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[sgl-router] Fail fast on prefill errors and isolate PD transfer groups - #40606
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A failed prefill leaves decode waiting for KV that will never arrive. PD selection also needs to keep incompatible transfer groups apart.
Modifications
Wait for prefill's outcome alongside decode; preserve prefill 4xx responses and return 502
prefill_failedfor transport/server failures, dropping decode immediately. Prefill remains detached on client cancellation.Read the EndpointSlice
sglang.ai/transfer-grouplabel (configurable with--transfer-group-label). Both routing paths select compatible pairs, exclude orphan prefills, and readiness requires a complete pair. Unlabeled workers pair only with unlabeled workers; label changes refresh discovery.Stacked on #40605, which follows #40604. Most touched files only initialize the new worker metadata field.
Accuracy Tests
Workspace library and integration tests passed, including focused regressions for prefill failures, released load guards, group isolation, readiness, bucket routing, and discovery updates. Updated the old test that expected prefill failures to be hidden. Strict workspace Clippy and formatting passed.
Speed Tests and Profiling
Not run; no inference changes.
CI States
Latest PR Test (Base): ✅ Run #35682350023
Latest PR Test (Extra): ❌ Run #35682349542
Latest PR Test (AMD ROCm 10): ➖ No AMD PR run found for this commit.