[ExecuTorch][WebGPU] Add HuggingFace rotate-half RoPE

[JCNTH]

Stack from ghstack (oldest at bottom):

• [ExecuTorch][WebGPU] Lift FastVLM dispatch limits and harden graph construction #21602
• [ExecuTorch][WebGPU] Cover Conv1d routes and dynamic manifests #21601
• [ExecuTorch][WebGPU] Support general groups=1 Conv1d #21600
• [ExecuTorch][WebGPU] Test byte-packed BOOL tails #21599
• [ExecuTorch][WebGPU] Support byte-packed BOOL storage #21598
• [ExecuTorch][Vulkan] Preserve persistent buffer mutations #21597
• [ExecuTorch][WebGPU] Preserve Linear and Q4 embedding params across dynamic resize #21483
• [ExecuTorch][WebGPU] Generate logical and arithmetic binary shader variants #21451
• [ExecuTorch][WebGPU] Generate extrema and unary shader variants #21450
• [ExecuTorch][WebGPU] Generate typed to_copy shader variants #21449
• [ExecuTorch][WebGPU] Make WGSL generation rollback-safe #21448
• [ExecuTorch][WebGPU] Add Qwen3 K16 attention and fp16 KV cache #21136
• -> [ExecuTorch][WebGPU] Add HuggingFace rotate-half RoPE #21135
• [ExecuTorch][WebGPU] Repair dynamic SDPA routing, add attestation #21134
• [ExecuTorch][WebGPU] Select emdawnwebgpu for Emscripten builds #21133
• [ExecuTorch][WebGPU] Add Llama K16 online causal attention #21132
• [ExecuTorch][WebGPU] Replace broad QKV fusion with BK64 kernel #21131
• [ExecuTorch][WebGPU] Route exact prefill shapes to the BK64 GEMM #21130
• [ExecuTorch][WebGPU] Fuse the SwiGLU elementwise chain #21129
• [ExecuTorch][WebGPU] Coordinate dynamic dispatch routes #21128
• [ExecuTorch][WebGPU] Add certified scoped output suppression #21127

Add HuggingFace rotate-half RoPE and migrate RoPE to shared dispatch construction

Qwen models pair the first and second halves of each head vector rather than adjacent elements. This adds the rotate-half operator with dynamic start-position updates, full-dimension Q/K handling, generated WGSL, and strict frequency-table bounds.

The shared RoPE handler also closes the dispatch-boilerplate review: it uses graph.device(), typed graph-owned parameter buffers, descriptor-driven bindings and pipelines, named validation and resize callbacks, generated shader-registry lookup, scoped ownership, and graph-owned workgroup recomputation. Interleaved shader math and output are unchanged.

Key changes:

• rotary_embedding_hf.wgsl and generated registry entry — one thread per pair for HuggingFace rotate-half.
• RotaryEmbedding.cpp — named validation, typed resize contexts, shared dispatch descriptors, and one initial/resize grid picker per route.
• Native tests — malformed input rejection, dynamic bounds, shrink/regrow reuse, and HF/interleaved lifecycle coverage.

Co-authored-with: Claude Code.
@exported-using-ghexport

Differential Revision: D113171746

Differential Revision: D113171746

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/21135

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

❌ 2 New Failures, 29 Pending

As of commit 2372deb with merge base 28a7fac ():

NEW FAILURES - The following jobs have failed:

• Cadence Build & Test / cpu-test / test-aot / test-aot (gh)
  ##[error]API rate limit exceeded for installation. If you reach out to GitHub Support for help, please include the request ID A6A0:E0E81:3793C26:BCF63CC:6A760B4A and timestamp 2026-08-07 16:43:54 UTC. For more on scraping GitHub and how it may affect your rights, please review our Terms of Service (https://docs.github.com/en/site-policy/github-terms/github-terms-of-service) - https://docs.github.com/en/rest/using-the-rest-api/getting-started-with-the-rest-api#rate-limiting
• Cadence Build & Test / cpu-test / test-ops / test-ops (gh)
  ##[error]API rate limit exceeded for installation. If you reach out to GitHub Support for help, please include the request ID ECAC:30BA9A:3991E73:C496DF7:6A760B49 and timestamp 2026-08-07 16:43:53 UTC. For more on scraping GitHub and how it may affect your rights, please review our Terms of Service (https://docs.github.com/en/site-policy/github-terms/github-terms-of-service) - https://docs.github.com/en/rest/using-the-rest-api/getting-started-with-the-rest-api#rate-limiting

This comment was automatically generated by Dr. CI and updates every 15 minutes.

[github-actions]

This PR needs a release notes: label

If your change should be included in the release notes (i.e. would users of this library care about this change?), please use a label starting with release notes:. This helps us keep track and include your important work in the next release notes.

To add a label, you can comment to pytorchbot, for example
@pytorchbot label "release notes: none"

For more information, see
https://github.com/pytorch/pytorch/wiki/PyTorch-AutoLabel-Bot#why-categorize-for-release-notes-and-how-does-it-work.

[SS-JIA]

Review automatically exported from Phabricator review in Meta.