Prevent profile from being overridden by defaults

Previously, when loading a custom profile via --profile, its settings
could be overridden by defaults from the initial Profile() instance
because argparse was initialized with those defaults, and
only None-valued arguments would be updated from the custom profile.
This caused issues like custom model settings being reset to the default
claude-3-5-sonnet-20241022.

This change:
- Creates a fresh Profile instance when loading custom profiles
- Tracks which arguments were explicitly provided via CLI
- Updates args from profile unless explicitly set via CLI

This ensures profile settings take precedence over defaults while
still allowing CLI arguments to override profile settings.

Example:
Before: Custom profile with model="gpt-4o-mini" would be overridden
by default model="claude-3-5-sonnet-20241022" unless --model was
explicitly set on command line.

After: Custom profile settings are preserved unless explicitly
overridden by command line arguments.

The provider auto-detection still works as expected:
- If profile sets both model and provider: uses those values
- If profile sets only model: provider=None allows auto-detection

Author: endolith

interpreter/cli.py

@@ -270,10 +270,16 @@ def parse_args():
             subprocess.run([opener, profile_dir])
         sys.exit(0)
 
+    # If custom profile specified, load it and update args
     if args["profile"] != profile.profile_path:
-        profile.load(args["profile"])
+        # Load the specified profile, ignoring any defaults
+        profile = Profile.from_file(args["profile"])
+        # Find which settings were explicitly set via command line flags
+        cli_provided = {k for k,v in parser._option_string_actions.items()
+                       if v.dest in args and sys.argv.__contains__(k)}
+        # Update args with profile values, preserving any CLI overrides
         for key, value in vars(profile).items():
-            if key in args and args[key] is None:
+            if key in args and key not in cli_provided:
                 args[key] = value
 
     if args["save"]: