fix(host-api-wrapper): return undefined from readJSON for absent keys

[cuteWarmFrog]

Problem

hostLocalStorage.readJSON(key) piped the read straight into JSON.parse:

readBytes(key).then(bytes => textDecoder.decode(bytes)).then(JSON.parse);

A never-written (or cleared) key reads back as undefined, and an empty value decodes to ''. JSON.parse('') throws SyntaxError: Unexpected end of JSON input — so the normal first-run path (key not written yet) surfaced as an error. Every product using readJSON for optional/first-run data had to wrap reads in a try/catch just to get a default.

This was observed in the wild via a product's forwarded console: [coinflipgame03.dot] Error reading from localStorage: SyntaxError: Unexpected end of JSON input on first launch, before flip_stats had ever been saved.

Fix

Guard the absent/empty case in readJSON and return undefined instead of parsing:

const bytes = await readBytes(key);
if (bytes === undefined || bytes.length === 0) return undefined;
return JSON.parse(textDecoder.decode(bytes));

• Missing / cleared key → undefined
• Empty stored value → undefined
• Valid JSON → parsed (unchanged)
• Genuinely malformed (non-empty) data still throws — real corruption stays visible

Tests

Added two cases to __tests__/hostApi/localStorage.spec.ts (missing key, empty value). Both reproduced the exact SyntaxError before the fix and pass after. Full suite green (673 passing), lint + typecheck clean.

https://claude.ai/code/session_01SqQTbeaAxijCffoCcp6Hyt