diff --git a/packages/ai/src/utils/schema/index.ts b/packages/ai/src/utils/schema/index.ts
index b89a511b8..971e88208 100644
--- a/packages/ai/src/utils/schema/index.ts
+++ b/packages/ai/src/utils/schema/index.ts
@@ -10,3 +10,4 @@ export * from "./normalize";
 export * from "./spill";
 export * from "./types";
 export * from "./wire";
+export * from "./zod-decontaminate";
diff --git a/packages/ai/src/utils/schema/normalize.ts b/packages/ai/src/utils/schema/normalize.ts
index befaf81a0..9983ae9a7 100644
--- a/packages/ai/src/utils/schema/normalize.ts
+++ b/packages/ai/src/utils/schema/normalize.ts
@@ -21,8 +21,8 @@ import {
 import { isValidJsonSchema } from "./meta-validator";
 import { type DescriptionSpillFormat, spillToDescription } from "./spill";
 import { enter, epochNext, exit, once, stamp } from "./stamps";
-import type { JsonObject } from "./types";
-import { isJsonObject } from "./types";
+import { isJsonObject, type JsonObject } from "./types";
+import { decontaminateZodInstance } from "./zod-decontaminate";
 
 export type ResidualSchemaIncompatibility = "type-array" | "type-null" | "nullable" | "combiners";
 
@@ -768,7 +768,8 @@ function hasResidualSchemaIncompatibilities(
 }
 
 export function normalizeSchema(value: unknown, options: NormalizeSchemaOptions): unknown {
-	const upgraded = upgradeJsonSchemaTo202012(value);
+	const detoxified = decontaminateZodInstance(value);
+	const upgraded = upgradeJsonSchemaTo202012(detoxified);
 	const dereferenced = dereferenceJsonSchema(upgraded);
 	let normalized = normalizeSchemaNode(dereferenced, {
 		...options,
diff --git a/packages/ai/src/utils/schema/wire.ts b/packages/ai/src/utils/schema/wire.ts
index 03ee7a2c7..d6e604856 100644
--- a/packages/ai/src/utils/schema/wire.ts
+++ b/packages/ai/src/utils/schema/wire.ts
@@ -18,7 +18,19 @@ import type { Tool, TSchema } from "../../types";
 import { upgradeJsonSchemaTo202012 } from "./draft";
 import { stamp } from "./stamps";
 
-/** True when `value` is a Zod schema instance. */
+/**
+ * True when `value` is a live Zod schema instance.
+ *
+ * The check is stricter than "has a `_zod` property" because a JSON
+ * round-trip preserves the `_zod` key as a plain object and would otherwise
+ * fool the predicate — see issue #1101, where MCP servers ship
+ * `JSON.stringify(zodSchemaInstance)` as a tool's `inputSchema` and the
+ * resulting plain object then explodes `z.toJSONSchema` because the prototype
+ * (and every Zod parsing method) is gone.
+ *
+ * Live Zod instances always carry a `.parse` function on the prototype;
+ * impostors do not.
+ */
 export function isZodSchema(value: unknown): value is ZodType {
 	return (
 		typeof value === "object" &&
@@ -30,7 +42,10 @@ export function isZodSchema(value: unknown): value is ZodType {
 		// (`ZodObject`, `ZodOptional`, etc.) and a tagged-union style check would
 		// have to enumerate them all.
 		"_zod" in value &&
-		typeof (value as { _zod?: { def?: unknown } })._zod === "object"
+		typeof (value as { _zod?: { def?: unknown } })._zod === "object" &&
+		// Reject JSON-roundtripped objects that kept the `_zod` key but lost the
+		// prototype. Real instances have `.parse` on the prototype chain.
+		typeof (value as { parse?: unknown }).parse === "function"
 	);
 }
 
diff --git a/packages/ai/src/utils/schema/zod-decontaminate.ts b/packages/ai/src/utils/schema/zod-decontaminate.ts
new file mode 100644
index 000000000..09491c18c
--- /dev/null
+++ b/packages/ai/src/utils/schema/zod-decontaminate.ts
@@ -0,0 +1,322 @@
+/**
+ * Defensive rewrite for nodes that look like `JSON.stringify(zodSchemaInstance)`
+ * output rather than JSON Schema. MCP servers using Zod 4 sometimes ship a
+ * serialised schema instance directly as a tool's `inputSchema`, because the
+ * fields Zod surfaces on its instances (`type`, `enum`, `options`, `def`) shadow
+ * (and clash with) JSON Schema keywords. The resulting payload is neither valid
+ * Zod nor valid JSON Schema 2020-12 and Anthropic's strict validator rejects
+ * the whole tool list.
+ *
+ * Symptoms we've observed (gitnexus_impact.direction):
+ *   {
+ *     def:   { type: "enum", entries: { upstream: "upstream", ... } },
+ *     type:  "enum",                       // <- invalid `type` value
+ *     enum:  { upstream: "upstream", ... }, // <- `enum` MUST be an array
+ *     options: ["upstream", "downstream"],
+ *   }
+ *
+ * This module recognises the shape (`def.type === node.type` and `def.type` is
+ * a known Zod kind) and rewrites it to clean JSON Schema where deterministic.
+ * For Zod kinds we don't fully model, we strip the toxic siblings (`def`,
+ * `options`, object-shaped `enum`) and drop an invalid `type` so the remainder
+ * passes meta-schema validation as a permissive node.
+ *
+ * Pure / identity-preserving: returns the input reference when nothing changes.
+ */
+
+import { isJsonObject, type JsonObject } from "./types";
+
+const VALID_JSON_SCHEMA_TYPES: Record<string, true> = {
+	string: true,
+	number: true,
+	integer: true,
+	boolean: true,
+	object: true,
+	array: true,
+	null: true,
+};
+
+/**
+ * Known Zod 4 schema kinds as surfaced on `_def.type` / `.type`. Matching this
+ * set (rather than just "has `def`") is what keeps us from rewriting legitimate
+ * JSON Schemas that happen to use `def` as a property name.
+ */
+const ZOD_KINDS: Record<string, true> = {
+	string: true,
+	number: true,
+	int: true,
+	boolean: true,
+	bigint: true,
+	null: true,
+	undefined: true,
+	void: true,
+	any: true,
+	unknown: true,
+	never: true,
+	date: true,
+	symbol: true,
+	nan: true,
+	enum: true,
+	literal: true,
+	object: true,
+	array: true,
+	tuple: true,
+	record: true,
+	map: true,
+	set: true,
+	union: true,
+	discriminatedUnion: true,
+	intersection: true,
+	lazy: true,
+	promise: true,
+	function: true,
+	file: true,
+	custom: true,
+	template_literal: true,
+	optional: true,
+	nullable: true,
+	default: true,
+	prefault: true,
+	catch: true,
+	pipe: true,
+	transform: true,
+	brand: true,
+	readonly: true,
+	success: true,
+	nonoptional: true,
+};
+
+const ZOD_SCALAR_TO_JSON_TYPE: Record<string, string> = {
+	string: "string",
+	number: "number",
+	int: "integer",
+	boolean: "boolean",
+	null: "null",
+	bigint: "string",
+	date: "string",
+	nan: "number",
+};
+
+const ZOD_NOISE_KEYS: Record<string, true> = {
+	def: true,
+	options: true,
+	_zod: true,
+	checks: true,
+};
+
+/**
+ * JSON Schema keywords where `null` is a legal value (literal payload positions).
+ * Anywhere else, a `null`-valued key is a meta-schema violation — Zod scalars
+ * leak `format: null`, `minLength: null`, etc. that we have to scrub.
+ */
+const KEYS_THAT_ACCEPT_NULL: Record<string, true> = {
+	default: true,
+	const: true,
+	examples: true,
+};
+
+function isZodLeak(node: JsonObject): boolean {
+	const def = node.def;
+	if (!isJsonObject(def)) return false;
+	const defType = def.type;
+	if (typeof defType !== "string" || !ZOD_KINDS[defType]) return false;
+	// Both surface and inner `.type` must agree — Zod always mirrors `_def.type`
+	// onto the instance, so this is a near-zero false-positive guard.
+	return node.type === defType;
+}
+
+function inferTypeFromValues(values: readonly unknown[]): string {
+	if (values.length === 0) return "string";
+	const first = values[0];
+	if (typeof first === "number") return Number.isInteger(first) ? "integer" : "number";
+	if (typeof first === "boolean") return "boolean";
+	if (first === null) return "null";
+	return "string";
+}
+
+function unwrapInnerSchema(def: JsonObject): unknown {
+	// Zod uses different fields depending on the wrapper:
+	//   optional/nullable/readonly/brand/default → `innerType`
+	//   pipe → `in` (or `out`)
+	//   lazy → `getter` (a function — gone after JSON.stringify); fall back to {}
+	return def.innerType ?? def.in ?? def.out ?? def.schema ?? def.element ?? {};
+}
+
+function copyWithoutNoise(node: JsonObject): JsonObject {
+	const out: JsonObject = {};
+	for (const key in node) {
+		if (ZOD_NOISE_KEYS[key]) continue;
+		const value = node[key];
+		if (value === null && !KEYS_THAT_ACCEPT_NULL[key]) continue;
+		out[key] = value;
+	}
+	return out;
+}
+
+function rewriteZodNode(node: JsonObject, seen: WeakSet<object>): unknown {
+	const def = node.def as JsonObject;
+	const kind = def.type as string;
+
+	switch (kind) {
+		case "enum": {
+			// Prefer node.options (array form Zod exposes) → def.entries values →
+			// object-shaped node.enum values. All three carry the same data.
+			const optionsArray = Array.isArray(node.options) ? (node.options as unknown[]) : null;
+			const entries = isJsonObject(def.entries) ? Object.values(def.entries) : null;
+			const enumObj = isJsonObject(node.enum) ? Object.values(node.enum) : null;
+			const values = optionsArray ?? entries ?? enumObj ?? [];
+			return { type: inferTypeFromValues(values), enum: values };
+		}
+
+		case "literal": {
+			const values = Array.isArray(def.values) ? (def.values as unknown[]) : [];
+			if (values.length === 1) {
+				return { const: values[0] };
+			}
+			if (values.length > 1) {
+				return { type: inferTypeFromValues(values), enum: values };
+			}
+			return {};
+		}
+
+		case "union":
+		case "discriminatedUnion": {
+			const arms = Array.isArray(def.options)
+				? (def.options as unknown[])
+				: Array.isArray(node.options)
+					? (node.options as unknown[])
+					: [];
+			return { anyOf: arms.map(x => walk(x, seen)) };
+		}
+
+		case "intersection": {
+			return {
+				allOf: [walk(def.left, seen), walk(def.right, seen)],
+			};
+		}
+
+		case "array": {
+			return { type: "array", items: walk(def.element, seen) };
+		}
+
+		case "set": {
+			const element = def.valueType ?? def.element;
+			return { type: "array", uniqueItems: true, items: walk(element, seen) };
+		}
+
+		case "tuple": {
+			const items = Array.isArray(def.items) ? (def.items as unknown[]) : [];
+			const out: JsonObject = { type: "array", prefixItems: items.map(x => walk(x, seen)) };
+			const rest = def.rest;
+			if (rest != null) out.items = walk(rest, seen);
+			return out;
+		}
+
+		case "record":
+		case "map": {
+			return { type: "object", additionalProperties: walk(def.valueType, seen) };
+		}
+
+		case "object": {
+			const shape = isJsonObject(def.shape) ? def.shape : ({} as JsonObject);
+			const properties: JsonObject = {};
+			const required: string[] = [];
+			for (const key in shape) {
+				const inner = walk(shape[key], seen);
+				properties[key] = inner;
+				if (!isOptionalEntry(shape[key])) required.push(key);
+			}
+			const out: JsonObject = { type: "object", properties };
+			if (required.length > 0) out.required = required;
+			return out;
+		}
+
+		case "nonoptional":
+		case "optional":
+		case "nullable":
+		case "default":
+		case "prefault":
+		case "catch":
+		case "readonly":
+		case "brand":
+		case "lazy":
+		case "pipe":
+		case "transform": {
+			const inner = walk(unwrapInnerSchema(def), seen);
+			if (kind === "nullable" && isJsonObject(inner) && typeof inner.type === "string") {
+				return { ...inner, type: [inner.type, "null"] };
+			}
+			return inner;
+		}
+
+		default: {
+			// Best-effort: drop the noise, map the kind to a JSON Schema type if
+			// we know one, otherwise drop `type` so the node validates as
+			// permissive.
+			const cleaned = copyWithoutNoise(node);
+			const mapped = ZOD_SCALAR_TO_JSON_TYPE[kind];
+			if (mapped) {
+				cleaned.type = mapped;
+			} else if (typeof cleaned.type === "string" && !VALID_JSON_SCHEMA_TYPES[cleaned.type]) {
+				delete cleaned.type;
+			}
+			// Object-shaped `enum` survives as a noise field — remove if present.
+			if (cleaned.enum !== undefined && !Array.isArray(cleaned.enum)) {
+				delete cleaned.enum;
+			}
+			return cleaned;
+		}
+	}
+}
+
+function isOptionalEntry(value: unknown): boolean {
+	if (!isJsonObject(value)) return false;
+	if (!isZodLeak(value)) return false;
+	const kind = (value.def as JsonObject).type;
+	return kind === "optional" || kind === "default" || kind === "prefault";
+}
+
+/**
+ * Walks a JSON value and rewrites every Zod-instance-shaped node into clean
+ * JSON Schema 2020-12. Identity-preserving when no rewrite fires. Tolerates
+ * self-referential graphs — a revisited node returns as-is.
+ */
+export function decontaminateZodInstance(value: unknown): unknown {
+	return walk(value, new WeakSet());
+}
+
+function walk(value: unknown, seen: WeakSet<object>): unknown {
+	if (Array.isArray(value)) {
+		if (seen.has(value)) return value;
+		seen.add(value);
+		let changed = false;
+		const out = value.map(entry => {
+			const rewritten = walk(entry, seen);
+			if (rewritten !== entry) changed = true;
+			return rewritten;
+		});
+		return changed ? out : value;
+	}
+	if (!isJsonObject(value)) return value;
+	if (seen.has(value)) return value;
+	seen.add(value);
+
+	if (isZodLeak(value)) {
+		// Rewrite the node itself, then recurse into the rewrite so any nested
+		// Zod-instance children get cleaned in the same pass.
+		const rewritten = rewriteZodNode(value, seen);
+		return rewritten === value ? value : walk(rewritten, seen);
+	}
+
+	// Plain JSON Schema node: recurse into children, preserving identity when
+	// nothing under us changed.
+	let changed = false;
+	const out: JsonObject = {};
+	for (const key in value) {
+		const child = value[key];
+		const rewritten = walk(child, seen);
+		if (rewritten !== child) changed = true;
+		out[key] = rewritten;
+	}
+	return changed ? out : value;
+}
diff --git a/packages/ai/test/schema-normalization.test.ts b/packages/ai/test/schema-normalization.test.ts
index a1e871b81..6f5aec377 100644
--- a/packages/ai/test/schema-normalization.test.ts
+++ b/packages/ai/test/schema-normalization.test.ts
@@ -348,6 +348,99 @@ describe("normalizeSchemaForMCP", () => {
 			description: "ID",
 		});
 	});
+
+	// Regression: issue #1101. Some MCP servers ship `JSON.stringify(zodSchema)`
+	// directly as a tool's `inputSchema`. Zod 4 surfaces `.type`, `.enum`,
+	// `.options`, and `.def` on every schema instance — those keys collide with
+	// JSON Schema keywords, producing payloads that fail Anthropic's strict
+	// JSON Schema 2020-12 validator (`"type":"enum"`, `"enum":{...}` as object).
+	// `normalizeSchemaForMCP` must rewrite the offending nodes into clean JSON
+	// Schema so the tool list still ships.
+	it("rewrites a Zod-enum instance leaked as inputSchema", () => {
+		const leaked = {
+			def: { type: "enum", entries: { upstream: "upstream", downstream: "downstream" } },
+			type: "enum",
+			enum: { upstream: "upstream", downstream: "downstream" },
+			options: ["upstream", "downstream"],
+		};
+		expect(normalizeSchemaForMCP(leaked)).toEqual({
+			type: "string",
+			enum: ["upstream", "downstream"],
+		});
+	});
+
+	it("rewrites a numeric Zod-enum (integer values keep integer type)", () => {
+		const leaked = {
+			def: { type: "enum", entries: { ONE: 1, TWO: 2 } },
+			type: "enum",
+			enum: { ONE: 1, TWO: 2 },
+			options: [1, 2],
+		};
+		expect(normalizeSchemaForMCP(leaked)).toEqual({
+			type: "integer",
+			enum: [1, 2],
+		});
+	});
+
+	it("rewrites a Zod-literal instance to a single-element enum", () => {
+		const leaked = {
+			def: { type: "literal", values: ["only"] },
+			type: "literal",
+			values: ["only"],
+		};
+		// Decontamination emits `{const:"only"}`; downstream normalizer collapses
+		// it to the equivalent enum form. End-to-end contract is what callers see.
+		expect(normalizeSchemaForMCP(leaked)).toEqual({ type: "string", enum: ["only"] });
+	});
+
+	it("rewrites a Zod-union of literals (downstream collapses anyOf-of-consts to enum)", () => {
+		const leaked = {
+			def: {
+				type: "union",
+				options: [
+					{ def: { type: "literal", values: ["on"] }, type: "literal", values: ["on"] },
+					{ def: { type: "literal", values: ["off"] }, type: "literal", values: ["off"] },
+				],
+			},
+			type: "union",
+		};
+		expect(normalizeSchemaForMCP(leaked)).toEqual({
+			type: "string",
+			enum: ["on", "off"],
+		});
+	});
+
+	it("strips null-valued JSON Schema keywords that Zod scalars leak (format: null, minLength: null)", () => {
+		const leaked = {
+			def: { type: "string", checks: [] },
+			type: "string",
+			format: null,
+			minLength: null,
+			maxLength: null,
+		};
+		expect(normalizeSchemaForMCP(leaked)).toEqual({ type: "string" });
+	});
+
+	it("drops invalid `type` for unmodelled Zod kinds so the residue stays valid", () => {
+		const leaked = {
+			def: { type: "any" },
+			type: "any",
+			description: "anything",
+		};
+		expect(normalizeSchemaForMCP(leaked)).toEqual({ description: "anything" });
+	});
+
+	it("leaves a genuine JSON Schema that happens to have a `def` property alone", () => {
+		// `def` is not a JSON Schema keyword but it's also not reserved. The
+		// detoxifier must only fire when `def.type` is a known Zod kind AND
+		// `node.type === def.type`, otherwise it would corrupt real schemas.
+		const schema = {
+			type: "object",
+			properties: { def: { type: "string" } },
+			required: ["def"],
+		};
+		expect(normalizeSchemaForMCP(schema)).toEqual(schema);
+	});
 });
 
 // ---------------------------------------------------------------------------
diff --git a/packages/ai/test/schema-wire.test.ts b/packages/ai/test/schema-wire.test.ts
new file mode 100644
index 000000000..03ca2744c
--- /dev/null
+++ b/packages/ai/test/schema-wire.test.ts
@@ -0,0 +1,44 @@
+import { describe, expect, it } from "bun:test";
+import { isZodSchema } from "@oh-my-pi/pi-ai/utils/schema";
+import { z } from "zod/v4";
+
+describe("isZodSchema", () => {
+	it("accepts a live Zod instance", () => {
+		expect(isZodSchema(z.object({ a: z.string() }))).toBe(true);
+		expect(isZodSchema(z.string())).toBe(true);
+		expect(isZodSchema(z.enum({ a: "a", b: "b" }))).toBe(true);
+	});
+
+	// Regression: issue #1101. Before tightening, `isZodSchema` returned true
+	// for `JSON.parse(JSON.stringify(zodSchema))` because the `_zod` property
+	// (and its object value) survived the round-trip — even though every Zod
+	// method had been stripped along with the prototype. The relaxed predicate
+	// fed garbage into `z.toJSONSchema` and (when callers bypassed conversion)
+	// shipped the raw Zod internals to Anthropic's strict validator.
+	it("rejects a JSON-roundtripped Zod schema (prototype lost)", () => {
+		const impostor = JSON.parse(JSON.stringify(z.object({ a: z.string() })));
+		expect(isZodSchema(impostor)).toBe(false);
+	});
+
+	it("rejects the raw gitnexus_impact.direction payload from issue #1101", () => {
+		const impostor = {
+			def: { type: "enum", entries: { upstream: "upstream", downstream: "downstream" } },
+			type: "enum",
+			enum: { upstream: "upstream", downstream: "downstream" },
+			options: ["upstream", "downstream"],
+		};
+		expect(isZodSchema(impostor)).toBe(false);
+	});
+
+	it("rejects plain JSON Schema objects", () => {
+		expect(isZodSchema({ type: "object", properties: {} })).toBe(false);
+		expect(isZodSchema({ type: "string" })).toBe(false);
+	});
+
+	it("rejects non-objects", () => {
+		expect(isZodSchema(null)).toBe(false);
+		expect(isZodSchema(undefined)).toBe(false);
+		expect(isZodSchema("string")).toBe(false);
+		expect(isZodSchema(42)).toBe(false);
+	});
+});
diff --git a/packages/coding-agent/src/extensibility/typebox.ts b/packages/coding-agent/src/extensibility/typebox.ts
index e8182933b..52849961a 100644
--- a/packages/coding-agent/src/extensibility/typebox.ts
+++ b/packages/coding-agent/src/extensibility/typebox.ts
@@ -21,7 +21,7 @@
  * `@sinclair/typebox` directly in their own package.
  */
 
-import { areJsonValuesEqual } from "@oh-my-pi/pi-ai/utils/schema";
+import { areJsonValuesEqual, zodToWireSchema } from "@oh-my-pi/pi-ai/utils/schema";
 import {
 	type ZodArray,
 	type ZodEnum,
@@ -104,19 +104,46 @@ interface ObjectOpts extends Meta {
 // Helpers
 // ---------------------------------------------------------------------------
 
-function withMeta<T extends ZodType>(schema: T, opts: Meta | undefined): T {
-	if (!opts) return schema;
-	let out: ZodType = schema;
-	if (typeof opts.description === "string") out = out.describe(opts.description);
-	if ("default" in opts) out = out.default(opts.default as never) as unknown as ZodType;
-
-	const metadata: Record<string, unknown> = {};
-	for (const [key, value] of Object.entries(opts)) {
-		if (key === "description" || key === "default" || key === "additionalProperties") continue;
-		metadata[key] = value;
+/**
+ * Stamp a non-enumerable `toJSON()` on a schema so `JSON.stringify(schema)`
+ * yields a clean draft 2020-12 JSON Schema — matching real TypeBox semantics
+ * where the schema object IS already a JSON Schema. Without this, an extension
+ * author who serialises the schema across any JSON boundary (worker
+ * postMessage, MCP transport, config persistence, network hop, structuredClone
+ * fallback) ships the raw Zod internals (`def`, `_zod`, object-shaped `enum`,
+ * `"type":"enum"`) — neither valid JSON Schema nor parseable Zod. See
+ * issue #1101 for the symptoms when this leaks into a tool's `input_schema`.
+ *
+ * Idempotent: re-stamping the same instance is a no-op.
+ */
+function wire<T extends ZodType>(schema: T): T {
+	if (!Object.hasOwn(schema as object, "toJSON")) {
+		Object.defineProperty(schema as object, "toJSON", {
+			value: function toJSON(this: ZodType) {
+				return zodToWireSchema(this);
+			},
+			enumerable: false,
+			writable: true,
+			configurable: true,
+		});
 	}
-	if (Object.keys(metadata).length > 0) out = out.meta(metadata);
-	return out as T;
+	return schema;
+}
+
+function withMeta<T extends ZodType>(schema: T, opts: Meta | undefined): T {
+	let out: ZodType = schema;
+	if (opts) {
+		if (typeof opts.description === "string") out = out.describe(opts.description);
+		if ("default" in opts) out = out.default(opts.default as never) as unknown as ZodType;
+
+		const metadata: Record<string, unknown> = {};
+		for (const key in opts) {
+			if (key === "description" || key === "default" || key === "additionalProperties") continue;
+			metadata[key] = opts[key];
+		}
+		if (Object.keys(metadata).length > 0) out = out.meta(metadata);
+	}
+	return wire(out as T);
 }
 
 // ---------------------------------------------------------------------------
@@ -313,7 +340,8 @@ function tRecord<V extends ZodType>(key: ZodType, value: V, opts?: Meta): ZodTyp
 }
 
 function tOptional<E extends ZodType>(schema: E, _opts?: Meta): ZodOptional<E> {
-	return isOptional(schema) ? (schema as unknown as ZodOptional<E>) : (schema.optional() as ZodOptional<E>);
+	if (isOptional(schema)) return wire(schema as unknown as ZodOptional<E>);
+	return wire(schema.optional() as ZodOptional<E>);
 }
 
 function tNullable<E extends ZodType>(schema: E, opts?: Meta): ZodType {
@@ -322,27 +350,26 @@ function tNullable<E extends ZodType>(schema: E, opts?: Meta): ZodType {
 
 function tReadonly<E extends ZodType>(schema: E): E {
 	// TypeBox's `Type.Readonly` is purely a marker; runtime parsing is identical.
-	return schema;
+	return wire(schema);
 }
 
 function tPartial<P extends ZodRawShape>(obj: ZodObject<P>): ZodObject<P> {
-	return obj.partial() as unknown as ZodObject<P>;
+	return wire(obj.partial() as unknown as ZodObject<P>);
 }
 
 function tRequired<P extends ZodRawShape>(obj: ZodObject<P>): ZodObject<P> {
-	return obj.required() as unknown as ZodObject<P>;
+	return wire(obj.required() as unknown as ZodObject<P>);
 }
 
 function tPick<P extends ZodRawShape, K extends keyof P>(obj: ZodObject<P>, keys: readonly K[]): ZodObject<Pick<P, K>> {
 	const mask = Object.fromEntries(keys.map(k => [k as string, true]));
-	return obj.pick(mask as never) as unknown as ZodObject<Pick<P, K>>;
+	return wire(obj.pick(mask as never) as unknown as ZodObject<Pick<P, K>>);
 }
 
 function tOmit<P extends ZodRawShape, K extends keyof P>(obj: ZodObject<P>, keys: readonly K[]): ZodObject<Omit<P, K>> {
 	const mask = Object.fromEntries(keys.map(k => [k as string, true]));
-	return obj.omit(mask as never) as unknown as ZodObject<Omit<P, K>>;
+	return wire(obj.omit(mask as never) as unknown as ZodObject<Omit<P, K>>);
 }
-
 function tComposite(objects: readonly ZodObject<ZodRawShape>[], opts?: Meta): ZodObject<ZodRawShape> {
 	// `Type.Composite([...])` flattens every object schema into one object schema
 	// rather than producing an intersection. Mirror that via repeated `extend`.
diff --git a/packages/coding-agent/test/extensibility/typebox-shim.test.ts b/packages/coding-agent/test/extensibility/typebox-shim.test.ts
index 9514cbac4..4f0fa4006 100644
--- a/packages/coding-agent/test/extensibility/typebox-shim.test.ts
+++ b/packages/coding-agent/test/extensibility/typebox-shim.test.ts
@@ -1,5 +1,5 @@
 import { describe, expect, it } from "bun:test";
-import { toolWireSchema } from "@oh-my-pi/pi-ai/utils/schema";
+import { isValidJsonSchema, toolWireSchema } from "@oh-my-pi/pi-ai/utils/schema";
 import { Type } from "../../src/extensibility/typebox";
 
 describe("pi.typebox compatibility shim", () => {
@@ -68,4 +68,40 @@ describe("pi.typebox compatibility shim", () => {
 			expect((parsed.data as { extra?: unknown }).extra).toBe(1);
 		}
 	});
+
+	// Regression: issue #1101. Real TypeBox lets extension authors do
+	// `JSON.stringify(schema)` and get a clean JSON Schema — that's the
+	// contract the shim is impersonating. Without a `toJSON` stamp, the shim
+	// leaks raw Zod internals (`def`, `_zod`, object-shaped `enum`,
+	// `"type":"enum"`) and breaks any pipeline that crosses a JSON boundary.
+	describe("JSON.stringify produces valid JSON Schema (TypeBox contract)", () => {
+		it("emits clean JSON Schema for a complex object", () => {
+			const schema = Type.Object({
+				direction: Type.Enum({ upstream: "upstream", downstream: "downstream" }),
+				depth: Type.Optional(Type.Integer({ minimum: 1, maximum: 10, default: 3 })),
+				tags: Type.Array(Type.String()),
+			});
+			const round = JSON.parse(JSON.stringify(schema)) as Record<string, unknown>;
+			expect(isValidJsonSchema(round)).toBe(true);
+			// No raw Zod internals leak through.
+			expect(round).not.toHaveProperty("_zod");
+			expect(round).not.toHaveProperty("def");
+			expect(round.type).toBe("object");
+		});
+
+		it("emits valid JSON Schema for composition operators", () => {
+			const base = Type.Object({ a: Type.String(), b: Type.Number() });
+			for (const schema of [
+				Type.Partial(base),
+				Type.Required(base),
+				Type.Pick(base, ["a"]),
+				Type.Omit(base, ["a"]),
+				Type.Composite([base, Type.Object({ c: Type.Boolean() })]),
+			]) {
+				const round = JSON.parse(JSON.stringify(schema)) as Record<string, unknown>;
+				expect(isValidJsonSchema(round)).toBe(true);
+				expect(round).not.toHaveProperty("_zod");
+			}
+		});
+	});
 });