EPBDS-16211 F1 step 4: vendor the semantic CSS — output byte-identical

[AlexSamBY]

src/style/vendor/semantic-reset.less and semantic-dropdown.less, generated by scripts/vendor-semantic-css.js. _semantic.less imports them instead of reaching into node_modules/semantic-ui-less.

Parity, in two independent forms

• the gate passes on all 285 rules — selector, declarations and cascade order;
• static/all.css has the same sha256 (dcdb0a40…) built from master and from this branch. The artifact a consumer downloads does not change at all.

The :extend thread, since that is what this dig was about

Vendoring has to produce a .less file, not .css: our own stylesheets extend Semantic's selectors, and @import (inline) would put them out of :extend's reach. That constraint is what makes the rest delicate — a .less file is re-evaluated, not copied.

Four traps, each caught by the gate rather than by reading

1. .loadUIOverrides() is not just our hook. theme.less defines it as two optional imports, and the first is the theme's own overrides — which for globals/reset is where normalize.css lives. Stripping it produced a 7-rule reset with the normalize body gone.
2. Redefining @siteFolder to exclude our overrides does nothing, silently. A LESS mixin resolves variables in the scope where it is defined, and that mixin is defined in theme.less. Replaced by a LESS file manager — which must implement the sync path too, or LESS takes a different route through the whole compile and folds calc() differently.
3. LESS re-evaluates what it parses. Semantic builds calc(100% + 2px) from escaped strings precisely so LESS leaves it alone; as a plain literal in a .less file it folded to calc(102%) — and 100% + 2px is not 102%. The generator re-escapes every calc(...) on the way out.
4. Our override/**.overrides must use @import (multiple) — the form loadUIOverrides itself used. With a plain @import, the .outline() mixin's nested .inverted & block emitted twice and duplicated two rules.

Two false alarms from the gate itself

Both looked exactly like product bugs and cost real time, so both are now comments in the generator:

• The generator detects live imports by line shape and did not recognise @import (multiple) "...". The baseline compile then kept our overrides while the full compile also had them — so 47 rules subtracted themselves away and the gate reported them missing from the output when they were only missing from the measurement.
• Two of four apparent "duplicates" occur twice on master as well. Measuring a suspicious count against the same count on master, before theorising about a cause, would have saved the detour.

A gate that measures by difference needs its difference to be exact. That is the durable lesson here, and it is worth more than either fix.

What is left of step 4

Deleting semantic-ui-less and its theme.config machinery: three webpack aliases (the plan names two — webpack.watch.config.mjs is the third), the node_modules copy in scripts/install-theme-config.js and its three call sites, and the now-unreferenced override/ tree.

Gates

jsdom 167 suites / 2540 tests / 38 snapshots on React 16.14, 17 and 18.3; Chrome 41/41; lint:css and css:fixture:check green; published CSS byte-identical.

🤖 Generated with Claude Code