[anth-volk]

Fixes #4306

Summary

• The simulation-service client (policyengine_api/libs/simulation_reports.py) no longer sends a dataset_name key on economy simulation, economy report or budget-window requests. Household reports and re-runs never sent one.
• POST /v2/reports (economy and budget-window kinds) and POST /v2/simulations no longer take dataset_name: it leaves EconomySimulationFields and ReportDefinitionFields, so their strict request models refuse it, as a value or as null, with 422 before any service is called.
• Reads are unchanged: GET /v2/reports and GET /v2/simulations still name the dataset a stored report or simulation used.
• Docstrings, the create routes' 503 descriptions and the caller-row refusal codes' comment now say the caller names a region or dynamic, and the dataset is the region's.
• Changelog fragment: changelog.d/c1-29-no-dataset-name.removed.md.

Order of the dataset_name removal

The simulation service (PolicyEngine/policyengine-sim-api) is dropping dataset_name from its EconomyReportRequest, EconomySimulationRequest and BudgetWindowReportRequest, which refuse unknown fields. The agreed order:

1. This PR merges and deploys to production. It stacks on nothing and needs nothing deployed first: today's simulation service declares dataset_name: … | None = None, so a body without the key is valid before and after its change.
2. Then the simulation service's change (data_source: "local_area_dataset" for UK-wide and nation reports, and the outright removal of dataset_name) merges and deploys. Until this PR is in production there, that change must not deploy, or every create this Public API sends with the key would be refused with 422.

A later Public API change passes data_source through POST /v2/reports.

Testing

Each change was test-first: the failing tests were committed first (76736d048), seen failing for the expected reasons (the bodies still carried "dataset_name": None, and the routes answered 201), then passing. Run by node ID only:

• tests/unit/libs/test_simulation_reports.py: test_a_report_is_posted_and_the_created_report_returned, test_a_report_sends_its_options_and_spm_settings_only_when_given, test_a_simulation_is_posted_and_the_created_simulation_returned, test_a_row_the_caller_named_that_the_service_cannot_find_is_refused (comment only).
• tests/unit/libs/test_simulation_budget_window_reports.py: test_a_budget_window_is_posted_to_reports_and_its_window_run_returned[201] and [202], test_a_budget_window_sends_its_spm_settings_only_when_given.
• tests/unit/v2/test_report_create_routes.py: test_a_malformed_report_is_refused_before_the_service[names-a-dataset] and [null-dataset], test_a_malformed_simulation_is_refused_before_the_service[names-a-dataset] and [null-dataset], test_a_simulation_is_created_and_answered_as_stored.
• tests/unit/v2/test_budget_window_report_create_routes.py: test_a_budget_window_the_tables_cannot_hold_is_refused[names-a-dataset] and [null-dataset].

make quality (ruff, ruff format, Import Linter, mypy, the quality guards) passes on each commit. One read-only adversarial review round found no bugs; its documentation findings are fixed in f9f8e23b5.

No schema, workflow, Dockerfile or environment-variable change.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.45%. Comparing base (f9c619d) to head (f9f8e23).
⚠️ Report is 7 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4307      +/-   ##
==========================================
- Coverage   93.47%   93.45%   -0.02%     
==========================================
  Files         369      369              
  Lines       21442    21453      +11     
  Branches     3400     3400              
==========================================
+ Hits        20043    20049       +6     
- Misses        816      822       +6     
+ Partials      583      582       -1     

Flag	Coverage Δ
integration	56.61% <ø> (+0.02%)	⬆️
unit	91.01% <ø> (-0.02%)	⬇️

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