effect(zod-adapter-removal): drop fromZod shim and unused zod dep

Replace the last fromZod consumer (LeaseMutableEffectSchema in
messages/events.ts) with a native Effect schema that uses Schema.mutable
on the record and the inner array so DelegateBody.lease_request stays
assignment-compatible with the zod-derived Lease = Record<string, string[]>
contract used across runtime/job-runner.ts. Delete messages/zod-adapter.ts
and its dedicated test file. Drop zod from @arcp/client/package.json
(client/src has zero direct zod imports).

zod remains a direct dep of @arcp/core and @arcp/runtime because
envelope.ts, brands.ts, errors.ts, messages/{lease-schema,events,session,
execution,index}.ts, store/eventlog.ts, and runtime/session-context.ts
still consume zod schemas. Full removal would require migrating envelope.ts
+ brands.ts + every messageEnvelope() payload twin + every .safeParse
caller (client-dispatch.ts, session-context.ts) — deferred to a follow-up
since it cascades beyond the 600 LOC slice budget.

All gates green: lint, typecheck, build, 442/442 tests including SDK
integration 45/45.

Closes #50
Closes #30

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Nick Ficano

packages/client/package.json

@@ -44,8 +44,7 @@
   "dependencies": {
     "@arcp/core": "workspace:*",
     "@effect/platform": "^0.96.1",
-    "effect": "^3.21.2",
-    "zod": "^3.23.8"
+    "effect": "^3.21.2"
   },
   "devDependencies": {
     "@types/node": "^22.7.5",

packages/core/src/messages/events.ts

@@ -4,9 +4,8 @@ import { z } from "zod";
 import { ERROR_CODES } from "../errors.js";
 
 import { ArtifactRefSchema } from "./artifacts.js";
-import { LeaseConstraintsSchema, LeaseZodSchema } from "./lease-schema.js";
+import { LeaseConstraintsSchema } from "./lease-schema.js";
 import { LogPayloadSchema, MetricPayloadSchema } from "./telemetry.js";
-import { fromZod } from "./zod-adapter.js";
 
 // ARCP v1.0 §8 + v1.1 §8.2/§8.4 — `job.event` body schemas.
 //
@@ -93,13 +92,21 @@ export const StatusBodySchema = Schema.Struct({
 });
 export type StatusBody = Schema.Schema.Type<typeof StatusBodySchema>;
 
-// `LeaseSchema` infers `Record<string, ReadonlyArray<string>>`; the rest of
-// the runtime (lease.ts, job-runner.ts) treats `Lease` as the mutable
-// `Record<string, string[]>` shape from the zod twin. Bridge through
-// `fromZod` so the inferred `DelegateBody.lease_request` stays
-// assignment-compatible with the zod-derived `Lease` alias until slice #50
-// migrates the `Lease` consumers to readonly arrays.
-const LeaseMutableEffectSchema = fromZod(LeaseZodSchema);
+// `LeaseSchema` in `lease-schema.ts` infers
+// `Record<string, ReadonlyArray<string>>`; the rest of the runtime (lease.ts,
+// job-runner.ts) treats `Lease` as the mutable `Record<string, string[]>`
+// shape from the zod twin. Define a native Effect mirror that wraps the
+// inner array in `Schema.mutable` and applies `Schema.mutable` to the record
+// so the inferred `DelegateBody.lease_request` stays assignment-compatible
+// with the zod-derived `Lease` alias used across the runtime.
+const LeaseMutableEffectSchema = Schema.mutable(
+  Schema.Record({
+    key: Schema.String.pipe(Schema.nonEmptyString()),
+    value: Schema.mutable(
+      Schema.Array(Schema.String.pipe(Schema.nonEmptyString())),
+    ),
+  }),
+);
 
 /** §8.2 `delegate` event-kind body. */
 export const DelegateBodySchema = Schema.Struct({

packages/core/src/messages/index.ts

@@ -19,7 +19,6 @@ export * from "./execution.js";
 export * from "./session.js";
 export * from "./telemetry.js";
 export type * from "./types.js";
-export { fromZod } from "./zod-adapter.js";
 
 const ALL_ENVELOPES = [
   ...SESSION_ENVELOPES,