feat: implement .from() method for exception chaining

[martyy-code]

Summary

Add .from(cause) method to ErrorInstance for exception chaining:

consterr=ValidationError({field: 'email'}).from(newNetworkError('Connection failed'));

Features

• Cause chaining: Sets err.cause property
• Full chain: Maintains err.causes array with complete history
• Method chaining: err.from(a).from(b) works
• Native support: Works with native JS errors
• Nested chains: Preserves nested cause chains

Implementation

• Added .from() method to ErrorInstance type
• Method returns instance for chaining
• Causes array maintains chronological order: newest first

Test plan

• 67 tests passing
• TypeScript strict mode passes
• ESLint passes

🤖 Generated with Claude Code

[martyy-code]

PR Review: feat: implement .from() method for exception chaining

Summary

The .from() implementation for exception chaining is well-designed and correctly handles the core requirements. The cause chain building logic properly preserves nested cause arrays and maintains chronological order.

What Works Well

• Correct cause chain building: The spread order [cause, ...cause.causes, ...instance.causes] correctly maintains newest-first ordering
• Handles native errors: Properly defaults to [] when cause has no causes property (native Error objects)
• Type signature is correct: from(cause: Error | ErrorInstance): ErrorInstance<TFields> matches the implementation that checks for causes property
• Method chaining: Returns instance allowing .from(a).from(b) pattern
• Test coverage: Comprehensive tests covering basic usage, nested chains, chaining, type safety, and edge cases

Suggestion (Non-blocking)

The type guard 'causes' in cause && Array.isArray(cause.causes) could theoretically fail if someone attached a non-array causes property to an error. However, this is an extremely unlikely scenario that does not warrant a blocking issue.

Recommendation

Approve - The implementation is clean, well-tested, and follows the design correctly.