nobu121/dsh-opencode-session

dsh-opencode-session

A DeepSeek Harness (DSH) plugin that automatically sends the x-opencode-session request header on model calls routed to OpenCode / OpenCode Go providers — one stable session id per DSH conversation.

Why

Since 2026-09-05 OpenCode's relay requires an x-opencode-session header on API requests (tracked upstream in deepseek-harness discussion #5495); without it, requests fail with 400 MissingSessionID-style errors. Requests that share the same header value are pinned to the same upstream backend, which is also what keeps OpenCode's prompt cache warm across the turns of one conversation.

This plugin:

• fixes the 400 by always attaching the header to OpenCode(Go) requests,
• keeps the cache/affinity benefit by using a value that is unique per conversation and stable across that conversation's turns (by default the DSH session id itself, the same identity the official DeepSeek adapter already sends as x-deepseek-harness-session-id),
• leaves every other provider, and every request that already carries the header, untouched.

Install

From the npm registry (once published):

dsh plugin --profile web add dsh-opencode-session

From a local checkout:

dsh plugin --profile web add ./path/to/dsh-opencode-session

Then fully restart your dsh profile (bundle layers are read at startup). The startup log shows:

[opencode-go-session-header] active for providers [opencode, opencode-go] with mode session-id

If you run DSH from a source checkout instead, load it as an overlay: pnpm dsh web --patch ./cordis.patch.yml.

Configuration

The plugin row lives in the bundle's cordis.patch.yml; all keys are optional:

- insert:
    - id: opencode-go-session-header
      name: dsh-opencode-session
      config:
        providers: [opencode, opencode-go]   # route keys to attach the header to
        mode: session-id                     # 'session-id' | 'uuid'
        debug: false
        debugFile: null                      # optional absolute path

• providers — provider route keys whose requests get the header. The defaults cover the pi-ai catalog ids opencode and opencode-go; add your own route key when you serve OpenCode through a custom provider name.
• mode
  • session-id (default) — header value = the DSH session id of the model call. Unique per conversation, stable across turns, compaction, retries and process restarts.
  • uuid — a random UUID derived once per DSH session id (opaque; kept in memory, so it resets when the process restarts).
• debug — log every streamed call that receives the header via ctx.logger (the dsh process console).
• debugFile — optional absolute path. When set, every streamed call that receives the header appends one JSON line ({"ts","provider","model","session","header","value"}) to that file — handy when the dsh console is not visible.