Migrate from mypy to ty type checker

[pamelafox]

Purpose

Migrates from mypy to ty, Astral's Rust-based Python type checker, for faster CI runs. ty is significantly faster than mypy due to its Rust implementation.

Closes #2910

Changes include:

• Replace mypy with ty in requirements-dev.txt
• Configure ty in pyproject.toml with Python 3.10 target and source paths
• Update CI workflow to use ty check command
• Fix type errors found by ty's stricter checking (pdfparser.py, app.py, blobmanager.py)
• Remove unused type: ignore comments from mypy era
• Add .ty_cache to .gitignore and VS Code settings
• Update AGENTS.md and PR template with ty instructions

Does this introduce a breaking change?

When developers merge from main and run the server, azd up, or azd deploy, will this produce an error?
If you're not sure, try it out on an old environment.

[ ] Yes
[x] No

Does this require changes to learn.microsoft.com docs?

This repository is referenced by this tutorial
which includes deployment, settings and usage instructions. If text or screenshot need to change in the tutorial,
check the box below and notify the tutorial author. A Microsoft employee can do this for you if you're an external contributor.

[ ] Yes
[x] No

Type of change

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[x] Refactoring (no functional changes, no api changes)
[ ] Documentation content changes
[ ] Other... Please describe:

Code quality checklist

See CONTRIBUTING.md for more details.

• The current tests all pass (python -m pytest).
• I added tests that prove my fix is effective or that my feature works
• I ran python -m pytest --cov to verify 100% coverage of added lines
• I ran ty check to check for type errors
• I either used the pre-commit hooks or ran ruff and black manually on my code.

[Copilot]

Pull request overview

This pull request migrates the type checking system from mypy to ty, Astral's Rust-based Python type checker, to achieve faster CI runs. The migration includes configuration changes, dependency updates, and fixes for type errors identified by ty's stricter checking.

Changes:

• Replaced mypy with ty (>=0.0.1a12) in development dependencies
• Updated pyproject.toml with ty-specific configuration for Python 3.10
• Modified CI workflow to use ty check command instead of separate mypy checks
• Fixed type errors in several backend files and added/removed type: ignore comments as needed
• Updated documentation (AGENTS.md, PR template) with ty instructions
• Added .ty_cache to .gitignore and VS Code exclusions

Reviewed changes

Copilot reviewed 13 out of 14 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
requirements-dev.txt	Replaced mypy==1.14.1 with ty>=0.0.1a12
pyproject.toml	Removed mypy configuration and added ty configuration with Python 3.10 target, source paths, and rule overrides
.github/workflows/python-test.yaml	Simplified type checking from separate mypy commands to single ty check command
scripts/auth_init.py	Added assert statement to satisfy ty's type narrowing limitation and pragma: no cover comment
app/backend/prepdocslib/servicesetup.py	Removed unnecessary type: ignore comment for api_key parameter
app/backend/prepdocslib/pdfparser.py	Added defensive check for doc_for_pymupdf and changed caption.content handling to explicit str() conversion
app/backend/prepdocslib/page.py	Removed unnecessary type: ignore comment for tuple assignment
app/backend/prepdocslib/blobmanager.py	Added type: ignore comment for upload_blob arg-type issue
app/backend/chat_history/cosmosdb.py	Removed unnecessary type: ignore comment for continuation_token
app/backend/app.py	Added type: ignore comment for SpeechSynthesisOutputFormat attribute
AGENTS.md	Updated type checking instructions to use ty check instead of separate mypy commands
.github/PULL_REQUEST_TEMPLATE.md	Updated checklist to reference ty check instead of python -m mypy
.vscode/settings.json	Added .ty_cache to file exclusions
.gitignore	Added .ty_cache/ to ignored directories

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[Copilot]

Pull request overview

Copilot reviewed 13 out of 14 changed files in this pull request and generated 1 comment.

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Pull request overview

Copilot reviewed 16 out of 17 changed files in this pull request and generated 3 comments.

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Pull request overview

Copilot reviewed 16 out of 17 changed files in this pull request and generated no new comments.

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