Diffs: Migrate tool usage guidance from before_prompt_build to a plugin skill (#32630)

Merged via squash.

Prepared head SHA: 585697a4e1
Co-authored-by: sircrumpet <4436535+sircrumpet@users.noreply.github.com>
Co-authored-by: gumadeiras <5599352+gumadeiras@users.noreply.github.com>
Reviewed-by: @gumadeiras

src/agents/skills.loadworkspaceskillentries.test.ts

@@ -48,6 +48,36 @@ async function setupWorkspaceWithProsePlugin() {
   return { workspaceDir, managedDir, bundledDir };
 }
 
+async function setupWorkspaceWithDiffsPlugin() {
+  const workspaceDir = await createTempWorkspaceDir();
+  const managedDir = path.join(workspaceDir, ".managed");
+  const bundledDir = path.join(workspaceDir, ".bundled");
+  const pluginRoot = path.join(workspaceDir, ".openclaw", "extensions", "diffs");
+
+  await fs.mkdir(path.join(pluginRoot, "skills", "diffs"), { recursive: true });
+  await fs.writeFile(
+    path.join(pluginRoot, "openclaw.plugin.json"),
+    JSON.stringify(
+      {
+        id: "diffs",
+        skills: ["./skills"],
+        configSchema: { type: "object", additionalProperties: false, properties: {} },
+      },
+      null,
+      2,
+    ),
+    "utf-8",
+  );
+  await fs.writeFile(path.join(pluginRoot, "index.ts"), "export {};\n", "utf-8");
+  await fs.writeFile(
+    path.join(pluginRoot, "skills", "diffs", "SKILL.md"),
+    `---\nname: diffs\ndescription: test\n---\n`,
+    "utf-8",
+  );
+
+  return { workspaceDir, managedDir, bundledDir };
+}
+
 describe("loadWorkspaceSkillEntries", () => {
   it("handles an empty managed skills dir without throwing", async () => {
     const workspaceDir = await createTempWorkspaceDir();
@@ -93,4 +123,36 @@ describe("loadWorkspaceSkillEntries", () => {
 
     expect(entries.map((entry) => entry.skill.name)).not.toContain("prose");
   });
+
+  it("includes diffs plugin skill when the plugin is enabled", async () => {
+    const { workspaceDir, managedDir, bundledDir } = await setupWorkspaceWithDiffsPlugin();
+
+    const entries = loadWorkspaceSkillEntries(workspaceDir, {
+      config: {
+        plugins: {
+          entries: { diffs: { enabled: true } },
+        },
+      },
+      managedSkillsDir: managedDir,
+      bundledSkillsDir: bundledDir,
+    });
+
+    expect(entries.map((entry) => entry.skill.name)).toContain("diffs");
+  });
+
+  it("excludes diffs plugin skill when the plugin is disabled", async () => {
+    const { workspaceDir, managedDir, bundledDir } = await setupWorkspaceWithDiffsPlugin();
+
+    const entries = loadWorkspaceSkillEntries(workspaceDir, {
+      config: {
+        plugins: {
+          entries: { diffs: { enabled: false } },
+        },
+      },
+      managedSkillsDir: managedDir,
+      bundledSkillsDir: bundledDir,
+    });
+
+    expect(entries.map((entry) => entry.skill.name)).not.toContain("diffs");
+  });
 });