fix(metro): drop Metro's transform cache under bundle=load too

[exo-nikita]

The error

Failed to construct transformer:  Error: Cannot find module 'metro-transform-worker'
  imported from node_modules/metro/src/DeltaBundler/getTransformCacheKey.js
    at State.getImport (stasis-core/src/state.js)
    at resolve (stasis-core/src/hooks.js)
    at Module._load (stasis-core/src/hooks.js)

The file is in the bundle and on disk. Only the edge is missing — nothing ever recorded that getTransformCacheKey.js imports metro-transform-worker, so load mode fails closed on it.

Why the edge can't exist

withStasis dropped cacheStores for a capture or a frozen verify but left them alone under bundle=load, reasoning that a hit there costs no attestation because the transform derives from the bundle's own bytes. It costs something else: the transform cache decides which modules Metro itself loads.

// metro/src/DeltaBundler/Transformer.js
this._cache = new Cache(config.cacheStores);
...
const globalCacheKey = this._cache.isDisabled ? '' : getTransformCacheKey({...});

Cache.isDisabled is exactly stores.length === 0. So getTransformCacheKey() — and its whole call tree: require(transformerPath), then Transformer.getCacheKey() reaching metro-transform-plugins.getTransformPluginCacheKeyFiles() and its require.resolve() calls — runs only when the cache is enabled. A capture has it disabled, so it never executes that tree and cannot record its edges. The replay has it enabled, executes it for real, and getImport rejects an edge no capture could have produced.

Instrumented at that exact branch on the repro (real Metro 0.87.0, 4 workers, --child-process, withStasis):

run	stores	isDisabled	getTransformCacheKey	result
capture --lock=add --bundle=add	0	true	never called	ok
replay --lock=frozen --bundle=load (before)	1	false	CALLED	ERR_MODULE_NOT_FOUND
replay --lock=frozen --bundle=load (after)	0	true	never called	ok, 3/3

Metro swallows the throw into Failed to construct transformer: and then dies in Bundler.end on the half-built instance (Cannot read properties of undefined (reading 'end')).

Why it's intermittent: which module in that tree throws first depends on which resolver the resolution reaches — the fail-closed getImport path, or the Module._resolveFilename shim, which falls through to disk for an edge the bundle lacks. My repro first failed on require.resolve('./index.js') from metro-transform-plugins/src/index.js; the report above failed one frame earlier on require(transformerPath). Same cause, and one run out of several passed outright.

The fix

needsTransforms no longer excludes loadBundle, so the stores are dropped in every active mode. The loaded set then can't diverge between record and replay — the same reason a capture drops them.

Capture behaviour is untouched: the attested set is identical before and after (105 buckets, 639 files, 1243 formats, same file/format hashes), and the replay now exits 0 and writes its output bundle.

The bundle=load test asserted the old behaviour, with the reasoning this disproves, so it's inverted rather than deleted: a replay must drop the stores, and replacing a caller's own stores must still be announced.

Cost, and the follow-up

A load build no longer reuses transforms. For --lock=frozen that's a gain — #152 already notes a verify over a warm cache "passes vacuously, it verifies transforms nobody performed", and the loadBundle exclusion quietly re-admitted that for frozen+load, which is the standard verify invocation. But a long-lived --bundle=load dev server now re-transforms on every start.

Keeping the cache under load requires the capture to run the cache-key path so those edges get recorded: leave the stores in place and force a full miss with a per-run cacheVersion nonce — the mechanism already in #156 for hand-wired configs. That's strictly better on speed and stops overriding the user's cacheStores at all, but it's a bigger change; this PR fixes the broken build first.

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