feat(iter-13): keyboard shortcuts panel, interest accrual & SRM levels 74-75

[martinl5]

Summary

• Navigator's Chart keyboard shortcuts panel — ? button and ? key open a floating maritime-themed shortcuts reference card listing all key bindings (Run ⌘↵, Submit ⇧⌘↵, toggle ?, close Esc) with gold <kbd> chips and a Compass icon
• Level 74 — Active Loan Interest Accrual — simple-interest date arithmetic (JULIANDAY days / 365) on 12 active loans; teaches the MAS/IFRS 9 accrual formula used in regulatory loan-book reporting
• Level 75 — A/B Test Sample-Ratio Mismatch (SRM) Check — three-CTE pattern (counts → total CROSS JOIN → deviation_pct + CASE srm_check); teaches the Experimentation platform guard mandated before any A/B result can be trusted

[UI/UX Improvements]

Added the "Navigator's Chart" floating shortcuts panel to SQLPanel.tsx:

• HelpCircle icon button in the header (left of Run), toggles on click or ? key press
• Suppresses ? when the Monaco editor textarea has focus (avoids intercepting SQL input)
• Escape closes the panel
• Gold-bordered floating card with Compass icon, four shortcut rows (⌘↵, ⇧⌘↵, ?, Esc), maritime footer note
• Implements "Accessibility & DX: keyboard shortcuts" from the UI/UX rotation

[Game Design Tweaks]

Level 74 (Expert, difficulty 4) — Interest Accrual:

• Formula: principal × (rate/100) × JULIANDAY_days / 365 computed inline — no CTE needed
• 12 active loans ordered by accrued interest DESC; spans ~$87k (450k loan, 2018 start) → ~$1.1k (8k loan, 2024 start)
• Pattern mirrors IFRS 9 ECL provisioning and Basel III RWA calculations at GIC, JPMorgan, DBS

Level 75 (Expert, difficulty 4) — A/B Test SRM Check:

• Three-CTE chain: counts → total → expected (CROSS JOIN); outer query: deviation_pct + CASE srm_check
• Balanced 50/50 data (10 per group) yields both groups PASS with 0.0% deviation — valid test, clean result
• SRM guard mandated in Experimentation platforms at Booking.com, Airbnb, Netflix, Meta

[Database & Code Optimizations]

• LevelUpModal hint map extended with entries for levels 74 and 75; nextHintKey sentinel extended […,73] → […,73,74,75]; fallback ?? 73 → ?? 75
• MAX_LEVEL auto-derives from levels[levels.length-1].id (75) — no other touch points
• No new DB tables, seed rows, or indexes — both levels use existing loans, customers, and customers.ab_test_group

Test Results

• npm ci — ✅ installed (7 pre-existing vulnerabilities, none introduced)
• npx tsc --noEmit — ✅ 0 errors
• npm test — ✅ 415 tests pass (up from 395 in iter-12; both new levels auto-picked up by determinism invariants suite)

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Project	Deployment	Actions	Updated (UTC)
sqlwak	Ready	Preview, Comment	Jul 6, 2026 5:13pm