The OOM detection markers look correct for Apple Silicon. The main paths MLX raises on unified memory exhaustion are:

1. "failed to allocate" from allocator.cpp when MTLDevice allocateBuffer returns nil -- this is the most common path and you've got it covered.
2. "Metal error: command buffer execution failed due to out of memory" from command buffer submission failure -- also covered.

One gap: when mx.metal.set_memory_limit() is active, MLX can throw "Attempting to allocate X bytes which is greater than the maximum allowed buffer size" (from the metal::malloc limit check). The "failed to allocate" marker wouldn't match that. Worth adding "attempting to allocate" or "maximum allowed buffer size" to the marker list.

The deferred-200 pattern for non-streaming is a good fix. The streaming error path handling (pre-stream vs mid-stream headers) is also correct.

Minor: the error response includes retry_after: 30 which is a reasonable default, but memory recovery on Apple Silicon (unified memory, no separate GPU eviction) really depends on whether other processes release memory. A shorter default (5-10s) might give a better user experience for transient spikes.