fix(local): round-trip RPC success values through marker serialization

[asterikx]

Bug

alchemy dev (since the capnweb RPC split) crashes on any provider whose result contains an Effect Redacted:

TypeError: Cannot serialize value: <redacted>
    at evaluateImpl (capnweb/dist/index.js:1636:48)
    at provider.update (alchemy/src/Apply.ts:123:14)

Repro: any Cloudflare Container with a Redacted env value (e.g. Config.redacted(...) or an Output-mapped Redacted.make) under alchemy dev @ 2.0.0-beta.63 — create/update of the container fails, alchemy dev: apply failed. The container provider's result embeds dev.env: Record<string, string | Redacted> (LocalContainerProvider), which capnweb (correctly) refuses to serialize.

Cause

Local/RpcSerialization.ts marker-encodes RPC arguments (serializeRpcArgs/deserializeRpcArgs turn Redacted/Output into {_tag} markers) — but wrapRpcEffectHandler returns { _tag: "Success", value: exit.value } with the value raw, and unwrapRpcEffectHandler does Exit.succeed(exit.value) without decoding.

Fix

Success values now round-trip the same marker (de)serialization as arguments, on both sides. Two return-value tests added — they fail on current main and pass with the fix (14/14 in test/Local/RpcSerialization.test.ts).

Note

wrapRpcStreamHandler/unwrapRpcStreamHandler pipe stream elements raw as well — if streamed values can ever carry Redacted/Output, the same treatment is needed there. Left out of this PR since I couldn't confirm a live path that streams such values; happy to extend if you want it symmetric.

We hit this in production dev-loop usage (zero-cache + Python containers with secret env under alchemy dev) and are running exactly this change as a local patch meanwhile.

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[sam-goodwin]

Is there a test we can add?

[asterikx]

There are two in the PR already — packages/alchemy/test/Local/RpcSerialization.test.ts gains a return value serialization block:

• round-trips a Redacted return value — a handler returning Redacted.make("hush"); the existing roundTrip harness threads the JSON wire hop, so on main the value comes back corrupted instead of a reconstructed Redacted
• round-trips Redacted values nested in a returned object — the container-provider shape ({ env: { TOKEN: Redacted } }) that crashes alchemy dev in practice

Red/green verified: on main (fix stashed) exactly these two fail — Tests: 2 failed | 12 passed; with the fix 14 passed.

Happy to also cover the stream-element path (wrapRpcStreamHandler has the same gap), but that needs the symmetric stream fix first — say the word and I will extend the PR to both.

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