[41604] SETTINGS REST API Fix: Validate parameters in wp/v2/settings endpoint to prevent incorrect responses

[Vedanshmini26]

Trac: https://core.trac.wordpress.org/ticket/41604

Problem
The /wp/v2/settings endpoint currently accepts POST requests with empty bodies or invalid parameters and incorrectly returns the site settings instead of proper error responses.
Current behavior (incorrect):
POST /wp/v2/settings with empty body → Returns settings (should be 400)
POST /wp/v2/settings with {"invalid_param": "value"} → Returns settings (should be 400)
POST /wp/v2/settings with {"title": "New", "invalid_param": "value"} → Returns settings (should be 400)

Root Cause
The WordPress REST API args validation system only validates known parameters defined in the schema. When no settings are registered with show_in_rest => true, or when unknown parameters are provided, the validation framework doesn't reject the request, allowing the update_item() callback to execute and return settings data.

Solution
Added parameter validation in the update_item() method of WP_REST_Settings_Controller to:
Reject empty request bodies - POST/PUT/PATCH requests must contain parameters
Reject invalid parameters - Only allow parameters that correspond to registered settings
Return appropriate HTTP 400 errors with descriptive messages

Expected Behavior After Fix

• Proper error responses:

1. POST /wp/v2/settings with {} → 400: "Request body cannot be empty."
2. POST /wp/v2/settings with {"invalid_param": "value"} → 400: "Invalid parameter(s) provided."
3. POST /wp/v2/settings with {"title": "New", "invalid_param": "value"} → 400: "Invalid parameter(s) provided."

• Valid requests still work:

1. POST /wp/v2/settings with {"title": "New Title"} → Updates setting and returns updated settings

[github-actions]

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[github-actions]

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[github-actions]

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