Dev Diary Command

Command

/diary

Description

Creates a structured development diary entry documenting what was done, why, what alternatives were considered, and what trade-offs were made. Maintains a chronological log that explains the "why" behind technical decisions -- the most valuable form of documentation that is almost never written.

Behavior

Arguments

• $ARGUMENTS -- Topic or summary of what to document (e.g., "chose Redis over Memcached for session store")

Steps

1. Analyze the current session context:

   • What was changed? (git diff)
   • What was the goal?
   • What decisions were made?

2. Generate the diary entry with these sections:

   • Date and context
   • Decision or change summary
   • Alternatives considered
   • Trade-offs and rationale
   • Future implications

3. Append to diary file at .claude/dev-diary.md

Entry Template

Copy
---

## 2025-03-25: Chose Redis for Session Storage

### Context
Migrating from JWT-based auth to session-based auth. Needed a
fast, distributed session store that works across multiple
app server instances.

### Decision
Using Redis (via ioredis) as the session store backend.

### Alternatives Considered
| Option | Pros | Cons |
|--------|------|------|
| Redis | Fast, TTL support, pub/sub for invalidation | Extra infrastructure |
| PostgreSQL | Already have it, ACID compliance | Slower for high-frequency reads |
| Memcached | Simple, fast | No persistence, no data types |
| In-memory | Zero overhead | Lost on restart, not distributed |

### Rationale
- Sub-millisecond reads for session validation on every request
- Built-in TTL for automatic session expiration
- Already running Redis for caching, no new infrastructure
- Pub/sub channel enables real-time session invalidation across instances

### Trade-offs
- Sessions are lost if Redis restarts (mitigated by Redis persistence config)
- Additional memory usage (~500 bytes per session)
- Need to monitor Redis connection pool in production

### Future Implications
- Can reuse this Redis instance for rate limiting and real-time features
- If we need ACID guarantees for sessions, will need to add PostgreSQL fallback
- Redis Cluster needed if we exceed single-instance memory

### Related Files
- `src/config/redis.ts` -- Redis connection config
- `src/middleware/session.ts` -- Session middleware setup
- `src/services/sessionStore.ts` -- Session CRUD operations

Output Format

The formatted diary entry is appended to .claude/dev-diary.md and displayed in the response.

Examples

Copy
# Document a technology choice
/diary chose Redis over Memcached for session storage

# Document an architecture decision
/diary decided to use event sourcing for order processing

# Document a trade-off
/diary chose server-side rendering over static generation for product pages

# Document a debugging lesson
/diary learned that Prisma connection pool needs explicit sizing in serverless