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.

scripts/gen-cordis-catalog.ts

@@ -202,6 +202,7 @@ export const LINK_MAP: Readonly<Record<string, string>> = {
   ToolExecutionResult: 'tools.md',
   ToolExecutionToken: 'tools.md',
   ToolGuard: 'tools.md',
+  ToolPresentationMode: 'tools.md',
   ToolRegistry: 'tools.md',
   ToolRestriction: 'tools.md',
   ToolSchema: 'tools.md',

scripts/verify-package-readme-model-experience.ts

@@ -46,6 +46,7 @@ const SENTENCE_MODEL_EXPERIENCE: Readonly<Record<string, SentenceContract>> = {
   'packages/bash/bash-local': { kind: 'indirect', reason: 'The executor backend delegates model rendering to dsh-tool-bash.' },
   'packages/bash/pwsh-local': { kind: 'indirect', reason: 'The executor backend delegates model rendering to dsh-tool-pwsh.' },
   'packages/code-runtime/code-runtime': { kind: 'indirect', reason: 'The service interface delegates model rendering to Code Mode in dsh-tools.' },
+  'packages/core/agent-tool-mode': { kind: 'indirect', reason: 'The row only selects between the two projections dsh-tools owns; it registers no prompt, schema, or result of its own.' },
   'packages/code-runtime/code-runtime-worker': { kind: 'indirect', reason: 'The worker backend delegates model rendering to Code Mode in dsh-tools.' },
   'packages/client/ui-agent-preset': { kind: 'indirect', reason: 'Browser-side settings row; the preset it selects owns every model-facing effect.' },
   'packages/preset/agent-presets': { kind: 'indirect', reason: 'The mount installs a preset\'s own plugins, which own every model-facing registration it makes visible.' },