[ExecuTorch][WebGPU] Add certified scoped output suppression

[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

When a caller discards a model's terminal output tensor, the backend still
dispatches the final quantized-linear range and reads it back, wasting a
dispatch and a device-to-host copy on every execution. This adds a default-off,
certificate-bound execution option that suppresses exactly one explicitly
certified terminal output dispatch range and its readback. The certificate must
bind the exact PTE and method and prove a single delegate, no portable nodes,
and a unique leaf output resolving to the caller's host buffer; anything
ambiguous, aliased, portable, or uncertified fails closed and executes
normally. No Vulkan analogue (WebGPU runtime output-contract change).

Key changes:

• WebGPUExecutionOptions.{h,cpp}: certificate struct, RAII
  ScopedWebGPUExecutionOptions, and plan_webgpu_execution suppression planner.
• WebGPUGraph.{cpp,h}: resolve the certified output ordinal and skip its
  dispatch range and readback when suppression is active.
• WebGPUBackend.cpp: thread the scoped option through execution.
  @exported-using-ghexport

Differential Revision: D113171751

Differential Revision: D113171751

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/21127

• 📄 Preview Python docs built from this PR

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

❌ 10 New Failures, 45 Pending, 1 Unrelated Failure

As of commit 53fc165 with merge base 28a7fac ():

NEW FAILURES - The following jobs have failed:

• Cadence Build & Test / cpu-build / build (gh)
  ##[error]API rate limit exceeded for installation. If you reach out to GitHub Support for help, please include the request ID 8B8A:236993:4FE4919:10E03256:6A760B83 and timestamp 2026-08-07 16:44:51 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
• pull / test-models-linux (emformer_join, portable, linux.4xlarge.memory) / linux-job (gh)
  ##[error]API rate limit exceeded for installation. If you reach out to GitHub Support for help, please include the request ID CBD2:34749A:63574F1:1506C720:6A760B7E and timestamp 2026-08-07 16:44:46 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
• pull / test-models-linux (emformer_join, xnnpack-quantization-delegation, linux.4xlarge.memory) / linux-job (gh)
  ##[error]API rate limit exceeded for installation. If you reach out to GitHub Support for help, please include the request ID EC16:1196:85E5B8A:1C25E96C:6A760B7B and timestamp 2026-08-07 16:44:43 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
• pull / test-models-linux (ic4, portable, linux.4xlarge.memory) / linux-job (gh)
  ##[error]API rate limit exceeded for installation. If you reach out to GitHub Support for help, please include the request ID AB78:30BA9A:39A2BAD:C4D019B:6A760B79 and timestamp 2026-08-07 16:44:41 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
• pull / test-models-linux (ic4, xnnpack-quantization-delegation, linux.4xlarge.memory) / linux-job (gh)
  ##[error]API rate limit exceeded for installation. If you reach out to GitHub Support for help, please include the request ID B854:2AB583:90DC79E:1E6E2424:6A760B89 and timestamp 2026-08-07 16:44:57 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
• pull / test-models-linux (llama3_2_vision_encoder, portable, linux.4xlarge.memory) / linux-job (gh)
  ##[error]API rate limit exceeded for installation. If you reach out to GitHub Support for help, please include the request ID BFAC:285D:4A5D3AA:FC51B32:6A760B7A and timestamp 2026-08-07 16:44:42 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
• pull / test-models-linux (phi_4_mini, portable, linux.4xlarge.memory) / linux-job (gh)
  ##[error]API rate limit exceeded for installation. If you reach out to GitHub Support for help, please include the request ID 8662:362BDF:38B026C:C0ED9E4:6A760B77 and timestamp 2026-08-07 16:44:39 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
• pull / test-models-linux (w2l, portable, linux.4xlarge.memory) / linux-job (gh)
  ##[error]API rate limit exceeded for installation. If you reach out to GitHub Support for help, please include the request ID CE88:1B7A58:8D9BB00:1DB47249:6A760B81 and timestamp 2026-08-07 16:44:49 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
• pull / test-parakeet-xnnpack-linux / linux-job (gh)
  ##[error]An error occurred trying to start process '/usr/bin/bash' with working directory '/home/ec2-user/actions-runner/_work/executorch/executorch/pytorch/executorch'. No such file or directory
• pull / test-voxtral-realtime-xnnpack-linux / linux-job (gh)
  ##[error]API rate limit exceeded for installation. If you reach out to GitHub Support for help, please include the request ID 99A8:AD45:36FA48A:BB4DD64:6A760B93 and timestamp 2026-08-07 16:45:07 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

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• pull / test-models-linux (add_mul, portable, linux.2xlarge) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The runner has received a shutdown signal. This can happen when the runner service is stopped, or a manually started runner is canceled.

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.