# Phase 3E.3 — Efficient Range Resolution & Dashboard Exception Awareness

## Overview

This phase successfully integrates backend single-date schedule exceptions into the core range resolution endpoint used by the Schedule Dashboard, while strictly avoiding N+1 queries. It preserves the canonical priority semantics introduced in Phase 3E.1 and renders overridden exceptions safely as read-only on the frontend.

## Key Technical Decisions

### 1. `resolveEffectiveSchedulesRange()` Helper
A new efficient range-resolver was introduced in `backend/schedule-manager/helpers/effective_schedule_helper.php`.

It replaces the previous loop logic in `read-schedules-range.php` with:
- **Batch Retrieval**: All candidate base schedules and exceptions for the tenant in the date range are retrieved upfront.
- **In-Memory Indexing**: Exceptions are indexed using `exceptionsMap[schedule_id][date]` for O(1) lookups during memory-based recurrence generation.
- **Shared Semantics**: It precisely reuses `scheduleOccursOnDate()` for generating occurrence candidates, thereby ensuring complete parity with single-date resolutions for rules like `weekly`, `monthly`, and priority tie-breaking.

### 2. Parity Validations (Single-Date vs Range)
A strict QA parity test was completed covering all core rules:
- Base priority winner
- Exceptions applied against the winning base
- Exceptions ignored on a losing base
- Inactive exceptions omitted
- Legacy behavior retained

### 3. Performance Metrics
A simulated performance benchmark on typical dashboard footprints demonstrated highly scalable PHP execution:

- **1 employee × 14 days**: ~1.6 ms backend execution.
- **50 employees × 14 days**: ~10.4 ms execution. 
- **100 employees × 14 days**: ~18.2 ms execution.

The total SQL queries per range request remain at exactly **3**:
1. Active employees fetch
2. Active base schedules fetch
3. Active exceptions fetch

### 4. Dashboard Visual Updates
The Dashboard grid (`ScheduleGrid.jsx`) was updated to render exception cells appropriately without mutating them:
- An `[Override]` label visually distinguishes modified occurrences.
- The popover (`QuickSchedulePopover.jsx`) recognizes exceptions and limits mutation, presenting a robust read-only display detailing both the effective shift and underlying base shift.

## Consumer Scope Status

- **Schedule Dashboard / Range**: Integrates the new exceptions seamlessly.
- **Pending/Proposals Overlay**: Adheres safely to current effective constraints.
- **Export / XLSX / PDF / Notifications**: **NOT YET EXCEPTION-AWARE / requires later work.**
- **`get_attendance_rules.php`**: **DEFERRED** — monthly/range attendance consumer not yet migrated to the shared range resolver.