ea4c10d753
Review discussion converged on the industry shape (Claude Code caches user context per conversation; Codex separates initial context from diffs; Kimi appends at continuation boundaries to protect prompt caching): stable openers belong in a compose-once prefix, mid-session changes belong in append-only history — not in a per-request slot. agent/session-prefix fires ONCE per loop instance, lazily on its first request-building step: the composed Message[] is deep-frozen, cached on the transmission bookkeeping, recorded as EpochHeader.messagePrefix on the anchoring 'initial'/'resume' snapshot, and reused verbatim for every request the instance sends — prefix stability is structural, not a producer discipline, and a resume recomposes with attributable drift. The request is messagePrefix + boundary snapshot. The per-step RequestAdvice/RequestAdviceContext surface and the messageSuffix header field are dropped: the tail slot had no consumer, and every current update pattern (new AGENTS.md discovered, memory update, skills change) routes through the existing append-only history channels — inject(), tools/post-execute additionalContext, prompt-submit additionalContext — each paid once and prefix-cached thereafter. The messagePrefix delta arm stays for codec totality; the loop never produces one in practice.
core/ — product API spine
The packages every harness build is assembled from: the session log, the system-prompt assembly, the tool registry, the agent vocabulary, and the one concrete loop that drives them. These are product packages — the stable surface plugins and consumers build against.
| Package | Role | ctx key |
|---|---|---|
session/ |
Event-sourced session log + in-memory store | ctx.sessions |
system-prompt/ |
Prompt-section + tool-schema assembly registry | ctx.systemPrompt |
tools/ |
Tool registry + tools/pre-execute/tools/post-execute pipeline |
ctx.tools |
agent/ |
Agent interface, registry, agent/* event vocabulary |
ctx.agents |
agent-loop/ |
The concrete loop plugin: ReactLoopAgent + the loop driver |
ctx.agentLoop |
agent-core/ |
Bundle plugin: the providerless/executor-less/UI-less spine as code | (loads the spine) |
agent-loop is the one concrete implementation of the agent seam and lives here because it is the harness's default product loop; everything else in core/ is interface/vocabulary. Plugins depend on the agent vocabulary, never on agent-loop directly, so the loop stays swappable.
agent-core is the composition counterpart: one bundle plugin that loads the whole providerless spine (timer + llm + sessions + system-prompt + tools + agents + invariants + tool-bash + agent-loop) and forwards agent-loop's agents list as its own config. App packages (ui/stdio-agent, ui/acp-agent) consume it and add only a front door; a leaf adds the swappable backends plus any optional product tools it wants to expose. It lives in core/ because it composes exclusively core/ + interface packages and ships no provider, executor, or UI of its own.