fix(cli): read an array preload back whatever quotes it is written in

[mhenrixon]

Summary

Packager#extract_existing_pin_options read an array preload: back through JSON.parse. Two shapes broke on it:

pin "x", preload: ["admin"]        => {preload: ["admin"]}
pin "x", preload: ["admin", "app"] => {preload: ["admin", "app"]}
pin "x", preload: []               => {}                       # dropped silently
pin 'x', preload: ['admin']        => JSON::ParserError: unexpected character

Single-quoted pins are a supported shape in this gem — test/packager_single_quotes_test.rb and the single_quote_* fixtures are there for it — so an app with pin 'x', preload: ['admin'] crashed on every command that reads a pin, not only the one rewriting it. And preload: [] never matched PRELOAD_OPTION_REGEXP (\[[^\]]+\] needs a character), so the next pin/update/pristine wrote the line back without it and restored the preload: true default on a package the app had asked to preload for no entry point.

Three additive changes in lib/importmap/packager.rb:

• PRELOAD_OPTION_REGEXP — [^\]]+ → [^\]]*, so [] matches.
• preload_from_string — the entry points are scanned out of the literal (value.scan(/["']([^"']*)["']/)) instead of parsed. config/importmap.rb is Ruby, not JSON.
• preload — return "" if preloads.nil? before Array(), which flattens nil and [] to the same thing; [] now writes preload: [].

Docs page updated: docs/app/views/docs/pages/pinning.rb ("Pin options survive a rewrite" now lists the array and empty-array forms and says quoting doesn't matter).
CHANGELOG entry under ## 1.2.0 → ### Fixed.

Closes #28

Test plan

• bundle exec rake test — 437 runs, 0 failures, with bun installed
• --minify tests ran rather than skipped (test/minifier_test.rb 5 runs / 0 skips, commands_test.rb -n /minify/ 2 runs / 0 skips)
• cd docs && bundle exec rake lint && bundle exec rspec — 53 files no offenses, 54 examples passed
• New tests seen RED first on the pre-fix tree: JSON::ParserError for the single-quoted cases, {} and pin "react" for the empty-array ones
• Manual: put pin 'md5', preload: ['admin'] and pin "crypt", preload: [] in an app's config/importmap.rb, run bin/importmap update md5, and confirm both lines come back with their preloads intact

Deviations & judgment calls

• Scan instead of normalising quotes before JSON.parse. The issue offered either. The scan needs no JSON at all and also accepts the Ruby-isms JSON rejects (a trailing comma, [ ]), which is the right bar for a file that is Ruby.
• A single-element array still normalises to a string — preload: ["admin"] is rewritten as preload: "admin". Not fixed on purpose: the CLI's --preload admin arrives at preload() as exactly the same value (["admin"]), Map compares both through Array() so the meaning is identical, and test/packager_test.rb:79 has asserted the string form since upstream. Telling the two apart would mean moving CLI-shape normalisation out of preload() — a restructure of an upstream-owned method for no semantic gain.
• No live commands_test.rb case. No new CDN contract and no new printed sentence; .claude/rules/testing.md says each live case costs a round-trip on every matrix cell. The round-trip is proven at unit level instead (read → pin_for → same line).
• extract_existing_pin_options with single quotes is regression coverage, not proof. It passes on main too — a boolean preload with single quotes always worked. It is there because that test class covered only packaged? and remove. The array cases are the ones that were red.
• pin --vendor silently discards a custom-URL pin and vendors from the resolved CDN instead #29 is a separate PR. It was picked in the same batch but lands in commands.rb on a different code path and has its own product decision; the diffs don't overlap.

---

Summary by cubic

Fixes array preload: handling when CLI commands read pins back from config/importmap.rb. Previously single-quoted pins like pin 'md5', preload: ['admin'] crashed with JSON::ParserError, and preload: [] was silently dropped, so pin, update, and pristine restored the preload: true default.

• Scans entry points out of the Ruby literal instead of parsing it as JSON, so quote style no longer matters.
• Preserves preload: [] in rewritten pins instead of omitting it.
• Single-element arrays still normalize to a string (preload: ["admin"] becomes preload: "admin"), matching existing CLI behavior.
• Adds regression tests, a fixture, a docs update, and a CHANGELOG entry.

Closes #28.

^{Written for commit 0018b3f. Summary will update on new commits.}