deps(py): bump mypy from 1.20.2 to 2.0.0 in /backend

[dependabot]

Bumps mypy from 1.20.2 to 2.0.0.

Changelog

Sourced from mypy's changelog.

Mypy Release Notes

Next Release

Mypy 2.0

We’ve just uploaded mypy 2.0.0 to the Python Package Index (PyPI). Mypy is a static type checker for Python. This release includes new features, performance improvements and bug fixes. There are also changes to options and defaults. You can install it as follows:

python3 -m pip install -U mypy

You can read the full documentation for this release on Read the Docs.

Enable --local-partial-types by Default

This flag affects the inference of types based on assignments in other scopes. For now, explicitly disabling this continues to be supported, but this support will be removed in the future as the legacy behaviour is hard to support with other current and future features in mypy, like the daemon or the new implementation of flexible redefinitions.

Contributed by Ivan Levkivskyi, Jukka Lehtosalo, Shantanu in PR 21163.

Enable --strict-bytes by Default

Per PEP 688, mypy no longer treats bytearray and memoryview values as assignable to the bytes type.

Contributed by Shantanu in PR 18371.

New Behavior for --allow-redefinition

The --allow-redefinition flag now behaves like --allow-redefinition-new in mypy 1.20 and earlier. The new behavior is generally more flexible. For example, you can have different types for a variable in different blocks:

# mypy: allow-redefinition
def foo(cond: bool) -> None:
if cond:
for x in ["a", "b"]:
# Type of "x" is "str" here
...
else:
for x in [1, 2]:
# Type of "x" is "int" here
...

... (truncated)

Commits

• 7a76500 Remove +dev from version
• 5a3ab3b Changelog for mypy 2.0 (#21422)
• f9c86e2 Some changelog updates for 2.0 (#21413)
• 519eaf1 Bump librt to 0.10.0 (#21415)
• 158a620 Fix negative narrowing for containers (#21411)
• e556eb9 Try fixing mypy mypyc wheels (#21392)
• f2c9797 Expose --num-workers and --native-parser (#21387)
• db0cb2f Bump ast-serialize cache version (#21388)
• 1090ca6 Bump ast-serialize version to 0.3.0 only (#21391)
• 714ca9f [mypyc] Add note about librt.strings thread safety (#21383)
• Additional commits viewable in compare view

[github-actions]

Review Council Results

4 tests   2 ✅  0s ⏱️
1 suites  0 💤
1 files    2 ❌

For more details on these failures, see this check.

Results for commit 7d7b402.

♻️ This comment has been updated with latest results.

[Blb3D]

Dependabot sweep — Bucket A, blocked on Review Council

Classification: Bucket A — major bump (mypy 1.20.2 → 2.0.0) but mypy is on the dev-tooling allowlist; failures surface as red CI, cannot affect runtime.

CI status: all checks green (backend ✅ check-pro-code ✅ frontend ✅ CodeQL ✅) except Review Council → failure. This check is failing on every Dependabot PR in today's batch.

Note: mypy 2.0 enables --local-partial-types and --strict-bytes by default. If this PR causes mypy to report new errors in the backend CI check, that will show up as a red CI job and block merge naturally. Current backend check is green.

Per the merge policy, all visible checks must be SUCCESS before auto-merging. Deferring to human to resolve the Review Council gate, after which this PR is clear to merge.

---

Generated by Claude Code

[Blb3D]

Deferring this major-version bump for now.

Rationale: mypy is not currently invoked in any .github/workflows/*.yml, so the green CI on this PR does not actually validate mypy 2.0 against this codebase. Merging would risk surprising contributors who run mypy locally — the 2.0 defaults flip several behaviors:

• --local-partial-types on by default
• --strict-bytes on by default (PEP 688: bytearray/memoryview no longer assignable to bytes)
• --allow-redefinition semantics changed (now matches the old --allow-redefinition-new)

When we want to take this upgrade:

1. First land a CI workflow step that runs mypy backend/app so the upgrade is actually validated.
2. Address any new errors surfaced by the stricter defaults in a separate PR (or pass overrides via mypy.ini/pyproject.toml).
3. Then @dependabot recreate here, or pin to mypy>=2.0,<3 directly.

Until then, mypy==1.20.2 continues to work for anyone who runs it locally.

Co-authored-by: Claude claude@anthropic.com
Agent-Session: 5a809249-bd8d-4006-9f3c-d1b2824dfc2c