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.

pnpm-lock.yaml

@@ -140,6 +140,9 @@ importers:
       '@cordisjs/plugin-timer':
         specifier: workspace:*
         version: link:../../vendor/timer
+      '@deepseek-ai/dsh-agent-tool-mode':
+        specifier: workspace:^
+        version: link:../../packages/core/agent-tool-mode
       '@deepseek-ai/dsh-app-boot':
         specifier: workspace:^
         version: link:../../packages/ui/app-boot
@@ -2806,6 +2809,37 @@ importers:
         specifier: ^4.0.0-rc.7
         version: link:../../../vendor/cordis
 
+  packages/core/agent-tool-mode:
+    dependencies:
+      schemastery:
+        specifier: ^3.18.0
+        version: link:../../../vendor/schemastery
+    devDependencies:
+      '@deepseek-ai/dsh-agent':
+        specifier: workspace:^
+        version: link:../agent
+      '@deepseek-ai/dsh-code-runtime':
+        specifier: workspace:^
+        version: link:../../code-runtime/code-runtime
+      '@deepseek-ai/dsh-invariants':
+        specifier: workspace:^
+        version: link:../../support/invariants
+      '@deepseek-ai/dsh-scope':
+        specifier: workspace:^
+        version: link:../scope
+      '@deepseek-ai/dsh-session':
+        specifier: workspace:^
+        version: link:../session
+      '@deepseek-ai/dsh-system-prompt':
+        specifier: workspace:^
+        version: link:../system-prompt
+      '@deepseek-ai/dsh-tools':
+        specifier: workspace:^
+        version: link:../tools
+      cordis:
+        specifier: ^4.0.0-rc.7
+        version: link:../../../vendor/cordis
+
   packages/core/scope:
     devDependencies:
       '@deepseek-ai/dsh-invariants':