u1 KNOWN_AXES tuple gains slide_css entry in src/user_overrides_io.py
(snake_case parity with image_overrides); round-trip test extends
to 6 axes.
u2 src/mdx_normalizer.py surfaces nested slide_overrides.css from the
MDX frontmatter into the normalize_mdx_content return dict; absent
key -> {}, non-string css drops. 4 unit cases in tests/test_mdx_normalizer.py
(present / absent / non-string / title-only).
u3 src/slide_css_injector.py NEW (88 lines) mirrors the
inject_image_overrides_style contract from src/image_id_stamper.py:
marker pair <!--IMP45-SLIDE-CSS:OPEN--> / <!--IMP45-SLIDE-CSS:CLOSE-->,
idempotent re-injection, </head> > <body> > document-start three-tier
fallback, empty/None -> unchanged. 8 fixtures in
tests/test_slide_css_injector.py mirror test_image_id_stamper.py.
u4 run_phase_z2_mvp1 accepts override_slide_css: Optional[str] = None;
None -> frontmatter slide_overrides.css fallback. Step 13 calls
inject_slide_css after image override injection and before the
final.html disk write, so CLI/CI/regression renders observe the same
backend artifact.
u5 argparse adds mutually-exclusive --override-slide-css TEXT (inline
CSS, <style> wrapper optional) and --slide-css-file PATH (UTF-8 read,
fail-closed sys.exit(2) on missing path / decode error / both flags
present). Resolved string is forwarded as override_slide_css kwarg.
6 cases in tests/test_phase_z2_cli_overrides.py (inline / file / both
/ missing / non-utf8 / neither).
u6 samples/mdx_batch/04.mdx frontmatter gains slide_overrides.css
block (verbatim of the former MDX04_DEFAULT_OVERRIDE_CSS constant,
no sample/frame gate). Subprocess smoke in
tests/test_phase_z2_slide_css_smoke.py verifies the marker pair and
CSS substring land in final.html.
u7 Front/client removes the sample/frame-gated frontend-only injection:
Home.tsx drops the MDX04_DEFAULT_OVERRIDE_CSS constant and the
sample==="04"+frame==="process_product_two_way" branch (-28 lines);
SlideCanvas.tsx drops the iframe contentDocument.head injection of
that prop (-14 lines). Live preview now reads backend final.html only.
u8 tests/regression/fixtures/89a_pre_baseline_sha.json 04.mdx entry
resyncs to the live SHA ddb6bf2f... / 28042 bytes (overwrites the
earlier 5-byte-drift d02c76fd... / 28047). Other entries untouched.
Note: 01.mdx baseline drift (ad6f16a3... / 29089 -> live f26a7fac...
/ 29084) predates this branch and is split to a follow-up issue per
the closed-issue fresh validation rule.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
