fix(core): keep a folder's pin when the folder lands (B148)

A folder pinned before its mkdir landed kept the placeholder uid in
pins.uid, which named no node once the landing moved the row to the
real uid. The landing now moves the pin with it.

docs/BUGS.md

@@ -12,6 +12,23 @@ Conventions:
 
 ---
 
+## B148 — A folder pinned before it has reached Drive loses its pin
+
+**Status:** Fixed (unverified).
+**Found:** 2026-10-04, while planning the move of queued ops to local ids: every table keyed by
+uid was checked for what happens when a placeholder lands, and `pins` was the one no landing
+touched.
+
+**Where:** `adopt_placeholder_row_tx` in `crates/pdfs-core/src/db/nodes.rs`.
+
+**Cause.** A folder made through the mount has a placeholder uid (`local~…`) until its mkdir lands.
+Pinning it then stored the placeholder in `pins.uid`. The landing moved the node row, the children
+and the queued ops to the real uid, but not the pin, which then named no node: the folder was no
+longer kept offline and the pin list showed an entry for nothing.
+
+**Fix.** The landing moves the pin to the real uid in the same transaction. A pin the real uid
+already has wins, and the placeholder's is dropped.
+
 ## B147 — A new file made under a name just renamed away can share the first file's node
 
 **Status:** Fixed (unverified).