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/core/tools/README.md

@@ -2,7 +2,7 @@
 
 English | [中文](README.zh.md)
 
-Tool registry and execution pipeline. Tool plugins register their schemas and executors; the agent loop executes each call through `tools/pre-execute` (the extensible allow/deny gate) → monotonic registered guards → `tools/execute` (an around-dispatch wrapper for timeout/retry/metrics plugins) → `tools/post-execute` (inspect/replace the result, attach context) → the definition-owned `finalizeContent` boundary → the observe-only `tools/result` notification. The registry also owns HOW its tools are presented to the model — its `mode` config selects native function calling, [Code Mode](#code-mode), or both.
+Tool registry and execution pipeline. Tool plugins register their schemas and executors; the agent loop executes each call through `tools/pre-execute` (the extensible allow/deny gate) → monotonic registered guards → `tools/execute` (an around-dispatch wrapper for timeout/retry/metrics plugins) → `tools/post-execute` (inspect/replace the result, attach context) → the definition-owned `finalizeContent` boundary → the observe-only `tools/result` notification. The registry also owns HOW its tools are presented to the model — its `mode` config selects native function calling, [Code Mode](#code-mode), or both, and one agent shadows that default for itself with `presentAs`.
 
 ## Service: `ToolRegistry` (ctx key: `tools`)
 
@@ -13,11 +13,12 @@ tools:
   mode: native   # native (default) | code | both
 ```
 
-`native` contributes visible tools as function definitions. `code` contributes the reserved `run_code` transport and generated `tools:sdk` section; `both` contributes both forms. The reserved transport cannot be registered, shadowed, restricted, or removed. Non-native modes require a TypeScript `ctx.codeRuntime`, and a `systemPrompt.toolOrder` entry for a tool the mode does not contribute rejects prompt assembly. A `system-prompt/assemble` listener may replace the registry's contributions; its returned assembly is authoritative, so that listener owns preserving a usable Code Mode protocol.
+`native` contributes visible tools as function definitions. `code` contributes the reserved `run_code` transport and generated `tools:sdk` section; `both` contributes both forms. This is the default for agents that declare none of their own — an agent preset selects its own with [`dsh-agent-tool-mode`](../agent-tool-mode/README.md). The reserved transport cannot be registered, shadowed, restricted, or removed, and its name is reserved whatever the configured mode, because any agent may select a code mode. Non-native modes require a TypeScript `ctx.codeRuntime`, and a `systemPrompt.toolOrder` entry for a tool the mode does not contribute rejects prompt assembly. A `system-prompt/assemble` listener may replace the registry's contributions; its returned assembly is authoritative, so that listener owns preserving a usable Code Mode protocol.
 
 ### Public API
 
 - `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 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-explicit-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)).
@@ -190,6 +191,6 @@ Append-only; newly visible content follows the reusable request prefix and does
 - **`tools/pre-execute` deliberately cannot rewrite `exec.arguments`** — logged and rendered args would desync from what ran; the rewrite design is [a proposed Agent Note](../../../.agents/notes/proposed/feature/2026-06-30-pre-tool-input-rewrite.md).
 - **Caller-defined subagent and workflow structured outputs remain object-rooted** — this is a consumer-level guard; the shared schema vocabulary and tool outputs support every JSON root.
 - **`timeoutMs` on a definition is declarative only** — the registry never enforces deadlines; enforcement requires the `@deepseek-ai/dsh-timeout-policy` wrapper.
-- **Code Mode is TypeScript-only and the presentation mode is service-wide** — `mode: code`/`both` rejects prompt assembly unless `ctx.codeRuntime.language === 'typescript'`; scoped restrictions/shadows still choose each agent's visible bindings, but one tool cannot be native-only while another is code-only.
+- **Code Mode is TypeScript-only, and a presentation is per agent rather than per tool** — `mode: code`/`both` rejects prompt assembly unless `ctx.codeRuntime.language === 'typescript'`; scoped restrictions/shadows and `presentAs` choose each agent's visible bindings and their form, but within one agent no tool can be native-only while another is code-only.
 - **Code Mode intermediate values are execution-local and unbounded by bytes** — the canonical typed values cannot be reconstructed from session replay and may exhaust process or worker memory; only the outer `run_code` output has the worker's configurable hard cap. The durable log copy of each sub-call IS bounded: the `tools/code-dispatch-log` waterfall lets the spill policy replace an oversized `tool/code-dispatch` content with a preview + locator ([rationale](../../../.agents/notes/implemented/feature/2026-07-26-code-dispatch-log-spill.md)).
 - **`run_code` state is fresh per run** — a persistent REPL-style kernel is rejected for the MVP (cross-call state would be invisible to the log); see [the Code Mode Agent Note](../../../.agents/notes/implemented/feature/2026-06-15-code-mode.md).