Fleet UI: Multi-package add-conflict error copy (#49309)

[RachelElysia]

Issue

Resolves #49309.

Description

The frontend collapses every backend "already ..." conflict into the generic "installer available" flash, wiping the FMA / VPP / package-limit specificity from the design. This routes each backend message to its design-specific copy (title + fleet bolded), and handles the "different file type" error at the two Custom Package callsites by prepending the title from form context.

Also plumbs the software title through SoftwareTitleDetailsPage → AddPackageModal so the multi-package modal can produce the same design copy.

Screenrecording

Testing

• Added/updated automated tests
• QA'd all new/changed functionality manually

[codecov]

Codecov Report

❌ Patch coverage is 89.28571% with 3 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (feat/28108-multiple-custom-packages@f29ecfa). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
...ge/SoftwareCustomPackage/SoftwareCustomPackage.tsx	0.00%	1 Missing ⚠️
.../SoftwareAddPage/SoftwareCustomPackage/helpers.tsx	75.00%	1 Missing ⚠️
...tleDetailsPage/AddPackageModal/AddPackageModal.tsx	0.00%	1 Missing ⚠️

Additional details and impacted files

@@                          Coverage Diff                           @@
##             feat/28108-multiple-custom-packages   #49336   +/-   ##
======================================================================
  Coverage                                       ?   65.73%           
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  Files                                          ?     3768           
  Lines                                          ?   239429           
  Branches                                       ?    12725           
======================================================================
  Hits                                           ?   157387           
  Misses                                         ?    67220           
  Partials                                       ?    14822           

Flag	Coverage Δ
frontend	59.96% <89.28%> (?)

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[RachelElysia]

Quick pass — mostly clean, a few small notes. Feature-branch base so nothing here is release-critical.

Should fix

• frontend/pages/SoftwarePage/SoftwareAddPage/SoftwareCustomPackage/SoftwareCustomPackage.tsx:167 — the softwareTitle arg being passed to getErrorMessage is formData.software?.name, which is the File name (e.g. Zoom-6.4.pkg), not the software title. If formatDifferentFileTypeMessage ever fires here, the flash will bold the filename instead of the title. In practice the "different file type" error is only emitted by UpdateSoftwareInstaller (backend ee/server/service/software_installers.go:524) — SoftwareCustomPackage calls UploadSoftwareInstaller, which can't hit it — so this is dead defensive code today. Two options: (1) drop the arg here entirely and let it fall through, or (2) add a comment explaining why the filename is acceptable if you want to keep the safety net. AddPackageModal is doing the right thing already since it plumbs the real title.

Nit

• frontend/pages/SoftwarePage/SoftwareAddPage/helpers.tsx:26 — six sequential regex match()es for the same string is fine and readable, but if this grows again consider a [{ pattern, render }] table. Not blocking.
• helpers.tsx:66 — limitMatch extracts the count as a string via (\d+) and drops it back into JSX unchanged. Works, but a Number(limitMatch[2]) would document intent (and let TS catch a future regex tweak that broke the digit constraint). Nit.
• formatDifferentFileTypeMessage uses msg.includes(...) while the "already" formatters anchor with ^. Using includes is slightly more permissive — likely fine because the sentinel string is distinctive, but worth being aware of if another error message ever quotes this string.

Nice

• Test coverage on formatAlreadyAvailableInstallMessage is thorough — FMA / VPP / package / limit / two legacy forms / prefix-stripped / null / empty. Good defensive net for the regex refactor.
• Keeping the legacy SoftwareInstaller "X" already exists with fleet "Y" fallback rather than deleting it is the right call — that string is still emitted by alreadyExists(...).WithTeamName(...) in the mysql layer per the code comment.