docs: clarify subagent vs delegation distinction in Lesson 16

Separate the three overloaded meanings of "delegation" so the lesson
no longer conflates distinct execution models:

- Move `/delegate` out of "Triggering subagents reliably" into its own
  "Full delegation with `/delegate`" section. It hands the whole request
  to a cloud runner and does not spawn a subagent, so listing it as a
  subagent trigger taught the wrong mental model.
- Add a comparison table contrasting subagents (in-session, isolated
  context) with `/delegate` (separate cloud runner, fresh environment).
- Add a framing note at the top of Concepts flagging the three senses of
  "delegation": subagents, pipelines and `/delegate`.
- Cross-reference Lesson 12's `infer: true` for the auto-delegation
  behaviour so that thread reads as one concept across both lessons.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: calebwilson706

tutorial/lessons/16-agent-delegation.md

@@ -6,6 +6,8 @@ What subagents are and why they exist — the execution model behind everything
 
 ## Concepts
 
+> **"Delegation" means three different things in this lesson:** spinning up a **subagent** (the main focus below), chaining custom agents into a **pipeline**, and full handoff to a cloud runner via **`/delegate`**. Keep them distinct as you read.
+
 ### Subagents: what's actually happening under the hood
 
 When you ask Copilot something complex, it sometimes delegates pieces of work to **subagents** — separate AI processes with their own context windows that run independently and report back. You may have noticed this already: indented exploration steps, parallel investigations, tool calls happening before Copilot gives you an answer.
@@ -62,9 +64,20 @@ Copilot may choose to use subagents automatically on complex requests, but the m
 "Use a subagent to check whether validators.ts and tasks.ts are consistent."
 ```
 
-**3. Match a custom agent's description** — if your prompt closely matches the `description` field of a custom agent, Copilot will often invoke it automatically. Well-written descriptions are what make this work reliably.
+**3. Match a custom agent's description** — if your prompt closely matches the `description` field of a custom agent, Copilot will often invoke it automatically (this is the `infer: true` auto-delegation introduced in Lesson 12). Well-written descriptions are what make this work reliably.
+
+> **Note:** All three approaches above run subagents *inside your current session*. To hand the whole request to a separate cloud runner instead, see "Full delegation with `/delegate`" below, which is a different mechanism rather than a subagent trigger.
+
+### Full delegation with `/delegate`
+
+`/delegate` is **not** a way to trigger a subagent. It hands off your *entire* request to a **cloud agent runner** (a fresh, separate execution environment) rather than spinning up an isolated subagent within your current session.
 
-**4. Fully delegate with `/delegate`** — hands off the entire request to a cloud agent runner. Useful for simpler, well-scoped tasks that benefit from a fresh context.
+| | Subagent | `/delegate` |
+|---|----------|-------------|
+| Runs where | Your current session | Separate cloud runner |
+| Scope | A slice of the work, reported back | The whole request |
+| Context | Isolated window, same session | Entirely fresh environment |
+| Best for | Parallel exploration, specialist hand-offs | Simpler, well-scoped tasks that benefit from a clean slate |
 
 ### Agent pipelines: `tools: ["agent"]`