test(sglang): add EAGLE3 disagg KV-router e2e

[livingshade]

Follows #15251 (merged).

Summary

Second PR for #15250: EAGLE3 speculative decoding with disaggregated prefill/decode behind the KV router.

• New nightly test_router_decisions_sglang_disagg_eagle in tests/router/test_router_e2e_with_sglang.py: 2 prefill workers on GPU 0, 1 decode worker on GPU 1, EAGLE3 on both sides. It uses the Qwen3-8B + Tengyunw/qwen3_8b_eagle3 pair.
• On top of the existing checks (all requests go to the same prefill worker, and that worker is not a decode worker), it asserts the chain from the issue:
  • Worker and router KV hashes match. Requests 2 to 4 share a prefix with the previous request, so the test requires nvext.timing.kv_hit_rate > 0. With EAGLE, SGLang keys its radix cache by token bigrams, and the router has to align its hashes the same way. If they don't match, the overlap stays 0 while requests can still land on the same worker by chance, so we need to explicity use hit rate to verify the path works.
  • Decode keeps speculating after the KV and EAGLE state transfer. After the requests, the test scrapes the decode worker's /metrics with SGLangSpecDecodeMetricsPayload: spec_verify_calls_total > 0, and more than 1.2 tokens per verify step.
• Harness changes (backend-agnostic parts go in common.py / e2e_harness.py, per tests/router/AGENTS.md):
  • SGLangProcess accepts extra_args.
  • _test_router_decisions_disagg takes a require_kv_hit flag, off by default.
  • run_disagg_router_decisions_test takes a post_check(prefill_workers, decode_workers) hook that runs while the workers are still up.

Fixes that also re-enable test_router_decisions_sglang_disagg

The EAGLE variant first failed the same way as the skipped non-EAGLE disagg test. Two causes, both in the test setup:

1. Bootstrap server bound to loopback. SGLang 0.5.19 binds the KV bootstrap server to --host (default 127.0.0.1), but dynamo.sglang advertises the auto-detected local IP to decode workers. Decode got Connection refused. Fixed now by using 0.0.0.0.
2. kv_transfer_estimated_latency_ms can legitimately be 0. Since fix(router): record SGLang prefill completion after stream ends #14968, SGLang prefill completion is recorded when the prefill stream ends. On the bootstrap path, decode runs in parallel and can emit its first token first, so the saturating difference is 0. The harness already has enable_bootstrap=True to skip this check. SGLang always takes the bootstrap path, so both SGLang disagg tests now pass it.

Where should the reviewer start?

test_router_decisions_sglang_disagg_eagle and the --host 0.0.0.0 line in SGLangProcess.

Validation

2x H200, SGLang 0.5.19:

• Ran pytest tests/router/test_router_e2e_with_sglang.py -m gpu_2 -k disagg → 2 passed in 317 s.
  • test_router_decisions_sglang_disagg_eagle: all 4 requests went to one prefill worker; kv_hit_rate per request was 0.0 / 0.40 / 0.57 / 0.56.
  • Decode worker: sglang:spec_verify_calls_total = 238, 2.16 tokens per verify step.
  • test_router_decisions_sglang_disagg: all 4 requests went to one prefill worker; kv_hit_rate was 0.0 / 0.50 / 0.50 / 0.625.
  • Peak VRAM: 36.1 GiB on GPU 0 (two prefill workers), 18.2 GiB on GPU 1.
• Negative control: with enable_eagle forced off in register.py (router hashes not bigram-aligned), the test fails as intended with Request 2: expected kv_hit_rate > 0 on a shared prefix, got 0.0, and request 2 goes to the other prefill worker.
• Before the --host fix, the EAGLE test failed with the bootstrap Connection refused above. Before the enable_bootstrap change, the EAGLE and non-EAGLE tests both failed intermittently on kv_transfer_estimated_latency_ms > 0 ... got: 0.0.
• Peak VRAM: about 36 GiB on GPU 0 (two prefill workers) and about 18 GiB on GPU 1, so the test carries h100. timeout(300) is about 3x the observed runtime. Like the other gpu_2 tests in this file, it does not carry profiled_vram_gib.
• pre-commit run on the changed files: all hooks pass.

Related Issues

• Relates to [CONTRIBUTION]: Align SGLang speculative decoding support and documentation #15250
• Follows test(sglang): add EAGLE3 speculative decoding e2e #15251 (merged)

Summary by CodeRabbit

• New Features
  • Added an SGLang launcher for EAGLE3 speculative decoding with Qwen3-8B and its draft model. The launcher enables metrics, supports configurable HTTP and system ports, and can apply a GPU KV-token limit when configured.
• Tests
  • Added coverage for SGLang speculative decoding and disaggregated routing, including checks for accepted draft tokens and KV-cache hits.

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Walkthrough

Adds an SGLang EAGLE3 speculative-decoding launcher and serving test. Adds disaggregated router coverage that checks speculative-decoding metrics and KV hit rates.

Changes

SGLang EAGLE3 speculative decoding

Layer / File(s)	Summary
Launcher and serving metrics tests/utils/payloads.py, examples/backends/sglang/launch/agg_spec_decoding.sh, tests/serve/test_sglang.py	Adds an EAGLE3 launcher and a serving scenario for Qwen3-8B. The metrics payload checks for verify calls and requires the token-per-verify average to exceed its threshold.
Disaggregated router test support tests/router/common.py, tests/router/e2e_harness.py, tests/router/test_router_e2e_with_sglang.py	Adds optional positive-KV-hit assertions and a post-check callback. SGLang workers accept extra arguments and bind to 0.0.0.0; the existing disaggregation test is enabled with bootstrap.
EAGLE3 disaggregated router test tests/router/test_router_e2e_with_sglang.py	Adds an EAGLE3 router test that checks decode-worker metrics and KV hits for requests that share a prefix.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: 🔵 Low · up to 123c9

The nightly test can pass without demonstrating draft-token acceptance. Correct the metric check to make that coverage reliable; the remaining merge risk is bounded.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 12 functions across 6 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly identifies the main change: adding an SGLang EAGLE3 disaggregated KV-router end-to-end test.
Description check	✅ Passed	The description is mostly complete. It explains the implementation, test coverage, reviewer starting points, validation results, and related issues. It uses a Summary heading instead of the template's…

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Inline comments:
In `@tests/utils/payloads.py`:
- Around line 2152-2190: Update SGLangSpecDecodeMetricsPayload.validate to
determine draft acceptance from SGLang’s accepted-draft metric, such as
spec_accept_length, or a cumulative accepted-draft counter; do not infer
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📒 Files selected for processing (6)

• examples/backends/sglang/launch/agg_spec_decoding.sh
• tests/router/common.py
• tests/router/e2e_harness.py
• tests/router/test_router_e2e_with_sglang.py
• tests/serve/test_sglang.py
• tests/utils/payloads.py

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[ShangmingCai]

This test adding PR looks good to me

[rmccorm4]

/ok to test 656aafa

[livingshade]

Hi @ishandhanani could you also take a look at this?

[rmccorm4]

/ok to test ff0fd30

[devin-ai-integration]

✅ Dynamo PR CI passed — run 36942622859 (attempt 1) on ff0fd309bf

Gate checks: ✅ backend-status-check · ✅ deploy-status-check · ✅ dynamo-status-check

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[livingshade]

@rmccorm4 @jain-ria After your approvals I had to merge main to resolve a conflict (one docstring line in tests/router/common.py, after #15251 landed; no code changes), which reset the approval. Could you re-approve when you get a chance? Thanks!