Coexistence with a core outputStyles capability

dsh-output-styles is the standalone Claude Code outputStyles-equivalent. If DeepSeek Harness ships a first-party outputStyles feature, the two would otherwise both inject an output-style directive into the system prompt. This plugin ships a coexistence policy that detects the core capability and degrades to the incremental surface it uniquely adds.

Detection

The core capability is detected through its reserved service seam, not by name guessing. A core implementation publishes the outputStyles service; the plugin probes it at mount:

import { detectCoreOutputStyles } from 'dsh-output-styles'

// ctx is the plugin-scoped Cordis context.
const coreActive = detectCoreOutputStyles(ctx)

• Core absent → standalone mode: the plugin injects the style section (systemPrompt.section('output-style:selection') plus the system-prompt/assemble waterfall for keep-coding-instructions: false).
• Core present → degraded mode: prompt injection is left to the core, and the plugin keeps only hot-switch (/style), rules, and /export.

Runnable verification

coexistenceReport is the runnable check for one composition:

import { coexistenceReport } from 'dsh-output-styles'

const report = coexistenceReport(ctx)
// report = { coreActive, mode: 'standalone' | 'degraded',
//            promptInjection: 'enabled' | 'disabled', retained, disabled }

It is also covered by the test suite (tests/coexist.spec.ts), which mounts the plugin with a fake outputStyles service and asserts the injected section is absent while /style and the renderer registry stay active.

Forcing injection

A deployment that wants this plugin to keep injecting regardless of the core can set respectCoreOutputStyles: false in cordis.yml. The default is true (honor the core and avoid duplicate injection).

Degraded surface

In degraded mode the plugin still contributes:

• Hot-switch — /style listing/selection, per-session persistence over the output_style domain, and the style session projection.
• Rules — the output.render.* renderer registry, the output.render/before waterfall, and per-session/per-tool rules.
• Export — /export (Markdown / sanitized HTML) through the renderer pipeline, with approval-gated --save.

Only the two prompt-injection registrations (the prompt section and the system-prompt/assemble waterfall) are skipped.