### What this PR does / why we need it?
This PR lets NPU platform provide its own default
`max_cudagraph_capture_size` via
`NPUPlatform.apply_config_platform_defaults()`.
Previously, when cudagraph sizing was left unset, Ascend inherited
vLLM's upstream default heuristic in `_set_cudagraph_sizes()`, which
uses `max_num_seqs * decode_query_len * 2`. This PR changes Ascend's
default to `min(max_num_seqs * decode_query_len, 512)` while keeping the
rest of vLLM's cudagraph sizing logic unchanged.
### Does this PR introduce _any_ user-facing change?
Yes, but only for Ascend when users do not explicitly configure
cudagraph sizing.
If `max_cudagraph_capture_size` and `cudagraph_capture_sizes` are both
unset, we now uses `max_num_seqs * decode_query_len` (capped at `512`)
instead of the upstream `* 2` default. Explicit user settings are
unchanged.
### How was this patch tested?
Add unit tests to cover:
- default max injection via `apply_config_platform_defaults()`
- explicit `max_cudagraph_capture_size` is preserved
- explicit `cudagraph_capture_sizes` are preserved
- Ascend default max no longer uses the upstream `* 2`
- late `_set_cudagraph_sizes()` recomputation reuses the current max
input
- vLLM version: v0.18.0
- vLLM main:
ed359c497a
---------
Signed-off-by: linfeng-yuan <1102311262@qq.com>
05a561129e