Harden Types

# Harden Types Command

**Arguments:** [path] [--dry-run] [--max-iterations=N]

**Description:** Incrementally improve type safety in TypeScript files by replacing string literals with enums, narrowing `any` types, and using shared types. Works in small, verified batches.

---

## Usage

```bash
/harden-types backend/src/services/auth.service.ts   # Single file
/harden-types backend/src/services/                  # Directory
/harden-types --dry-run                              # Analysis only, no changes
/harden-types backend/src --max-iterations=5         # Limit iterations

---

Workflow

Step 1: Parse Arguments

TARGET="${1:-}"
DRY_RUN=false
MAX_ITERATIONS=10

for arg in "$@"; do
  case $arg in
    --dry-run) DRY_RUN=true ;;
    --max-iterations=*) MAX_ITERATIONS="${arg#*=}" ;;
  esac
done

# If no target, prompt user
if [ -z "$TARGET" ]; then
  echo "Which file or directory to harden?"
  read -p "Path: " TARGET
fi

Step 2: Safety Check

# Ensure git is clean (can rollback safely)
if [ -n "$(git status --porcelain)" ]; then
  echo "⚠️ Warning: Uncommitted changes exist"
  echo "Recommend: git stash or commit first"
  read -p "Continue anyway? (y/n): " CONTINUE
  [ "$CONTINUE" != "y" ] && exit 1
fi

Step 3: Load Type Hardening Skill

Read and apply .claude/skills/quality/type-hardening/SKILL.md

Key steps from skill:

1. Discover existing types (Prisma enums, shared types, constants)
2. Analyze target file(s) for hardening opportunities
3. Prioritize: Prisma enums → Shared types → Constants → New types
4. Apply 1-3 changes at a time
5. Verify with tsc --noEmit after each batch
6. Commit atomically

Step 4: Execute Hardening Loop

For each file in TARGET:
  1. Read file and identify opportunities
  2. If --dry-run: report opportunities only
  3. Otherwise:
     a. Apply batch of 1-3 type improvements
     b. Run: npx tsc --noEmit
     c. If pass: commit changes
     d. If fail: revert and report
  4. Continue until:
     - No more opportunities
     - Max iterations reached
     - Verification failure

Step 5: Report Results

## Type Hardening Report

**Target**: ${TARGET}
**Mode**: ${DRY_RUN ? "Dry Run" : "Applied"}
**Iterations**: ${COUNT}/${MAX_ITERATIONS}

### Files Processed
| File | Changes | Status |
|------|---------|--------|
| auth.service.ts | 5 | ✅ |
| user.service.ts | 3 | ✅ |

### Summary
- String literals replaced: 12
- Any types narrowed: 4
- Shared types used: 6
- New types created: 1

### Remaining Opportunities
[List if any remain]

---

Options

Flag	Description	Default
--dry-run	Analyze only, no changes	false
--max-iterations	Stop after N iterations	10

---

Integration

With /refactor

Can be invoked as a strategy:

/refactor --target=file.ts --strategy=types

With Gemini Delegation

Safe to delegate to Gemini with proper guardrails:

/delegate-gemini task="Type hardening on backend/src/services/"

With Quality Gate

Can be run as part of quality checks:

/audit --include-type-hardening

---

Examples

Example 1: Single File

/harden-types backend/src/services/notification.service.ts

Output:

Analyzing: notification.service.ts
Found 4 hardening opportunities:
  L23: 'info' → NotificationType
  L45: 'admin' → UserRole.admin
  L67: any → NotificationPayload
  L89: 'success' → NotificationType

Applying batch 1/2...
  ✅ L23, L89: Replaced with NotificationType
  ✅ tsc --noEmit passed
  ✅ Committed: "refactor: harden types in notification.service.ts"

Applying batch 2/2...
  ✅ L45: Replaced with UserRole.admin
  ✅ L67: Narrowed to NotificationPayload
  ✅ tsc --noEmit passed
  ✅ Committed: "refactor: harden types in notification.service.ts"

✅ Complete: 4 improvements applied

Example 2: Dry Run Analysis

/harden-types backend/src/ --dry-run

Output:

=== Type Hardening Analysis (Dry Run) ===

backend/src/services/auth.service.ts
  L34: 'admin' → UserRole.admin
  L56: any → TokenPayload

backend/src/services/user.service.ts
  L12: 'active' → UserStatus.ACTIVE
  L78: any → UserProfile (specific type, not unknown)

backend/src/routes/notifications.ts
  No opportunities found ✅

Summary: 4 opportunities in 2 files
Run without --dry-run to apply changes

---

Safety

• Always verifies with tsc --noEmit after changes
• Reverts on verification failure
• Commits atomically (one commit per successful batch)
• Preserves functionality (no logic changes)
• Checks existing types before creating new ones
• No unknown cheating: Replacing any with unknown is NOT an improvement - must narrow to a SPECIFIC type or leave as-is with a TODO comment

---

Related

• Skill: .claude/skills/quality/type-hardening/SKILL.md
• Agent: .claude/agents/refactor.md (Pattern 6)
• Workflow: .agent/workflows/harden-types.md (project-specific)