Four values complete the vocabulary, so the opaque body is reached only by producers that genuinely promise no shape. `snapshot` — current state a later snapshot supersedes. system-prompt now exposes `renderContextSections()`, the named contributions `renderContextSnapshot()` already joins for the model, so the body attributes each part to the subsystem that produced it instead of re-splitting joined prose. The runtime snapshot, time-context, and tmux-context declare it. `notice` — a one-off account of what just happened, declared by tool-tasks, goal state changes, tool-goal wrap-up, plan-mode switches, and repeat-tool-guard. Its `summary` rides the COLLAPSED row: these five are the majority of shipped producers and none of them needs expanding to be read. The task summary bounds itself because its inputs are unbounded caller text. `relay` — a message another agent addressed to this one; both subagent sources declare it and the body names the sender above what it said. `recall` — material lifted from another session's log. session-reference needed no new field: its references already record retained and omitted counts and the truncation flag, which the body shows first, because recalled context is bounded on the way in. `ContextFormed` is now discriminated by `form`, so a producer cannot declare a shape without the facts that shape is presented from — a notice without its summary, or a snapshot without its sections, fails to compile. Only the two hook bridges stay opaque, by design: their content is whatever an external program printed, so no shape can be promised for it. Unknown kinds and unreadable records land there too.
core/ — product API spine
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The session log, system-prompt assembly, tool registry, agent vocabulary, and concrete loop that form the harness's default control spine. These are product packages — the stable surface plugins and consumers build against.
| Package | Role | ctx key |
|---|---|---|
scope/ |
Scoped-context registration primitive (scope tags, scope-filtered dispatch) | (library — no ctx key) |
session/ |
Event-sourced session log + in-memory store | ctx.sessions |
system-prompt/ |
Prompt-section + tool-schema assembly registry | ctx.systemPrompt |
tools/ |
Scoped tool registry + pre-policy, guards, around-dispatch, post-policy, and final-result observation | ctx.tools |
agent/ |
Agent interface, live registry, process-local initiator scope, agent/* event vocabulary |
ctx.agents |
agent-loop/ |
Concrete plugin implementing the public Agent contract and owning the loop driver |
ctx.agentLoop |
scope/ is the one non-service package here: a dependency-free library (createScope/scopeOf/scopeTarget) the registries and the loop build per-agent scoping on — it sits below session/ and system-prompt/ in the module graph precisely so they can consume it without a cycle.
agent-loop is the one concrete implementation of the agent seam and lives here because it is the harness's default product loop. It runs each driver inside ctx.agents.withInitiator(). Extension plugins depend on agent, including when they need the initiating Agent, and never on agent-loop directly, so the loop stays swappable.
The default composition that wires this spine into a runnable agent lives in examples/agent-spine-demo: one bundle plugin that loads the control spine plus selected default capabilities (timer + llm + sessions + fallback session titles + system-prompt + tools + agents + invariants + the local skill family + tool-bash + workspace-context + agent-loop) and forwards agent-loop's agents list as its own config. It sits in examples/ — ready-to-run demo/reference bundles — not in core/: core/ ships the swappable spine pieces, while a demo bundle picks one concrete composition of them and adds a front door.