fix(rivetkit): bind methods through createWriteThroughProxy

[abcxff]

Fixes an error that occurs when inspector state attempts to serialize non trivial values (ie Date).

[railway-app]

🚅 Deployed to the rivet-pr-4987 environment in rivet-frontend

Service	Status	Web	Updated (UTC)
kitchen-sink	❌ Build Failed (View Logs)	Web	May 14, 2026 at 6:09 pm
website	😴 Sleeping (View Logs)	Web	May 13, 2026 at 8:32 pm
frontend-cloud	❌ Build Failed (View Logs)	Web	May 13, 2026 at 8:18 pm
ladle	❌ Build Failed (View Logs)	Web	May 13, 2026 at 8:18 pm
frontend-inspector	❌ Build Failed (View Logs)	Web	May 13, 2026 at 8:17 pm
mcp-hub	✅ Success (View Logs)	Web	May 6, 2026 at 8:30 pm

[abcxff]

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• [slop]fix(workflow-engine): only commit step state after success #5010 : 2 dependent PRs (#5050 , #5052 )
• fix(rivetkit): bind methods through createWriteThroughProxy #4987 👈 (View in Graphite)
• fix(rivetkit): remove client-side connection request size check #5057
• main

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[claude]

PR Review: fix(rivetkit): bind methods through createWriteThroughProxy

Overview

This PR fixes actor state not being tracked when methods are called on complex objects like Date, Map, Set, and typed arrays (e.g. state.date.setFullYear(2030) silently failing to persist). The root cause was the old hand-rolled Proxy-based createWriteThroughProxy only intercepting property set/deleteProperty traps — it never saw mutations via method calls. The fix replaces it with @rivetkit/on-change, which wraps those methods internally.

The PR also:

• Introduces JsonCompatValue type and assertJsonCompatValue to validate state at write-time (replacing the boolean-returning isCborSerializable predicate removed from utils.ts).
• Adds explicit Set support to encodeJsonCompatValue/reviveJsonCompatValue (new $Set tag).
• Strengthens encodeJsonCompatValue to throw TypeError on unserializable values rather than silently passing them through.
• Adds actor field to AsyncAPI inspector schemas (appears unrelated to the core fix — worth calling out in the PR description).

---

Issues

Missing NaN/Infinity validation

The old isCborSerializable explicitly checked !Number.isFinite(value) and returned false. assertJsonCompatValue accepts all typeof value === "number" values including NaN and Infinity, which are not valid JSON or CBOR. These should either be rejected or have a test asserting the intended behavior.

Map key is not validated through the proxy

onValidate in @rivetkit/on-change is called with the new property value (second argument), not the Map key. So state.map.set(nonSerializableKey, "v") will bypass assertJsonCompatValue — the key is never checked. Add a test and either validate keys separately or document the gap.

encodeJsonCompatValue is a silent breaking change

The old function ended with return input — class instances would pass through. Now any non-whitelisted object throws TypeError. If any existing actor state contains class instances, they'll fail at runtime with no migration path. Worth noting in the PR description or changelogs.

No cleanup / unsubscribe for the on-change proxy

onChange() returns a proxy. The on-change library exposes onChange.unsubscribe(proxy) to stop tracking. The current code never calls unsubscribe. Verify that @rivetkit/on-change does not hold strong references to the proxied object, and add a comment if confirmed safe.

onValidate always returning true is subtle

onValidate(_path: string, newValue: unknown) {
    beforeChange?.(newValue);
    return true;
},

This is fine but an unchecked throw from beforeChange for a non-validation reason would also silently prevent mutation. A one-line comment clarifying that rejection is always throw-based would help future readers.

---

Suggestions

Test coverage gap: Map/Set method mutations through onValidate

There is no test for map.set("k", () => {}) or set.add(() => {}) through the proxy with a beforeChange that calls assertJsonCompatValue. The existing tests only verify direct property assignment. Consider adding:

test("beforeChange rejects non-serializable Map value", () => {
    const state = createWriteThroughProxy(
        { m: new Map<string, unknown>() },
        vi.fn(),
        (v) => assertJsonCompatValue(v),
    );
    expect(() => state.m.set("k", () => {})).toThrow(TypeError);
    expect(state.m.has("k")).toBe(false);
});

Dropped ws peer dep for openai

In the lockfile, openai@6.26.0(zod@4.3.6) loses the ws optional dep. Verify this doesn't affect WebSocket-based streaming in any pi agent path.

@ungap/structured-clone deprecation

The lockfile notes a CWE-502 deprecation on @ungap/structured-clone@1.3.0 — worth bumping to >=1.3.1 to clear the warning.

---

Strengths

• The core fix is correct and well-motivated. Replacing the hand-rolled proxy with a dedicated library that properly intercepts method calls on Date/Map/Set/TypedArray is the right call.
• assertJsonCompatValue is a significant improvement over the old predicate — fail-by-default at write time matches the CLAUDE.md "Fail-By-Default Runtime" constraint.
• Test coverage for the proxy and encoding round-trips is thorough.
• Extracting createWriteThroughProxy into its own file improves maintainability.
• The Set encode/revive round-trip (via $Set tag) is a genuine correctness fix — previously Sets were silently lost on serialization.