[AZ-365] Refactor C12: decompose RouteService.CreateRouteAsync

Extract RouteValidator (aggregating validator), RoutePointGraphBuilder
(point interpolation + sequence numbering), GeofenceGridCalculator
(NW/SE region centers), and RouteResponseMapper (entity -> DTO; also
used by GetRouteAsync, eliminating duplicate DTO assembly).

CreateRouteAsync shrinks 184 -> 52 LOC of orchestration. RouteService.cs
shrinks 295 -> 138 LOC overall. Validation aggregates all failures into
a single ArgumentException (AC-2); single-violation messages preserved
verbatim so existing RouteServiceTests pass unchanged. 28 new unit
tests for the four helpers (112/112 unit tests, smoke green).

Co-authored-by: Cursor <cursoragent@cursor.com>

_docs/02_tasks/done/AZ-365_refactor_decompose_route_create_method.md

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+# Refactor: decompose RouteService.CreateRouteAsync 165-LOC method
+
+**Task**: AZ-365_refactor_decompose_route_create_method
+**Name**: Split CreateRouteAsync into validator + builder + grid + mapper
+**Description**: Extract `RouteValidator`, `RoutePointGraphBuilder`, `GeofenceGridCalculator`, and `RouteResponseMapper` from `RouteService.CreateRouteAsync`.
+**Complexity**: 5 points
+**Dependencies**: None
+**Component**: Services.RouteManagement
+**Tracker**: AZ-365
+**Epic**: AZ-350
+
+## Problem
+
+`SatelliteProvider.Services.RouteManagement/RouteService.cs:27-211` is a 165-LOC method that does input validation (4 separate rules, ~25 LOC of nested `if` chains), point-graph construction with `GeoUtils.CalculateIntermediatePoints`, route entity persistence, route-points persistence, geofence polygon validation, geofence grid generation, geofence region requests, and response mapping. Five distinct responsibilities in one method.
+
+## Outcome
+
+- `CreateRouteAsync` is reduced to orchestration of the four extracted helpers (~30-50 LOC).
+- Validation aggregates errors instead of short-circuiting on the first.
+- Each helper is unit-testable in isolation.
+- 37 unit + 5 smoke tests stay green.
+
+## Scope
+
+### Included
+- Extract `RouteValidator` (all `ArgumentException`-throwing checks; aggregates errors instead of short-circuiting).
+- Extract `RoutePointGraphBuilder` (interpolation + sequence numbering — pure).
+- Extract `GeofenceGridCalculator` (NW/SE → list of region centers — promote the existing private method).
+- Extract `RouteResponseMapper` (entity → DTO; eliminates duplication with `GetRouteAsync`).
+- Add unit tests for each helper.
+
+### Excluded
+- Changing the response shape.
+- Changing the persistence calls.
+- Changing the geofence semantics.
+
+## Acceptance Criteria
+
+**AC-1: CreateRouteAsync is now an orchestrator**
+Given the post-refactor source
+When `CreateRouteAsync` is inspected
+Then it is reduced to ~30-50 LOC of `_validator.Validate(...)`, `_pointGraphBuilder.Build(...)`, `_geofenceGridCalculator.GenerateRegions(...)`, `_responseMapper.Map(...)` calls (or equivalent).
+
+**AC-2: Validation aggregates errors**
+Given an input with multiple validation failures
+When validated
+Then all failures are collected and surfaced as a single 400 response (still typed as `ArgumentException` or a typed `ValidationException`).
+
+**AC-3: Same persistence + same response**
+Given any input that succeeds today
+When the post-refactor code runs
+Then the same DB rows are created and the same response shape is returned.
+
+**AC-4: Tests stay green**
+Given the post-refactor build
+When `scripts/run-tests.sh --smoke` runs
+Then all 37 unit + 5 smoke scenarios pass; `RouteServiceTests` is unchanged.
+
+## Constraints
+
+- Same persistence calls.
+- Same response shape (no DTO change).
+- 400 status preserved for validation failures.
+
+## Risks & Mitigation
+
+**Risk 1: aggregated validation surfaces multiple errors but tests assert on first**
+- *Risk*: existing tests may assert on a specific single-error message.
+- *Mitigation*: update test assertions to allow a list of errors.
+
+Full change entry: `_docs/04_refactoring/03-code-quality-refactoring/list-of-changes.md` (C12).