refactor: remove dead embedding/classify code from regular PreparationStage

[CatherineSue]

Description

Problem

EmbeddingPreparationStage was wired into the regular PreparationStage delegator for Embedding and Classify request types. However, these requests are routed to their own dedicated pipelines (new_embeddings / new_classify) by the gRPC router and never reach the regular pipeline — making this delegation dead code.

Additionally, EmbeddingPreparationStage had an inconsistent construction style compared to other stages: it used ::new() in some places and bare struct syntax in others.

Solution

• Remove EmbeddingPreparationStage from the delegating PreparationStage and replace the Embedding/Classify match arms with an error (matching the existing Responses arm pattern)
• Restore new() on EmbeddingPreparationStage for consistency with other stages constructed in pipeline.rs
• Remove the unnecessary Default impl that was only needed to satisfy clippy for the now-removed new()

Changes

• preparation.rs (delegator): Remove embedding_stage field and Embedding/Classify match arms; collapse into a single error arm for unexpected request types
• embedding/preparation.rs: Restore new() constructor, remove Default impl
• pipeline.rs: Use EmbeddingPreparationStage::new() consistently

Test Plan

• Pre-commit hooks pass (rustfmt, clippy)
• No behavioral change: Embedding/Classify requests already route to dedicated pipelines

Checklist

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

Summary by CodeRabbit

• Refactor
  • Streamlined internal request handling pipeline and improved error messaging for enhanced maintainability.

[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 EmbeddingPreparationStage by eliminating its new() and Default implementations, which were unnecessary for a unit struct. The change promotes consistency across preparation stages by directly instantiating EmbeddingPreparationStage where it is used, simplifying the codebase and removing boilerplate.

Highlights

• Code Refactoring: Removed redundant new() and Default implementations from the EmbeddingPreparationStage unit struct, as they are unnecessary for types without fields.
• Consistency: Updated all instantiation sites to directly use EmbeddingPreparationStage, aligning its usage with other similar preparation stages like ChatPreparationStage and GeneratePreparationStage.

Changelog

• model_gateway/src/routers/grpc/pipeline.rs
  • Updated EmbeddingPreparationStage instantiation from EmbeddingPreparationStage::new() to EmbeddingPreparationStage in RequestPipeline::new_regular and RequestPipeline::new_streaming methods.
• model_gateway/src/routers/grpc/regular/stages/embedding/preparation.rs
  • Removed the impl EmbeddingPreparationStage block containing the new() function.
  • Removed the impl Default for EmbeddingPreparationStage block.
• model_gateway/src/routers/grpc/regular/stages/preparation.rs
  • Updated embedding_stage initialization in PreparationStage::new from EmbeddingPreparationStage::new() to EmbeddingPreparationStage.

Activity

• Pre-commit hooks (rustfmt, 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: a6f5c520-e8bc-4200-adab-985affa7033e

📥 Commits

Reviewing files that changed from the base of the PR and between b02a8e5 and 585c669.

📒 Files selected for processing (2)

• model_gateway/src/routers/grpc/regular/stages/embedding/preparation.rs
• model_gateway/src/routers/grpc/regular/stages/preparation.rs

💤 Files with no reviewable changes (1)

• model_gateway/src/routers/grpc/regular/stages/embedding/preparation.rs

---

📝 Walkthrough

Walkthrough

The changes remove embedding preparation stage integration from the main preparation router. The EmbeddingPreparationStage's Default implementation is deleted, and the embedding_stage field is removed from PreparationStage struct, along with updates to request type handling logic.

Changes

Cohort / File(s)	Summary
Embedding Preparation Removal model_gateway/src/routers/grpc/regular/stages/embedding/preparation.rs, model_gateway/src/routers/grpc/regular/stages/preparation.rs	Removed Default trait implementation for EmbeddingPreparationStage; removed embedding_stage field from PreparationStage struct; refactored request type branching to use generic fallback and dynamic error messages instead of static embedding/classify handling.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 The embedding stage has hopped away,
Simpler flows now light the day,
Fewer branches, cleaner code so bright,
The router's refactored just right! ✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title describes the main refactoring: removing dead embedding/classify code from PreparationStage, which aligns with the core changes removing EmbeddingPreparationStage usage and related branching logic.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

_{✏️ 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

---

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[gemini-code-assist]

Code Review

This is a good refactoring that improves code consistency by removing the unnecessary new() and Default implementations from the EmbeddingPreparationStage unit struct. The changes are correct and well-contained.

I've added a suggestion to apply a similar simplification to PreparationStage itself.

For further consistency, you might consider applying the same refactoring to other unit structs in a follow-up PR, such as:

• EmbeddingRequestBuildingStage
• EmbeddingResponseProcessingStage
• ClassifyResponseProcessingStage

Overall, a solid cleanup.