Fix large-payload-tester: add missing test data mount to MCP gateway#735
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Fix large-payload-tester: add missing test data mount to MCP gateway#735
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…ateway Co-authored-by: lpcox <15877973+lpcox@users.noreply.github.com>
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[WIP] Fix output for large-payload-tester agentic workflow
Fix large-payload-tester: add missing test data mount to MCP gateway
Feb 5, 2026
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Pull request overview
This PR fixes a mount configuration issue in the large-payload-tester workflow that prevented the agent from accessing test data through the filesystem MCP server. The MCP Gateway uses Docker-in-Docker to launch backend servers, requiring host directories to be mounted to the gateway before they can be propagated to backend containers.
Changes:
- Added missing
/tmp/mcp-test-fs:/tmp/mcp-test-fs:romount to the gateway's sandbox configuration - Updated the compiled lock file with the corresponding docker command change and new frontmatter hash
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| .github/workflows/large-payload-tester.md | Added /tmp/mcp-test-fs mount to sandbox.mcp.mounts enabling gateway to access test data |
| .github/workflows/large-payload-tester.lock.yml | Updated docker command to include the new mount and regenerated frontmatter hash |
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This was referenced Feb 6, 2026
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The large-payload-tester agent couldn't access test data via the filesystem MCP server due to missing gateway mount configuration.
Problem
MCP gateway uses Docker-in-Docker to launch backend servers. Host directories must be mounted to the gateway before they can be propagated to backend containers. The workflow defined filesystem server mounts but only exposed
/tmp/jq-payloadsto the gateway - not/tmp/mcp-test-fswhere test data resides.Changes
Added missing mount to gateway configuration:
This enables the gateway to access test data and propagate it to the filesystem MCP server at
/workspace/test-data.Verification
Gateway docker command now includes both required mounts:
-v /tmp/mcp-test-fs:/tmp/mcp-test-fs:ro-v /tmp/jq-payloads:/tmp/jq-payloads:rw💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.