Problem

Issue #3 identified critical validation bugs in src/sequentialthinking/lib.ts:

1. Falsy checks reject valid values: Lines 30-35 used !data.thoughtNumber which incorrectly rejects 0
2. No bounds checking: Negative numbers, NaN, and Infinity passed validation
3. Unsafe type assertions: Lines 45-49 used as boolean | undefined without runtime validation
4. Empty strings allowed: Falsy check on thought allowed empty strings to pass

Solution

Replaced unsafe falsy checks with explicit validation:

Required Fields

• thought: Check typeof === 'string' AND length > 0
• thoughtNumber & totalThoughts:
  • Type check: typeof === 'number'
  • Finite check: Number.isFinite() (rejects NaN/Infinity)
  • Bounds check: >= 1 (rejects negatives and zero)
• nextThoughtNeeded: Type check only (boolean)

Optional Fields

• Only validate when !== undefined
• isRevision, needsMoreThoughts: Boolean type check
• revisesThought, branchFromThought: Number type + finite + bounds
• branchId: String type + non-empty check

Test Coverage

Added 12 new edge case tests:

• ✅ Negative numbers (thoughtNumber, totalThoughts, revisesThought)
• ✅ Zero values (thoughtNumber, totalThoughts)
• ✅ NaN and Infinity
• ✅ Wrong types for optional fields (string instead of number, etc.)
• ✅ Empty strings for branchId

All 37 tests pass
Coverage: 94.59% statements, 91.8% branches

Why This First?

This PR establishes the foundation. Validation must be bulletproof before tackling:

• PR Create package for each server #2: State isolation (race conditions)
• PR Added SQLite Notes To Do Server #3: Memory cleanup
• PR Update Puppeteer (Code & README) #4: Display formatting
• PR update git server to most recent MCP SDK #5: Test coverage

Garbage in, garbage out. Fix validation first.

Files Changed

• src/sequentialthinking/lib.ts (validateThoughtData method)
• src/sequentialthinking/__tests__/lib.test.ts (12 new tests)

Testing

cd src/sequentialthinking
npm ci
npm test    # All 37 tests pass
npm run build  # TypeScript compiles clean

Closes #3