Accumulate all validation errors before reporting

[aryasaatvik]

Problem

Bunli currently throws on the first validation error. If a user passes --port abc --env invalid, they only see the --port error, fix it, re-run, and then see the --env error. This is a poor CLI experience.

Solution

Validate all options in a command, collect all failures, and report them together:

$ mycli deploy --port abc --env invalid

Error: 2 validation errors in "deploy":
  --port: expected number, got "abc"
  --env: must be one of: dev, staging, prod

Design

1. New error class in errors.ts:

export class AggregateValidationError extends TaggedError('AggregateValidationError')<{
  message: string
  command: string
  errors: BunliValidationError[]
}>() {}

2. Refactor parseArgs() in parser.ts:

   • Change validateOption() to return a Result instead of throwing
   • Accumulate all BunliValidationError instances during parsing
   • After all options processed, throw AggregateValidationError if any errors

3. Update error rendering in cli.ts:

   • renderValidationError() handles AggregateValidationError
   • Display all issues with consistent formatting

Edge cases

• Repeatable options: one error per option (not per item)
• Default application failures (trailing loop) must also accumulate
• mergeProvidedFlags() in execute() path should also accumulate
• Valid options should still be parsed correctly alongside invalid ones

Files

• packages/core/src/errors.ts — add AggregateValidationError
• packages/core/src/parser.ts — refactor for error accumulation
• packages/core/src/validation.ts — update validateValues() to use structured error
• packages/core/src/cli.ts — update error rendering
• packages/core/src/output/serialize.ts — serialize aggregate errors
• packages/core/src/index.ts — export new error type

Depends on

• Auto-coercion pipeline for CLI flag values #49 — coercion changes how values are processed before validation