fix(nc/webdav): honour Overwrite on MOVE; restore-onto-existing → 412

Closes G4 / G5 / K5.

handle_move now resolves the destination once before the file/folder
dispatch and applies RFC 4918 §9.9.4:

  - Overwrite: F on a collision → 412 Precondition Failed, source
    untouched, destination untouched.
  - Overwrite: T (or absent) on a collision → delete the existing
    destination, then proceed → 204 No Content.
  - No collision → 201 Created (unchanged).

The same destination lookup powers the 201-vs-204 status decision, so
adding the precondition guard adds zero extra DB hits on the happy
path.

handle_restore now catches the unique-index collision out of
restore_item and returns 412 instead of letting it bubble as 500.
Mirrors the G4 semantics for the trashbin surface (restore has no
Overwrite header so the refusal is unconditional; client resolves by
renaming the live file first).

Sabre/DAV's CorePlugin and our test pins agreed independently — NC
clients expect this exact behavior, and the new G5b/G5c positive-case
tests guard against a regression that hard-rejected every MOVE.

tests/webdav/test_nc_move_copy_delete_trash.sh

@@ -108,64 +108,65 @@ STATUS=$(nc_curl -o /dev/null -w "%{http_code}" -X MOVE \
 pass "G3: URL-encoded destination decoded correctly"
 
 # ─────────────────────────────────────────────────────────────
-# G4 / G5 — Overwrite header behaviour (pinned: not honoured)
+# G4 / G5 / G5b — Overwrite header (RFC 4918 §9.9.4)
+#
+# G4  : Overwrite: F + destination exists → 412 (refuse)
+# G5  : Overwrite: T + destination exists → 204 (replace)
+# G5b : Overwrite header absent → default T per spec → 204
+# G5c : Overwrite: F + destination ABSENT → 201 (normal create)
 # ─────────────────────────────────────────────────────────────
-echo "  G4: MOVE with Overwrite: F to an existing path (pinned: SERVER BUG — leaks 500)"
+echo "  G4: MOVE with Overwrite: F to an existing path → 412"
 put_nc_file "g4-src.txt"  "G4 source"
 put_nc_file "g4-dest.txt" "G4 destination (should remain)"
 STATUS=$(nc_curl -o /dev/null -w "%{http_code}" -X MOVE \
     -H "Destination: $NC_FILES_BASE/g4-dest.txt" \
     -H "Overwrite: F" \
     "$NC_FILES_BASE/g4-src.txt")
-case "$STATUS" in
-    500)
-        # KNOWN BUG: the NC MOVE handler doesn't intercept
-        # `Overwrite: F` and doesn't map the domain-layer
-        # `AlreadyExists` to 412. It tries to rename, the
-        # storage layer 409s "name already taken", and the
-        # handler bubbles that up as 500. NC desktop will
-        # interpret 500 as "server transient error" and
-        # retry, which masks the real conflict.
-        #
-        # The right fix is in `interfaces/nextcloud/webdav_handler.rs::handle_move`:
-        # check `Overwrite: F` BEFORE attempting the rename, return
-        # 412 on collision; OR when Overwrite is omitted/T, delete
-        # the destination first (replace semantics, → 204).
-        pass "G4: Overwrite: F → 500 (KNOWN BUG: should be 412 per RFC 4918 §9.9.4 — pinned)"
-        ;;
-    412)
-        fail "G4: server now correctly returns 412 for Overwrite: F. Bug is fixed — update this pin to assert == 412."
-        ;;
-    201|204)
-        fail "G4: server now silently overwrites despite Overwrite: F (status $STATUS) — this would be a *different* bug; RFC requires 412."
-        ;;
-    *)
-        fail "G4: unexpected status $STATUS"
-        ;;
-esac
+[[ "$STATUS" == "412" ]] \
+    || fail "G4: expected 412 Precondition Failed for Overwrite: F + collision, got $STATUS"
+# Source and destination must both still exist with original contents.
+[[ "$(nc_status_propfind_depth0 "$NC_FILES_BASE/g4-src.txt")" == "207" ]] \
+    || fail "G4: source disappeared after 412 (move should have been refused, not partially applied)"
+[[ "$(nc_status_propfind_depth0 "$NC_FILES_BASE/g4-dest.txt")" == "207" ]] \
+    || fail "G4: destination disappeared after 412"
+pass "G4: Overwrite: F + collision → 412, source and destination intact"
 
-echo "  G5: MOVE with Overwrite: T to an existing path (pinned: SERVER BUG — leaks 500)"
+echo "  G5: MOVE with Overwrite: T to an existing path → 204"
 put_nc_file "g5-src.txt"  "G5 source"
 put_nc_file "g5-dest.txt" "G5 destination (to be replaced)"
 STATUS=$(nc_curl -o /dev/null -w "%{http_code}" -X MOVE \
     -H "Destination: $NC_FILES_BASE/g5-dest.txt" \
     -H "Overwrite: T" \
     "$NC_FILES_BASE/g5-src.txt")
-case "$STATUS" in
-    500)
-        # Same root cause as G4: the handler doesn't consider the
-        # `Overwrite` header at all. With `Overwrite: T` it SHOULD
-        # delete the destination first and proceed (→ 204), but
-        # today it bubbles up the storage-layer "Already Exists".
-        pass "G5: Overwrite: T → 500 (KNOWN BUG: should be 204 per RFC 4918 §9.9.4 — pinned)"
-        ;;
-    204)
-        fail "G5: server now correctly returns 204 for Overwrite: T. Bug is fixed — update this pin to assert == 204."
-        ;;
-    *)
-        fail "G5: unexpected status $STATUS"
-        ;;
-esac
+[[ "$STATUS" == "204" ]] \
+    || fail "G5: expected 204 No Content for Overwrite: T + collision, got $STATUS"
+# Source gone, destination now has the source's content.
+[[ "$(nc_status_propfind_depth0 "$NC_FILES_BASE/g5-src.txt")" == "404" ]] \
+    || fail "G5: source still present after successful overwrite move"
+DEST_BODY=$(nc_curl -s "$NC_FILES_BASE/g5-dest.txt")
+[[ "$DEST_BODY" == "G5 source" ]] \
+    || fail "G5: destination content not replaced; got '$DEST_BODY'"
+pass "G5: Overwrite: T + collision → 204, destination replaced"
+
+echo "  G5b: MOVE with no Overwrite header to an existing path → 204 (default T)"
+put_nc_file "g5b-src.txt"  "G5b source"
+put_nc_file "g5b-dest.txt" "G5b destination (default-overwrite target)"
+STATUS=$(nc_curl -o /dev/null -w "%{http_code}" -X MOVE \
+    -H "Destination: $NC_FILES_BASE/g5b-dest.txt" \
+    "$NC_FILES_BASE/g5b-src.txt")
+[[ "$STATUS" == "204" ]] \
+    || fail "G5b: expected 204 No Content for missing Overwrite header (default T), got $STATUS"
+pass "G5b: absent Overwrite defaults to T → 204"
+
+echo "  G5c: MOVE with Overwrite: F to a NEW path → 201 (no collision to refuse)"
+put_nc_file "g5c-src.txt"  "G5c source"
+STATUS=$(nc_curl -o /dev/null -w "%{http_code}" -X MOVE \
+    -H "Destination: $NC_FILES_BASE/g5c-fresh-dest.txt" \
+    -H "Overwrite: F" \
+    "$NC_FILES_BASE/g5c-src.txt")
+[[ "$STATUS" == "201" ]] \
+    || fail "G5c: expected 201 Created for Overwrite: F + no collision, got $STATUS"
+pass "G5c: Overwrite: F + new destination → 201"
 
 # ─────────────────────────────────────────────────────────────
 # G6 — MOVE a folder (subtree)
@@ -408,28 +409,17 @@ TRASHED_ID=$(basename "$TRASHED_HREF")
 STATUS=$(nc_curl -o /dev/null -w "%{http_code}" -X MOVE \
     -H "Destination: $NC_FILES_BASE/k5-conflict.txt" \
     "$NC_TRASH_BASE/$TRASHED_ID")
-case "$STATUS" in
-    201|204)
-        pass "K5: restore-onto-existing → $STATUS (current behaviour pinned: collision NOT prevented at this layer)"
-        ;;
-    412)
-        pass "K5: restore-onto-existing → 412 (current behaviour pinned: precondition-style refusal)"
-        ;;
-    409)
-        pass "K5: restore-onto-existing → 409 (current behaviour pinned: name conflict)"
-        ;;
-    500)
-        # Same shape as the G4/G5 bug — restore is a MOVE under
-        # the hood, and the handler doesn't catch the storage-
-        # layer "Already Exists" before it becomes an internal
-        # error. Pinned because that's the actual current
-        # behaviour, not because it's correct.
-        pass "K5: restore-onto-existing → 500 (KNOWN BUG: same root cause as G4/G5 — pinned)"
-        ;;
-    *)
-        fail "K5: unexpected status $STATUS — pin needs reviewing"
-        ;;
-esac
+[[ "$STATUS" == "412" ]] \
+    || fail "K5: expected 412 Precondition Failed for restore-onto-existing, got $STATUS"
+# The trashed item must still be in the trash (refused restore mustn't
+# half-delete the trash row).
+[[ -n "$(extract_response_href_containing "$(nc_curl -X PROPFIND -H "Depth: 1" "$NC_TRASH_BASE/")" "k5-doomed")" ]] \
+    || fail "K5: trash entry vanished after a refused restore"
+# The conflicting live file must still be there with its original content.
+LIVE_BODY=$(nc_curl -s "$NC_FILES_BASE/k5-conflict.txt")
+[[ "$LIVE_BODY" == "k5 original (stays)" ]] \
+    || fail "K5: conflicting live file mutated; got '$LIVE_BODY'"
+pass "K5: restore-onto-existing → 412, trash row and live file intact"
 
 # ── Cleanup ──────────────────────────────────────────────────────────────────
 echo "  cleanup: empty trash + remove residual fixtures"