Add RPC message logging with privacy-preserving payload preview

[Copilot]

Implements comprehensive logging of all RPC messages (requests/responses) sent and received by the gateway, with privacy preservation, server attribution, and payload previews.

Implementation

New RPC Logger (internal/logger/rpc_logger.go)

• Dual logging to text (mcp-gateway.log) and markdown (gateway.md) formats
• Privacy-preserving: reuses existing sanitizeSecrets() to filter tokens, API keys, passwords
• Payload preview: 10KB for text logs, 120 characters for markdown logs
• Metadata captured: direction (IN/OUT), server ID, method, payload size
• Concise format: Short, intuitive symbols and minimal verbosity for quick scanning

Integration Points

• internal/mcp/connection.go: New SendRequestWithServerID() method logs all backend communication
• internal/server/*.go: Updated callers to pass server ID for attribution

Log Format

Text (concise, scannable, up to 10KB payload):

github→tools/list 58b {"jsonrpc":"2.0"...}
github←resp 284b err:timeout {"result":{...}}

Markdown (inline, intuitive, up to 120 chars payload):

**github**→`tools/list` `{"jsonrpc":"2.0"...}`
**github**←resp ⚠️`timeout` `{"result":{...}}`

Format Features:

• Directional arrows: → (outbound), ← (inbound)
• Concise size notation: 58b
• Server attribution: **server**
• Inline payload preview: 10KB for text logs, 120 chars for markdown
• Error indicators: err:message (text), ⚠️ (markdown)

Testing

• 10 new unit tests covering truncation (10KB text, 120 chars markdown), sanitization, formatting, concurrency
• All existing tests pass (600+ unit, integration)

Original prompt

Add logging of every rpc message sent and received in the text and markdown logs.

• privacy preserving
• associate to server
• message type, payload size or essential field
• first few 120 characters of payload (filter secrets)

In markdown, always attribute messages to server

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[pelikhan]

@copilot make the format short, intuitive and less verbose . Assume the user will learn.

[Copilot]

@copilot make the format short, intuitive and less verbose . Assume the user will learn.

Updated format to be shorter and more intuitive (commit 6be2a4b):

Text: github→tools/list 58b {"jsonrpc":"2.0"...}
Markdown: **github**→\tools/list` `{"jsonrpc":"2.0"...}``

• Removed verbose labels ([OUT], server=, method=)
• Use arrows: → (out), ← (in)
• Concise size: 58b vs size=58
• Inline payload (no code blocks)

[pelikhan]

the text format can inline the first 10kb of the json message payload

[pelikhan]

@copilot the text format can inline the first 10kb of the json message payload

[Copilot]

@copilot the text format can inline the first 10kb of the json message payload

Increased text log payload preview to 10KB (commit d46148b). Markdown logs remain at 120 chars for readability.

Text format now inlines up to 10,240 bytes of sanitized JSON
Markdown format keeps 120 char limit for human readability