fix: preserve auto-captured skill updates

src/skills/research/autocapture.test.ts

@@ -1,7 +1,13 @@
+import fs from "node:fs/promises";
+import path from "node:path";
 import { afterEach, beforeEach, describe, expect, it } from "vitest";
 import { captureEnv } from "../../test-utils/env.js";
 import { createTrackedTempDirs } from "../../test-utils/tracked-temp-dirs.js";
-import { inspectSkillProposal, listSkillProposals } from "../workshop/service.js";
+import {
+  applySkillProposal,
+  inspectSkillProposal,
+  listSkillProposals,
+} from "../workshop/service.js";
 import { runSkillResearchAutoCapture } from "./autocapture.js";
 
 const tempDirs = createTrackedTempDirs();
@@ -88,4 +94,61 @@ describe("skill research auto-capture", () => {
 
     expect((await listSkillProposals({ workspaceDir })).proposals).toHaveLength(0);
   });
+
+  it("preserves existing skill content when auto-capturing an update", async () => {
+    const workspaceDir = await makeWorkspace();
+    const skillFile = path.join(workspaceDir, "skills", "github-pr-workflow", "SKILL.md");
+    await fs.mkdir(path.dirname(skillFile), { recursive: true });
+    await fs.writeFile(
+      skillFile,
+      [
+        "---",
+        'name: "github-pr-workflow"',
+        'description: "Existing GitHub PR workflow."',
+        "---",
+        "",
+        "# GitHub PR Workflow",
+        "",
+        "- Preserve this original review checklist.",
+        "",
+      ].join("\n"),
+      "utf8",
+    );
+
+    await runSkillResearchAutoCapture({
+      event: {
+        success: true,
+        messages: [
+          {
+            role: "user",
+            content:
+              "From now on, when working on GitHub PRs, always check CI before final response.",
+          },
+        ],
+      },
+      ctx: { workspaceDir, agentId: "main" },
+      config: {
+        skills: {
+          workshop: {
+            autonomous: {
+              enabled: true,
+            },
+          },
+        },
+      },
+    });
+
+    const proposals = await listSkillProposals({ workspaceDir });
+    expect(proposals.proposals).toHaveLength(1);
+    expect(proposals.proposals[0]).toMatchObject({
+      kind: "update",
+      status: "pending",
+      skillKey: "github-pr-workflow",
+    });
+
+    await applySkillProposal({ workspaceDir, proposalId: proposals.proposals[0].id });
+    const updatedSkill = await fs.readFile(skillFile, "utf8");
+    expect(updatedSkill).toContain("Preserve this original review checklist.");
+    expect(updatedSkill).toContain("always check CI before final response");
+  });
 });

src/skills/research/autocapture.ts

@@ -17,6 +17,12 @@ type SkillResearchAgentContext = {
 
 const log = createSubsystemLogger("skills/research");
 
+function buildAutoCaptureUpdateContent(existingSkill: string, capturedContent: string): string {
+  return [existingSkill.trimEnd(), "", "## Captured Update", "", capturedContent.trim(), ""].join(
+    "\n",
+  );
+}
+
 export async function runSkillResearchAutoCapture(params: {
   event: SkillResearchAgentEndEvent;
   ctx: SkillResearchAgentContext;
@@ -73,7 +79,7 @@ export async function runSkillResearchAutoCapture(params: {
             config: params.config,
             agentId: params.ctx.agentId,
             skillName: proposal.skillName,
-            content: proposal.content,
+            content: buildAutoCaptureUpdateContent(existingSkill, proposal.content),
             createdBy: "skill-workshop",
             goal: proposal.goal,
             evidence: proposal.evidence,