docs: R-200 Part 0 shipped; R-203 recorded (mandatory userdata dir missing from the offsite snapshot while the run says ok)

CONTEXT.md

@@ -1672,6 +1672,33 @@ Last updated: 2026-06-13 (v0.60.0 backlog-Medium cleanup)
 
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+## R-203 (2026-08-04) — a MANDATORY userdata directory can be absent from the off-site snapshot while the run says `ok`
+
+Found live on demo-hp while staging the R-201 drill, and it **halted that drill**.
+
+`NamespaceRoot(drivePath, inGuestDrive)` (`appbackup/paths.go:28-33`) appends the `felhom-data` segment
+**when the drive IS the system data path** — `m.namespaceRoot` = `NamespaceRoot(drivePath, drivePath !=
+m.systemDataPath)` (`backup/backup.go:331`). The deploy-time bind does not: `${USERDATA_PATH}` is
+`<HDD_PATH>/userdata` (`stacks/classify_binds.go:14`).
+
+With `system_data_path: /mnt/sys_drive` and `calibre-web` deployed at `HDD_PATH=/mnt/sys_drive`:
+
+    live bind (files land here):  /mnt/sys_drive/userdata/media/books           ← exists
+    capture set looked for:       /mnt/sys_drive/felhom-data/userdata/media/books ← does not
+
+**The same compose used BOTH roots** — `${IMPORT_PATH}` resolved *with* the segment,
+`${USERDATA_PATH}` *without*. The run logged one `[WARN] mandatory data path missing on disk, skipped
+from offsite`, then `0 mandatory path(s)` and **`backup OK: 3 app(s), 3 snapshot(s)`**, with
+`last_status: ok`. Nothing customer-visible or hub-visible said the directory was dropped.
+
+**Not established:** whether `HDD_PATH == system_data_path` is a supported deploy. It was accepted
+(HTTP 202) one call after the NAS path was correctly refused (R-108). **Either branch is a defect** —
+broken resolution, or a missing refusal.
+
+**Two things a fix must do:** make the two roots one function, and make a skipped **MANDATORY** path a
+customer/hub-visible signal rather than a container-log WARN. `opengist`/`privatebin` declare no
+mandatory userdata paths and are unaffected.
+
 ## R-200 (v0.195.0) — the offsite key recovery diagnostic
 
 `--recover-offsite-check` is a `docker exec` escape hatch (the `--print-reset-code` shape), NOT a page