test: add missing parse test cases for confirmed specs

[roottool]

Description

Add three missing test cases to parse.test.ts for specs that were already confirmed but untested.

Added tests

valid input

• Empty FormData returns data: {} and issues: [] (boundary value)
• File values are stored as-is in data

duplicate key detection

• Appending the same key 3+ times reports one duplicate_key issue per extra occurrence (3 appends → 2 issues)

Type of Change

• Bugfix (non-breaking change fixing an issue)
• Security fix (non-breaking change addressing a security issue)
• Documentation (changes to documentation only)
• Refactoring (non-breaking change improving code structure)
• Tests (adding or updating tests)
• Tooling / CI (changes to build tools, CI configuration)

Boundary Checklist

• This is a non-implementation change (Documentation, Tooling, or CI only)
• No interpretation — Keys treated as opaque strings, no structural inference
• No silent behavior — No merging, overwriting, or implicit resolution
• Boundary respected — No validation, coercion, or business logic

📘 AGENTS.md

Security & API Stability

• No security impact (forbidden keys, prototype safety unaffected)
• No changes to public API (parse, ParseResult, ParseIssue, IssueCode)
• No breaking changes; or justified with version bump rationale
• Compatible with current v0.x versioning policy

Testing

• bun run check:type:source passes
• bun run test passes
• bun run build passes

---

Signature

🤖 Generated with Claude Code

Co-Authored-By: Claude noreply@anthropic.com

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (7f79fd9) to head (ecb5786).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #69   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines           21        21           
  Branches         5         5           
=========================================
  Hits            21        21           

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