PHASE 1: VISUAL DECONSTRUCTION - **Fabric Physics:** The source garment appears to be a textured, heavyweight cotton blend or a terry-cloth/towel-like material. It is matte with high surface friction, meaning it will absorb light rather than reflect it (diffuse reflection only). It has moderate stiffness; it will not cling to the muscles like the user's current thin t-shirt but will hold a "boxy" structure. - **Key Features:** The abstract brown embroidery (linear face on the left chest, palm tree graphic on the lower right) is the critical visual anchor and must not be distorted. The "camp collar" (open, flat-laying lapels) and the vertical button placket must be rendered crisply. The fabric's "nubby" surface texture must be preserved via bump mapping. PHASE 2: FIT & DRAPE SIMULATION - **Body Mapping:** The source shirt is a relaxed/regular fit, while the user has a slim/athletic build. The simulation must show a "loose fit" drape. The fabric should hang vertically from the shoulder points (acromion), leaving negative space between the fabric and the user's torso, specifically at the waist. The sleeves are wider than the user's arm; they must cylinder around the bicep without hugging it. - **Occlusion Handling:** The user's hands are positioned at the hips. Depending on the length of the generated hemline, the wrists and forearms must layer *over* the garment if it falls that low. Crucially, the new collar is an open V-neck, whereas the current shirt is a high crew-neck; the simulation must inpaint/generate accurate skin texture for the exposed upper chest/neck area that is currently covered by white fabric. PHASE 3: ENVIRONMENT & LIGHTING - **Light Match:** The user image has a strong, somewhat harsh top-down light source (likely a ceiling bulb), creating a bright highlight on the upper chest and deep shadows under the chin. The new garment must replicate this top-down gradient: brighter on the shoulders/collar, fading to slightly darker towards the hem. Shadows must be cast specifically *under* the lapels and inside the open sleeves. - **Color Calibration:** The User Image has a slightly cool/magenta indoor tint. The Source Garment is a warm cream/off-white. The new shirt must be color-graded to match the room's white balance (slightly cooler temperature) so it doesn't look like a "sticker" placed on top. PHASE 4: IDENTITY PROTECTION - **Facial Lock:** The user's chin, jawline, and the specific shadow cast by the chin onto the neck must be preserved (though the shadow shape may need slight adjustment for the new open collar). - **Body Integrity:** Strictly forbidden to "bulk up" the user to fill the shirt. The user's waist width and arm thickness must remain constant. The dark blue trousers and the background environment (door details, reflections) are exclusion zones and must remain pixel-untouched.