test: pin drawImage's exact drawn region and its missing-file error type

[dmccoystephenson]

Summary

Stage B (unit-test expansion) cycle targeting drawImage. No production code is changed.

• New test test_draw_image_fills_exactly_the_requested_region. Every existing drawImage test scales to a square size (10x10, 12x12) or a single-pixel-high one (2x1), so nothing distinguished width from height. A mutant scaling to (height, width) was confirmed to pass all 53 existing tests. The new test draws a non-square 6x5 region at offset (3, 4) and pins every corner plus the first pixel past each edge. That also pins the documented top-left anchoring to the pixel, mirroring test_draw_rectangle_fills_exactly_the_requested_region.
• Tightened missing-file assertions. test_draw_image_missing_file_raises (renamed ..._raises_file_not_found_error) and test_draw_image_does_not_cache_a_failed_load accepted (FileNotFoundError, pygame.error). The drawImage docstring promises FileNotFoundError for a missing path and reserves pygame.error for undecodable files, so both now assert FileNotFoundError only. It was confirmed empirically that pygame.image.load raises FileNotFoundError for a missing .bmp or .png path. The comment on the neighboring undecodable-file test, which described the old loose assertion, was updated to match.

No tracking issue. The gap was found during triage.

Mutation evidence

Mutant in graphik.py (reverted after each run)	Existing tests	New test
size = (height, width)	all pass	fails
blit at (xpos + 1, ypos)	1 fails (transparent-pixel test)	fails
center-anchored blit	4 fail	fails

Test plan

• python3 -m py_compile src/main/python/preponderous/graphik/graphik.py
• Import smoke test (import preponderous.graphik) prints 0.3.0.dev20260808
• python3 -m pytest: 54 passed, run locally on Python 3.8 / pygame 2.1.2 with the conftest's dummy SDL drivers
• CI Test workflow green across 3.9–3.13 (this also confirms that the newer pygame wheels raise FileNotFoundError too)

Triage notes (skipped issues)

• release: version tags are pushed without the 'v' prefix publish.yml requires, so no release has ever been published #34 (release tag prefix): this is a maintainer decision that touches .github/workflows/ and the release process, which are excluded from autonomous change.
• ci: test.yml's header comment claims it runs on every push, but pushes outside main are only covered via pull_request #39 (test.yml header comment): this only touches .github/workflows/test.yml, which is on the do-not-auto-merge list. The issue also leaves the trigger-vs-comment choice to the maintainer.
• packaging: the empty preponderous/__init__.py ships a regular package, which will collide with any future preponderous.* distribution #40 (preponderous/__init__.py namespace package): per the issue itself, this needs a maintainer check of sibling Preponderous-Software package conventions first.
• release: publish.yml's wheel smoke test never imports Graphik, so a wheel missing graphik.py would still publish #46 (filed this cycle): a documentation-accuracy sweep found that RELEASING.md describes a "canonical import" smoke test, but publish.yml never imports Graphik. The workflow is at fault rather than the docs, and workflows are excluded from autonomous change. The rest of the sweep found no drift in README.md, RELEASING.md, or the docstrings.

This PR description was drafted during a Gardener session (https://github.com/Stephenson-Software/gardener).

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drafted by Claude on behalf of Daniel Stephenson

🤖 Generated with Claude Code

[dmccoystephenson]

Self-review rubric (performed inline in the same session, so it is not independent review):

• Scope: PASS. Only src/test/python/preponderous/graphik/test_graphik.py is modified (+36/−6), and every hunk belongs to one of the two drawImage characterizations described in the PR body.
• Tests-new: N/A. No new public method was added.
• Tests-fix: N/A. This is a characterization-only change with no production fix. Mutation runs stand in for it: a (height, width) scale mutant survived all 53 pre-existing tests and was caught only by the new test. Off-by-one and center-anchor blit mutants were also caught. Every mutant was reverted with git checkout --, and the final tree has no change under src/main.
• Sibling structure: PASS. The new test follows test_draw_rectangle_fills_exactly_the_requested_region (corner and edge-plus-one assertions, _make_graphik, _rgb, and _write_solid_image helpers).
• Sibling renames: PASS. test_draw_image_missing_file_raises was renamed to match its sibling test_draw_image_undecodable_file_raises_pygame_error, and the only prose that referenced the old loose assertion (the undecodable-file test's comment) was updated in the same commit.
• Docs: PASS. No documented behavior changed. The drawImage docstring's Raises: section is now what the tests assert, and the README makes no exception-type claim.
• Issue resolution: N/A. There is no Closes #N, and the gap was found during triage.
• Manual validation: PASS. Locally, py_compile, the import smoke test, and pytest (54 passed) all succeeded. The CI Test workflow passed on 3.9, 3.10, 3.11, 3.12, and 3.13, which also confirms that current pygame wheels raise FileNotFoundError for a missing path.
• camelCase / Backward-compat / Version sync / No new deps: PASS. No change was made to graphik.py, the public surface, version sources, or imports.
• Headless: PASS. The new test uses _make_graphik under the conftest's dummy SDL drivers.

Findings:

• src/test/python/preponderous/graphik/test_graphik.py:131 — nit: the comment's "scaling to (height, width) instead passes all of them" is true against today's suite, but it will go stale if a later non-square test is added. This is acceptable because it records why the test exists, and was left as-is.
• src/test/python/preponderous/graphik/test_graphik.py:164 — tightening to FileNotFoundError relies on pygame's missing-file behavior. That behavior was verified locally on pygame 2.1.2 and in CI on the current wheels, so the tighter assertion now also acts as an early warning if a pygame release changes it.

The PR is ready to merge. It contains test-only changes, no do-not-auto-merge path is touched, and CI is green.

This review comment was drafted during a Gardener session (https://github.com/Stephenson-Software/gardener).

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drafted by Claude on behalf of Daniel Stephenson