Restore the source package manifests; check the built ones in CI

The six wasm packages carried the build's rewritten package.json as their
source: exports, browser and react-native pointing at ./build/cjs/*, main at
./build/cjs/index.js. The build rewrote them again, so the published 7.5.17
and 7.5.19 had exports naming files that are not in the package (init's
"." resolved to ./build/cjs/wasm.js) and './package.json' spread into an
object of characters. This is the January 2026 ./cjs/cjs/ fault in another
form; its cause was committing built manifests, not the build script.

main, module, types, exports, browser, react-native and sideEffects are back
to the form of the upstream sources they were renamed from; the build
generates the rest. scure-sr25519 has no upstream counterpart and a
consistent hand-written manifest, so it is left as it is.

CI now checks every build/package.json: each entry point must name a file
that is there, with no ./build/ or ./cjs/cjs/ path, no numeric keys in
exports and no workspace/portal ranges. Red on the 7.5.19 build, green on
this one.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

scripts/check-built-manifests.py

@@ -0,0 +1,99 @@
+#!/usr/bin/env python3
+"""Check the package.json the build wrote into each packages/*/build directory.
+
+This is the manifest npm receives. It fails on what broke the January 2026
+releases and wasm 7.5.19: an entry point (main, module, types, browser,
+react-native, every exports target) naming a file that is not in the build
+directory, a path with ./build/ or a doubled ./cjs/cjs/ in it, numeric keys
+inside exports (a string spread into an object), and workspace:/portal:/link:
+dependency ranges.
+
+    check-built-manifests.py <repo-dir> [package ...]
+
+Prints one line per package and exits 1 if any package fails.
+"""
+import json
+import pathlib
+import sys
+
+ENTRY_FIELDS = ('main', 'module', 'types', 'typings', 'browser', 'react-native')
+DEP_FIELDS = ('dependencies', 'peerDependencies', 'optionalDependencies')
+
+
+def targets(node, path):
+    """Yield (json-path, target string) for every string leaf under exports."""
+    if isinstance(node, str):
+        yield path, node
+    elif isinstance(node, dict):
+        for key, value in node.items():
+            yield from targets(value, f'{path}/{key}')
+    elif isinstance(node, list):
+        for i, value in enumerate(node):
+            yield from targets(value, f'{path}[{i}]')
+
+
+def numeric_keys(node, path):
+    if isinstance(node, dict):
+        for key, value in node.items():
+            if key.isdigit():
+                yield f'{path}/{key}'
+            yield from numeric_keys(value, f'{path}/{key}')
+
+
+def check(build):
+    problems = []
+    manifest = build / 'package.json'
+    if not manifest.is_file():
+        return ['no build/package.json']
+    pkg = json.loads(manifest.read_text())
+
+    def check_path(where, target):
+        if not isinstance(target, str) or not target.startswith('.'):
+            return
+        if '/build/' in target or target.startswith('./build') or '/cjs/cjs/' in target:
+            problems.append(f'{where}: suspicious path {target}')
+        if '*' in target:
+            base = build / target.split('*', 1)[0]
+            if not base.parent.exists():
+                problems.append(f'{where}: {target} has no directory')
+            return
+        if not (build / target).is_file():
+            problems.append(f'{where}: {target} does not exist')
+
+    for field in ENTRY_FIELDS:
+        value = pkg.get(field)
+        if isinstance(value, str):
+            check_path(field, value)
+    for where, target in targets(pkg.get('exports'), 'exports'):
+        check_path(where, target)
+    for where in numeric_keys(pkg.get('exports'), 'exports'):
+        problems.append(f'{where}: numeric key (a string spread into an object)')
+    for field in DEP_FIELDS:
+        for dep, rng in (pkg.get(field) or {}).items():
+            if str(rng).startswith(('workspace:', 'portal:', 'link:', 'file:')):
+                problems.append(f'{field}.{dep}: {rng}')
+    return problems
+
+
+def main():
+    repo = pathlib.Path(sys.argv[1])
+    names = sys.argv[2:]
+    builds = [repo / 'packages' / n / 'build' for n in names] if names else sorted(repo.glob('packages/*/build'))
+    failed = 0
+    for build in builds:
+        problems = check(build)
+        name = build.parent.name
+        if problems:
+            failed += 1
+            print(f'FAIL {name}')
+            for p in problems[:12]:
+                print(f'     {p}')
+            if len(problems) > 12:
+                print(f'     ... {len(problems) - 12} more')
+        else:
+            print(f'ok   {name}')
+    sys.exit(1 if failed else 0)
+
+
+if __name__ == '__main__':
+    main()