establishment: block stops being a name, and enumerate learns to page

P2 of docs/establishment-planes-plan.md. usb-storage serves nameless — one
process per stick cannot share an exclusive bind, and a second stick used to
die silently on -EBUSY before ever helloing. Its one hello now moves both
directions at once: the block-serving endpoint up, its controller channel
down. fat finds its volume through the manager — a new `.consumer` role asks
for the channel of the driver BOUND TO a device (distinct from the device's
reporter), found by enumerating the tree for the mass-storage identity.
fat stays single-volume; the boot-volume-by-content choice is M21.

The conversion immediately caught a live truncation of exactly the audit's
shape: ChildEntry grew to 32 bytes, one enumerate reply holds ~7, and a real
tree carries a dozen ACPI nodes before the first USB child — the storage
entry silently never fit (the protocol comment already said "paging joins
the protocol if a tree ever outgrows one packet"). enumerate is now paged:
Header.target is the start cursor, a short page is the end; device-list's
page-0 read is unchanged.

Grant rows move with the code: the block bind and fat's block open die, fat
gains open device-manager. Gate: 18 cases green including the registry
trio, device-list, and both IOMMU storage variants.

library/device/block/block.zig

@@ -7,10 +7,8 @@
 //! `runtime.dma.alloc`), so whole sectors move without crossing the IPC size
 //! limit — the same handoff usb-storage uses toward the controller.
 
-const channel = @import("channel");
 const envelope = @import("envelope");
 const ipc = @import("ipc");
-const time = @import("time");
 const block_protocol = @import("block-protocol");
 
 const Protocol = block_protocol.Protocol;
@@ -75,26 +73,7 @@ pub const Device = struct {
     }
 };
 
-/// One open attempt, no waiting — for a server that retries on its own
-/// timer (the fat service) instead of blocking its harness in here.
-pub fn tryOpen() ?Device {
-    if (channel.openEndpoint("block")) |handle| return .{ .endpoint = handle };
-    return null;
-}
-
-/// Open `/protocol/block`, retrying generously while the USB storage chain
-/// (controller reset, enumeration, mass-storage bring-up) comes up.
-pub fn open() ?Device {
-    // Patient: the whole USB storage chain (firmware discovery, xHCI reset and
-    // enumeration, mass-storage bring-up) must complete first, which can take
-    // tens of seconds under emulation.
-    var attempts: usize = 0;
-    // 30 s covers the slowest observed healthy chain (a flaky QEMU enumeration
-    // completed at ~24 s); a machine whose stick genuinely failed setup should
-    // not sit a further minute pretending otherwise.
-    while (attempts < 600) : (attempts += 1) {
-        if (channel.openEndpoint("block")) |handle| return .{ .endpoint = handle };
-        time.sleepMillis(50);
-    }
-    return null;
-}
+// There is deliberately no open-by-name here: `block` is not a registry name.
+// One storage process serves each volume, and a consumer receives its volume's
+// channel from the device manager (establishment by lineage, communication.md
+// "Establishment: two planes"), then wraps it: `block.Device{ .endpoint = c }`.