diff --git a/pkgs/a/aarch64-virt-rt.lua b/pkgs/a/aarch64-virt-rt.lua
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+++ b/pkgs/a/aarch64-virt-rt.lua
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+-- aarch64-virt-rt — board support for QEMU's aarch64 `virt` machine, on the
+-- zero-libc tier.
+--
+-- Form A (`mcpp = "*/mcpp.toml"`) rather than an inline Form B table, for the
+-- reason `riscv-virt-rt` records at length: this package ships a `build.mcpp`,
+-- and mcpp looks for that at the PACKAGE ROOT. Form B would leave it one level
+-- down inside the tarball's wrap directory, unfound, and the package would
+-- resolve, compile its module, and then link against nothing.
+--
+-- ⭐ `deps` NAMES THE EMULATOR AND NOTHING ELSE, AND THE ABSENCE OF A C LIBRARY
+-- IS THE POINT OF THE PACKAGE.
+--
+-- `riscv-virt-rt`'s three platform blocks name both `xim:picolibc-riscv` and
+-- `xim:qemu-riscv`, and the picolibc entry is there because of a regression
+-- that took five versions to surface: a manifest's `[xlings] deps` is a
+-- DECLARATION and installs nothing, so the target's C library has to be made to
+-- EXIST by the index descriptor, whose platform `deps` ARE installed with the
+-- package.
+--
+-- This board is on the zero-libc tier and references no C library symbol, so
+-- there is nothing for it to install. `aarch64-none-elf` carries an empty
+-- C-library column in mcpp's target table, which means a project targeting it
+-- begins on that tier without asking. `xim:picolibc-aarch64` exists and a
+-- project that wants it declares it — that is the project's choice, and naming
+-- it here would make the board the thing that decided.
+--
+-- ⚠️ THE EMULATOR IS STILL DECLARED, AND FOR THE OTHER HALF OF THE SAME REASON.
+-- Nothing else installs it either, and a board that resolves and then cannot
+-- run is the failure `mcpp run` reports as "no runner is configured" — true in
+-- general and not the cause. The package's own build program says so through
+-- `mcpp::warning()` when it happens, which is a diagnostic rather than a
+-- substitute for the dependency.
+--
+-- ⭐ WHY THIS PACKAGE EXISTS AT ALL: the board-package model had been validated
+-- by exactly one board, and a model validated by one board cannot be
+-- distinguished from a model that happens to fit that board. Measured from the
+-- two build programs' own cache records — the engine's account of what each
+-- emitted, not a reading of their source:
+--
+--     riscv-virt-rt      ldflag runner
+--     aarch64-virt-rt    ldflag runner
+--
+-- The same two directives. The C library shows up as different VALUES under
+-- `ldflag`, not as a directive one board needs and the other cannot express.
+-- The board-package interface is therefore complete, and "board package" and
+-- "C library provider" are separable roles.
+package = {
+    spec        = "1",
+    namespace   = "mcpplibs",
+    name        = "aarch64-virt-rt",
+    description = "Board support for QEMU's aarch64 virt machine — memory layout, startup, console and runner, on the zero-libc tier",
+    licenses    = {"Apache-2.0"},
+    repo        = "https://github.com/mcpplibs/aarch64-virt-rt",
+    type        = "package",
+
+    xpm = {
+        linux = {
+            deps = { "xim:qemu-arm@9.2.4-1" },
+            ["0.1.0"] = {
+                url    = {
+                    GLOBAL = "https://github.com/mcpplibs/aarch64-virt-rt/archive/refs/tags/0.1.0.tar.gz",
+                    CN     = "https://gitcode.com/mcpp-res/aarch64-virt-rt/releases/download/0.1.0/aarch64-virt-rt-0.1.0.tar.gz",
+                },
+                sha256 = "776b7fe4a801194db31e8136febef610ca756178122b1118df322aaadb0666a0",
+            },
+        },
+        macosx = {
+            deps = { "xim:qemu-arm@9.2.4-1" },
+            ["0.1.0"] = {
+                url    = {
+                    GLOBAL = "https://github.com/mcpplibs/aarch64-virt-rt/archive/refs/tags/0.1.0.tar.gz",
+                    CN     = "https://gitcode.com/mcpp-res/aarch64-virt-rt/releases/download/0.1.0/aarch64-virt-rt-0.1.0.tar.gz",
+                },
+                sha256 = "776b7fe4a801194db31e8136febef610ca756178122b1118df322aaadb0666a0",
+            },
+        },
+        windows = {
+            deps = { "xim:qemu-arm@9.2.4-1" },
+            ["0.1.0"] = {
+                url    = {
+                    GLOBAL = "https://github.com/mcpplibs/aarch64-virt-rt/archive/refs/tags/0.1.0.tar.gz",
+                    CN     = "https://gitcode.com/mcpp-res/aarch64-virt-rt/releases/download/0.1.0/aarch64-virt-rt-0.1.0.tar.gz",
+                },
+                sha256 = "776b7fe4a801194db31e8136febef610ca756178122b1118df322aaadb0666a0",
+            },
+        },
+    },
+
+    -- The package's own manifest, inside the tarball's wrap directory.
+    mcpp = "*/mcpp.toml",
+}