Lean server does not accept `exit` notification before `initialize`

Prerequisites

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Description

The server does not properly accept exit notifications before an initialize. This violates the LSP specification (see here). The server also does not properly respond to an invalid initial request (the specification requires a response with code: -32002 whereas the sever just exits with error code 1).

Steps to Reproduce

As notification:

echo -n $'Content-Length: 45\r\n\r\n{"jsonrpc":"2.0","method":"exit","params":[]}' | lean --server

As request:

echo -n $'Content-Length: 52\r\n\r\n{"jsonrpc":"2.0","method":"exit","params":[],"id":1}' | lean --server

Expected behavior:

The server to exit gracefully with code 0 upon receiving an initial exit notification.

Actual behavior:

As notification:

Watchdog error: Cannot read LSP request: Expected JSON-RPC request, got: '{"params":[],"method":"exit","jsonrpc":"2.0"}'

As request:

Watchdog error: Cannot read LSP request: Expected method 'initialize', got method 'exit'

Reproduces how often:

Always.

Versions

Windows 10 20H2
Lean (version 4.0.0-nightly-2022-06-14, commit 77ae79be466c, Release)

Start by running the two provided lean --server reproductions and compare their behavior with the linked LSP initialize specification. Trace the server's pre-initialize request handling; done means an initial exit notification exits with code 0 and an initial exit request receives the specified -32002 response.