PHASE 1: VISUAL DECONSTRUCTION - **Fabric Physics:** The source garment appears to be a chambray or linen-cotton blend with a heathered texture. It possesses a matte finish with low reflectivity. The physics engine must simulate a medium-weight fabric that holds creases slightly (semi-rigid) rather than draping like a fluid silk; it should exhibit resistance to stretching. - **Key Features:** The button-down collar points, the single chest pocket on the wearer's left side, the white 4-hole buttons on the central placket, and the specific heathered grey texture must be preserved. The short-sleeve structure is critical, distinct from the user's current long sleeves. PHASE 2: FIT & DRAPE SIMULATION - **Body Mapping:** Due to the user leaning back against the tree, gravity will pull the hemline slightly backward and down towards the tree bark. The crossed-arm pose dictates high compression across the chest; the fabric must crease and fold realistically around the biceps and under the forearms where they press against the torso. The collar must sit naturally around the neck, respecting the slight backward tilt of the head. - **Occlusion Handling:** The user's crossed arms (specifically the left forearm and hand, and the right wrist area) are major occlusion zones. The new shirt must be rendered *behind* the arms and watch. Since the target garment is short-sleeved and the user is wearing long sleeves, the system must generate realistic skin texture for the forearms and elbows to replace the current grey sleeves, ensuring seamless blending with the neck skin tone. PHASE 3: ENVIRONMENT & LIGHTING - **Light Match:** The scene utilizes natural, outdoor ambient lighting with a warm, sun-dappled quality typical of a forest setting. The light source appears to be coming from the front-right. The new shirt must reflect this warm color temperature (casting yellow/orange highlights) rather than the cool, sterile studio lighting of the source image. - **Color Calibration:** The neutral grey of the source shirt must be color-graded to accept the environmental bounce light from the brown tree bark and the green foliage. Deep, soft shadows must be cast by the crossed arms onto the shirt fabric to ground it in the scene. PHASE 4: IDENTITY PROTECTION - **Facial Lock:** The user's entire head (hair, forehead, eyes, nose, mouth, jawline) and the exposed neck area must be masked and frozen to prevent any AI hallucination or distortion. - **Body Integrity:** The user's shoulder width and torso volume must remain unchanged. Do not artificially slim the waist or broaden the chest; the silhouette of the new shirt must follow the boundary of the user's current sweater to maintain his actual physical build.