Add automatic rule file reloading with selective serve_once tracking

[Copilot]

Rules files are now monitored for changes and reloaded automatically without server restart. This eliminates the need to restart the server when updating access control rules.

Implementation

• Background monitoring: Daemon thread polls rules directory using file modification timestamps (default: 3s interval, configurable via watch_interval)
• Thread safety: Locks protect shared state (rules, served_once_rules) across monitoring and request handler threads
• Selective serve_once tracking: Only rules from changed files have tracking reset; unchanged rules preserve their served state
• Zero-downtime reloads: Old rules remain active during reload; failed reloads retain existing rules
• Configuration: watch_rules boolean to disable monitoring if needed

Key Changes

class RuleFileMonitor:
    def reload_rules(self):
        changed_files = self.get_changed_rule_files()  # Track which files changed
        new_rules = load_rules(self.rules_dir)
        
        with self.rules_lock:
            self.rules = new_rules
            self.file_mtimes = self.get_rule_files()
        
        # Only reset serve_once for changed rules
        if self.reload_callback:
            self.reload_callback(new_rules.copy(), changed_files)

Configuration

config:
  watch_rules: true        # Enable/disable monitoring (default: true)
  watch_interval: 3.0      # Poll interval in seconds (default: 3.0)

Behavior

• Adding/modifying/deleting rule files triggers reload within poll interval
• Rules with serve_once: true maintain state unless their file changed
• Errors during reload preserve existing rules and log the issue

Original prompt

We need to add functionality that will detect changes to rules files and reload them when the change is detected. Ideally this should be done very quickly, either through a thread polling the rules files to identify changes, or some other mechanism that will have the same outcome but be more lightweight. This should not be intense polling - once every few seconds is sufficient.

If a rule change is detected, the server should reload with the newly defined rule(s). It will be important to ensure that rules are still enforced during startup and shutdown of the server to prevent accidental leaks of files being served.

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