feat: add banner option for root command output

Allows `Cli.create` to accept a `banner` option that renders custom
text (branding, live status, warnings) above the auto-generated root
help. Supports sync/async functions with silent error swallowing and
a `mode` option ('all' | 'human' | 'agent') to target TTY or non-TTY
consumers.

Author: franklad

.changeset/root-banner.md

@@ -0,0 +1,5 @@
+---
+'incur': minor
+---
+
+Added `banner` option to `Cli.create` for displaying custom content above root help output. Supports sync/async functions, error swallowing, and a `mode` option (`'all'` | `'human'` | `'agent'`) to target specific consumers.

src/Cli.test.ts

@@ -2054,6 +2054,113 @@ describe('help', () => {
     `)
   })
 
+  test('banner is printed before root help', async () => {
+    const cli = Cli.create({
+      name: 'mycli',
+      banner: () => '  status: all good',
+    })
+    cli.command('ping', { description: 'Health check', run: () => ({ pong: true }) })
+
+    const { output } = await serve(cli, [])
+    expect(output).toContain('status: all good')
+    expect(output.indexOf('status: all good')).toBeLessThan(output.indexOf('mycli'))
+  })
+
+  test('async banner is supported', async () => {
+    const cli = Cli.create({
+      name: 'mycli',
+      banner: async () => '  async banner',
+    })
+    cli.command('ping', { description: 'Health check', run: () => ({ pong: true }) })
+
+    const { output } = await serve(cli, [])
+    expect(output).toContain('async banner')
+  })
+
+  test('banner returning undefined shows only help', async () => {
+    const cli = Cli.create({
+      name: 'mycli',
+      banner: () => undefined,
+    })
+    cli.command('ping', { description: 'Health check', run: () => ({ pong: true }) })
+
+    const { output } = await serve(cli, [])
+    expect(output).toMatch(/^mycli/)
+  })
+
+  test('banner errors are swallowed', async () => {
+    const cli = Cli.create({
+      name: 'mycli',
+      banner: () => {
+        throw new Error('boom')
+      },
+    })
+    cli.command('ping', { description: 'Health check', run: () => ({ pong: true }) })
+
+    const { output } = await serve(cli, [])
+    expect(output).toMatch(/^mycli/)
+    expect(output).not.toContain('boom')
+  })
+
+  test('banner is skipped for subcommands', async () => {
+    const cli = Cli.create({
+      name: 'mycli',
+      banner: () => 'BANNER',
+    })
+    cli.command('ping', {
+      description: 'Health check',
+      run: () => ({ pong: true }),
+      output: z.object({ pong: z.boolean() }),
+    })
+
+    const { output } = await serve(cli, ['ping'])
+    expect(output).not.toContain('BANNER')
+  })
+
+  test('banner with mode "agent" shows in non-TTY', async () => {
+    const cli = Cli.create({
+      name: 'mycli',
+      banner: { render: () => 'AGENT BANNER', mode: 'agent' },
+    })
+    cli.command('ping', { description: 'Health check', run: () => ({ pong: true }) })
+
+    const { output } = await serve(cli, [])
+    expect(output).toContain('AGENT BANNER')
+  })
+
+  test('banner with mode "human" is skipped in non-TTY', async () => {
+    const cli = Cli.create({
+      name: 'mycli',
+      banner: { render: () => 'HUMAN BANNER', mode: 'human' },
+    })
+    cli.command('ping', { description: 'Health check', run: () => ({ pong: true }) })
+
+    const { output } = await serve(cli, [])
+    expect(output).not.toContain('HUMAN BANNER')
+  })
+
+  test('banner object with default mode shows for all', async () => {
+    const cli = Cli.create({
+      name: 'mycli',
+      banner: { render: () => 'ALL BANNER' },
+    })
+    cli.command('ping', { description: 'Health check', run: () => ({ pong: true }) })
+
+    const { output } = await serve(cli, [])
+    expect(output).toContain('ALL BANNER')
+  })
+
+  test('banner is skipped for --help flag', async () => {
+    const cli = Cli.create({
+      name: 'mycli',
+      banner: () => 'BANNER',
+    })
+    cli.command('ping', { description: 'Health check', run: () => ({ pong: true }) })
+
+    const { output } = await serve(cli, ['--help'])
+    expect(output).not.toContain('BANNER')
+  })
+
   test('--help on leaf shows command help', async () => {
     const cli = Cli.create('tool')
     cli.command('greet', {

src/Cli.ts

@@ -278,6 +278,7 @@ export function create(
       return serveImpl(name, commands, argv, {
         ...serveOptions,
         aliases: def.aliases,
+        banner: def.banner,
         config: def.config,
         description: def.description,
         envSchema: def.env,
@@ -323,6 +324,19 @@ export declare namespace create {
       : Record<string, string> | undefined
     /** Alternative binary names for this CLI (e.g. shorter aliases in package.json `bin`). Shell completions are registered for all names. */
     aliases?: string[] | undefined
+    /**
+     * Text to display above root help output (e.g. branding, live status). Only called when the CLI is invoked with no subcommand. Errors are silently swallowed.
+     *
+     * Pass a function for all consumers, or an object with `mode` to target `'human'`, `'agent'`, or `'all'` (default).
+     */
+    banner?:
+      | (() => string | undefined | Promise<string | undefined>)
+      | {
+          render: () => string | undefined | Promise<string | undefined>
+          /** @default 'all' */
+          mode?: 'all' | 'human' | 'agent' | undefined
+        }
+      | undefined
     /** Zod schema for positional arguments. */
     args?: args | undefined
     /** Enable config-file defaults for command options. */
@@ -869,6 +883,16 @@ async function serveImpl(
     if (options.rootCommand || options.rootFetch) {
       // Root command/fetch with no args — treat as root invocation
     } else {
+      if (options.banner && !help) {
+        const banner = typeof options.banner === 'function' ? { render: options.banner, mode: 'all' as const } : options.banner
+        const mode = banner.mode ?? 'all'
+        if (mode === 'all' || (mode === 'human' && human) || (mode === 'agent' && !human)) {
+          try {
+            const text = await banner.render()
+            if (text) writeln(text)
+          } catch {}
+        }
+      }
       writeln(
         Help.formatRoot(name, {
           aliases: options.aliases,
@@ -1948,6 +1972,14 @@ declare namespace serveImpl {
           command?: string | undefined
         }
       | undefined
+    /** Banner config, called before root help. */
+    banner?:
+      | (() => string | undefined | Promise<string | undefined>)
+      | {
+          render: () => string | undefined | Promise<string | undefined>
+          mode?: 'all' | 'human' | 'agent' | undefined
+        }
+      | undefined
     /** Root command handler, invoked when no subcommand matches. */
     rootCommand?: CommandDefinition<any, any, any> | undefined
     /** Root fetch handler, invoked when no subcommand matches and no rootCommand is set. */