[PM-20344] Disallow multiple attachments with the same name, handle existing in zip export format

[mcamirault]

🎟️ Tracking

https://bitwarden.atlassian.net/browse/PM-20344

📔 Objective

Currently when a cipher has multiple attachments with the same filename only one of them will be included when exporting in Bitwarden's zip format. This PR handles conflicting attachment filenames by having duplicates use a numeric suffix, and also makes the overall attachment folder easier to parse by using cipher names instead of IDs for the folders that contain the individual attachments (again handling duplicate names by using a numeric suffix).

For example, consider a vault that has two ciphers with the same name ("Test Cipher"), and each cipher has two attachments whose names are the same (one has two called "foo.txt" and the other has two called "bar.txt"). The exported attachments folder structure will look like this:

attachments
└───Test Cipher
│   │   foo.txt
│   │   foo_1.txt
|
└───Test Cipher_1
    │   bar.txt
    │   bar_1.txt

This PR also adjusts the Vault item attachments component to no longer allow duplicate attachment names and show an error toast if a duplicate upload is attempted.

📸 Screenshots

Screen.Recording.2026-06-30.at.13.11.37.mov

[github-actions]

🤖 Bitwarden Claude Code Review

Overall Assessment: REQUEST CHANGES

Reviewed the attachment duplicate-name handling for the Bitwarden zip export and the new client-side guard against uploading duplicate attachment names. The export now folders attachments by cipher name (with (N) prefixes for duplicate cipher and attachment names) instead of cipher IDs, and the attachments component blocks duplicate uploads with an error toast. The new i18n key was correctly added to the browser, desktop, and web en locales, and test coverage was added on both the export service and the component.

Code Review Details

• ⚠️ : Unsanitized cipher.name used as zip folder name can break export or create unintended nested paths
  • libs/tools/export-vault-core/src/services/individual-vault-export.service.ts:123

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 96.55172% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 49.70%. Comparing base (e672eec) to head (e1aefd2).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...onents/attachments/cipher-attachments.component.ts	83.33%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #21596      +/-   ##
==========================================
+ Coverage   49.69%   49.70%   +0.01%     
==========================================
  Files        4119     4119              
  Lines      129334   129361      +27     
  Branches    19816    19819       +3     
==========================================
+ Hits        64271    64298      +27     
+ Misses      60298    60297       -1     
- Partials     4765     4766       +1     

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[nick-livefront]

Vault changes look good ✅

[nick-livefront]

@mcamirault FYI, some conflicts to fix!