Say when hosted rollback removes go.work.sum

The docs said rollback deletes a go.work.sum "the pin alone created".
Hosted mode keeps no record of which files existed before a pin, so it
deletes any go.work.sum that stripping the Socket lines leaves empty,
including one a user created empty. go never writes an empty
go.work.sum, so that only happens to a file made empty by hand. Say
so, rather than claim rollback can tell the cases apart.

Assisted-by: Claude Code:claude-opus-5-5

Author: mikolalysenko

crates/socket-patch-core/src/patch/redirect/upstream/golang.rs

@@ -12,7 +12,8 @@
 //! beside a go.mod directive (its pin pruned it there); for a go.work
 //! directive, which prunes nothing, only when no sum file holds it, into
 //! each that held the socket pair, else go.work.sum. A go.work.sum left
-//! empty was created for the pin and is removed.
+//! empty is removed: nothing records whether it existed before the pin,
+//! and go never writes an empty one, so the pin almost always created it.
 //!
 //! A directive the hosted run took over from the user (a pre-existing
 //! `replace` it superseded) is not recorded anywhere, so the restore always
@@ -225,7 +226,7 @@ pub(crate) async fn restore(
         if view.read(&file).await.ok().flatten().as_deref() == Some(text.as_str()) {
             continue;
         }
-        // The hosted run created go.work.sum for the pin alone.
+        // go never writes an empty go.work.sum: the pin created it.
         if file == GO_WORK_SUM && text.is_empty() {
             view.remove(&file);
         } else {

docs/ecosystems.md

@@ -1591,7 +1591,9 @@ source `go.work`, hosted pins checked against `go.work.sum`), `remove` and
 `vendor --revert` drop the replace from `go.work` byte for byte (the vendored
 ledger records the wiring file as `go.work`), and `rollback` of a hosted pin
 removes the `go.work` replace and the Socket lines of `go.work.sum`, deletes a
-`go.work.sum` the pin alone created, and puts the upstream pair back only
+`go.work.sum` those lines leave empty (hosted mode keeps no record of whether
+the file existed before the pin; go never writes an empty one, so only a
+`go.work.sum` you created empty yourself is lost), and puts the upstream pair back only
 where no sum file still holds it (a member's `go.mod` pin rolled back with it
 gets the pair back in that member's `go.sum`, as every `go.mod` pin does). A committed workspace `vendor/` directory
 needs `go work vendor` after any of these