Add markdown log writer for GitHub workflow preview

[Copilot]

Adds a second log file (gateway.md) formatted as GitHub-flavored markdown for workflow run previews. Logs important diagnostic events with visual indicators and automatic secret redaction.

Implementation

• New markdown logger (internal/logger/markdown_logger.go)

  • Wraps content in collapsible <details> HTML element
  • Emoji-prefixed bullet points: ✓ INFO, ⚠️ WARN, ✗ ERROR, 🔍 DEBUG
  • Automatic secret sanitization (GitHub PATs, API keys, bearer tokens, JWTs)
  • Thread-safe with immediate flush for real-time viewing
  • Code blocks for multi-line/technical content
  • Clean, concise format with emojis providing visual hierarchy

• Integrated at critical log points

  • Startup/shutdown events
  • Authentication failures
  • Backend connection errors
  • Client connection rejections

Output Format

<details>
<summary>MCP Gateway</summary>

- ✓ **startup** MCPG Gateway version: dev
- ✗ **backend**

MCP backend connection failed, command=docker, args=[run --rm -e TOKEN=[REDACTED] -i image]

- ✗ **client** MCP connection rejected: no Authorization header
- ✓ **shutdown** Shutting down gateway...

</details>

File written to {log-dir}/gateway.md alongside existing mcp-gateway.log.

Original prompt

Add a second log file writer (gateway.md) that writes the logs in github flavored markdown. This file will be used as a preview for the github action workflow run.

• content wrapped in a HTML details where summary is "MCP gateway"
• use simple bullet point list with clear emojis for conciseness
• log important information to help with diagnosing issues
• use basic markdown syntax: lists and code section. Do not use headers.
• careful about not logging secrets

The file will be written at {log-dir}/gateway.md

---

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[pelikhan]

@copilot

• the emojis are enough, remove [INFO] ...
• remove timestamps

[Copilot]

@copilot

• the emojis are enough, remove [INFO] ...
• remove timestamps

Done in fd677df. Removed timestamps and log level labels ([INFO], [WARN], [ERROR], [DEBUG]) from markdown output - emojis now provide all the visual hierarchy needed.

Before:

- ✓ `14:13:42` **startup** [INFO] MCPG Gateway version: dev
- ✗ `14:14:10` **backend** [ERROR] MCP backend connection failed...

After:

- ✓ **startup** MCPG Gateway version: dev
- ✗ **backend** MCP backend connection failed...

The output is now cleaner and more concise while maintaining clear visual indicators with emojis (✓ ✗ ⚠️ 🔍).

[pelikhan]

@copilot lint go

[Copilot]

@copilot lint go

✅ All Go linting checks pass:

• make lint completes successfully
• go vet passes on all modified packages
• gofmt shows no formatting issues

No code changes needed.