fix: atomic-pager showing non-existent page on last page

[Copilot]

Problem

atomic-pager displayed an extra non-existent page button on the last page. With 10 total pages, the last page showed buttons [7, 8, 9, 10, 11], where clicking page 11 resulted in an empty results page.

Root Cause

Index mismatch: Search Headless uses 1-indexed pages (currentPage: 1-10, maxPage: 10), while pager-utils expects 0-indexed internally (0-9). The code converted currentPage but not maxPage.

Changes

atomic-pager.ts line 147:

// Before
getCurrentPagesRange(
  this.pagerState.currentPage - 1,
  this.numberOfPages,
  this.pagerState.maxPage  // ❌ 1-indexed value
);

// After
getCurrentPagesRange(
  this.pagerState.currentPage - 1,
  this.numberOfPages,
  this.pagerState.maxPage - 1  // ✅ Convert to 0-indexed
);

Unit Tests Added:
Added comprehensive unit tests in atomic-pager.spec.ts that verify the pager displays the correct number of page buttons for various combinations of total results and results per page:

• 100 results with 10 per page (maxPage = 10)
• 47 results with 10 per page (maxPage = 5)
• 250 results with 25 per page (maxPage = 10)
• 23 results with 5 per page (maxPage = 5)

Each test calculates maxPage = Math.ceil(totalResults / resultsPerPage) and verifies that on the last page, only valid page buttons are displayed without showing non-existent pages. This prevents regression of the off-by-one bug.

Note: atomic-commerce-pager unaffected—Commerce Headless uses 0-indexing throughout.

https://coveord.atlassian.net/browse/KIT-5338

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[Copilot]

Pull request overview

This PR fixes an off-by-one indexing bug in atomic-pager that caused a non-existent page button to appear on the last page. The root cause was an inconsistent index conversion between Search Headless (1-indexed) and the pager utility functions (0-indexed).

Key Changes:

• Fixed getCurrentPagesRange call to convert maxPage from 1-indexed to 0-indexed
• Aligned with existing conversions for currentPage parameter in the same function call
• Ensures consistency with atomic-commerce-pager pattern (which doesn't need conversion as Commerce Headless is already 0-indexed)

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[louis-bompart]

@copilot add a unit tests that for a given number of results (and a given result per page number), the pager displays the right number of page button.

[Copilot]

@copilot add a unit tests that for a given number of results (and a given result per page number), the pager displays the right number of page button.

Added unit tests in commit 7f471d3 that verify the pager displays the correct number of page buttons for various combinations of total results and results per page:

• 100 results with 10 per page → maxPage = 10
• 47 results with 10 per page → maxPage = 5
• 250 results with 25 per page → maxPage = 10
• 23 results with 5 per page → maxPage = 5

Each test calculates maxPage = Math.ceil(totalResults / resultsPerPage) and verifies that on the last page, only valid page buttons are displayed (not showing non-existent pages like the original bug).