fix(copilot): support arbitrary HOME directory, not just /home/runner (#38725)

* fix: support arbitrary HOME directory, not just /home/runner

* Recompile lock files for $HOME-based Copilot config paths

* Fix MCP gateway review feedback

Co-authored-by: zarenner <13670625+zarenner@users.noreply.github.com>

* docs(adr): add draft ADR-38725 for $HOME-based Copilot config paths

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

---------

Co-authored-by: Zach Renner <13670625+zarenner@users.noreply.github.com>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: 4 people

.changeset/patch-copilot-home-expansion-self-hosted-runners.md

@@ -82,11 +82,12 @@ env:
   DD_API_KEY: ${{ secrets.DD_API_KEY }}
   DD_APPLICATION_KEY: ${{ secrets.DD_APPLICATION_KEY }}
   DD_SITE: ${{ secrets.DD_SITE || 'datadoghq.com' }}
-  GH_AW_MCP_CONFIG: /home/runner/.copilot/mcp-config.json
   COPILOT_GITHUB_TOKEN: ${{ secrets.COPILOT_GITHUB_TOKEN }}
   # ... other env vars
 ```
 
+`GH_AW_MCP_CONFIG` is intentionally NOT in the YAML `env:` block — it is exported from the run script (`export GH_AW_MCP_CONFIG="$HOME/.copilot/mcp-config.json"`) so `$HOME` is resolved at runtime. GitHub Actions does not shell-expand `env:` values, so the path must be set via `export` to work on self-hosted/containerized runners where `HOME` is not `/home/runner`.
+
 ## Implementation Details
 
 ### Key Functions