A regression from the previous commit. The object branch was a spread, which
*defines* properties and is therefore safe; rewriting it into a per-key loop to
filter unserializable values turned it into `out[key] = value`, which *sets* —
so a persisted `"__proto__"` key vanished on reload and, with an object value,
gave the returned metadata a caller-controlled prototype. The legacy branch had
already been fixed for exactly this.
Fixed at the root rather than the site: both branches now go through one
`defineMetadataKey`, so a change to how one stores a key cannot leave the other
behind. That split is what let the earlier fix fail to protect this path.
The test uses `JSON.parse('{"__proto__":…}')`, not an object literal — a
literal `__proto__:` key sets the prototype at construction and creates no own
property, so a test written that way passes against the broken code. Confirmed
by reverting the line: only the parsed case fails.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0177mPHAdECD18nLLCTwR5rh
Signed-off-by: cliffhall <cliff@futurescale.com>
bc433bbf72