/challenge

name: challenge
description: Challenge mode reviews - rigorous questioning before approving changes. Use when you want thorough scrutiny of Ecto changes, LiveView events, OTP designs, or PR readiness.
effort: high
argument-hint: ecto | liveview | pr

Challenge Mode Reviews

Rigorous, critical review patterns inspired by Boris Cherny's "Grill me" approach. Push beyond first solutions to ensure quality.

Iron Laws - Never Violate These

1. **No approval without verification** - Don't approve until all concerns addressed 2. **Assume bugs exist** - Look for edge cases, race conditions, missing handlers 3. **Question everything** - Even "obvious" code can hide issues 4. **Demand proof** - Ask for tests, show state transitions, verify behavior

Adversarial Lenses (Apply to ALL Modes)

1. **"What Would Break This?"** — Production failure modes under load, during deploys, with unexpected data 2. **"Assumption Stress Test"** — List every assumption; which are most fragile? 3. **"Contradictions Finder"** — Find contradictions between tests/implementation, docs/behavior, or within the changeset

Challenge Modes

Ecto Challenge (`/phx:challenge ecto`)

Grill the developer on database changes:

**Migration Safety**

• Will this migration lock the table in production?
• What happens to existing records without the new field?
• Is the migration reversible?
• Are there any unsafe operations (column removal, type change)?

**Query Performance**

• Have you introduced any N+1 queries?
• Are there missing indexes for new WHERE clauses?
• Will this query scale with data growth?

**Schema Integrity**

• Are all constraints enforced at database level?
• What happens during rolling deployment (old code, new schema)?
• Are foreign key cascades correct?

**Backward Compatibility**

• Will old code work during deployment?
• Are there any breaking changes to the context API?

LiveView Challenge (`/phx:challenge liveview`)

Prove the LiveView handles all cases:

**Event Coverage**

• List every `handle_event` clause and expected socket state
• What happens if socket assigns are missing when event fires?
• Are there race conditions between user events and server pushes?

**PubSub Handling**

• List every `handle_info` clause and when it's triggered
• Do all PubSub subscriptions have corresponding handlers?
• What happens if a message arrives before mount completes?

**State Transitions**

• Show the event → handler → state transition table
• Are all error states handled gracefully?
• What's the recovery path from each error state?

**Memory & Performance**

• Are large lists using streams?
• Is transient data using temporary_assigns?
• What's the memory footprint per connected user?

PR Challenge (`/phx:challenge pr`)

Senior engineer review checklist:

**Must Pass**

• [ ] No direct Repo calls in controllers/LiveViews
• [ ] All Ecto queries use explicit preloads
• [ ] Changesets validate all user input
• [ ] No atoms created from params
• [ ] Error cases handled (not just happy path)
• [ ] Tests cover new functionality

**Performance**

• [ ] No queries in Enum.map loops
• [ ] LiveView streams for lists > 100 items
• [ ] Indexes exist for WHERE clause columns

**OTP**

• [ ] GenServers have supervision
• [ ] Timeouts set for GenServer.call
• [ ] No unbounded process spawning

**Security**

• [ ] No SQL injection via raw queries
• [ ] No path traversal in file handling
• [ ] Authorization checks present

Prior Findings Deduplication (MANDATORY)

CRITICAL: Prevents re-discovering identical issues across consecutive runs.

1. **Search** `.claude/plans/*/reviews/` and `.claude/reviews/` for prior findings 2. **Read ALL** prior findings before analyzing code 3. **Check each finding** against priors:

• Fixed → **SKIP** | Still present → **PERSISTENT** (one line) | New → **NEW** (full analysis) | Reintroduced → **REGRESSION**

4. **Present**: NEW first (full), then PERSISTENT (one-line), then REGRESSION

Example Challenge Output

## Challenge: Ecto — Orders Migration

### FINDING 1: Table lock risk (HIGH)
AddColumn on `orders` (2.1M rows) will lock table during deploy.
**Proof needed**: Run `SELECT count(*) FROM orders` — if >1M, use
`ALTER TABLE ... ADD COLUMN ... DEFAULT NULL` (no lock).

### FINDING 2: Missing index (MEDIUM)
New `WHERE status = ?` query on line 45 has no index.
**Action**: Add `create index(:orders, [:status])` to migration.

### Status: BLOCKED — 2 unresolved findings

Usage

Run `/phx:challenge [mode]` to initiate a rigorous review. The reviewer will not approve until all concerns are addressed with evidence.

Example workflow:

1. Run `/phx:challenge ecto` after migration changes 2. Answer each question with code references or test results 3. Address all concerns before proceeding to PR