Prevented Ciruclar dependencies using DFS(Depth First Search) Algorithm

[arjav1528]

Description

Problem

Tasks could form circular dependencies (e.g., A → B → C → A), making them impossible to complete.

Solution

• Added circular dependency detection utility using DFS algorithm
• Integrated validation in EditTaskHandler to check dependencies before allowing edits
• Added comprehensive tests for all edge cases

Changes

• backend/utils/validation.go: Added DetectCircularDependency function
• backend/controllers/edit_task.go: Added validation before task edits
• backend/utils/utils_test.go: Added test coverage

Fixes the issue where circular dependencies could be created without validation.

• Fixes: Circular dependency in task dependencies #308

Checklist

• Ran npx prettier --write . (for formatting)
• Ran gofmt -w . (for Go backend)
• Ran npm test (for JS/TS testing)
• Added unit tests, if applicable
• Verified all tests pass
• Updated documentation, if needed

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