Summary

mkdocs serve (with no flags) silently runs without livereload when Click ≥ 8.3 is installed. Symptoms:

• No Watching paths for changes: log line at startup.
• Edits to docs files do not trigger a rebuild — no Detected file changes / Building documentation....
• Served HTML does not contain the livereload poller <script>, so the browser never refreshes.

Root cause

The serve command declares the livereload flag with two separate @click.option decorators sharing the same parameter name and using flag_value:

@click.option('--no-livereload', 'livereload', flag_value=False, help=no_reload_help)
@click.option('--livereload',    'livereload', flag_value=True, default=True, hidden=True)

Up to Click 8.2.1 this resolved the parameter's default to True. Click 8.3 (pallets/click#3084) changed the resolution rules so the first decorator wins the default, leaving livereload=False when no flag is passed. serve.py then skips the entire if livereload: block (no server.watch(), no observer, no <script> injection).

Reproduction:

import click
from click.testing import CliRunner

@click.command()
@click.option('--no-livereload', 'livereload', flag_value=False)
@click.option('--livereload',    'livereload', flag_value=True, default=True, hidden=True)
def cmd(livereload):
    print('livereload =', livereload)

CliRunner().invoke(cmd, [])
# Click 8.2.1 → livereload = True
# Click 8.3.x → livereload = False

Fix

Collapse the two flag_value options into a single boolean option:

@click.option('--livereload/--no-livereload', 'livereload', default=True, help=no_reload_help)

This is the canonical Click way to express a "yes/no" boolean flag and is robust to the 8.3 resolution change. Both --livereload and --no-livereload continue to work; the help text remains attached to the visible secondary form.

Fixes #4032
Fixes #4055

Test plan

• mkdocs serve (no flags) shows Watching paths for changes: 'docs', 'mkdocs.yml' on startup.
• Editing a docs file emits FileModifiedEvent → Detected file changes → Building documentation....
• Served HTML contains the livereload(epoch, request_id) <script>.
• mkdocs serve --no-livereload continues to disable the watcher and skip script injection.
• mkdocs serve --livereload (explicit) behaves the same as the new default.
• mkdocs serve --help documents --livereload / --no-livereload with the existing help string.
• Verified end-to-end on Click 8.3.3, MkDocs installed from this branch, mkdocs-ivory theme.