refactor: give the frozen right header band its own width slack

[ghiscoding]

verified by Copilot using GPT-5.3-Codex

Port bug fix from 6pac/SlickGrid PR 6pac/SlickGrid#1275 into slickgrid-universal

Warning

Stacked on 6pac/SlickGrid#1274 (this PR's base branch is refactor/headers-width-slack) — it uses the HEADER_WIDTH_SLACK constant and the scroll-sync pin spec introduced there. Please merge 6pac/SlickGrid#1274 first; GitHub will retarget this PR to master when that branch is deleted.

Resolves Q15 from the quirks triage (discussion 6pac/SlickGrid#1247): under a left freeze, the right header band's width was cumulative — headersWidthR = max(sumR, viewportW) + headersWidthL — sizing the right band to include the entire left band's width for no stated reason.

Why it survived until now (the load-bearing part)

Every header band is built with left: -1000px on the columns container plus an injected .slick-header-column { left: 1000px; } rule, so each band's width must include 1000px of shift compensation or its columns overflow it. In the frozen path, the right band's compensation was delivered through headersWidthL (= sumL + slack) — which is why the triage classified Q15 as unknown-business-path and why a naive "drop the + headersWidthL" would genuinely break the right band (clipped header columns, scroll clamping short at full right scroll — the pin spec fails exactly there on the naive version).

The borrowed sumL on top of that compensation was the phantom part.

The change

One line: the right band now carries its own compensation —

this.headersWidthR = Math.max(this.headersWidthR, this.viewportW) + HEADER_WIDTH_SLACK;

The right header container gets sumL narrower (inert — it is clipped), and its post-offset extent becomes max(sumR + gutter, viewportW): exactly the regime the unfrozen band has always run in (its +1000 was likewise consumed by the -1000px offset all along). The frozen right band now matches that long-standing contract instead of exceeding it by an arbitrary, frozen-band-width-dependent margin.

This supersedes the triage's "defer normalization to the branch rework" position — the deferral existed because there was no safety net, and 6pac/SlickGrid#1274 pin spec is that net.

Validation

• headers-width-scroll-sync.cy.ts (from refactor: single scrollbar add and named slack in getHeadersWidth https://github.com/6pac/SlickGrid/pull/1274) passes unchanged — its frozen-grid checks (header scroll range covers body range, header reaches the body scrollLeft at full right scroll with no clamping, last-column header/cell alignment) exercise exactly this contract.
• example-frozen-columns-and-rows.cy.ts green (8/8).
• Full cypress suite: all specs passed — 652 tests, 650 passing, 2 pre-existing skips (3m46s).

(With this and 6pac/SlickGrid#1274, every actionable width-arithmetic item from discussion 6pac/SlickGrid#1247 is resolved; Q14's shift-compensation slack is now named and documented, and the Q15 entry in the tracking notes moves from keep-as-is to normalized.)

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.0%. Comparing base (8f19df5) to head (4802689).
⚠️ Report is 1 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2718   +/-   ##
=======================================
  Coverage   100.0%   100.0%           
=======================================
  Files         200      200           
  Lines       25507    25507           
  Branches     9012     9012           
=======================================
  Hits        25507    25507           

Flag	Coverage Δ
angular	100.0% <ø> (ø)
universal	100.0% <100.0%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[pkg-pr-new]

angular-slickgrid

npm i https://pkg.pr.new/angular-slickgrid@2718

aurelia-slickgrid

npm i https://pkg.pr.new/aurelia-slickgrid@2718

slickgrid-react

npm i https://pkg.pr.new/slickgrid-react@2718

slickgrid-vue

npm i https://pkg.pr.new/slickgrid-vue@2718

@slickgrid-universal/angular-row-detail-plugin

npm i https://pkg.pr.new/@slickgrid-universal/angular-row-detail-plugin@2718

@slickgrid-universal/aurelia-row-detail-plugin

npm i https://pkg.pr.new/@slickgrid-universal/aurelia-row-detail-plugin@2718

@slickgrid-universal/react-row-detail-plugin

npm i https://pkg.pr.new/@slickgrid-universal/react-row-detail-plugin@2718

@slickgrid-universal/vue-row-detail-plugin

npm i https://pkg.pr.new/@slickgrid-universal/vue-row-detail-plugin@2718

@slickgrid-universal/binding

npm i https://pkg.pr.new/@slickgrid-universal/binding@2718

@slickgrid-universal/common

npm i https://pkg.pr.new/@slickgrid-universal/common@2718

@slickgrid-universal/composite-editor-component

npm i https://pkg.pr.new/@slickgrid-universal/composite-editor-component@2718

@slickgrid-universal/custom-footer-component

npm i https://pkg.pr.new/@slickgrid-universal/custom-footer-component@2718

@slickgrid-universal/custom-tooltip-plugin

npm i https://pkg.pr.new/@slickgrid-universal/custom-tooltip-plugin@2718

@slickgrid-universal/empty-warning-component

npm i https://pkg.pr.new/@slickgrid-universal/empty-warning-component@2718

@slickgrid-universal/event-pub-sub

npm i https://pkg.pr.new/@slickgrid-universal/event-pub-sub@2718

@slickgrid-universal/excel-export

npm i https://pkg.pr.new/@slickgrid-universal/excel-export@2718

@slickgrid-universal/graphql

npm i https://pkg.pr.new/@slickgrid-universal/graphql@2718

@slickgrid-universal/odata

npm i https://pkg.pr.new/@slickgrid-universal/odata@2718

@slickgrid-universal/pagination-component

npm i https://pkg.pr.new/@slickgrid-universal/pagination-component@2718

@slickgrid-universal/pdf-export

npm i https://pkg.pr.new/@slickgrid-universal/pdf-export@2718

@slickgrid-universal/row-detail-view-plugin

npm i https://pkg.pr.new/@slickgrid-universal/row-detail-view-plugin@2718

@slickgrid-universal/rxjs-observable

npm i https://pkg.pr.new/@slickgrid-universal/rxjs-observable@2718

@slickgrid-universal/sql

npm i https://pkg.pr.new/@slickgrid-universal/sql@2718

@slickgrid-universal/text-export

npm i https://pkg.pr.new/@slickgrid-universal/text-export@2718

@slickgrid-universal/utils

npm i https://pkg.pr.new/@slickgrid-universal/utils@2718

@slickgrid-universal/vanilla-bundle

npm i https://pkg.pr.new/@slickgrid-universal/vanilla-bundle@2718

@slickgrid-universal/vanilla-force-bundle

npm i https://pkg.pr.new/@slickgrid-universal/vanilla-force-bundle@2718

@slickgrid-universal/web-mcp

npm i https://pkg.pr.new/@slickgrid-universal/web-mcp@2718

commit: 4802689