Dev/anushakolan/set default log level none

[anushakolan]

PR Description

Why make this change?

Closes #3275 - When --mcp-stdio is used, control the output

When DAB runs as an MCP server with --mcp-stdio, stdout must be reserved exclusively for JSON-RPC protocol messages. Any log output (even informational) causes MCP clients like Claude Desktop to interpret them as protocol violations, displaying warnings like "Discovered 7 tools" mixed with actual tool discovery results.

Related: #3274 - MCP logging/setLevel method not found

What is this change?

This PR implements proper output control for MCP stdio mode:

1. Default log level is None when --mcp-stdio is used (no CLI or config override)

   • Ensures zero characters are emitted to stdout/stderr by default
   • No log noise interfering with MCP protocol

2. Output redirection based on log level:

   • LogLevel.None: Both stdout and stderr → TextWriter.Null (zero output)
   • Other levels: stdout → stderr (logs appear on stderr, JSON-RPC stays on stdout)

3. Log level precedence: CLI --LogLevel > Config runtime.telemetry.log-level > MCP logging/setLevel

   • CLI passes --LogLevelFromConfig flag when config specifies a log level
   • Service correctly identifies the source and blocks MCP override if appropriate

4. Early logging suppression in CLI before Service starts

   • Added IsMcpStdioMode flag to suppress CLI's own logging in MCP mode

How was this tested?

• Manual Tests
  • Configured mcp.json to run DAB with --mcp-stdio
  • Verified zero output when no log-level specified (default LogLevel.None)
  • Verified config override by adding "log-level": { "default": "Error" } to runtime.telemetry - logs appeared on stderr
  • Verified CLI override (--LogLevel) takes precedence over config
• Unit Tests
  • DynamicLogLevelProviderTests (5 tests) - CLI > Config > MCP precedence
  • StartCommandTests (39 tests) - CLI start command functionality

Sample Request(s)

CLI Usage - Default (Zero Output)

dab start --mcp-stdio --config dab-config.json

With no log-level in config, MCP mode produces zero log output.

CLI Usage - Config Override

Config file (dab-config.json):

{
  "runtime": {
    "telemetry": {
      "log-level": {
        "default": "Warning"
      }
    }
  }
}

dab start --mcp-stdio --config dab-config.json

Logs at Warning level appear on stderr; MCP logging/setLevel requests are accepted but ignored.

CLI Usage - CLI Override (Highest Priority)

dab start --mcp-stdio --LogLevel Error --config dab-config.json

Logs at Error level appear on stderr; both config and MCP logging/setLevel are ignored.

MCP logging/setLevel Request

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "logging/setLevel",
  "params": {
    "level": "info"
  }
}

Only changes log level if neither CLI nor config specified a level.