Merge ChatReadRetrieveReadApproach into Approach class

[pamelafox]

Purpose

Since the Ask tab was removed (#2834), there is now only one approach implementation. This refactor merges ChatReadRetrieveReadApproach into the base Approach class, simplifying the codebase by removing the unnecessary inheritance hierarchy.

Does this introduce a breaking change?

- [ ] Yes
- [x] No

Type of change

- [ ] Bugfix
- [ ] Feature
- [x] Code style update (formatting, local variables)
- [x] Refactoring (no functional changes, no api changes)
- [ ] Documentation content changes
- [ ] Infrastructure-related changes (Bicep files, GitHub Actions workflows)
- [ ] Other... Please describe:

What is the current behavior?

• The Approach class was an abstract base class (ABC) in approach.py
• ChatReadRetrieveReadApproach extended it in a separate file chatreadretrieveread.py
• This inheritance pattern was designed for multiple approach implementations (Ask and Chat tabs)

What is the new behavior?

• Approach class now contains the full implementation (no longer ABC)
• chatreadretrieveread.py has been deleted
• app.py imports and uses Approach directly
• All tests updated to use new import paths
• Documentation updated to reflect simplified architecture

Other information

Files changed:

• app/backend/approaches/approach.py: Merged all chat-specific code, removed ABC
• app/backend/approaches/chatreadretrieveread.py: Deleted
• app/backend/app.py: Updated imports to use Approach directly
• tests/conftest.py: Updated chat_approach fixture
• tests/test_chatapproach.py: Updated imports
• tests/test_app.py: Updated monkeypatch paths
• docs/architecture.md: Simplified architecture diagram and descriptions
• docs/customization.md: Updated file references
• AGENTS.md: Updated approach file reference

All 457 tests pass ✅

[Copilot]

Pull request overview

This PR simplifies the codebase by merging ChatReadRetrieveReadApproach into the base Approach class following the removal of the Ask tab (#2834). Since only one approach implementation remains (the Chat approach), the inheritance hierarchy is no longer necessary. The refactor consolidates all RAG functionality into a single class while maintaining the same behavior.

Key changes:

• Merged ChatReadRetrieveReadApproach implementation into Approach class
• Removed unused Ask-related code (routes, components, prompts, snapshots)
• Updated all imports and references throughout tests and application code
• Simplified architecture documentation and developer guides

Reviewed changes

Copilot reviewed 67 out of 68 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
app/backend/approaches/approach.py	Merged chat implementation from ChatReadRetrieveReadApproach; added run(), run_stream(), and retrieval methods; removed ABC inheritance
app/backend/approaches/chatreadretrieveread.py	Deleted (merged into Approach)
app/backend/approaches/retrievethenread.py	Deleted (Ask approach no longer needed)
app/backend/approaches/prompts/ask_answer_question.prompty	Deleted (Ask prompt no longer needed)
app/backend/app.py	Removed /ask endpoint; removed CONFIG_ASK_APPROACH; updated to instantiate Approach directly
app/backend/config.py	Removed CONFIG_ASK_APPROACH constant
tests/test_chatapproach.py	Updated imports to use Approach instead of ChatReadRetrieveReadApproach; fixed constant reference
tests/test_app.py	Removed Ask-related tests; updated monkeypatch paths from chatreadretrieveread to approach
tests/conftest.py	Updated chat_approach fixture to use Approach class
tests/e2e.py	Removed test_ask end-to-end test
app/frontend/src/pages/ask/Ask.tsx	Deleted Ask page component
app/frontend/src/index.tsx	Removed /qa route
app/frontend/src/api/api.ts	Removed askApi function
app/frontend/src/pages/layout/Layout.tsx	Simplified header; removed navigation menu
app/frontend/vite.config.ts	Removed /ask proxy endpoint
app/frontend/src/locales/*/translation.json	Removed "qa" translation key from all language files
docs/architecture.md	Updated diagram and descriptions to reflect single approach
docs/customization.md	Removed Ask-specific documentation; updated file references
AGENTS.md	Updated approach file references
README.md	Removed reference to Q&A interface
evals/evaluate_config.json	Updated target URL from /ask to /chat
evals/results*/baseline-ask/*	Deleted Ask-specific evaluation results

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