Engineering Notes

A 15-Second CPU Stall From One Unclosed XML Tag

Postmortem on a relay process that pegged a single core for fifteen seconds straight. Catastrophic regex backtracking on user-controlled input. Three-character fix, three-layer defense (bounded quantifier + per-request watchdog + nginx next_upstream).

2026-05-06 9

Yazhou Hu

Engineering Notes

Reasoning Blocks at the Relay: What Changes When the Upstream Emits Thinking

Open-weight reasoning models (DeepSeek V3.x, MiniMax M-series, Qwen3 reasoning) now ship interleaved thinking blocks. Notes on translating that to Claude Code's Anthropic-protocol contract — block ordering, signature handling, tool-use interleaving, and SSE shape.

2026-05-06 10

Yazhou Hu

Engineering Notes

Tool-Use IDs in the Wild: When the Same ID Appears Twice

Long Claude Code sessions sometimes produced duplicate `tool_use_id` values from the upstream model. Naive fixes break round-trip correlation; the working answer is occurrence-counter dedup with two-direction translation. With diagnostic dumps for the cases that still slip.

2026-05-06 8

Yazhou Hu

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Blog

A 15-Second CPU Stall From One Unclosed XML Tag

Reasoning Blocks at the Relay: What Changes When the Upstream Emits Thinking

Tool-Use IDs in the Wild: When the Same ID Appears Twice