dsh-session-header

The LLM call path inside DeepSeek Harness exposes no per-request header seam: GenerateOptions carries no headers field, and every adapter assembles its wire headers internally. If your model gateway, reverse proxy, or audit middleware keys routing, caching, or log correlation on a session-identifying header, Harness cannot send it out of the box — dsh-session-header closes exactly that gap.

The plugin composes two official interception points — the llm/stream waterfall and a globalThis.fetch patch — and uses AsyncLocalStorage to track precisely which fetch belongs to which LLM call. In practice this means the main session, compaction and title helper calls, and spawned subagents each carry their own session UUID; any header already present (case-insensitively) is never overwritten; non-LLM traffic such as Web RPC, telemetry, and tool calls passes through untouched; and unloading the plugin restores the original fetch. A fixed-value mode is available for gateways that expect a single static token.

It is a fit for teams running self-built gateways or enterprise proxies that perform session-level canary routing, cache-hit optimization, or call auditing, and for anyone who needs a consistent session identifier across multiple LLM providers without touching adapter source code.