fix(tools): isolate tool schemas and waterfall failures

packages/system-prompt/src/index.ts

@@ -123,8 +123,11 @@ export class SystemPrompt extends Service {
    */
   assemble(): Promise<PromptAssembly> {
     const assembly: PromptAssembly = {
-      sections: [...this.sections].sort((a, b) => a.order - b.order),
-      tools: this.toolProviders.flatMap(provider => provider()),
+      sections: this.sections
+        .map(section => ({ ...section }))
+        .sort((a, b) => a.order - b.order),
+      tools: this.toolProviders.flatMap(provider =>
+        provider().map(tool => ({ ...tool, parameters: structuredClone(tool.parameters) }))),
     }
     return this.ctx.waterfall(this, 'system-prompt/assemble', assembly, () => Promise.resolve(assembly))
   }

packages/system-prompt/tests/system-prompt.spec.ts

@@ -107,6 +107,23 @@ describe('SystemPrompt', () => {
     expect(assembly.sections).toHaveLength(0)
   })
 
+  it('assembles snapshots so one-step mutations do not leak into future assemblies', async () => {
+    const ctx = new Context()
+    await ctx.plugin(SystemPrompt)
+    ctx.systemPrompt.section({ name: 'base', order: 0, text: 'base' })
+    ctx.systemPrompt.tools(() => [{ name: 't', description: 'tool', parameters: { type: 'object', properties: {} } }])
+
+    const first = await ctx.systemPrompt.assemble()
+    first.sections[0]!.name = 'mutated'
+    first.tools[0]!.description = 'mutated'
+    const firstParameters = first.tools[0]!.parameters as { properties: Record<string, unknown> }
+    firstParameters.properties['leak'] = { type: 'string' }
+
+    const second = await ctx.systemPrompt.assemble()
+    expect(second.sections.map(section => section.name)).toEqual(['base'])
+    expect(second.tools).toEqual([{ name: 't', description: 'tool', parameters: { type: 'object', properties: {} } }])
+  })
+
   it('filters out empty section text from renderPrompt', () => {
     // Direct test of renderPrompt: function returning empty string, and empty static text
     const result = renderPrompt({

packages/tools/src/index.ts

@@ -173,7 +173,10 @@ export class ToolRegistry extends Service {
   schemas(): ToolSchema[] {
     // Rest-destructure to drop `execute`; the unused binding is the idiom.
     // eslint-disable-next-line @typescript-eslint/unbound-method, @typescript-eslint/no-unused-vars
-    return [...this.store.values()].map(({ execute, ...schema }) => schema)
+    return [...this.store.values()].map(({ execute, ...schema }) => ({
+      ...schema,
+      parameters: structuredClone(schema.parameters),
+    }))
   }
 
   /**
@@ -201,6 +204,14 @@ export class ToolRegistry extends Service {
           ...info ? { error: info } : {},
         }
       }
+    }).catch((error: unknown): ToolExecutionResult => {
+      const info = errorInfo(error)
+      return {
+        callId: exec.callId,
+        content: [{ type: 'text', text: `Error: ${errorMessage(error)}` }],
+        isError: true,
+        ...info ? { error: info } : {},
+      }
     })
   }
 }

packages/tools/tests/tools.spec.ts

@@ -122,6 +122,38 @@ describe('ToolRegistry', () => {
     expect(order).toEqual(['first:before', 'second:before', 'second:after', 'first:after'])
   })
 
+  it('returns an isError result when a tools/execute listener throws', async () => {
+    const ctx = await setup()
+    ctx.tools.register(echoTool)
+    ctx.on('tools/execute', async () => {
+      throw new Error('permission hook broke')
+    })
+
+    const result = await ctx.tools.execute({ callId: CallId('c1'), name: 'echo', arguments: { text: 'hi' } })
+
+    expect(result).toEqual({
+      callId: CallId('c1'),
+      content: [{ type: 'text', text: 'Error: permission hook broke' }],
+      isError: true,
+    })
+  })
+
+  it('schemas() snapshots tool schemas instead of exposing registry objects', async () => {
+    const ctx = await setup()
+    ctx.tools.register(echoTool)
+
+    const first = ctx.tools.schemas()
+    const firstParameters = first[0]!.parameters as { properties: Record<string, unknown> }
+    firstParameters.properties['mutated'] = { type: 'string' }
+    first[0]!.description = 'mutated'
+
+    expect(ctx.tools.schemas()).toEqual([{
+      name: 'echo',
+      description: 'echo arguments back',
+      parameters: { type: 'object', properties: { text: { type: 'string' } } },
+    }])
+  })
+
   it('rejects duplicate names and unregisters on fiber dispose (HMR safety)', async () => {
     const ctx = await setup()
     ctx.tools.register(echoTool)