last-context

A DeepSeek Harness (dsh) plugin that adds a Context tab to the web UI — right beside Chat and Trajectory — so you can see what the model's context window is actually made of, and how it evolves across the conversation.

Why

Every model request packs the same window from six sources: the system prompt, tool schemas, your messages, injected context (skills, AGENTS.md, runtime snapshots), assistant replies, and tool results. When a conversation degrades or gets compacted, which part ate the budget is usually invisible. last-context makes it observable:

• Current composition — a stacked bar of the six categories, scaled against the model's context window (the gray track is your remaining headroom), plus the top-5 most expensive tool schemas.
• History — one stacked bar per model request (finer than per-turn), with Y-axis ticks and gridlines. Click any bar for its full breakdown, including the provider-reported prompt/output tokens next to the estimate. ✂ marks where compaction/pruning happened — watch the bars drop.
• Context events — compactions, tool-output prunes, skill injections (Skill injected (code-review)), plugin context injections, model switches — each with its token delta and timestamp.
• Messages — the currently model-visible surface, message by message, with per-message token costs.

The UI is bilingual (中文/English) and follows the dsh locale automatically.

Install

last-context is a dynamic Cordis plugin: two plain-JavaScript halves (host.js, client.js) loaded into a running dsh process — no build step, no restart.

Option 1: ask the agent (easiest)

In any dsh session with the Cordis tools available, say:

加载 ~/dev/last-context 里的 dsh 插件（host.js + client.js），用 cordis_define 和 cordis_run 运行

The agent will define the package and run it; approve the client bundle when prompted, and the Context tab appears in every session view.

Option 2: load it yourself

Call cordis_define with the file contents as code.host / code.client, then cordis_run:

// code.host   = contents of host.js
// code.client = contents of client.js
cordis_define({ plugin: { kind: 'new', idPrefix: 'lctx' }, name: 'last-context', purpose: '…', code })
cordis_run({ pluginId, packageId, mode: 'run' })

Dynamic plugins are process-local: they disappear when dsh restarts. To make it permanent, wrap the two halves as a plugin package (a package.json with a dsh field, like @deepseek-ai/dsh-client-ui-trajectory) and add a row to your agent preset's cordis.yml — see the dsh plugin docs.

Usage

Open any session and click 上下文 / Context (to the right of Chat and Trajectory). Data refreshes every 2 seconds while the tab is open; switching sessions switches the view to that session's log — including historical, persisted sessions.

• Hover a history bar for a quick tooltip; click it to pin the breakdown below the chart.
• The overview bar is scaled to the model's context window, so ~13% full means ~13% of the window is spoken for.
• Numbers are estimates using the same fixed-density heuristic as dsh's built-in tokenMeter (~4 chars ≈ 1 token), so they match the harness's own stats. Wherever the provider reported real usage, it's shown alongside as "actual".

How it works

• Data source: the session's durable event log. Live sessions are folded straight from the in-memory log (sessions.get(id).events — no clone, no disk parse); persisted sessions fall back to sessionQuery.readSession.
• Incremental fold: per-session fold state lives in the Host half, so each poll only processes newly appended events — reopening the tab is instant.
• Events decoded: request/header (system prompt + tool schemas), surface events with surfaceOp (append/replace — compaction rewrites history in place), compaction/summary|prune, assistant/message.usage (real provider tokens), and message source metadata (plugin forms, skill-invocation) for injection events.
• Architecture: host.js folds the log and serves a package-private snapshot RPC; client.js registers the tab in the conversation.view slot and renders with bare React.createElement — zero dependencies, theme-native via dsh CSS variables.

Files

File	Role
host.js	Host half: incremental log fold, category accounting, snapshot RPC
client.js	Client half: tab registration, bilingual chart UI
docs/screenshot.png	The UI in action

License

MIT