test(toolchain): [MOD-01] evaluate isolated Bun installs and retain Yarn

refactor/scripts/install-compare.mjs

@@ -0,0 +1,37 @@
+import assert from 'node:assert/strict'
+import fs from 'node:fs'
+import path from 'node:path'
+import process from 'node:process'
+
+const directory = path.resolve(process.argv[2])
+const read = name => JSON.parse(fs.readFileSync(path.join(directory, name), 'utf8'))
+const yarn = read('yarn-graph.json')
+const bun = read('bun-graph.json')
+const unique = values => [...new Set(values)].sort()
+function differences(left, right) {
+  const a = new Set(left)
+  const b = new Set(right)
+  return { yarnOnly: [...a].filter(value => !b.has(value)).sort(), bunOnly: [...b].filter(value => !a.has(value)).sort() }
+}
+const tools = graph => Object.fromEntries(graph.rootTools.map(edge => [edge.name, edge.resolved]))
+const leftTools = tools(yarn)
+const rightTools = tools(bun)
+assert.deepEqual(Object.keys(leftTools).sort(), Object.keys(rightTools).sort())
+const rootToolChanges = Object.keys(leftTools).filter(name => leftTools[name] !== rightTools[name]).map(name => ({ name, yarn: leftTools[name], bun: rightTools[name] }))
+const edges = graph => unique(graph.requests.map(edge => `${edge.parent} ${edge.field} ${edge.name}@${edge.range} -> ${edge.resolved}`))
+const resources = graph => unique(graph.resources.map(item => `${item.package} ${item.path} ${item.bytes} ${item.sha256}`))
+const missing = graph => unique(graph.missing.map(edge => `${edge.parent} ${edge.field} ${edge.name}@${edge.range} optional=${edge.optional}`))
+const report = {
+  task: 'MOD-01',
+  source: read('snapshot.json').source,
+  counts: Object.fromEntries([['yarn', yarn], ['bun', bun]].map(([name, graph]) => [name, { packageInstances: graph.packages.length, uniquePackages: unique(graph.packages.map(pkg => `${pkg.name}@${pkg.version}`)).length, resolvedEdges: graph.requests.length, uniqueResources: resources(graph).length }])),
+  rootToolChanges,
+  packages: differences(yarn.packages.map(pkg => `${pkg.name}@${pkg.version}`), bun.packages.map(pkg => `${pkg.name}@${pkg.version}`)),
+  requests: differences(edges(yarn), edges(bun)),
+  missing: differences(missing(yarn), missing(bun)),
+  resources: differences(resources(yarn), resources(bun)),
+  missingRequired: Object.fromEntries([['yarn', yarn], ['bun', bun]].map(([name, graph]) => [name, graph.missing.filter(edge => !edge.optional && edge.field !== 'peerDependencies')])),
+  note: 'Physical hoisting differences are excluded from semantic comparisons. Missing optional/platform and peer requests remain explicit; this report alone does not determine build compatibility.',
+}
+fs.writeFileSync(path.join(directory, 'comparison.json'), `${JSON.stringify(report, null, 2)}\n`)
+console.log(JSON.stringify({ counts: report.counts, rootToolChanges, resources: report.resources, missingRequired: report.missingRequired }, null, 2))