docs: add backend selection lookup table

[akihikokuroda]

Misc PR

Type of PR

• Bug Fix
• New Feature
• Documentation
• Other

Description

• Link to Issue: fix: Add backend selection lookup table for agent and human quick reference #842
• Closes Add backend selection lookup table for agent and human quick reference #842

Testing

• Tests added to the respective file if code was changed
• New code has 100% coverage if code as added
• Ensure existing tests and github automation passes (a maintainer will kick off the github automation when the rest of the PR is populated)

Attribution

• AI coding assistants used

[github-actions]

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[planetf1]

The issue link format fix: #842 won't auto-close on merge — use Closes #842 instead.

[planetf1]

The five rows are technically accurate (class names, imports, extras, backend_name strings all check out). Two things worth flagging:

The table is organised around start_session() keys, which silently excludes Bedrock — mellea/backends/bedrock.py exists but create_bedrock_mantle_backend() returns an OpenAIBackend with no backend_name equivalent. Similarly, Vertex AI uses LiteLLMBackend but has no row. It would be worth adding a short note below the table explaining that Bedrock and Vertex AI sit outside the start_session() system and linking to their integration pages. The broader LiteLLM docs gaps are tracked in #642.

[planetf1]

Agree with changes overall - it's reminded me there's more work to do on the docs here such as with litellm (added a note -- one minor comment about adding a footnote for now)