fix(file-operations): unify same-folder and cross-folder paste #395

Split from the grouped rename and copy/paste report (#354, item 5 of 5).

Sibling issues already filed for other slices of that report: copy undo (#390), conflict dialog X (#391), destination selection (#392), rename caret (#394). This issue is the remaining product inconsistency between pasting into the current folder and pasting into a different folder — naming / collision policy — not those completion behaviors.

Strata version

Reproduced on Strata debug build at commit 183d744 with fixture source/report.txt and dest/report.txt.

What happened?

Copy/paste does not behave the same way when the destination is the current folder versus a different folder.

In practice:

• Pasting a file into the folder it already occupies silently creates name (1).ext (then (2), …) and never asks.
• Pasting that same file into another folder that already has name.ext raises “File already exists” with Replace / Skip / Cancel, and has no “keep both / unique name” choice.

That makes it hard to predict whether a paste will auto-rename, prompt, replace, or no-op.

Steps to reproduce

Use a writable fixture with source/report.txt and dest/report.txt (same basename, different files).

Same-folder paste (auto-duplicate)

1. Open source/.
2. Copy report.txt and paste into source/.
3. Observe a new report (1).txt with no dialog.

Cross-folder paste (conflict dialog)

1. Copy source/report.txt.
2. Open dest/ and paste.
3. Observe the “File already exists” dialog instead of a generated unique name.
4. Choose Replace, Skip, and Cancel on separate runs and compare outcomes.

Expected behavior

Same-folder and cross-folder paste share consistent naming and collision policy (auto unique name, prompt, or a prompt that includes “keep both”), and share the same dialog actions when a prompt is required.

Duplicate and clipboard paste into the source’s parent must stay on that shared path so Ctrl+V in the current folder and an explicit duplicate do not diverge again.

Selection / undo / dialog X belong to the sibling issues above; the unified paste path should use those once they exist.

Screenshots or video

Full walkthrough (~91s) — same-folder unique name, conflict dialog Cancel/Skip, Miller context check:

https://cursor.com/artifacts/v/art-86a1f3a7-9cee-47d1-8ac9-a381187a9b2b

Clean side-by-side (~28s) — silent report (1).txt, then conflict dialog → Replace:

https://cursor.com/artifacts/v/art-785334c0-28ba-46e3-b57f-36e626141119

Additional context

Paste enters BrowserState::start_transfer. transfer_has_collision returns false when the source equals the would-be target, so same-folder pastes bypass the dialog and take the path where local_operations allocates name (1).ext via duplicate_target. Only genuine cross-folder collisions reach confirm_replace_conflict, which offers Replace / Skip / Cancel with no generate-unique-name choice.

TransferConflict only has FailIfExists and ReplaceExisting — there is no keep-both / unique-name option for the cross-folder dialog.

Acceptance criteria

• Same-folder and cross-folder paste use one naming and collision policy, including generated unique names and conflict-resolved names.
• Duplicate, clipboard paste into the source folder, and clipboard paste into another folder share completion, selection, and undo behavior (via the sibling fixes).
• The conflict dialog, when shown, offers the same actions regardless of which path produced the collision; Cancel / Escape / X do not modify files.
• Automated tests cover: same-folder generated names, cross-folder unique-name or replace/skip outcomes under the chosen policy, and mixed multi-item pastes.

Labels suggestion: bug, UX