bug(`forge doc --serve`): Panics on nightly version with Nesting at the root is no longer supported

[pmprete]

Component

Forge

Have you ensured that all of these are up to date?

• Foundry
• Foundryup

What version of Foundry are you on?

forge Version: 1.2.3-v1.2.3 Commit SHA: a813a2c Build Timestamp: 2025-06-08T14:03:57.241711000Z (1749391437) Build Profile: maxperf

What version of Foundryup are you on?

No response

What command(s) is the bug in?

forge doc --serve

Operating System

macOS (Apple Silicon)

Describe the bug

When running forge doc --serve it fails with the following error. This is working correctly if a downgrade to v1.2.3 using foundryup -v v1.2.3

forge doc --serve                                                 28s 15:17:19
Warning: This is a nightly build of Foundry. It is recommended to use the latest stable version. To mute this warning set `FOUNDRY_DISABLE_NIGHTLY_WARNING` in your environment. 

Serving on: http://localhost:3000
The application panicked (crashed).
Message:  Nesting at the root is no longer supported. Use fallback_service instead.
Location: crates/forge/src/cmd/doc/server.rs:97

This is a bug. Consider reporting it at https://github.com/foundry-rs/foundry

  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ BACKTRACE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
                                ⋮ 8 frames hidden ⋮                               
   9: forge::cmd::doc::server::serve::{{closure}}::hb23f67d2e2a8fee3
      at <unknown source file>:<unknown line>
  10: std::sys::backtrace::__rust_begin_short_backtrace::hae6adc70294c476a
      at <unknown source file>:<unknown line>
  11: core::ops::function::FnOnce::call_once{{vtable.shim}}::hbf838240e914d23e
      at <unknown source file>:<unknown line>
  12: std::sys::pal::unix::thread::Thread::new::thread_start::he7774aa0ca446eef
      at <unknown source file>:<unknown line>
  13: __pthread_deallocate<unknown>
      at <unknown source file>:<unknown line>

Run with COLORBT_SHOW_HIDDEN=1 environment variable to disable frame filtering.
[1]    57073 abort      RUST_BACKTRACE=full forge doc --serve

[yash-atreya]

hey, @pmprete, thanks for flagging? Can you provide a minimal reproduction?