fix(mcp): fix issues with the MCP server mode#272
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dmcilvaney
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- Serialize tool handlers to prevent concurrent corruption of captured output
- Mark read-only tools with readOnlyHint for client auto-approval
- Clarify MCP tool exposure guidance for managed project state
- Report correct server name (azldev) and build-stamped version
- Drain tool output concurrently to avoid pipe buffer deadlock
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Pull request overview
This PR improves azldev’s MCP server mode by making tool execution safer under concurrency, improving client metadata (read-only hints), and reporting accurate server identity/version.
Changes:
- Serialize MCP tool execution to avoid concurrent stdout-capture corruption and drain captured output concurrently to prevent pipe-buffer deadlocks.
- Add an azldev-level “read-only MCP tool” annotation and mirror it into the MCP tool schema (
readOnlyHint) for client auto-approval. - Report the MCP server name/version from the root command name and build-stamped version.
Reviewed changes
Copilot reviewed 11 out of 11 changed files in this pull request and generated 1 comment.
Show a summary per file
| File | Description |
|---|---|
| scenario/snapshots/TestMCPServerMode_1.snap.json | Updates scenario snapshot to reflect read-only hint exposure for tools. |
| internal/app/azldev/core/mcp/mcpserver.go | Serializes tool handlers, reports server name/version correctly, propagates read-only hints, and introduces concurrent stdout capture draining. |
| internal/app/azldev/core/mcp/mcpserver_internal_test.go | Adds regression tests for large-output capture deadlock and error propagation. |
| internal/app/azldev/command.go | Introduces a read-only MCP annotation and helper to mark commands as read-only MCP tools. |
| internal/app/azldev/cmds/pkg/list.go | Marks pkg list as a read-only MCP tool. |
| internal/app/azldev/cmds/image/list.go | Marks image list as a read-only MCP tool. |
| internal/app/azldev/cmds/config/schema.go | Marks config schema as a read-only MCP tool. |
| internal/app/azldev/cmds/config/dump.go | Marks config dump as a read-only MCP tool. |
| internal/app/azldev/cmds/component/list.go | Marks component list as a read-only MCP tool. |
| internal/app/azldev/cmds/component/history.go | Marks component history as a read-only MCP tool. |
| internal/app/azldev/cmds/component/changed.go | Marks component changed as a read-only MCP tool. |
Tonisal-byte
approved these changes
Jul 9, 2026
liunan-ms
approved these changes
Jul 10, 2026
- Serialize tool handlers to prevent concurrent corruption of captured output - Mark read-only tools with readOnlyHint for client auto-approval - Clarify MCP tool exposure guidance for managed project state - Report correct server name (azldev) and build-stamped version - Drain tool output concurrently to avoid pipe buffer deadlock
captureStdout mutates the process-global os.Stdout while draining command output through a pipe. If the captured action panicked, the normal cleanup path was skipped, leaving os.Stdout redirected and the drain goroutine waiting on a writer that would never close. Run cleanup from a defer, still closing the writer before waiting for the drain goroutine, and add a panic regression test that verifies os.Stdout is restored.
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| capturedText, execErr := captureStdout(func() error { | ||
| env.SetReportFile(os.Stdout) // os.Stdout is the capture pipe for the duration of this call | ||
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| return cmd.Root().Execute() | ||
| }) |
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| // (specs, locks, config) on their own: read-only commands (marked with | ||
| // [azldev.ExportAsReadOnlyMCPTool]), or ones that write solely to a caller-provided output | ||
| // path, such as 'docs markdown' or 'component diff-sources --output-file'. |
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