[ccoventry]

Release note: none

Part of #1107 (audit batch B2: frontend duplicates).

What changes

No visible change: every size and file name reads exactly as before. The copies go.

• File name from a path: fileNameOf in path_display.js already existed, yet four modules defined their own fileName (batch_catch_up.js, combine_clips.js, render_history.js, split_pane.js, which analyzer_pane.js imported from) and nine more inlined split(/[\\/]/).pop(). All use fileNameOf now. The two sites that showed the whole path when the name came out empty (batch_catch_up.js, project_session.js) still do (fileNameOf(p) || p).
• Byte sizes: new byte_size.js with BYTES_PER_KB/MB/GB/TB (standard section 4: no magic numbers) and the two formats that were copied:
  • gbOrMbText ("3.00 GB" / "20.9 MB"): was in batch_results.js and audit_duplicates.js.
  • renderSizeText(bytes, gbDecimals) (STRINGS.RENDER.fileSizeGb/Mb): was in render_pane.js, render_while_capturing.js and take_cleanup.js, which differ only in GB decimals (kept: 2, 1, 2).
  • setup_checklist.js, hd_progress.js, folder_pools.js, auditor_pane.js, capture_pane.js, scan_workers.js keep their own formats but use the constants.
• shared_helpers_only.test.js: fails on a new split(/[\\/]/).pop() outside path_display.js or a 1024 * 1024 * 1024 / 1024 ** 3 outside byte_size.js, so the copies don't come back.

Decisions

• Formats not unified. The audit suggested one formatter "with the variants as options". Unifying would change what some tabs show (decimals, TB handling), and this batch is behaviour-preserving, so only the identical copies were merged. Whether every tab should show sizes one way is a UI question for the user (noted on [Chore] Audit the codebase's health, legibility and organisation #1107).
• Left alone: analyzer_damage.js's sizeText (MB/KB, and the web analyzer keeps a checked copy of analyzer code), and capture_pane.js's free-space warnings, which divide by 1e9 (decimal GB) where the rest of the app uses 1024-based GB. That one is a real inconsistency (the Capture tab's "not enough space" numbers are about 7% bigger than the same bytes elsewhere) but fixing it changes what users see, so it is listed on [Chore] Audit the codebase's health, legibility and organisation #1107 for a separate PR.
• analyzer_pane.js's private formatDuration (same name as rescan_estimate.js's, different output) is left for the analyzer_pane split (B7), which moves that code anyway.

Test done

• npm run test:unit: 122 files, 1,097 tests pass (adds byte_size.test.js, shared_helpers_only.test.js).
• CI=1 npx playwright test (all specs, including app-boot.spec.js), own port: 449 passed.
• No Rust changes.

🤖 Generated with Claude Code

[ccoventry]

Review: ready to merge.

I compared every call site with the old code:

• fileNameOf (String(path || '').split(/[\\/]/).pop()) gives the same result for every string path these sites pass. The two that fell back to the whole path (batch_catch_up, project_session) keep their || path.
• gbOrMbText is the same as the old wastedSizeText and batch_results.formatBytes. renderSizeText(bytes, 2|1) is the same as take_cleanup, render_while_capturing and render_pane. One tiny difference: render_pane.formatFileSize now runs Number() on its input, so a non-number shows "0 MB" instead of "NaN MB". Not reachable from real data.
• The removed exports (split_pane.fileName, batch_results.formatBytes) had no other importers. setup_checklist.formatBytes is unchanged and still imported by movie_copy.js.
• Nit, not worth a CI run: render_history.js keeps two blank lines where fileName was.

Merge notes:

• Analyzer: the Explorer browser moves to its own module, and its path rules get tests (part of #1107) #1173 will conflict in analyzer_pane.js, in two hunks. Imports: keep both the path_display.js import and Analyzer: the Explorer browser moves to its own module, and its path rules get tests (part of #1107) #1173's analyzer_browser.js imports and re-export. Split toast: keep fileNameOf(w.path) together with Analyzer: the Explorer browser moves to its own module, and its path rules get tests (part of #1107) #1173's await relistFolderOf(path);.
• Capture: after Studio closes or crashes mid-batch, it offers to capture the clips the game never got to (#20, part of #545) #1171 (feat/capture-recovery-20) adds path.split(/[\\/]/).pop() || path in batch_resume.js, which this PR's shared_helpers_only.test.js will fail once Capture: after Studio closes or crashes mid-batch, it offers to capture the clips the game never got to (#20, part of #545) #1171 merges dev in. The fix there is fileNameOf(path) || path.
• Capture tab's not-enough-space numbers use different gigabytes from the rest of the app #1181's fix is stacked on this branch as Capture tab: not-enough-space numbers in the same gigabytes as the rest of the app (#1181) #1183.