#22540: fix(signal): preserve original filename in outbound attachments

## Summary - **Bug**: Signal outbound attachments arrive with UUID-only filenames instead of the original filename - **Root cause**: `resolveOutboundAttachmentFromUrl` in `src/media/outbound-attachment.ts` discards `media.fileName` returned by `loadWebMedia`, never passing it to `saveMediaBuffer` - **Fix**: Pass `media.fileName` as the `originalFilename` parameter to `saveMediaBuffer` Fixes #22487 ## Problem When sending a file via Signal, the file arrives in the recipient's client with a UUID name (e.g. `533d51fb-ca5b-42ef-ab0d-a1bc68e10892.zip`) instead of the original filename. The root cause is in `resolveOutboundAttachmentFromUrl`: 1. `loadWebMedia()` returns `{ buffer, contentType, kind, fileName }` — `fileName` is populated from `path.basename(mediaUrl)` 2. `saveMediaBuffer()` already supports an `originalFilename` parameter (5th arg) that embeds the name in the stored path as `{sanitized}---{uuid}.ext` 3. But `resolveOutboundAttachmentFromUrl` never passes `media.fileName` through — it calls `saveMediaBuffer` with only 4 args **Before fix:** ``` Input: mediaUrl = "/path/to/MyDocument.txt" Output: saved path = "07ea27ef-66d6-4da8-918d-bcef93d25a5c.txt" ``` ## Changes - `src/media/outbound-attachment.ts` — pass `media.fileName` to `saveMediaBuffer` as the 5th argument - `src/media/outbound-attachment.test.ts` — new regression test **After fix:** ``` Input: mediaUrl = "/path/to/MyDocument.txt" Output: saved path = "MyDocument---711c4d08-d9f5-4b7e-82d3-ee49bdebce7d.txt" ``` ## Test plan - [x] New test: `outbound-attachment.test.ts` — verifies filename preservation for normal files and extensionless files - [x] All 18 existing `store.test.ts` tests pass - [x] Format check passes (`oxfmt --check`) ## Effect on User Experience **Before:** Every file sent via Signal arrives with a UUID filename (e.g. `533d51fb-...-.zip`), confusing recipients who download the file. **After:** Files arrive with their original filename preserved (e.g. `MyDocument.zip`). <!-- greptile_comment --> <h3>Greptile Summary</h3> Fixes Signal outbound attachments to preserve original filenames instead of UUID-only names. The fix passes `media.fileName` from `loadWebMedia` through to `saveMediaBuffer` as the 5th argument (`originalFilename`), enabling the existing filename-embedding feature that creates paths like `MyDocument---{uuid}.txt` instead of just `{uuid}.txt`. - Fixed `src/media/outbound-attachment.ts:18` by adding `media.fileName` as the 5th parameter to `saveMediaBuffer` - Added regression tests in `src/media/outbound-attachment.test.ts` covering normal files and extensionless files - Updated `CHANGELOG.md` with user-facing fix description <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk - The fix is a simple one-line change that passes an existing parameter to an already-tested function. The `saveMediaBuffer` function already has comprehensive test coverage for the `originalFilename` parameter (lines 236-303 in `store.test.ts`), and the new regression tests verify the end-to-end behavior. The change is backwards-compatible (passing `undefined` falls back to UUID-only behavior), and the logic matches the PR description perfectly. - No files require special attention _{Last reviewed commit: 5505e23} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->