fix(agent-loop): preserve unified send contracts

packages/skill/tool-skill/src/index.ts

@@ -1,11 +1,12 @@
 /**
- * Session-prefix skill catalog and model-facing `skill` loader tool.
+ * Durable session skill catalog and model-facing `skill` loader tool.
  *
  * @module @deepseek-ai/dsh-tool-skill
  */
 
 import type { Context } from 'cordis'
 import z from 'schemastery'
+import type { Agent } from '@deepseek-ai/dsh-agent'
 import { defineTool } from '@deepseek-ai/dsh-tools'
 import { assertNever, type Message } from '@deepseek-ai/dsh-llm'
 import { isSkillName, type SkillDefinition, type SkillSummary } from '@deepseek-ai/dsh-skill'
@@ -115,12 +116,19 @@ export function apply(ctx: Context, config: Config = {}): void {
 
   // Register after the tool so reverse teardown removes guidance first. Exact definition
   // identity prevents a scoped shadow merely named `skill` from inheriting this catalog.
-  ctx.on('agent/session-prefix', async (agent, _prefix, signal, next): Promise<Message[]> => {
-    if (ctx.tools.get(skillTool.name, agent) !== registeredSkillTool) return await next()
+  const catalogLoaded = new WeakSet<object>()
+  ctx.on('agent/step', async (agent: Agent, _turn, _step, signal): Promise<void> => {
+    if (catalogLoaded.has(agent.session)) return
+    if (ctx.tools.get(skillTool.name, agent) !== registeredSkillTool) {
+      catalogLoaded.add(agent.session)
+      return
+    }
     const skills = await ctx.skills.list({ cwd: agent.session.header.cwd, signal })
-    const rest = await next()
-    if (skills.length === 0) return rest
-    return [renderCatalogMessage(skills, catalogDescriptionMaxLength), ...rest]
+    if (skills.length > 0) {
+      const catalog = renderCatalogMessage(skills, catalogDescriptionMaxLength)
+      agent.inject(catalog.content, { source: { kind: 'plugin', plugin: 'dsh-tool-skill' } })
+    }
+    catalogLoaded.add(agent.session)
   })
 }