Resolving package.json conflicts by unioning unique lines is right for a file
that holds one entry per line. Applied to ordinary source it duplicates
declarations, because both sides of a hunk keep their copy and nothing
de-duplicates across the join.
Eleven plugin entry points ended with the same import twice, and the poster
renderer with two identical `const sheet`. Each is a SyntaxError: every one of
those bundles would have failed to build, and the poster export would not run.
Found by parse-checking every changed .js against the merge base, not by the
gates -- gates:pre passed 101 of 102 with all twelve files broken, because its
parse gates do not cover plugin entry points.
One measurement trap worth recording. `node --check` on a .js file parses it as
CommonJS, so a bare `import` is a syntax error and ALL 28 entry points appear
broken, on development too. That reading says the tree is on fire and is simply
wrong. Copying each file to a .mjs and checking that parses it as a module,
which separates the eleven that are genuinely broken here from the rest that
are fine.
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