docs: update Learning Hub for recent Copilot CLI, app, and VS Code releases

Add documentation for GitHub Copilot updates from the past week:

- copilot-configuration-basics.md: document copilot-cli v1.0.85 features
  (--json on plugin/marketplace list commands, opt-in context management
  tools for agents/subagents, concise transcriptView grouping)
- building-custom-agents.md: document the v1.0.86 `include-custom-instructions`
  agent frontmatter field for opting into AGENTS.md/copilot-instructions.md/
  CLAUDE.md
- agents-and-subagents.md: document VS Code 1.138 Agent Host features
  (Automations enabled by default and shareable, local Dev Container
  sessions, expanded Codex harness support)
- github-copilot-app.md: document Copilot app v1.1.21 Files tab refinement

Sources:
- https://raw.githubusercontent.com/github/copilot-cli/main/changelog.md (v1.0.85, v1.0.86)
- https://raw.githubusercontent.com/github/app/main/changelog.md (v1.1.21, v1.1.22)
- https://raw.githubusercontent.com/microsoft/vscode-docs/main/release-notes/v1_138.md

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

website/src/content/docs/learning-hub/agents-and-subagents.md

@@ -3,7 +3,7 @@ title: 'Agents and Subagents'
 description: 'Learn how delegated subagents differ from primary agents, when to use them, and how to launch them in VS Code and Copilot CLI.'
 authors:
   - GitHub Copilot Learning Hub Team
-lastUpdated: 2026-09-12
+lastUpdated: 2026-09-19
 estimatedReadingTime: '9 minutes'
 tags:
   - agents
@@ -202,6 +202,12 @@ This pairs with **improved workspace resolution**: agents can resolve a workspac
 
 **Shareable session links** *(VS Code 1.138+)*: Agent Host sessions and chats now provide browser-addressable links, so you can reopen or share a specific Agents window session directly from another app, a GitHub issue, or terminal output — useful when handing off a delegated subagent's work to a teammate for review. You can also start a new session beside the current one in one step, keeping the current work visible while a second session starts.
 
+**Automations enabled by default** *(VS Code 1.138+)*: `chat.automations.enabled` — Scheduled and template-driven automations in the Agents window are now on by default, and you can export or import them to share a recurring task across environments or with your team. This mirrors the automations workflow in the [GitHub Copilot app](../using-automations-in-copilot-app/), so a team can standardize on the same automation regardless of which surface members prefer.
+
+**Run agent sessions in local Dev Containers** *(VS Code 1.138+, `chat.agentHost.devContainer.enabled`)*: A delegated or orchestrator session can run inside a local folder's Dev Container instead of your host machine, so the agent uses the project's own toolchain and dependencies rather than whatever happens to be installed locally. This is particularly useful for coordinator/worker patterns where different workers need different, isolated environments.
+
+**Expanded Codex support in the agent host** *(VS Code 1.138+)*: The Codex harness in the agent host can now use either a GitHub Copilot subscription or a ChatGPT subscription (switching between Copilot- and ChatGPT-backed models without losing the conversation), continue the same session between the ChatGPT app and VS Code, and call the full set of VS Code tools — including MCP tools — during a delegated session.
+
 ## Common questions
 
 **Do users always invoke subagents directly?**

website/src/content/docs/learning-hub/building-custom-agents.md

@@ -3,7 +3,7 @@ title: 'Building Custom Agents'
 description: 'Learn how to create specialized GitHub Copilot agents with custom personas, tool integrations, and domain expertise.'
 authors:
   - GitHub Copilot Learning Hub Team
-lastUpdated: 2026-09-05
+lastUpdated: 2026-09-19
 estimatedReadingTime: '10 minutes'
 tags:
   - agents
@@ -108,6 +108,18 @@ tools: ['codebase', 'terminal', 'github']
 
 For MCP server tools, reference them by server name (e.g., `postgres`, `docker`). See [Understanding MCP Servers](../understanding-mcp-servers/) for details.
 
+**include-custom-instructions** *(v1.0.86+)*: By default, a custom agent's own Markdown instructions are the sole source of guidance — repository instruction files aren't automatically layered in. Set `include-custom-instructions: true` in the frontmatter to have the agent also pick up repository-level instruction files (`AGENTS.md`, `.github/copilot-instructions.md`, `CLAUDE.md`, and similar sibling formats). This is useful for agents that should respect your team's general coding conventions in addition to their specialized persona:
+
+```yaml
+---
+name: 'API Design Reviewer'
+description: 'Reviews API designs for consistency, RESTful patterns, and team conventions'
+model: Claude Sonnet 4
+tools: ['codebase', 'github']
+include-custom-instructions: true
+---
+```
+
 ### Agent Instructions
 
 After the frontmatter, write Markdown instructions that define the agent's behavior. Structure these clearly:

website/src/content/docs/learning-hub/copilot-configuration-basics.md

@@ -3,7 +3,7 @@ title: 'Copilot Configuration Basics'
 description: 'Learn how to configure GitHub Copilot at user, workspace, and repository levels to optimize your AI-assisted development experience.'
 authors:
   - GitHub Copilot Learning Hub Team
-lastUpdated: 2026-09-12
+lastUpdated: 2026-09-19
 estimatedReadingTime: '10 minutes'
 tags:
   - configuration
@@ -926,6 +926,22 @@ copilot skill enable my-skill    # enable a specific skill
 
 > **Breaking change (v1.0.84+)**: The cross-kind `--kind`, `--scope`, `--mcp`, and `--skill` flags have been removed from `copilot plugins`. `copilot plugins list` is now an alias of `copilot plugin list` and reports only plugins — not MCP servers, skills, instructions, or LSP servers. Scripts that installed skills with `copilot plugins install --skill [--scope project]` should switch to `copilot skill add [--project]`, and scripts reading `.plugins` from `copilot plugins list --json` should expect a flat array instead of the previous `{ plugins, errors }` object.
 
+**Scriptable plugin listings** *(v1.0.85+)*: Add `--json` to `copilot plugin list`, `copilot plugin marketplace list`, and `copilot plugin marketplace browse` to get machine-readable output for scripts and CI checks instead of parsing the interactive table:
+
+```bash
+copilot plugin list --json
+copilot plugin marketplace list --json
+copilot plugin marketplace browse awesome-copilot --json
+```
+
+### Context Management Tools for Agents and Subagents
+
+*(v1.0.85+)* Opt in from `/settings` to give agents and subagents dedicated context management tools, letting them actively manage what stays in their own context window during long or complex sessions instead of relying solely on automatic compaction.
+
+### Concise Transcript View
+
+*(v1.0.85+)* Set `transcriptView` to `"concise"` in `/settings` to group related tool activity into expandable work summaries instead of a long flat list of individual tool calls. This keeps the timeline readable during sessions that make many small tool calls in a row, while still letting you expand any summary to see the underlying steps.
+
 ### The `/config` Sidebar
 
 *(v1.0.84+)* Run `/config` to open a dedicated sidebar configuration screen inside the CLI, giving you a browsable view of your active settings without leaving the terminal session or hand-editing `config.json`:

website/src/content/docs/learning-hub/github-copilot-app.md

@@ -3,7 +3,7 @@ title: 'Getting Started with the GitHub Copilot app'
 description: 'Learn about the GitHub Copilot app, a desktop experience built for agent-native development. Understand its key features and who it''s for.'
 authors:
   - GitHub Copilot Learning Hub Team
-lastUpdated: 2026-09-12
+lastUpdated: 2026-09-19
 estimatedReadingTime: '8 minutes'
 tags:
   - copilot-app