fix(skills): harden slash skill activation across chat channels (#3466)

* support slash skill activation

* format slash skill activation

* Preserve slash skill activation with uploads

* Address slash skill review feedback

* Address slash skill follow-up review

* Fix lazy slash skill storage resolution

* Keep slash skill activation out of system prompt

* Address slash skill review issues

* fix: harden slash skill command handling

* feat(frontend): add slash skill autocomplete

* fix: address slash skill review feedback

* fix: preserve slash skill text for IM uploads

frontend/tests/unit/core/messages/utils.test.ts

@@ -11,6 +11,7 @@ import {
   hasContent,
   hasReasoning,
   isAssistantMessageGroupStreaming,
+  stripUploadedFilesTag,
 } from "@/core/messages/utils";
 
 function aiMessage(content: string): Message {
@@ -173,6 +174,38 @@ describe("inline <think> tag splitting", () => {
   });
 });
 
+describe("human message internal context stripping", () => {
+  test("strips slash skill activation context from display content", () => {
+    const content =
+      "<slash_skill_activation>\n<skill_content># Secret SKILL.md</skill_content>\n</slash_skill_activation>\nreal user task";
+
+    expect(stripUploadedFilesTag(content)).toBe("real user task");
+  });
+
+  test("hides leaked slash skill activation messages with no user text", () => {
+    const messages = [
+      {
+        id: "slash-activation",
+        type: "human",
+        content:
+          "<slash_skill_activation>\n<skill_content># Secret SKILL.md</skill_content>\n</slash_skill_activation>",
+      },
+      {
+        id: "ai-1",
+        type: "ai",
+        content: "Public answer",
+      },
+    ] as Message[];
+
+    const groups = getMessageGroups(messages);
+
+    expect(groups.map((group) => group.type)).toEqual(["assistant"]);
+    expect(
+      groups.flatMap((group) => group.messages).map((message) => message.id),
+    ).toEqual(["ai-1"]);
+  });
+});
+
 test("hides internal todo reminder messages from message groups", () => {
   const messages = [
     {

frontend/tests/unit/core/threads/export.test.ts

@@ -260,6 +260,22 @@ describe("formatThreadAsJSON", () => {
     expect(raw).toContain("real user text");
   });
 
+  it("strips <slash_skill_activation> as defence in depth", () => {
+    // Slash activation normally rides in a hidden HumanMessage. If a replay
+    // or state merge loses the flag, export must still not leak full SKILL.md
+    // content into a user-visible transcript.
+    const leaky = human("real user task", {
+      id: "leak-slash-skill",
+      content:
+        "<slash_skill_activation>\n<skill_content># Secret SKILL.md\nUse internal source.</skill_content>\n</slash_skill_activation>\nreal user task",
+    } as unknown as Partial<Message>);
+    const raw = formatThreadAsJSON(makeThread(), [leaky]);
+    expect(raw).not.toContain("<slash_skill_activation>");
+    expect(raw).not.toContain("Secret SKILL.md");
+    expect(raw).not.toContain("internal source");
+    expect(raw).toContain("real user task");
+  });
+
   it("sanitises tool message content when includeToolMessages is true", () => {
     const message = {
       id: "t-leak",