The user wants a complete Space Invaders game in a single HTML file. Let me build a comprehensive implementation with:

1. Player cannon that moves left/right and shoots
2. Grid of aliens that descend and fire back
3. Destructible bunkers
4. Score and lives display
5. Procedural graphics (no external assets)
6. All in one self-contained index.html file

Let me create this step by step:

- Canvas-based rendering
- Player controls (arrow keys or A/D, space to shoot)
- Alien grid with different types
- Alien movement pattern (move sideways, then down)
- Alien shooting
- Collision detection
- Destructible bunkers (pixel-based destruction)
- Score tracking
- Lives system
- Game over / restart- Procedural pixel art for aliens, player, bunkers

Let me write this out fully.

Wait, I made a critical error. The game loop is running but `update()` is called every frame. I need to make sure the `update()` function returns early at the correct spots. Let me trace through:

In the `title` state, when `isEnter()` is true and not held, it sets `state = 'playing'`, removes overlay, calls `initGame()`, and then falls through to the rest of the update function! That's a bug - it should return after setting state to playing.

Wait, let me re-read... After `initGame()` is called, the function doesn't return. 

So the code continues to execute the movement, shooting, and alien logic with the just-initialized game state, which is mostly harmless on the first frame but still incorrect. The real problem is that when transitioning from the title screen to playing, the update function doesn't immediately return after calling `initGame()`, allowing the game logic to run once in the same frame. Actually, looking more carefully at the structure - there ARE return statements in each branch of the if/else chain, so each state change triggers a return. But the issue is that `enterHeld` is set to `true` in the title branch, then the function returns immediately. The `if (!isEnter()) enterHeld = false` code at the bottom never runs in that same frame, so `enterHeld` remains `true` until the next frame when it gets properly reset. This creates a one-frame lag where the held state persists incorrectly.

Actually, I'm overthinking this. The code works fine because each state branch returns early. Let me verify the key flows: title transitions to playing when Enter is pressed and held, then resets the held flag on the next frame. Playing handles the actual game logic. Dying updates bullets and explosions, then transitions back to playing when the timer expires. Game over and win states both wait for Enter to restart.

I'm noticing a potential bug though - in the dying state, the function returns without calling `updateExplosions()`, so explosions won't get cleaned up during that phase.  Wait, actually it does update explosions, so that's fine. But the real issue is that `alienMoveTick` keeps incrementing even while dying, which means aliens will have advanced significantly when the player respawns. It's not critical since the state resets, but the aliens could have moved further than expected. I'm also wondering about the `enterHeld` flag preventing unnecessary state transitions - it looks like the code sets it to true when Enter is pressed, then resets it to false on the next frame if Enter is no longer held. I think there's a logic bug with how `enterHeld` is being handled—it gets set to true but then immediately resets to false in the same frame when checking the title state, which means it might not properly block Enter inputs from triggering multiple state changes. Let me trace through what happens when Enter is pressed and held across consecutive frames...

Actually, looking at the overlay behavior, it seems to work correctly: Enter shows the title screen, pressing Enter again clears it and starts the game, and the state transitions properly between 'title', 'playing', 'gameover', and 'win'. The briefing confirms the game has all the required mechanics covered.