fix(frontend): find the preset to replace by value, not by reference

[mengw15]

What changes were proposed in this PR?

PresetService.updatePreset located the preset to replace with lodash indexOf, which compares by reference. The list it searches comes straight out of JSON.parse, so the lookup always returned -1 while the contains guard above it — which compares with isEqual — still let execution through. Both arms then did the wrong thing:

• presets[-1] = replacementPreset writes a non-index property on the array, so the edit was silently discarded and the unchanged list written back.
• presets.splice(-1, 1) removes the last element, so replacing a preset with one that already existed deleted the wrong preset.

The sibling updateOrCreatePreset directly below already used a deep-equality findIndex, with a comment naming this cause; this applies the same lookup to updatePreset. indexOf is no longer used in the file, so the import drops with it.

Three tests come with it — the two that reproduce the defect (an in-place replace, and a replace onto an existing preset), plus the absent-entry case that reaches the ?? "[]" default. They fail against the old code with exactly the wrong values described above.

Any related issues, documentation, discussions?

Closes #7795

Both lines were unhit, which is how this went unnoticed; they are among the gaps listed in #7777, so that issue's PresetService portion is handled here.

How was this PR tested?

Unit tests, run locally in frontend/:

ng test --watch=false --include .../preset.service.spec.ts
# Test Files 1 passed (1) | Tests 61 passed (61)
prettier --write / eslint   # clean

The failure path was verified by reverting the production change and re-running: the run exits non-zero with 2 failed | 59 passed, the in-place replace writing back the unchanged list and the merge case deleting v2 instead of v1. The coverage report over this spec now shows no unhit line and no partial branch in preset.service.ts.

Was this PR authored or co-authored using generative AI tooling?

Generated-by: Claude Code (Opus 4.8 [1M context])

[github-actions]

Backport auto-label report

This fix: PR was checked against each actively-supported release branch. release/* labels drive the post-merge backport, so add or remove one to change where this fix lands.

Release branch	Analysis
✅ release/v1.2	Change detected on this branch — label added; this fix is queued to backport here. Requested review from @xuang7.

Auto-label run.

[github-actions]

Automated Reviewer Suggestions

Based on the git blame history of the changed files, we recommend the following reviewers:

• Contributors with relevant context: @aglinxinyuan, @Ma77Ball
  You can notify them by mentioning @aglinxinyuan, @Ma77Ball in a comment.

[Copilot]

Pull request overview

Fixes preset updates by locating JSON-parsed presets using deep equality instead of reference equality.

Changes:

• Replaces indexOf lookups with deep-equality findIndex.
• Adds regression coverage for replacement, merging, and missing storage.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
preset.service.ts	Corrects preset replacement and removal lookup logic.
preset.service.spec.ts	Adds regression tests for affected update paths.

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