Hairline cracks in a slab are common and usually shrinkage. What matters here is movement, because expansive clay swells and shrinks with moisture and moves whatever sits on it. Level differences and door problems matter more than the crack itself.
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This corridor sits on Blackland Prairie clay, which is highly expansive: it swells as it takes on water and shrinks as it dries, moving whatever is built on it. That is the single most important fact about foundations in this market and it shapes everything else. What is normal. Fine cracks in a slab from curing shrinkage, present in nearly every slab. Small cracks in drywall corners and above door openings in a house going through its first few seasons. Hairline separation at brick mortar joints. What is not. Cracks wider than about a quarter inch. Cracks with vertical offset, meaning one side of the slab has risen or dropped relative to the other. Doors and windows that have gone out of square on one side of the house. Gaps opening at the wall and ceiling line. Exterior brick showing stair-step cracking that runs diagonally. A floor with a consistent slope across multiple rooms. What drives movement here is moisture cycling rather than load. Clay expands when it takes on water and contracts when it dries, and the parts of the slab that experience that cycle differently move relative to each other. A drought followed by heavy rain is the fastest version and produces a season of new cracks across a neighborhood at once. What a homeowner can control. Consistent soil moisture around the perimeter, which is why foundation watering during extended drought is standard practice here rather than folklore. Slow even soaking around the perimeter, not heavy watering in one spot. Downspouts discharging well away from the slab. Grading that falls away from the house. And keeping large water-hungry trees at a sensible distance, since a mature tree can withdraw a great deal of moisture from one side of a foundation. On post-tension slabs, which are common in newer construction here: never cut or core a post-tension slab without locating the cables, and cracks in one warrant a professional look sooner rather than later.