Mod-registered tools cannot be scoped to a specific agent — addTool is global and no blocking hook receives agent identity

Authorship note: This issue was written by an AI assistant (Command Code) on behalf of a human user who hit the problem and explicitly asked that it be filed. The user directed the investigation and the framing; the AI wrote this text. No paths, account names, repository names, project names, or other identifying details are included, at the reporter's explicit request — so any template field below is left blank rather than partially filled.

Summary

A mod can add a tool to Command Code, but it cannot say who may use it. cmd.addTool registers into a single global tool registry with no scoping parameter, and the beforeToolCall hook — the only place a mod can block a call — receives no agent identity in its context. So a mod that intends a narrow, single-purpose tool for one sub-agent has no way to express that intent, and the tool silently ends up on the broadest surface available: the main loop.

The per-agent tools: frontmatter allowlist is the only lever, and it only ever narrows. Callers that declare no allowlist receive every registered tool by default.

What was observed

Setup: a mod registering one custom read-only tool, intended for a single sub-agent, declared in exactly one agent definition's tools: allowlist. Each caller was then spawned and asked to report its own available tools, and — where the tool was present — called it, which returned a real result:

The narrowing works where an allowlist exists. It does nothing where one does not. general is a bundled agent defined with the full tool set and holds a reserved name, so it cannot be shadowed with a locally-defined equivalent, and the main loop has no agent file at all. The mod author's assumption — that agents which do not list the tool simply do not get it — holds for exactly the agents that bothered to declare an allowlist, and fails for the two that matter most.

Why a mod cannot fix this itself

• cmd.addTool accepts a schema, a run function, and flags such as readOnly. There is no agent or scope parameter, so registration is global.
• beforeToolCall({toolCallId, toolName, input, state}, ctx) — ctx is {emit, signal, cwd, session}. There is no agent identity in it, so a mod cannot gate its own tool on "am I being called by agent X".
• Agent identity does surface as subagentType, but only on the subagent_start / subagent_progress events, which are observe-only (cmd.on). The blocking hook has no equivalent field.
• A permissions.deny rule is global, so removing the tool from the main loop also removes it from the one agent that legitimately uses it. There is no per-agent exemption, and deny outranks every narrower allow.

The practical result is that minimal-privilege tool design is unreachable for mods. The author's intent degrades silently: the tool works, appears correctly in the one intended agent, and is additionally present everywhere else — including the context with the largest tool surface and the least scrutiny.

Expected behavior

Any one of these would close it:

1. A scope on registration — an optional agents/scope field on addTool (by agent name, wildcard, or "main loop only").
2. Agent identity in the beforeToolCall context — subagentType, or an explicit "main loop" marker when there is none — so a mod can enforce its own scoping.
3. Agent-targeted deny / allow rules, so a tool can be withheld from the main loop while remaining available to a named agent.
4. If none of the above is intended: document plainly that mod-registered tools are global and cannot be scoped, so authors stop designing around a capability that does not exist.

Related

• #852 — sub-agent tool calls bypass PreToolUse hooks and mod beforeToolCall. Cited as related; not independently re-verified for this report. It compounds this one: if beforeToolCall does not run for sub-agent calls, then even option (2) above would leave no working seam. Both reports turn on the same underlying question — which execution contexts a mod's hooks and a mod's tools are actually scoped to.
• #861 — project-root resolution, which governs where mod files are discovered at all.

Command Code Version

1.54.0

Operating System

Linux

Confidence / what was not verified

• The caller/tool-availability table was reproduced by spawning each caller, having it report its own available tools, and invoking the tool where present. Rows marked yes executed the call and returned a real result.
• The absence of a scoping parameter on addTool, and of agent identity in the mod hook context, is read from the shipped mods and hooks reference documentation, not from the implementation.
• Not verified: whether beforeToolCall executes for sub-agent tool calls (see #852). The compounding interaction described under "Related" is conditional on that being true.

Inizia dalla documentazione di riferimento distribuita su mods e hooks, in particolare cmd.addTool, beforeToolCall, permissions.deny e gli eventi dei subagent. Traccia le differenze nella disponibilità degli strumenti tra il loop principale, gli agent general, explore e personalizzati. Il lavoro è completo quando è stato implementato o documentato un comportamento di scoping concordato e la matrice dei caller osservata è coperta dalla verifica.