feat(tools): let one agent choose its tool presentation, and ship code

Code Mode was a deployment-wide field on the host `tools` row: a
deployment ran every session that way or none. The obvious product
shape — 代码模式 beside 标准/极简/创造 in the preset picker — had
nothing to hang on.

The registry itself cannot move into a preset; the agent loop's
scheduler, the api-proxy's presenters, and every tool plugin are its
consumers. So split the registry from its projection: `presentAs(mode)`
writes one cell on the calling agent's scope layer, exactly as
`restrict()` does, and the three reads that decided presentation take
that scope's mode instead of the service's. The config `mode` becomes
the default agents shadow rather than a process-wide fact.

Two consequences are load-bearing. `run_code` now enters a view only
for scopes whose own mode presents it — a native agent must not find it
dispatchable because another agent in the process does — and the
reserved name holds whatever the configured mode, since any agent may
select a code mode later.

`dsh-agent-tool-mode` is the row a preset carries to declare this. A
code mode waits for the host's `codeRuntime` rather than assuming it,
so a runtime-less deployment fails the preset at mount, naming the
row, instead of at the session's first request.

The shipped `code` preset is `standard` plus that row, ordered second.

packages/cordis/tool-cordis/src/api-catalog.ts

@@ -1124,6 +1124,10 @@ export const SERVICE_API: readonly ServiceApiEntry[] = [
     key: 'tools',
     summary: 'Tool registry and execution pipeline.',
     methods: [
+      {
+        signature: 'presentAs(mode: ToolPresentationMode): () => void',
+        jsDoc: '/**\n * Present this agent\'s tools in `mode` instead of the deployment default.\n *\n * Scoped only, and one declaration per agent: this is how an agent preset\n * composes a Code Mode agent beside native ones in the same process, and a\n * process-global override would be the `mode` config field instead.\n * @param mode - the presentation this agent\'s model sees.\n * @returns the exact disposer that restores the deployment default.\n */',
+      },
       {
         signature: 'register(definition: ToolDefinition): () => void',
         jsDoc: '/**\n * Register globally or in the calling agent scope. Scoped tools shadow\n * globals; duplicates within one layer and the reserved `run_code` name fail.\n * @param definition - tool schema, execution, and optional finalization/presentation callbacks.\n * @returns the exact disposer that unregisters the tool.\n */',
@@ -3043,6 +3047,10 @@ export const TYPE_API: readonly TypeApiEntry[] = [
     name: 'ToolOutputDefinition',
     declaration: 'export interface ToolOutputDefinition {\n    readonly schema: JsonSchemaNode;\n    render(args: unknown, value: JsonValue): ContentBlock[];\n    presentationMeta?(args: unknown, value: JsonValue): JsonValue;\n}',
   },
+  {
+    name: 'ToolPresentationMode',
+    declaration: 'export type ToolPresentationMode = \'native\' | \'code\' | \'both\';',
+  },
   {
     name: 'ToolProviderResult',
     declaration: 'export interface ToolProviderResult {\n    readonly schemas: readonly ToolSchema[];\n    readonly knownNames?: readonly string[];\n}',