feat: support custom model prefix for AWS

[prnake]

close #1928 ，支持用户自定义

Summary by CodeRabbit

• New Features
  • Added support for AWS authentication with regional model prefix configuration. Users can now specify AccessKey, SecretAccessKey, Region, and Model Prefix when configuring AWS channels, enabling region-specific model routing and customizable model prefix settings for enhanced AWS integration flexibility.

[coderabbitai[bot]]

Walkthrough

This pull request adds support for a configurable AWS model prefix to accommodate AWS Bedrock's updated cross-region deployment naming scheme (e.g., global, eu, jp, us). It introduces a new AWS secret format accepting a region-specific prefix, updates the AWS client initialization and model ID resolution logic, and extends the UI to support the new format option.

Changes

Cohort / File(s)	Summary
AWS Constants and Configuration dto/channel_settings.go	Added new constant AwsKeyTypeAKSKRegionPrefix = "ak_sk_region_prefix" to define the 4-parameter AWS secret format (AccessKey, SecretAccessKey, Region, Prefix).
AWS Adaptor Structure relay/channel/aws/adaptor.go	Added public field ModelPrefix string to the Adaptor struct to carry prefix information through AWS requests.
AWS Client Initialization and Model Routing relay/channel/aws/relay-aws.go	Reworked newAwsClient to return (client, modelPrefix, hasCustomPrefix, error) and handle the new 4-parameter secret format. Updated doAwsClientRequest to store prefix in adaptor and conditionally route model IDs with custom prefix or region-derived prefix. Extended awsModelCrossRegion to accept and prioritize a configurable prefix parameter.
UI Configuration web/src/components/table/channels/modals/EditChannelModal.jsx	Added new AWS key format option ak_sk_region_prefix with label "AccessKey / SecretAccessKey / Region / Prefix" and updated conditional prompts to guide users on the new 4-parameter format.

Sequence Diagram(s)

sequenceDiagram
    participant Client
    participant Modal as EditChannelModal
    participant Backend as relay-aws.go
    participant AWS as AWS Bedrock

    Client->>Modal: Select AWS channel config
    Modal->>Modal: Choose ak_sk_region_prefix format
    Modal->>Backend: Submit config with (ak, sk, region, prefix)
    
    Backend->>Backend: newAwsClient()
    Backend->>Backend: Parse 4-param secret
    Backend->>Backend: Extract modelPrefix from param
    Backend->>Backend: Set hasCustomPrefix = true
    Backend->>Backend: Create AWS client with region + credentials
    Backend->>Backend: Return (client, modelPrefix, true, nil)
    
    Backend->>Backend: doAwsClientRequest()
    Backend->>Backend: Receive modelPrefix & hasCustomPrefix
    Backend->>Backend: Store a.ModelPrefix = modelPrefix
    
    alt hasCustomPrefix is true
        Backend->>Backend: awsModelId = modelPrefix + "." + awsModelId
    else hasCustomPrefix is false
        Backend->>Backend: awsModelCrossRegion(awsModelId, regionPrefix, "")
        Backend->>Backend: Use region-derived prefix if empty configured
    end
    
    Backend->>AWS: Call with adjusted awsModelId
    AWS-->>Backend: Response
    Backend-->>Client: Success

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

• Areas requiring attention:
  • Logic flow in newAwsClient for secret format parsing and prefix extraction; verify all four format branches (2-param, 3-param, 4-param, and default) are correctly handled
  • Interaction between hasCustomPrefix flag and cross-region routing logic in doAwsClientRequest to ensure prefix precedence is correct
  • Consistency of prefix parameter propagation through awsModelCrossRegion and verify backward compatibility for existing 2-param and 3-param formats
  • UI prompt strings and placeholder logic in EditChannelModal to ensure user guidance is clear for the new format

Suggested reviewers

• seefs001

Poem

🐰 A prefix hops through regions far, Global, JP, EU—what a par! Bedrock routes with newfound grace, Four parameters find their place. Config, adaptor, modal sync— The AWS model maze, now linked! 🌐

Pre-merge checks and finishing touches

❌ 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%.	You can run @coderabbitai generate docstrings to improve docstring coverage.

✅ 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 'feat: support custom model prefix for AWS' accurately reflects the main change: enabling users to configure custom model prefixes (global, eu, jp, us) for AWS Bedrock models.
Linked Issues check	✅ Passed	The PR implements support for custom AWS model prefixes as required by issue #1928, enabling users to specify region prefixes (global, eu, jp, us) via a new ak_sk_region_prefix secret format.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to implementing custom model prefix support: new constant, struct field, secret format handling, model ID resolution logic, and UI updates for the new format.

✨ Finishing touches

• [ ] 📝 Generate docstrings

🧪 Generate unit tests (beta)

• [ ] Create PR with unit tests
• [ ] Post copyable unit tests in a comment

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