chore: add CORE-003 roadmap task for mypy type safety

- Remove '|| true' from CI type-check job to enforce strict checking
- Begin type narrowing pattern in units.py with _typed property accessors
- Document all 42 type errors across 15 files in roadmap backlog
- Priority: medium, estimated 4-6 hours to complete

Type errors fall into categories:
- Union types not narrowed after __post_init__ coercion
- float() on object types
- Duplicate method definitions
- Provider interface type mismatches

.forgejo/workflows/ci.yaml

@@ -67,10 +67,5 @@ jobs:
           pip install mypy
           pip install nicegui fastapi uvicorn yfinance polars pandas pydantic pyyaml
           pip list
-      - name: Show working directory
-        run: pwd && ls -la
       - name: Run mypy
-        run: |
+        run: mypy app/core app/models app/strategies app/services --ignore-missing-imports --show-error-codes
-          echo "Running mypy on core modules..."
-          mypy app/core app/models app/strategies app/services --ignore-missing-imports --show-error-codes --show-traceback || true
-          echo "Type check completed (warnings allowed during development)"

app/domain/units.py

@@ -3,6 +3,7 @@ from __future__ import annotations
 from dataclasses import dataclass
 from decimal import Decimal
 from enum import StrEnum
+from typing import TYPE_CHECKING
 
 
 class BaseCurrency(StrEnum):
@@ -99,6 +100,11 @@ class Money:
         object.__setattr__(self, "amount", to_decimal(self.amount))
         object.__setattr__(self, "currency", _coerce_currency(self.currency))
 
+    @property
+    def _currency_typed(self) -> BaseCurrency:
+        """Type-narrowed currency accessor for internal use."""
+        return self.currency  # type: ignore[return-value]
+
     @classmethod
     def zero(cls, currency: BaseCurrency) -> Money:
         return cls(amount=Decimal("0"), currency=currency)
@@ -147,6 +153,15 @@ class Money:
         return Money(amount=-self.amount, currency=self.currency)
 
 
+if TYPE_CHECKING:
+    # Type narrowing: after __post_init__, these are the actual types
+    Money_amount: Decimal
+    Money_currency: BaseCurrency
+else:
+    Money_amount = Decimal
+    Money_currency = BaseCurrency | str
+
+
 @dataclass(frozen=True, slots=True)
 class Weight:
     amount: Decimal
@@ -156,49 +171,54 @@ class Weight:
         object.__setattr__(self, "amount", to_decimal(self.amount))
         object.__setattr__(self, "unit", _coerce_weight_unit(self.unit))
 
+    @property
+    def _unit_typed(self) -> WeightUnit:
+        """Type-narrowed unit accessor for internal use."""
+        return self.unit  # type: ignore[return-value]
+
     def to_unit(self, unit: WeightUnit) -> Weight:
-        return Weight(amount=convert_weight(self.amount, self.unit, unit), unit=unit)
+        return Weight(amount=convert_weight(self.amount, self._unit_typed, unit), unit=unit)
 
     def __add__(self, other: object) -> Weight:
         if not isinstance(other, Weight):
             return NotImplemented
-        other_converted = other.to_unit(self.unit)
+        other_converted = other.to_unit(self._unit_typed)
-        return Weight(amount=self.amount + other_converted.amount, unit=self.unit)
+        return Weight(amount=self.amount + other_converted.amount, unit=self._unit_typed)
 
     def __sub__(self, other: object) -> Weight:
         if not isinstance(other, Weight):
             return NotImplemented
-        other_converted = other.to_unit(self.unit)
+        other_converted = other.to_unit(self._unit_typed)
-        return Weight(amount=self.amount - other_converted.amount, unit=self.unit)
+        return Weight(amount=self.amount - other_converted.amount, unit=self._unit_typed)
 
     def __mul__(self, other: object) -> Weight | Money:
         if isinstance(other, bool):
             return NotImplemented
         if isinstance(other, Decimal):
-            return Weight(amount=self.amount * other, unit=self.unit)
+            return Weight(amount=self.amount * other, unit=self._unit_typed)
         if isinstance(other, int):
-            return Weight(amount=self.amount * Decimal(other), unit=self.unit)
+            return Weight(amount=self.amount * Decimal(other), unit=self._unit_typed)
         if isinstance(other, PricePerWeight):
-            adjusted_weight = self.to_unit(other.per_unit)
+            adjusted_weight = self.to_unit(other._per_unit_typed)
-            return Money(amount=adjusted_weight.amount * other.amount, currency=other.currency)
+            return Money(amount=adjusted_weight.amount * other.amount, currency=other._currency_typed)
         return NotImplemented
 
     def __rmul__(self, other: object) -> Weight:
         if isinstance(other, bool):
             return NotImplemented
         if isinstance(other, Decimal):
-            return Weight(amount=self.amount * other, unit=self.unit)
+            return Weight(amount=self.amount * other, unit=self._unit_typed)
         if isinstance(other, int):
-            return Weight(amount=self.amount * Decimal(other), unit=self.unit)
+            return Weight(amount=self.amount * Decimal(other), unit=self._unit_typed)
         return NotImplemented
 
     def __truediv__(self, other: object) -> Weight:
         if isinstance(other, bool):
             return NotImplemented
         if isinstance(other, Decimal):
-            return Weight(amount=self.amount / other, unit=self.unit)
+            return Weight(amount=self.amount / other, unit=self._unit_typed)
         if isinstance(other, int):
-            return Weight(amount=self.amount / Decimal(other), unit=self.unit)
+            return Weight(amount=self.amount / Decimal(other), unit=self._unit_typed)
         return NotImplemented
 
 
@@ -216,10 +236,20 @@ class PricePerWeight:
         object.__setattr__(self, "currency", _coerce_currency(self.currency))
         object.__setattr__(self, "per_unit", _coerce_weight_unit(self.per_unit))
 
+    @property
+    def _currency_typed(self) -> BaseCurrency:
+        """Type-narrowed currency accessor for internal use."""
+        return self.currency  # type: ignore[return-value]
+
+    @property
+    def _per_unit_typed(self) -> WeightUnit:
+        """Type-narrowed unit accessor for internal use."""
+        return self.per_unit  # type: ignore[return-value]
+
     def to_unit(self, unit: WeightUnit) -> PricePerWeight:
         return PricePerWeight(
-            amount=convert_price_per_weight(self.amount, self.per_unit, unit),
+            amount=convert_price_per_weight(self.amount, self._per_unit_typed, unit),
-            currency=self.currency,
+            currency=self._currency_typed,
             per_unit=unit,
         )
 
@@ -227,19 +257,19 @@ class PricePerWeight:
         if isinstance(other, bool):
             return NotImplemented
         if isinstance(other, Weight):
-            adjusted_weight = other.to_unit(self.per_unit)
+            adjusted_weight = other.to_unit(self._per_unit_typed)
-            return Money(amount=adjusted_weight.amount * self.amount, currency=self.currency)
+            return Money(amount=adjusted_weight.amount * self.amount, currency=self._currency_typed)
         if isinstance(other, Decimal):
-            return PricePerWeight(amount=self.amount * other, currency=self.currency, per_unit=self.per_unit)
+            return PricePerWeight(amount=self.amount * other, currency=self._currency_typed, per_unit=self._per_unit_typed)
         if isinstance(other, int):
-            return PricePerWeight(amount=self.amount * Decimal(other), currency=self.currency, per_unit=self.per_unit)
+            return PricePerWeight(amount=self.amount * Decimal(other), currency=self._currency_typed, per_unit=self._per_unit_typed)
         return NotImplemented
 
     def __rmul__(self, other: object) -> PricePerWeight:
         if isinstance(other, bool):
             return NotImplemented
         if isinstance(other, Decimal):
-            return PricePerWeight(amount=self.amount * other, currency=self.currency, per_unit=self.per_unit)
+            return PricePerWeight(amount=self.amount * other, currency=self._currency_typed, per_unit=self._per_unit_typed)
         if isinstance(other, int):
-            return PricePerWeight(amount=self.amount * Decimal(other), currency=self.currency, per_unit=self.per_unit)
+            return PricePerWeight(amount=self.amount * Decimal(other), currency=self._currency_typed, per_unit=self._per_unit_typed)
         return NotImplemented

docs/roadmap/ROADMAP.yaml

@@ -14,6 +14,7 @@ notes:
   - Alpha migration policy: once alpha is declared, compatibility only needs to move forward; backward migrations are not required.
 priority_queue:
   - EXEC-002
+  - CORE-003
   - DATA-DB-005
   - DATA-002A
   - DATA-001A

docs/roadmap/backlog/CORE-003-mypy-type-safety.yaml

@@ -0,0 +1,112 @@
+name: CORE-003 Mypy Type Safety
+description: |
+  Fix all mypy type errors to enable strict type checking in CI.
+  
+  Currently 42 errors in 15 files. The CI uses `|| true` to allow warnings,
+  but we should fix these properly with strong types and conversion functions.
+  
+status: backlog
+priority: medium
+created_at: 2026-03-29
+dependencies: []
+  
+acceptance_criteria:
+  - mypy passes with 0 errors on app/core app/models app/strategies app/services
+  - CI type-check job passes without `|| true`
+  - All type narrowing uses proper patterns (properties, cast(), or isinstance checks)
+  - No duplicate method definitions
+  
+scope:
+  in_scope:
+    - Fix type errors in app/domain/units.py
+    - Fix type errors in app/domain/portfolio_math.py  
+    - Fix type errors in app/models/portfolio.py
+    - Fix type errors in app/domain/backtesting_math.py
+    - Fix type errors in app/domain/instruments.py
+    - Fix type errors in app/services/*.py
+    - Fix type errors in app/pages/*.py
+    - Remove `|| true` from type-check job in CI
+    
+  out_of_scope:
+    - Adding new type annotations to previously untyped code
+    - Refactoring business logic
+    
+files_with_errors:
+  - file: app/domain/units.py
+    errors: 6
+    pattern: "WeightUnit | str" not narrowed after __post_init__
+    fix: Use _unit_typed property for type-narrowed access
+    
+  - file: app/models/portfolio.py  
+    errors: 1
+    pattern: "Duplicate _serialize_value definition"
+    fix: Remove duplicate method definition
+    
+  - file: app/domain/backtesting_math.py
+    errors: 1  
+    pattern: "assert_currency" argument type
+    fix: Use Money.assert_currency properly or add type narrowing
+    
+  - file: app/domain/instruments.py
+    errors: 1
+    pattern: "to_unit" argument type
+    fix: Use _unit_typed property or explicit coercion
+    
+  - file: app/domain/portfolio_math.py
+    errors: 11
+    pattern: "float(object), Weight | Money union, dict type mismatch"
+    fix: Add proper type guards and conversion functions
+    
+  - file: app/services/backtesting/ui_service.py
+    errors: 2
+    pattern: "Provider type mismatch, YFinance vs Databento source"
+    fix: Use proper union types for provider interface
+    
+  - file: app/services/event_comparison_ui.py
+    errors: 1
+    pattern: "FixtureBoundSyntheticHistoricalProvider type"
+    fix: Update type annotations for provider hierarchy
+    
+  - file: app/services/cache.py
+    errors: 1
+    pattern: "str | None to Redis URL"
+    fix: Add None check or use assertion
+    
+  - file: app/services/price_feed.py
+    errors: 2
+    pattern: "float(object)"
+    fix: Add explicit type coercion
+    
+  - file: app/pages/settings.py
+    errors: 1
+    pattern: "Return value on ui.button scope"
+    fix: Proper return type annotation
+
+implementation_notes: |
+  The root cause is that frozen dataclass fields with `Field: UnionType`
+  are not narrowed by `__post_init__` coercion. Mypy sees the declared
+  type, not the runtime type.
+  
+  Solutions:
+  1. Add `@property def _field_typed(self) -> NarrowType:` for internal use
+  2. Use `cast(NarrowType, self.field)` at call sites
+  3. Use `isinstance` checks before operations requiring narrow type
+  
+  Pattern example from units.py fix:
+  ```python
+  @property
+  def _unit_typed(self) -> WeightUnit:
+      """Type-narrowed unit accessor for internal use."""
+      return self.unit  # type: ignore[return-value]
+  
+  def to_unit(self, unit: WeightUnit) -> Weight:
+      return Weight(amount=convert_weight(self.amount, self._unit_typed, unit), unit=unit)
+  ```
+
+estimated_effort: 4-6 hours
+
+tags:
+  - type-safety
+  - mypy
+  - technical-debt
+  - ci-quality