[anth-volk]

Fixes #628

What and why

Three parts of policyengine-core sent HTTP requests to the PolicyEngine Public API (api.policyengine.org):

• Reform.from_api downloaded a saved policy by its numeric ID (GET /{country}/policy/{id}) and built a reform from it.
• Reform.api_id sent the reform's parameter values to POST /{country}/policy and returned the new policy's ID.
• policyengine_core.charts.api: get_api_chart_data read GET /{country}/metadata, then requested GET /{country}/economy/{reform}/over/{baseline} once a second until the result was ready, and intra_decile_chart and decile_chart plotted it. policyengine_core.charts re-exported all three.

The Public API depends on the country packages, which depend on policyengine-core, so these functions made the lowest-level package depend on the top-level service at run time. The Public API's newer policy routes also have no lookup by these numeric IDs.

Changes

1. Remove policyengine_core/charts/api.py and its re-export from policyengine_core.charts. The formatting helpers and bar charts stay. Because the removed module had no __all__, from policyengine_core.charts import * also no longer provides the requests and time modules it imported; nothing in the package relies on that.
2. Remove Reform.from_api and Reform.api_id, with the helpers only they used: _api_period_range (and its three tests), classproperty, and the requests import in policyengine_core/reforms/reform.py. The requests dependency stays, because policyengine_core/data/dataset.py uses it. The docstrings of Reform.country_id and Reform.parameter_values, and the reforms usage page, no longer describe them as inputs to Public API calls.
3. New tests/core/test_no_public_api_calls.py:
   • fails if any file in the package source contains api.policyengine.org, after first checking that the package directory it scans exists, so a moved package cannot make it pass with nothing scanned;
   • fails if Reform has a from_api or api_id attribute (looked up with inspect.getattr_static and a sentinel default, so the check never runs them and an attribute set to None still counts);
   • fails if policyengine_core.charts.api can be imported, or if policyengine_core.charts has any of the three chart functions.
4. A removed changelog fragment, so the release is a minor version (3.33.12 to 3.34.0 at the time of writing).

What this waits for

Do not merge until all of these have merged. Merging this PR publishes a new policyengine-core release to PyPI, and each of them stops using a removed function:

• Remove tests that call policyengine-core's Reform.from_api policyengine-uk#2555: removes the two core_reform_api test cases that call Reform.from_api. policyengine-uk accepts any policyengine-core>=3.32.27, so its tests would fail as soon as this release is published.
• One private repository: its Modal endpoint drops a legacy input that used Reform.from_api.
• Take the constituency app's reform as parameters instead of a Public API policy ID uk-local-area-calibration#35: the constituency app takes the reform as parameters instead of using Reform.from_api.
• Stop creating a Public API policy for each forecast obr-forecast#2: the forecast stops creating a policy with Reform.api_id.
• Write the saved policies' parameters into the notebook instead of downloading them from the Public API blank-slate-ubi-in-the-us#27: the notebook writes its policies' parameters in instead of using Reform.from_api and Reform.api_id.

A code search of PolicyEngine's repositories found no other users. Article notebooks in PolicyEngine/policyengine-app-v2 still contain old cells that used these functions; the site shows their saved outputs and does not re-run them, so they are left as they are.

Environment variables

None. The change reads no environment variables and touches no workflows.

Tests

Each commit was red-green:

• Commit 1 (7ca5e511): the two chart tests failed with the module still present (find_spec found policyengine_core.charts.api, and policyengine_core.charts had all three names), and pass after the removal.
• Commit 2 (ed369823): the host test failed naming reforms/reform.py, and the Reform test failed listing from_api and api_id; both pass after the removal.
• Commit 3 (d5d2bccb, test module only): a check of the tests themselves showed the host scan passing when pointed at a directory that does not exist, and the Reform check passing with Reform.api_id = None; both now fail in those cases, and the four tests pass on the real source.
• uv run pytest tests (the full suite): 2663 passed, 4 skipped, 3 xfailed at commit 1; 2662 passed, 4 skipped, 3 xfailed at commit 2 (three _api_period_range tests removed, two tests added).
• policyengine-core test policyengine_core/country_template/tests -c policyengine_core.country_template: 39 passed at commits 1 and 2.
• ruff format --check . and ruff check .: pass at each commit.
• One read-only review pass: no bugs; its two test-robustness findings are commit 3.
• Not run locally: make documentation (the usage-page change is text in a notebook that the docs build does not execute) and the country smoke tests, which CI runs.

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