5d2c943d38
The executor collapse landed without telling the model it exists. Every tool contributes its own guidance section naming its tool, none of them qualify how that tool is reached, and they all render before the SDK (orders 100-199 against SDK_SECTION_ORDER 150), so the prompt said "Use the read tool" eleven times and never said only run_code is callable. A real session shows the consequence: the model emitted a native call, read `unknown tool "read"` for a tool the same prompt declares, and concluded the deployment was inconsistent rather than routing through run_code. The registry now contributes `tools:code-only` at order 99 -- ahead of the guidance band -- stating the rule, registered wherever `tools:sdk` is and rendering empty outside an effective `code`. `both` renders it empty because its native calls do execute, which is also why both-mode-turn no longer shares code-mode-turn's expected prompt. The denial itself now names the route back, since a bare UNKNOWN_TOOL for a declared tool is what misled the model.
core/ — product API spine
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The session log, system-prompt assembly, tool registry, agent vocabulary, deployment-default model selection, 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 | library — no ctx key |
session/ |
Event-sourced session log and in-memory store | ctx.sessions |
system-prompt/ |
Prompt and tool-schema assembly registry | ctx.systemPrompt |
tools/ |
Scoped tool registry and execution pipeline | ctx.tools |
agent/ |
Agent interface, registry, and event vocabulary | ctx.agents |
agent-default-model/ |
Default model selection shared by Agent entry points | ctx.agentDefaultModel |
agent-loop/ |
Default concrete agent driver | ctx.agentLoop |
scope supplies the shared scoping primitive. agent owns the public contract, while agent-loop is its default implementation; extension plugins depend on the seam so the driver remains swappable. agent-default-model owns the deployment selection an Agent entry point uses only when a session has no selection of its own.
Runnable compositions belong to examples/agent-spine-demo; this group owns only the swappable spine pieces.
The subsystem reference — the package-by-package loop map, the Agent handle and its delivery/interception contracts — is docs/subsystems/core.md; the default runnable composition is examples/agent-spine-demo.