~143 mypy-style # type: ignore[code] comments do nothing under ty; global ty rule disables are broader than documented #507

Tier 3: type-checking hygiene

Problem

• The repo type-checks with ty. Nothing runs mypy (no references in the Makefile, pyproject or workflows).
• There are still about 143 # type: ignore[<mypy code>] comments: arg-type 60, attr-defined 35, call-arg 19, override 6, method-assign 6, and others.
• Tested with ty 0.0.89: a bare # type: ignore suppresses the whole line, but a bracketed one is matched against ty's rule names. So # type: ignore[attr-defined] did not suppress an invalid-return-type. ty also doesn't report these comments as unused, so they pile up as noise that misleads readers about what is being hidden.
• pyproject.toml:105-118 disables six rules globally. CLAUDE.md lists five; it also disables invalid-assignment.
• The global invalid-argument-type disable hides real bugs. Example: _tenant.py:63 passes an unvalidated object as tenant_id into TenantResolution, so a resolver returning a UUID or an int flows into string comparisons. The ignore comment on that line isn't what silences it; the global disable is.

Fix

1. Delete the mypy-coded ignores. Rewrite the few that are needed as # ty: ignore[<rule>], which ty does report when unused.
2. Narrow invalid-argument-type and invalid-assignment to per-path overrides, or to warn, instead of global ignore, and fix what turns up in non-ORM code.
3. Validate or coerce tenant_id to str at the resolver boundary in _tenant.py.
4. Update the CLAUDE.md list of disabled rules.