Okay, the user wants a full-screen flocking simulation of boids with separation, alignment, and cohesion. The boids should be oriented triangles that steer smoothly and flee from the mouse cursor. Let me think about how to approach this.

First, I need to create an HTML file that includes all the necessary CSS and JavaScript in one file. No external resources, so everything has to be inline. The canvas element will be used for rendering the simulation.

For the CSS, I'll set the html and body to have a height of 100% and use flexbox to center the canvas. The canvas should take up the full screen. Then, the JavaScript part.

The boid simulation requires a Boid class with position, velocity, and acceleration. The update method will handle the flocking rules: separation, alignment, and cohesion. Also, each boid needs to avoid the mouse cursor, which adds another force.

Separation: Each boid should steer away from nearby boids. Calculate the average position of nearby boids and steer away from that.

Alignment: Steer towards the average heading of nearby boids.

Cohesion: Steer towards the average position of nearby boids.

Flee from mouse: Calculate the direction from the boid to the mouse and apply a force to move away.

I'll need to create an array of boids and update their positions each frame. The draw function will clear the canvas and redraw each boid as a triangle, oriented in the direction they're moving.

For the triangles, using the canvas's fill method with a path that creates a triangle pointing in the direction of movement. The rotation will be based on the velocity vector.

Also, handling the mouse movement to get the current position. Using requestAnimationFrame for smooth animation.

I should make sure the canvas is responsive to window resizing, so adding an event listener for resize and adjusting the canvas dimensions accordingly.

Putting it all together in the index.html file with a <style> tag for CSS and a <script> tag for the JavaScript. Testing the code to ensure it works without errors and meets the user's requirements.

Okay, the user wanted a full-screen flocking simulation of boids with separation, alignment, cohesion, and fleeing from the mouse. I created an HTML file with all the necessary code.

First, I set up the canvas to cover the entire screen using CSS. Then, I defined the Boid class with methods for each flocking behavior. The alignment, cohesion, and separation rules are implemented with force calculations. The flee method checks the distance to the mouse and applies a force if it's within range.

I made sure to handle window resizing by updating the canvas dimensions. The draw loop uses requestAnimationFrame for smooth animation and clears the canvas with a semi-transparent fill to create a trailing effect. Each boid is drawn as a triangle oriented in their movement direction.

Testing the code, it should work without external resources. The boids should move smoothly, follow the flocking rules, and avoid the mouse. If there are any issues, like overlapping edits or missing features, I might need to adjust the force magnitudes or the perception radii. But overall, this should meet the user's requirements.