo +nightly fmt passes
• cargo clippy --all-targets --all-features -- -D warnings passes
• (Optional) Documentation updated

Summary by CodeRabbit

Bug Fixes

• Connection mode detection now consistently uses worker URL schemes to determine protocol selection (gRPC or HTTP) across all routing configurations, removing special-case handling and improving reliability.

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request refactors the connection mode detection logic within the gateway. It eliminates a specific handling for OpenAI, allowing all external providers to uniformly determine their connection mode through a single, consistent function call. This change simplifies the codebase, improves maintainability, and ensures future external providers are handled correctly without requiring additional special-casing.

Highlights

• Connection Mode Refactoring: Removed a redundant special-case match for RoutingMode::OpenAI in CliArgs::to_server_config(), streamlining connection mode detection for external providers.

Changelog

• model_gateway/src/main.rs
  • Removed the explicit RoutingMode::OpenAI match arm for ConnectionMode::Http.
  • Updated connection_mode assignment to unconditionally call Self::determine_connection_mode(&all_urls).

Activity

• The author provided a detailed problem description and solution for the change.
• A test plan was outlined, including cargo check and verification of no behavioral changes for external provider URLs.
• A checklist was included, indicating cargo fmt and cargo clippy passed.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: 8ab4b906-37b6-44db-a465-c1e42ab43d89

📥 Commits

Reviewing files that changed from the base of the PR and between 6db1723 and 30b4697.

📒 Files selected for processing (1)

• model_gateway/src/main.rs

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📝 Walkthrough

Walkthrough

The connection mode determination logic in the gateway's main entry point is refactored to consistently rely on URL scheme inspection rather than conditionally forcing Http mode when using OpenAI routing, simplifying the configuration flow.

Changes

Cohort / File(s)	Summary
Connection Mode Determination model_gateway/src/main.rs	Removed conditional logic that forced Http connection mode for OpenAI routing strategy; connection mode now consistently determined from worker URLs via the existing determine_connection_mode function based on URL schemes.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Suggested labels

model-gateway

Suggested reviewers

• key4ng

Poem

🐰 Hop! The gateway's logic now flows so clean,
No forced Http mode for OpenAI's scene,
Let URLs whisper which path to take,
Grpc or Http—a simpler way we make! ✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title accurately describes the main change: removing a redundant special-case for OpenAI's RoutingMode that hardcoded ConnectionMode selection, which is now determined consistently via URL scheme detection.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

• 📝 Generate docstrings (stacked PR)
• 📝 Generate docstrings (commit on current branch)

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch chang/cleanup-connection-mode

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[gemini-code-assist]

Code Review

This pull request refactors the connection mode detection by removing a special case for OpenAI providers. The change simplifies the logic by unconditionally using determine_connection_mode(), which correctly infers the connection type from the URL scheme. This is a good simplification that improves code clarity and makes it more robust for adding future external providers.