feat(mcp): render cta suggestions in tool result and error text

.changeset/mcp-cta-delivery.md

@@ -0,0 +1,5 @@
+---
+'incur': patch
+---
+
+Delivered CTA suggestions in MCP tool result and error text, keeping `_meta.cta` for structured consumers.

src/Mcp.test.ts

@@ -510,7 +510,7 @@ describe('Mcp', () => {
     expect(callRes.result.structuredContent).toBeUndefined()
   })
 
-  test('tools/call surfaces cta metadata without changing structured content', async () => {
+  test('tools/call appends cta suggestions to result text', async () => {
     const commands = new Map<string, any>()
     commands.set('show', {
       description: 'Show a record',
@@ -533,14 +533,53 @@ describe('Mcp', () => {
       { id: 2, method: 'tools/call', params: { name: 'show', arguments: {} } },
     ])
 
-    expect(res.result.content).toEqual([{ type: 'text', text: '{"id":"foo"}' }])
+    expect(res.result.content[0].text).toMatchInlineSnapshot(`
+      "{"id":"foo"}
+
+      Next:
+        test-cli list - List all"
+    `)
     expect(res.result.structuredContent).toEqual({ id: 'foo' })
     expect(res.result._meta?.cta).toEqual({
       description: 'Next:',
       commands: [{ command: 'test-cli list', description: 'List all' }],
     })
   })
 
+  test('tools/call appends cta suggestions to error text', async () => {
+    const commands = new Map<string, any>()
+    commands.set('deploy', {
+      description: 'Deploy a thing',
+      run(c: any) {
+        return c.error({
+          code: 'NOT_AUTHENTICATED',
+          message: 'not signed in',
+          cta: {
+            description: 'Next:',
+            commands: [{ command: 'login', description: 'Sign in' }],
+          },
+        })
+      },
+    })
+
+    const [, res] = await mcpSession(commands, [
+      { id: 1, method: 'initialize', params: initParams },
+      { id: 2, method: 'tools/call', params: { name: 'deploy', arguments: {} } },
+    ])
+
+    expect(res.result.isError).toBe(true)
+    expect(res.result.content[0].text).toMatchInlineSnapshot(`
+      "not signed in
+
+      Next:
+        test-cli login - Sign in"
+    `)
+    expect(res.result._meta?.cta).toEqual({
+      description: 'Next:',
+      commands: [{ command: 'test-cli login', description: 'Sign in' }],
+    })
+  })
+
   test('callTool serializes bigint values as strings', async () => {
     const result = await Mcp.callTool(
       {

src/Mcp.ts

@@ -3,7 +3,7 @@ import type { Readable, Writable } from 'node:stream'
 import { z } from 'zod'
 
 import * as Command from './internal/command.js'
-import { formatCtaBlock, type FormattedCtaBlock } from './internal/cta.js'
+import { formatCtaBlock, type FormattedCtaBlock, renderCtaText } from './internal/cta.js'
 import * as Json from './internal/json.js'
 import type { Handler as MiddlewareHandler } from './middleware.js'
 import * as Schema from './Schema.js'
@@ -167,24 +167,25 @@ export async function callTool(
     return { content: [{ type: 'text', text: Json.stringify(chunks) }] }
   }
 
-  if (!result.ok)
+  if (!result.ok) {
+    const cta = formatCtaBlock(options.name ?? tool.name, result.cta)
+    const text = result.error.fieldErrors
+      ? JSON.stringify(result.error)
+      : (result.error.message ?? 'Command failed')
     return {
-      content: [
-        {
-          type: 'text',
-          text: result.error.fieldErrors
-            ? JSON.stringify(result.error)
-            : (result.error.message ?? 'Command failed'),
-        },
-      ],
+      content: [{ type: 'text', text: cta ? `${text}\n\n${renderCtaText(cta)}` : text }],
+      ...(cta ? { _meta: { cta } } : undefined),
       isError: true,
     }
+  }
 
   const data = result.data ?? null
   const jsonData = Json.normalize(data)
   const cta = formatCtaBlock(options.name ?? tool.name, result.cta as Command.CtaBlock | undefined)
+  const text = Json.stringify(jsonData)
   return {
-    content: [{ type: 'text', text: Json.stringify(jsonData) }],
+    // Append rendered suggestions to the text so models see them (most clients drop _meta).
+    content: [{ type: 'text', text: cta ? `${text}\n\n${renderCtaText(cta)}` : text }],
     ...(data !== null && tool.outputSchema
       ? { structuredContent: jsonData as Record<string, unknown> }
       : undefined),

src/internal/cta.ts

@@ -43,6 +43,14 @@ export function formatCtaBlock(
   }
 }
 
+/** @internal Renders a formatted CTA block as plain text for inline tool output. */
+export function renderCtaText(block: FormattedCtaBlock): string {
+  const lines = [block.description]
+  for (const c of block.commands)
+    lines.push(`  ${c.command}${c.description ? ` - ${c.description}` : ''}`)
+  return lines.join('\n')
+}
+
 /** @internal Formats a CTA by prefixing the CLI name. */
 function formatCta(name: string, cta: Cta): FormattedCta {
   if (typeof cta === 'string') return { command: `${name} ${cta}` }