# Implementation Summary: Linear Adapter Field Validation and Project Read Support

## Overview
Implemented two critical fixes for mcp-ticketer to resolve user errors with Linear API integration.

## Changes Implemented

### Fix #1: Field Length Validation

#### Problem
Users encountered cryptic error: `Argument Validation Error: description must be at most 255 characters`
Linear API enforces strict 255-character limit on epic descriptions but adapter had no validation.

#### Solution
Created new field validation module with adapter-specific limits:

**New File**: `/Users/masa/Projects/mcp-ticketer/src/mcp_ticketer/core/validators.py`
- `FieldValidator` class with configurable limits per adapter
- Support for Linear, JIRA, GitHub field limits
- Optional truncation mode
- Clear error messages with actual vs. limit character counts

**Modified**: `/Users/masa/Projects/mcp-ticketer/src/mcp_ticketer/adapters/linear/adapter.py`
- Updated `update_epic()` method (lines 1044-1066)
- Added validation for `description` and `title` fields
- Raises `ValueError` with helpful message when limits exceeded

#### Impact
- Users get clear error message: "epic_description exceeds linear limit of 255 characters (got 300). Use truncate=True to auto-truncate."
- Prevents API errors before they reach Linear
- Supports other adapters (JIRA, GitHub) with different limits

### Fix #2: Extended Linear read() Method

#### Problem
Users got error: `Entity not found: Issue` when attaching files to projects
File attachment workflow calls `read()` to validate ticket exists, but `read()` only queried Issues, not Projects.

#### Solution
**Modified**: `/Users/masa/Projects/mcp-ticketer/src/mcp_ticketer/adapters/linear/adapter.py`
- Updated `read()` method (lines 1121-1170)
- Now tries to read as Issue first (most common case)
- Falls back to reading as Project if Issue not found
- Returns `Task | Epic | None` instead of `Task | None`

#### Implementation Details
```python
async def read(self, ticket_id: str) -> Task | Epic | None:
    # Try reading as issue first
    try:
        result = await self.client.execute_query(query, {"identifier": ticket_id})
        if result.get("issue"):
            return map_linear_issue_to_task(result["issue"])
    except TransportQueryError:
        pass

    # If not found as issue, try reading as project
    try:
        project_data = await self.get_project(ticket_id)
        if project_data:
            return map_linear_project_to_epic(project_data)
    except Exception:
        pass

    return None
```

#### Impact
- File attachments to epics (projects) now work correctly
- Maintains backward compatibility (issues still work)
- Graceful fallback with no performance penalty for common case

## Testing

### New Tests Created

#### Validator Tests
**File**: `/Users/masa/Projects/mcp-ticketer/tests/core/test_validators.py`
- 11 comprehensive tests covering all validation scenarios
- Tests for Linear, JIRA, GitHub limits
- Edge cases: None values, empty strings, unknown adapters
- Truncation mode testing
- Error message validation

**Results**: ✅ All 11 tests passing

#### Linear Adapter Tests
**File**: `/Users/masa/Projects/mcp-ticketer/tests/adapters/linear/test_adapter.py`
Added 3 test classes:
1. `TestLinearAdapterRead` - Tests for enhanced read() method
   - `test_read_issue`: Reading issues by identifier
   - `test_read_project`: Reading projects by UUID
   - `test_read_not_found`: Not found scenario

2. `TestLinearAdapterValidation` - Tests for field validation
   - `test_update_epic_validates_description_length`
   - `test_update_epic_validates_title_length`

**Results**: ✅ All 5 new tests passing

### Regression Testing
Ran full Linear adapter test suite: ✅ All 25 tests passing
No existing functionality broken by changes.

## Files Changed

### New Files (1)
1. `/Users/masa/Projects/mcp-ticketer/src/mcp_ticketer/core/validators.py` (71 lines)

### Modified Files (2)
1. `/Users/masa/Projects/mcp-ticketer/src/mcp_ticketer/adapters/linear/adapter.py`
   - Lines 1044-1066: Added validation to `update_epic()`
   - Lines 1121-1170: Extended `read()` to support Projects

2. `/Users/masa/Projects/mcp-ticketer/tests/adapters/linear/test_adapter.py`
   - Added 120 lines of comprehensive tests

### Test Files (1)
1. `/Users/masa/Projects/mcp-ticketer/tests/core/test_validators.py` (144 lines)

## Net Impact Metrics

### Code Statistics
- **New Lines**: 335 (71 validator + 120 tests + 144 validator tests)
- **Modified Lines**: ~50 (validation + read method)
- **Test Coverage**: 16 new tests
- **Net LOC Impact**: +335 lines (including comprehensive tests)

### Breaking Changes
**None** - All changes are backward compatible:
- `read()` return type expanded from `Task | None` to `Task | Epic | None`
- Existing code calling `read()` continues to work
- Validation only adds error checking, doesn't change happy path

## User Impact

### Before
❌ User tries to update epic with 2000-char description
```
Error: Argument Validation Error: description must be at most 255 characters
```
(No indication of actual length or how to fix)

❌ User tries to attach file to project
```
Error: Entity not found: Issue
```
(Confusing - they gave a valid project ID)

### After
✅ User tries to update epic with 2000-char description
```
ValueError: epic_description exceeds linear limit of 255 characters (got 2000).
Use truncate=True to auto-truncate.
```
(Clear message with actual vs. limit, suggests solution)

✅ User tries to attach file to project
```
Success: File attached to project
```
(Works correctly)

## Validation Limits Reference

| Adapter | Field | Limit |
|---------|-------|-------|
| Linear | epic_description | 255 chars |
| Linear | epic_name | 255 chars |
| Linear | issue_description | 100,000 chars |
| Linear | issue_title | 255 chars |
| JIRA | summary | 255 chars |
| JIRA | description | 32,767 chars |
| GitHub | title | 256 chars |
| GitHub | body | 65,536 chars |

## Future Enhancements

### Potential Improvements
1. **Auto-truncation option**: Add config flag for automatic truncation
2. **Smart truncation**: Truncate at word boundaries with ellipsis
3. **Warning thresholds**: Warn at 80% of limit before hard error
4. **Validation hooks**: Allow adapters to register custom validators
5. **Batch validation**: Validate multiple fields in single call

### Extensibility
The `FieldValidator` class is designed for easy extension:
```python
# Adding new adapter limits
LIMITS = {
    "new_adapter": {
        "field_name": max_length,
    }
}
```

## Acceptance Criteria

✅ User's oversized description (2000+ chars) gets clear error message
✅ User's project file attachment (6cf55cfcfad4) works correctly
✅ All existing tests still pass (25/25 passing)
✅ New validation tests pass (11/11 passing)
✅ New read tests pass (5/5 passing)
✅ No breaking changes to existing code
✅ Backward compatible API changes

## Deployment Notes

### No Migration Required
- No database schema changes
- No config file changes
- No environment variable changes
- Drop-in replacement

### Risk Assessment: LOW
- Changes are isolated to Linear adapter
- Comprehensive test coverage
- Backward compatible
- Fail-safe defaults (no truncation unless explicitly enabled)

## Documentation Updates Needed

1. Update Linear adapter documentation with field length limits
2. Add validation examples to user guide
3. Document `read()` method's expanded return type
4. Add troubleshooting section for validation errors

---

**Implementation Date**: 2025-11-20
**Engineer**: Claude (BASE_ENGINEER)
**Test Results**: ✅ 41 tests passing (11 validator + 5 new adapter + 25 existing)
**Status**: Ready for review and merge
