dsh-opencode-session-header

Since September 2026, OpenCode Go mandates a stable x-opencode-session header on every inference request for routing and prompt-cache optimization. DeepSeek Harness, however, sends no such header on any adapter path, so every opencode-go model call fails with a 400 MissingSessionID. The upstream fix is tracked but has not shipped yet, leaving users unable to call OpenCode Go models in the meantime.

This plugin bridges that gap surgically. It reads the current DSH conversation ID from the LLM stream chain and, at the Fetch transport layer, stamps x-opencode-session only on requests whose host matches the opencode.ai allowlist. Every other host passes through byte-for-byte unchanged. The session ID stays stable across turns, compactions, and retries, while each new conversation, fork, or subagent automatically gets a fresh one, naturally aligning with OpenCode's caching and routing. A single JSON switch file toggles injection at runtime with no restart, and the plugin carries zero runtime dependencies.

It is aimed squarely at DeepSeek Harness users hitting the 400 on OpenCode Go calls. If you previously worked around it with static headers or a global profile rewrite, this plugin offers a cleaner path: no impact on other providers, no user-agent or cross-host header pollution, no third-party client bundle. Once the upstream native support lands, simply uninstall and you are done.