diff --git a/src/features/background-agent/manager.test.ts b/src/features/background-agent/manager.test.ts
index 41f0d622..e340af68 100644
--- a/src/features/background-agent/manager.test.ts
+++ b/src/features/background-agent/manager.test.ts
@@ -643,3 +643,34 @@ describe("BackgroundManager.resume", () => {
     expect(result.progress?.toolCalls).toBe(42)
   })
 })
+
+describe("LaunchInput.skillContent", () => {
+  test("skillContent should be optional in LaunchInput type", () => {
+    // #given
+    const input: import("./types").LaunchInput = {
+      description: "test",
+      prompt: "test prompt",
+      agent: "explore",
+      parentSessionID: "parent-session",
+      parentMessageID: "parent-msg",
+    }
+
+    // #when / #then - should compile without skillContent
+    expect(input.skillContent).toBeUndefined()
+  })
+
+  test("skillContent can be provided in LaunchInput", () => {
+    // #given
+    const input: import("./types").LaunchInput = {
+      description: "test",
+      prompt: "test prompt",
+      agent: "explore",
+      parentSessionID: "parent-session",
+      parentMessageID: "parent-msg",
+      skillContent: "You are a playwright expert",
+    }
+
+    // #when / #then
+    expect(input.skillContent).toBe("You are a playwright expert")
+  })
+})
diff --git a/src/features/background-agent/manager.ts b/src/features/background-agent/manager.ts
index be52b08d..9b34192f 100644
--- a/src/features/background-agent/manager.ts
+++ b/src/features/background-agent/manager.ts
@@ -140,6 +140,7 @@ export class BackgroundManager {
       path: { id: sessionID },
       body: {
         agent: input.agent,
+        system: input.skillContent,
         tools: {
           task: false,
           call_omo_agent: false,
diff --git a/src/features/background-agent/types.ts b/src/features/background-agent/types.ts
index 661afa6c..415320d7 100644
--- a/src/features/background-agent/types.ts
+++ b/src/features/background-agent/types.ts
@@ -41,6 +41,7 @@ export interface LaunchInput {
   parentModel?: { providerID: string; modelID: string }
   model?: { providerID: string; modelID: string }
   skills?: string[]
+  skillContent?: string
 }
 
 export interface ResumeInput {
diff --git a/src/tools/sisyphus-task/tools.test.ts b/src/tools/sisyphus-task/tools.test.ts
index d3df0768..aed4e129 100644
--- a/src/tools/sisyphus-task/tools.test.ts
+++ b/src/tools/sisyphus-task/tools.test.ts
@@ -214,4 +214,56 @@ describe("sisyphus-task", () => {
       expect(SISYPHUS_TASK_DESCRIPTION).toContain("Array of skill names")
     })
   })
+
+  describe("buildSystemContent", () => {
+    test("returns undefined when no skills and no category promptAppend", () => {
+      // #given
+      const { buildSystemContent } = require("./tools")
+
+      // #when
+      const result = buildSystemContent({ skills: undefined, categoryPromptAppend: undefined })
+
+      // #then
+      expect(result).toBeUndefined()
+    })
+
+    test("returns skill content only when skills provided without category", () => {
+      // #given
+      const { buildSystemContent } = require("./tools")
+      const skillContent = "You are a playwright expert"
+
+      // #when
+      const result = buildSystemContent({ skillContent, categoryPromptAppend: undefined })
+
+      // #then
+      expect(result).toBe(skillContent)
+    })
+
+    test("returns category promptAppend only when no skills", () => {
+      // #given
+      const { buildSystemContent } = require("./tools")
+      const categoryPromptAppend = "Focus on visual design"
+
+      // #when
+      const result = buildSystemContent({ skillContent: undefined, categoryPromptAppend })
+
+      // #then
+      expect(result).toBe(categoryPromptAppend)
+    })
+
+    test("combines skill content and category promptAppend with separator", () => {
+      // #given
+      const { buildSystemContent } = require("./tools")
+      const skillContent = "You are a playwright expert"
+      const categoryPromptAppend = "Focus on visual design"
+
+      // #when
+      const result = buildSystemContent({ skillContent, categoryPromptAppend })
+
+      // #then
+      expect(result).toContain(skillContent)
+      expect(result).toContain(categoryPromptAppend)
+      expect(result).toContain("\n\n")
+    })
+  })
 })
diff --git a/src/tools/sisyphus-task/tools.ts b/src/tools/sisyphus-task/tools.ts
index c79999da..47bf9c94 100644
--- a/src/tools/sisyphus-task/tools.ts
+++ b/src/tools/sisyphus-task/tools.ts
@@ -90,6 +90,25 @@ export interface SisyphusTaskToolOptions {
   userCategories?: CategoriesConfig
 }
 
+export interface BuildSystemContentInput {
+  skillContent?: string
+  categoryPromptAppend?: string
+}
+
+export function buildSystemContent(input: BuildSystemContentInput): string | undefined {
+  const { skillContent, categoryPromptAppend } = input
+
+  if (!skillContent && !categoryPromptAppend) {
+    return undefined
+  }
+
+  if (skillContent && categoryPromptAppend) {
+    return `${skillContent}\n\n${categoryPromptAppend}`
+  }
+
+  return skillContent || categoryPromptAppend
+}
+
 export function createSisyphusTask(options: SisyphusTaskToolOptions): ToolDefinition {
   const { manager, client, userCategories } = options
 
@@ -111,15 +130,14 @@ export function createSisyphusTask(options: SisyphusTaskToolOptions): ToolDefini
       }
       const runInBackground = args.background === true
 
-      // Handle skills - resolve and prepend to prompt
+      let skillContent: string | undefined
       if (args.skills && args.skills.length > 0) {
         const { resolved, notFound } = resolveMultipleSkills(args.skills)
         if (notFound.length > 0) {
           const available = createBuiltinSkills().map(s => s.name).join(", ")
           return `❌ Skills not found: ${notFound.join(", ")}. Available: ${available}`
         }
-        const skillContent = Array.from(resolved.values()).join("\n\n")
-        args.prompt = skillContent + "\n\n---\n\n" + args.prompt
+        skillContent = Array.from(resolved.values()).join("\n\n")
       }
 
       const messageDir = getMessageDir(ctx.sessionID)
@@ -169,8 +187,8 @@ Use \`background_output\` with task_id="${task.id}" to check progress.`
       }
 
       let agentToUse: string
-
       let categoryModel: { providerID: string; modelID: string } | undefined
+      let categoryPromptAppend: string | undefined
 
       if (args.category) {
         const resolved = resolveCategoryConfig(args.category, userCategories)
@@ -180,6 +198,7 @@ Use \`background_output\` with task_id="${task.id}" to check progress.`
 
         agentToUse = SISYPHUS_JUNIOR_AGENT
         categoryModel = parseModelString(resolved.config.model)
+        categoryPromptAppend = resolved.promptAppend || undefined
       } else {
         agentToUse = args.subagent_type!.trim()
         if (!agentToUse) {
@@ -211,6 +230,8 @@ Use \`background_output\` with task_id="${task.id}" to check progress.`
         }
       }
 
+      const systemContent = buildSystemContent({ skillContent, categoryPromptAppend })
+
       if (runInBackground) {
         try {
           const task = await manager.launch({
@@ -222,6 +243,7 @@ Use \`background_output\` with task_id="${task.id}" to check progress.`
             parentModel,
             model: categoryModel,
             skills: args.skills,
+            skillContent: systemContent,
           })
 
           ctx.metadata?.({
@@ -284,6 +306,7 @@ System notifies on completion. Use \`background_output\` with task_id="${task.id
             body: {
               agent: agentToUse,
               model: categoryModel,
+              system: systemContent,
               tools: {
                 task: false,
                 sisyphus_task: false,