Implements icon validation to catch common issues that prevent icons from
displaying in Claude Desktop. Uses a non-blocking warning approach for
remote URLs to maintain flexibility for MCPB's evolving multi-platform
ecosystem.
## Changes
### Core Implementation (src/node/validate.ts)
- Add `isPNG()` helper to validate PNG file signatures via magic bytes
- Add `validateIcon()` function with comprehensive checks:
- **Warn** about remote URLs (non-blocking, best practice guidance)
- **Reject** ${__dirname} variable usage in icon field (doesn't work)
- **Reject** absolute paths (not portable)
- Verify icon file exists at specified path
- Verify icon file is valid PNG format
- Recommend 512×512 size for Claude Desktop
- Integrate icon validation into `validateManifest()` after schema validation
### Test Coverage
- Update `test/icon-validation.test.ts` - Remote URL test now expects warning
- Update `test/cli.test.ts` - Integration test updated for warnings
- All 109 tests passing
### Documentation Updates
- Update examples/hello-world-node/manifest.json to v0.3
## Validation Behavior
**Remote URLs (WARNING - non-blocking):**
```
Icon path uses a remote URL. Best practice for local MCP servers:
Use local files like "icon": "icon.png" for maximum compatibility.
Claude Desktop currently only supports local icon files in bundles.
```
**Result:** Validation passes, developer is informed
**Other Issues (ERROR - blocking):**
- ${__dirname} usage: Rejects (doesn't work)
- Absolute paths: Rejects (not portable)
- Missing files: Rejects (broken reference)
- Non-PNG files: Rejects (wrong format)
## Rationale
**Non-Blocking Approach:**
- Doesn't prevent valid bundles from being created
- Educates developers about best practices
- Maintains flexibility as MCPB evolves beyond Claude Desktop
- Future-proof if remote URL support is added
**Still Protective:**
- Blocks truly broken configurations (missing files, wrong formats)
- Provides actionable error messages for fixable issues
Based on real-world findings from investigating icon display issues in
Claude Desktop with production MCPB bundles.
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