docs: add MCP double-dash naming convention explanation

docs/mcp-double-dash-explanation.md

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+# MCP Routes Double Dash Explanation
+
+## Summary
+
+The double dashes (`--`) in MCP server routes are **intentional design choices**, not bugs. They serve as unambiguous delimiters between package names and tool names.
+
+## Root Cause
+
+The double dashes originate in `apps/web/src/lib/mcp/tool-converter.ts`.
+
+### Registry Tool Naming (lines 27-53)
+
+```typescript
+export function sanitizeMcpName(packageName: string, toolName: string): string {
+  // Remove @ and convert / to -
+  let sanitizedPkg = packageName.replace(/^@/, '').replace(/\//g, '-');
+
+  // Remove common prefixes to shorten
+  sanitizedPkg = sanitizedPkg.replace(/^tpmjs-tools-/, '');
+  sanitizedPkg = sanitizedPkg.replace(/^tpmjs-/, '');
+
+  // Remove 'Tool' suffix from tool name
+  const sanitizedTool = toolName.replace(/Tool$/, '');
+
+  const fullName = `${sanitizedPkg}--${sanitizedTool}`;  // <-- DOUBLE DASH
+  // ...
+}
+```
+
+### Bridge Tool Naming (lines 59-64)
+
+```typescript
+export function sanitizeBridgeToolName(serverId: string, toolName: string): string {
+  const sanitizedServer = serverId.replace(/[^a-zA-Z0-9_-]/g, '-');
+  const sanitizedTool = toolName.replace(/[^a-zA-Z0-9_-]/g, '-');
+  return `bridge--${sanitizedServer}--${toolName}`;  // <-- DOUBLE DASHES
+}
+```
+
+## Naming Patterns
+
+| Type | Pattern | Example |
+|------|---------|---------|
+| Registry tools | `{package}--{toolName}` | `unsandbox--executeCodeAsync` |
+| Bridge tools | `bridge--{serverId}--{toolName}` | `bridge--chrome--screenshot` |
+
+## Why Double Dashes?
+
+1. **Single dashes are allowed within names** - Package names like `@tpmjs/tools-hello-world` contain single dashes
+2. **Unambiguous delimiter** - A double dash provides a clear separator that won't appear within package or tool names
+3. **Correct parsing** - Enables reliable splitting of the full MCP tool name back into components
+
+## Parsing Logic
+
+In `apps/web/src/lib/mcp/tool-converter.ts` (lines 102-146):
+
+```typescript
+export function parseToolName(mcpName: string): ParsedToolName | null {
+  // Check for bridge tools first
+  const bridgeMatch = mcpName.match(/^bridge--([^-]+(?:-[^-]+)*)--(.+)$/);
+  if (bridgeMatch?.[1] && bridgeMatch[2]) {
+    return {
+      type: 'bridge',
+      serverId: bridgeMatch[1],
+      toolName: bridgeMatch[2],
+    };
+  }
+
+  // Parse registry tools
+  const match = mcpName.match(/^(.+)--(.+)$/);  // Split on double dash
+  if (!match || !match[1] || !match[2]) return null;
+  // ...
+}
+```
+
+## Files Involved
+
+| File | Lines | Purpose |
+|------|-------|---------|
+| `apps/web/src/lib/mcp/tool-converter.ts` | 27-53, 59-64, 102-146 | Tool name sanitization and parsing |
+| `apps/web/src/lib/mcp/handlers.ts` | 139-146 | Tool name parsing during MCP calls |
+
+## Conclusion
+
+The double dashes are a deliberate architectural decision to enable:
+- Clean separation of package and tool names
+- Support for single dashes within component names
+- Reliable bidirectional conversion between full MCP names and their components