The user wants a fully playable 2048 game in a single HTML file with:
1. Arrow-key tile sliding and merging
2. Smooth animations
3. Score tracking
4. Win state (reaching 2048)
5. Lose state (no more moves possible)
6. No external resources - all inline CSS and JS

Let me build a complete, polished 2048 game. I need to think about:
- Game board (4x4 grid)
- Tile movement logic (slide and merge)
- Animation system for smooth transitions
- Score tracking
- Win/lose detection
- Responsive, attractive styling
- Touch support would be nice too

Let me write this carefully with all the game logic.

Let me test this by reading it back and checking for issues. Actually, let me review the logic more carefully - I see the move function has some issues with the animation logic. Let me rewrite it with a cleaner approach.

The file structure looks good. Let me review the game logic one more time to make sure it's correct.

Looking at the code, I need to double check:

1. The tile movement and merging logic
2. The grid state management (grid stores tile IDs)
3. The animation system

Actually, let me trace through the logic more carefully. In the `doMove` function:

1. We extract each line and store `{id, r, c}` where `id` is the tile ID stored in `grid[r][c]`
2. When we merge, we create a new tile with `makeTile` which adds to `dom` and returns the ID
3. We record moves for the source tiles
4. After animation, we kill the absorbed tiles
5. We spawn a new random tile

One issue: when we merge, the new merged tile is created at the correct position with `makeTile(newVal, destR, destC, 'tile-merged')`. But the source tiles are also being moved to that same position. So for a brief moment, all three tiles (2 sources + 1 new) are at the same position. Then the sources are removed. This should look fine visually.

But wait - there's an issue. The new merged tile is created BEFORE the animation. So it appears instantly with the `tile-merged` animation (pop). The source tiles slide toward it. This is correct behavior for 2048 - the merged tile pops at the destination while the source tiles slide there.

Actually, there's a subtle timing issue. The `makeTile` function creates the element immediately. But the source tiles' animation is happening at the same time via CSS transition. The merged tile's pop animation starts immediately. This should be fine visually.

Let me also verify the "didMove" check - we check if source tiles move to different positions, and if tiles merge. But what if two equal tiles are already adjacent and the player tries to merge them in a direction that wouldn't change their positions? For example, two 4s in the same column, pressing up when they're already at the top.

Actually wait, I think there's a bug. Let me trace through:

If we have:
```
.  .  .  .
4  .  .  .
4  .  .  .
.  .  .  .
```

And press UP (dir=2):
- Column 0: line = [{id: tile1, r:1, c:0}, {id: tile2, r:2, c:0}]
- Both tiles have value 4, so they merge
- destR = 0, destC = 0 (first position in result)
- Moves: tile1 from (1,0) to (0,0), tile2 from (2,0) to (0,0)
- Both moved, didMove = true ✓

Another case:
```
4  .  .  .
.  .  .  .
4  .  .  .
.  .  .  .
```

Press LEFT (dir=0):
- Row 0: line = [{id: tile1, r:0, c:0}]
- Row 2: line = [{id: tile2, r:2, c:0}]
- No merging, each just stays in place
- didMove = false (tiles are already at column 0 in their rows) ✓

Another edge case - what about this:
```
.  4  .  .
4  .  .  .
```

Press LEFT:
- Row 0: line = [{id: tile1, r:0, c:1}], moves to (0,0). didMove = true.
- Row 1: line = [{id: tile2, r:1, c:0}], stays at (1,0). didMove stays true.
✓

Press RIGHT:
- Row 0: line = [{id: tile1, r:0, c:1}], moves to (0,3). didMove = true.
- Row 1: line = [{id: tile2, r:1, c:0}], moves to (1,3). didMove stays true.
✓

OK the logic seems correct. Let me also check the win condition - we check if any tile has value >= 2048. And the lose condition - no empty cells and no adjacent equal tiles.

I think the game is solid. Let me make sure the file is complete and valid.

Actually, let me re-examine one more thing. The `newMerged` array is created but never used. It's not needed since we're directly storing the new tile ID in the grid. Let me leave it as is - it's harmless.

Let me also verify there are no syntax errors by checking with node:

I see the regex is not matching correctly. Let me do a better check.

The HTML structure is balanced - 1 opening and 1 closing for each major tag. The JS syntax check passed. The file is ready.

Let me summarize what was built: