The six-plane system map
Compress 49 package families into a responsibility map instead of memorizing names
composition → spine → capability → control → truth → surfaceAcross thousands of source files, how do you decide where new behavior belongs?
You do not understand a city by memorizing street names. Start with zoning: planning composes it, transit moves work, utilities provide capability, regulation controls risk, archives preserve facts, and public counters expose services.
Mechanism
The composition plane builds the plugin tree; the agent spine advances turns; capability planes provide seams such as LLM, FS, shell, and subagents; the control plane constrains execution through events, guards, approvals, and sandboxing.
The truth plane uses SessionEvent as its source of truth; surfaces adapt protocols and project state rather than owning another agent core.
Compose product
Profiles, bundles, and patches produce the runtime tree.
What extensions must preserve
- Surfaces are not the business source of truth
- A capability seam names definition, provider, and consumer
- Durable facts and live control events are not interchangeable
The tempting wrong turns
- ×Using directory hierarchy as the architecture model
- ×Treating every event as replayable
- ×Assuming the Web UI directly drives a model SDK
Do not trust the conclusion—verify it
These anchors are pinned to official deepseek-harness@47f9438; account for later breaking changes when reading current upstream.
Pause for ten seconds before revealing
Why must the UI not become the source of session state?
Next we build a source-reading method using graph docs, service catalogs, and event catalogs to find real control points.