fix(tools): make schema traversal stack-safe

packages/core/tools/tests/json-schema.spec.ts

@@ -214,6 +214,14 @@ describe('the enforced raw JSON Schema subset', () => {
       .toEqual(['schema.properties.at must be a schema object'])
   })
 
+  it('asserts deeply nested raw unions without using the JavaScript call stack', () => {
+    const depth = 5_000
+    let schema: JsonSchemaNode = { type: 'string' }
+    for (let index = 0; index < depth; index++) schema = { oneOf: [schema, { type: 'null' }] }
+
+    expect(() => { assertSupportedJsonSchema(schema) }).not.toThrow()
+  })
+
   it('uses own-property semantics for required declarations', () => {
     expect(violationsOf({ type: 'object', properties: {}, required: ['toString'] }))
       .toEqual(['schema.required names "toString" which is not in properties'])
@@ -322,6 +330,17 @@ describe('validateJsonSchemaValue', () => {
     expect(validateJsonSchemaValue(overlap, 1.5)).toEqual([])
   })
 
+  it('validates deeply nested exact-one unions without using the JavaScript call stack', () => {
+    const depth = 5_000
+    let schema: JsonSchemaNode = { type: 'string' }
+    for (let index = 0; index < depth; index++) schema = { oneOf: [schema, { type: 'null' }] }
+    assertSupportedJsonSchema(schema)
+
+    expect(validateJsonSchemaValue(schema, 'leaf')).toEqual([])
+    expect(validateJsonSchemaValue(schema, 42))
+      .toEqual(['"value" must match exactly one oneOf branch (matched 0)'])
+  })
+
   it('an unconstrained schema accepts only lossless JSON values', () => {
     const anyJson = asserted({})
     for (const value of [null, true, 1, 'x', [1], { x: null }]) {

packages/core/tools/tests/schema.spec.ts

@@ -92,6 +92,23 @@ describe('the unified author schema DSL', () => {
     expect(() => parameterSchemaSpecToJsonSchema(properties as ParameterSchemaSpec)).toThrow(/circular/)
   })
 
+  it('compiles deeply nested author unions without using the JavaScript call stack', () => {
+    const depth = 5_000
+    let spec: unknown = { type: 'string' }
+    for (let index = 0; index < depth; index++) spec = { oneOf: [spec, { type: 'null' }] }
+
+    const compiled = valueSchemaSpecToJsonSchema(spec as ValueSchemaSpec)
+
+    let cursor = compiled
+    let layers = 0
+    while (cursor.oneOf !== undefined) {
+      cursor = cursor.oneOf[0]!
+      layers++
+    }
+    expect(layers).toBe(depth)
+    expect(cursor).toEqual({ type: 'string' })
+  })
+
   it('preserves a property literally named __proto__ as schema data', () => {
     const properties = Object.create(null) as ParameterSchemaSpec
     properties.__proto__ = { type: 'string', required: true }

packages/core/tools/tests/tools.spec.ts

@@ -8,7 +8,7 @@ import ToolRegistry, {
   defineTool, JsonSchemaError, parameterSchemaSpecToJsonSchema, validateArgs, ToolArgsError, ToolNotFoundError,
   TOOL_ABORTED, TOOL_ABORTED_BEFORE_DISPATCH,
   type InferArgs, type JsonValue, type ParameterSchemaSpec, type PreToolDecision, type PostToolDecision,
-  type ToolDispatchExecution, type ToolExecutionResult,
+  type JsonSchemaNode, type ToolDispatchExecution, type ToolExecutionResult,
 } from '@deepseek-ai/dsh-tools'
 
 const testToolSignal = new AbortController().signal
@@ -1289,6 +1289,41 @@ describe('ToolRegistry', () => {
     }])
   })
 
+  it('schemas() snapshots deeply nested parameters without using structured-clone recursion', async () => {
+    const ctx = await setup()
+    const depth = 5_000
+    let nested: JsonSchemaNode = { type: 'string' }
+    for (let index = 0; index < depth; index++) nested = { oneOf: [nested, { type: 'null' }] }
+    ctx.tools.register({
+      ...echoTool,
+      name: 'deep-schema',
+      parameters: { type: 'object', properties: { nested } },
+    })
+
+    const projected = ctx.tools.schemas()[0]!.parameters as JsonSchemaNode
+
+    let cursor = projected.properties!.nested!
+    let layers = 0
+    while (cursor.oneOf !== undefined) {
+      cursor = cursor.oneOf[0]!
+      layers++
+    }
+    expect(layers).toBe(depth)
+    expect(cursor).toEqual({ type: 'string' })
+  })
+
+  it('rejects schema projection when a raw registration is not lossless JSON', async () => {
+    const ctx = await setup()
+    ctx.tools.register({
+      ...echoTool,
+      name: 'lossy-schema',
+      parameters: { type: 'object', default: Number.NaN },
+    })
+
+    expect(() => ctx.tools.schemas())
+      .toThrow('tool "lossy-schema" parameters must be lossless JSON before schema projection')
+  })
+
   it('rejects a non-positive or non-finite registration timeout', async () => {
     const ctx = await setup()
     expect(() => ctx.tools.register({ ...echoTool, name: 'zero-timeout', timeoutMs: 0 }))

packages/core/tools/tests/ts-types.spec.ts

@@ -93,6 +93,17 @@ describe('jsonSchemaToTs', () => {
     expect(rendered).not.toContain('tool-*/ over')
     expect(rendered).toContain(String.raw`tool-*\/ over`)
   })
+
+  it('renders deeply nested unions without using the JavaScript call stack', () => {
+    const depth = 5_000
+    let schema: unknown = { type: 'string' }
+    for (let index = 0; index < depth; index++) schema = { oneOf: [schema, { type: 'null' }] }
+
+    const rendered = jsonSchemaToTs(schema)
+
+    expect(rendered.startsWith('string | null')).toBe(true)
+    expect(rendered.length).toBe('string'.length + depth * ' | null'.length)
+  })
 })
 
 describe('renderToolsSdk', () => {