Chunk 74.0

The user revealed that the root cause of the multi-round harness hang was a faulty client-side proxy, definitively clearing the engine and the `SGLANG_SM120_MMA_TARGET_CTAS=512` knob of suspicion. This directly contradicted the assistant's earlier working hypothesis, which had led to reverting the performance-enhancing environment variable. With the actual cause identified, the focus shifted to reclaiming the documented decode throughput gains (+12.8% at C64, +5.7% at C96) that had been mistakenly sacrificed. The assistant executed the user's request to restore the knob, adding `SGLANG_SM120_MMA_TARGET_CTAS=512` back into the decode service script. A full co-restart of the prefill, decode, and router services was performed to ensure clean state. All three services came back healthy, and the environment variable was verified to be live in the decode process environment. The system was immediately observed handling significant real-world load from the user's agent harness (decode_running peaked at 53), confirming the server was healthy and performant. The session concluded with a correction of the project documentation. The assistant updated `DSV4_PD_DEADLOCK_ISSUE.md` with a session-6 addendum, correcting the previous "co-restart fixes the wedge" narrative and documenting the actual proxy root cause, while retaining the orthogonal PD inflight-pin fixes as genuine improvements. A matching note was added to `DSV4_DECODE_PERF_PLAN.md` to record the revert/restore history. The core themes of the session were the importance of evidence-based debugging (the server was proven healthy on fresh connections), the dangers of premature root-cause attribution, and the successful recovery of performance after the real bottleneck was isolated.

The Reclamation: How Evidence-Based Debugging Reclaimed Lost Performance After a Wrongful Suspect 2451 words

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