dsh-ptc-router

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Per-task tool-presentation routing for DeepSeek Harness. Choose PTC or native for each task, and switch it mid-task without changing the session preset.

Why

DeepSeek Harness renders an agent's tools in one of two forms:

Form	The model sees	Best for
native	every visible tool as a JSON Schema	short, conversational, few-call turns
ptc	one run_code tool plus a generated SDK	batch, iterative, parallel, data-heavy work

The form is chosen when the agent is assembled — normally by an agent preset — so a session usually stays in one form from start to finish. Real sessions mix both: a batch migration, then “why did that one fail?”.

This plugin adds the missing per-task choice:

• Automatic routing at the start of a task, and again when a new task replaces the old one.
• Live switching from the model or the user, effective on the next step.
• Agent-scoped override that beats the preset's form and unwinds with the agent; subagents keep their own composition.
• Graceful fallback to native when the deployment mounts no PTC runtime.

Install

The plugin is a Host bundle: no build step, no runtime dependencies.

Plugins page (recommended)

Open Plugins, install from GitHub (use this repository) or from a local checkout, then enable dsh-ptc-router.

CLI

dsh plugin --profile web add github:<owner>/dsh-ptc-router   # <owner> = this repository's owner

Then enable dsh-ptc-router on the Plugins page. (The Plugins page updates the profile's bundle list for you; the bare CLI command only installs the package.)

Development overlay

dsh --profile web --patch ./dev/dev.patch.yml

dev/dev.patch.yml loads ../index.js from this checkout, so edits apply on the next boot/reload without installing anything into the profile.

Usage

Automatic

Nothing to do. At agent creation or resume the plugin reads the most recent substantive user message; each new user message is classified before its first model step. Short continuations (继续, 接着, ok, …) inherit the current form instead of triggering a re-classification.

/mode

/mode                 show the current form, its source, and the last decision
/mode native          pin native (suspends automatic routing)
/mode ptc             pin PTC
/mode auto            resume automatic routing and re-classify the current task

switch_tool_mode

The model calls it when the shape of the task changes:

switch_tool_mode({ mode: "ptc" | "native" | "auto", reason?: string })

In PTC mode the same tool is available inside a program as tools.switch_tool_mode.

How it decides

A weighted, bilingual heuristic over the task text.

• Towards PTC: batch / each / iterate, parallel work, scripts and pipelines, repository-wide scope, data processing, audits and migrations, multi-step briefs, long structured prompts, several file references.
• Towards native: short instructions, questions and explanations, single actions, greetings, visual/UI requests.

ptcScore - nativeScore >= threshold (default 2) selects PTC. Examples:

Task	Form
遍历所有文件，统计每个文件的行数并汇总	ptc
并行下载这些 URL 然后合并结果	ptc
解释一下这个函数的作用	native
帮我看下 README 第一段	native
继续	unchanged

The classifier is deliberately small and testable. The model can always override it with switch_tool_mode, and the user with /mode.

Configuration

Every field is optional; see cordis.patch.yml for inline comments.

Field	Default	Meaning
auto	true	classify tasks automatically
defaultMode	native	form before any task text, and for /mode auto with no history
forceMode	auto	native / ptc forces one form for every session
threshold	2	score difference needed to pick PTC
guidance	true	one short prompt paragraph telling the model it may switch
applyToSubagents	false	also adopt subagents (root agents only by default)
extraPtc	[]	extra PTC keywords (+2 each)
extraNative	[]	extra native keywords (−2 each)

Override in a profile patch:

- id: dsh-ptc-router
  config:
    threshold: 3
    extraPtc: ['screenshot diff', '批量截图']

How it works

ctx.tools.presentAs(mode) is a Cordis effect on the calling scope: one declaration per scope, and disposing it removes that scope's presentation layer. A switch is therefore “dispose, then declare again” on the agent's own scope — synchronous, and triggered from agent/inbox/inserted, which fires before the driver wakes and assembles the step.

A bare agent.ctx cannot access services, so the plugin injects a tools-scoped child (agent.ctx.inject(['tools'], …)) and declares there. The declaration keeps the agent's scope tag and unwinds with the agent. Because the agent scope is nearer than the preset scope, it overrides the preset's form while it lives. Disposal is synchronous for these effects, which is what makes the inbox path race-free; tools/change is emitted so other registries re-read the catalog.

Development

npm test                          # classifier + router state machine
npm run classify -- "遍历所有文件并统计行数"

The two integration harnesses mount the real host services, so they need the @deepseek-ai/* packages resolvable from dev/:

ln -s /path/to/dsh/node_modules dev/node_modules
npm run spike          # presentAs dispose/redeclare round-trip
npm run integration    # router on the real ToolRuntime / SystemPrompt

Limits

• A switch changes the tool catalog and the system prompt, so the next request rebuilds its prefix (one KV-cache miss). That is inherent to changing the form.
• A manual /mode pin is not persisted. After a restart the plugin re-classifies the latest task; use forceMode / defaultMode for deployment-wide policy.
• Root agents only by default; subagents keep their preset's form.
• ptc needs a mounted ptcRuntime. Without one the plugin stays native and says so in /mode.
• The live switch relies on presentAs's dispose-and-redeclare semantics (verified on 0.2.1-rc.2). Re-run npm run spike after upgrading the harness.

Repository layout

.
├── index.js                 # host plugin: events, /mode, switch_tool_mode
├── classifier.js            # pure weighted classifier
├── cordis.patch.yml         # bundle patch
├── package.json             # dsh.bundle manifest
├── locale/                  # plugin page title and description
├── icon.svg
├── bin/classify.mjs         # offline classifier CLI
├── test/                    # node:test suites
└── dev/                     # real-service harnesses and an overlay patch

License

MIT