fix(tools): collapse code-mode executor to run_code for model-direct calls

wireSchemas() already advertised only run_code under mode: 'code', but the
executor resolved every call through get(), which returns the full visible
map plus the reserved transport. A model could name a native tool directly
and bypass run_code entirely. Route the execution-path lookups through a
new private resolveExecution() that applies the mode collapse at the
operation boundary: model-direct calls under 'code' may only name run_code
(UNKNOWN_TOOL otherwise), while SDK sub-dispatches (parent token set) keep
every visible tool. get()/schemas() public semantics are unchanged.

The denial happens at createExecution, before the extensible policy
pipeline — pre-execute listeners, approval ask, and guards never observe
a call that is deterministically denied. A collapsed call honors the
pre-dispatch cancellation contract, routes aborted results through the
visible tool's finalizeContent, and captures the finalizer before
argument materialization.

Under code mode, a system-prompt/assemble listener filters out tool:*
guidance sections that told the model to call native tools directly.
The tools:sdk section and SDK types remain so programs can still use
all tools through run_code.

Fixes #1815

packages/core/tools/README.md

@@ -19,7 +19,7 @@ tools:
 
 - `ctx.tools.register(definition: ToolDefinition): () => void` Register a trusted typed same-process definition with a mandatory canonical `output` declaration. The layer is the calling context's scope: a plain plugin context registers globally; an agent's `agent.ctx` registers for that agent alone, shadowing a same-named global tool there. Duplicate names within one layer throw; non-native modes also reject the reserved `run_code` transport name. Missing or unsupported output declarations and a non-positive or non-finite `timeoutMs` fail at registration. The optional synchronous `finalizeContent` callback is snapshotted when a call starts and may replace only final model-facing content after every pipeline outcome is normalized, including an error discovered while materializing another result field. Disposed with the calling fiber.
 - `ctx.tools.presentAs(mode: ToolPresentationMode): () => void` selects this agent's model-facing presentation, shadowing the `mode` config for that agent alone; it throws from a plain context (a process-wide presentation is the config field) and from a second declaration in the same scope. A code mode also registers that agent's own `tools:sdk` section. The catalog is unchanged — `schemas(agent)` still reports the agent's capabilities; only the assembly's tools collapse. Disposed with the calling fiber.
-- `ctx.tools.restrict(filter)` applies an agent-scoped allow/deny mask to the tools that scope INHERITS — the global layer and every ancestor scope on its chain — and throws from a plain context. The scope's OWN registrations are exempt and merge afterwards, which is what keeps a delegated child's reporting and structured-output tools alive under a filter naming only the capabilities it may use. The filter is snapshotted at registration; multiple masks intersect, and a mask on an ancestor reaches every scope nested inside it. Deny masks admit later unnamed inherited tools, while allow masks exclude later names. Unknown, own-layer, or reserved names and empty filters reject. This is live visibility composition, not an authority boundary; see the [scope security non-goal](../../../.agents/notes/implemented/architecture/2026-07-08-agent-scope-contexts.md#security-and-authority-are-non-goals).
+- `ctx.tools.restrict(filter)` applies an agent-scoped allow/deny mask to global tools and throws from a plain context. The filter is snapshotted at registration; multiple masks intersect and scope-local tools merge afterwards. Deny masks admit later unnamed globals, while allow masks exclude later names. Unknown, local, or reserved names and empty filters reject. This is live visibility composition, not an authority boundary; see the [scope security non-goal](../../../.agents/notes/implemented/architecture/2026-07-08-agent-scope-contexts.md#security-and-authority-are-non-goals).
 - `ctx.tools.get(name: string, scope?: ScopeKey): ToolDefinition | undefined` Resolution as one scope sees it (shadowing applied; a restricted-away global reads as absent) — presenters pass the calling agent so the card matches what executed.
 - `ctx.tools.schemas(scope?: ScopeKey): ToolSchema[]` Schemas of everything the scope can see (without the `execute` functions). The shipped tools' schemas are catalogued in [docs/tool-catalog.md](../../../docs/tool-catalog.md), generated by booting each tool plugin and harvesting this method (see [the tool-schema-catalog Agent Note](../../../.agents/notes/implemented/process/2026-07-02-tool-schema-catalog.md)).
 - `ctx.tools.guard(guard: ToolGuard): () => void` Register a monotonic synchronous execution guard after `tools/pre-execute`: returning a reason denies the call, while `undefined` leaves it unchanged. A plain-context guard applies globally; an `agent.ctx` guard applies only to that agent. Later waterfall listeners cannot turn a guard denial back into permission. Disposed with the calling fiber.
@@ -66,7 +66,7 @@ First-party plugin authors can use the `defineTool()` helper (exported from this
 
 ```ts
 import { readFile } from 'node:fs/promises'
-import type { Context } from '@deepseek-ai/cordis'
+import type { Context } from 'cordis'
 import { defineTool } from '@deepseek-ai/dsh-tools'
 
 declare const ctx: Context