v0.317.0: a second copy counts only on a proven different disk; the no-drive install speaks in words (felhom.eu architecture/16, build A)

Tier-2 and the one-copy notice ask the host agent (POST /disks/same-disk, agent 0.157.0): different +
proven -> made and counted; same disk -> not made (D1); unknown (VM, hidden USB serial) -> made, not
counted, the row says why (D2); a NAS never counts and no longer hides the notice (R-1075). An older
agent keeps the st_dev rule, logged once. D4: a data-folder or media app on a box with no drive is
refused in words with a link to the drives page (R-1068's raw-error half). MinAgent 0.157.0.

Claude-Session: https://claude.ai/code/session_012qRErfCoiTkvDK9N5XHbzb

controller/internal/stacks/deploy_errors.go

@@ -28,6 +28,10 @@ var (
 	// deploy's own `up` makes BOTH fail, and the deploy then records „not deployed" over whatever
 	// containers the race left behind. Pinned by TestR634_StopAndStartRefuseADeployingStack.
 	ErrStackDeploying = errors.New("stack is being deployed")
+	// ErrNeedsDrive — a data-folder or media app on a box with NO drive (felhom.eu architecture/
+	// 16-storage-physical-identity.md §5, D4; R-1068). API: 400 with code "needs_drive" and a link to the
+	// drives page; the sentence never names the field. Pinned by TestD4_NoDriveRefusalSpeaksInWords.
+	ErrNeedsDrive = errors.New("a storage drive is needed")
 )
 
 // KeyMemoryOvercommitWarning is the soft overcommit warning's bundle key. It travels as a KEY from