feat(openkal-emscripten): the first implementation written above a C library (#393)

Every other implementation in this ecosystem is written on a kernel's own
interface: a register discipline, a trap instruction, a table of numbers.
Emscripten has no kernel to issue a call to; it has a C library over a
JavaScript host, and clause 2 of the specification permits exactly this
arrangement in as many words -- "an implementation may be built upon a C
library, beneath one, or without one".

TWELVE OF THE FIFTEEN INTERFACES, AND THE ABSENCE IS THE REPORT.
`openkal.process`, `openkal.exec` and `openkal.space` are not there: no fork,
no exec, no writable-then-executable memory, no second address space. A program
that uses one of those seventeen names fails at LINK naming the symbol, which is
clause 6.2's second time. Measured:

  wasm-ld: error: obj/main.o: undefined symbol: kal_process_spawn

Providing them so that they returned an error would be the shape the
specification forbids -- present and always failing, which the caller cannot
tell from a condition.

`openkal.task` is behind a feature, because `-pthread` selects a different C
library build, memory model and loader contract on this platform. Without it
the translation unit is empty and the eight symbols do not exist, which is the
same treatment the three absent interfaces get and for the same reason.

CONFORMANCE, measured with emsdk 6.0.9 under node: 86 held, 0 did not hold, 13
not observed. The exported surface is 86 names, twelve complete groups, three
absent groups, and nothing beginning with `kal_` the specification does not
name. The package's own CI asserts all four, plus the task gate in both
directions.

Both mirrors GET-verified byte for byte against the upstream tag archive:

  GLOBAL  github.com/mcpplibs/openkal-emscripten/archive/refs/tags/0.1.0.tar.gz
  CN      gitcode.com/mcpp-res/openkal-emscripten/releases/download/0.1.0/...
  sha256  9c5ca4ae4c3bb22b127e2fbf6ca5bd4ecbdd80eac4a28018e3deb0c7ebd07b6d
  bytes   39383, and `cmp` of the two downloads is silent

Listed for every platform because a platform table describes availability
rather than applicability. A project selects it with a conditional dependency
on `cfg(os = "emscripten")`, and one that selects it elsewhere fails at compile
time.

Co-authored-by: speak-agent <x.d2learn.org@gmail.com>

Author: Sunrisepeak

pkgs/o/openkal-emscripten.lua

@@ -0,0 +1,74 @@
+-- openkal-emscripten --- the first implementation written ABOVE a C library.
+--
+-- Every other implementation in this ecosystem is written on a kernel's own
+-- interface: a register discipline, a trap instruction, a table of numbers.
+-- Emscripten has no kernel to issue a call to; it has a C library over a
+-- JavaScript host, and clause 2 of the specification permits exactly this
+-- arrangement in as many words: "an implementation may be built upon a C
+-- library, beneath one, or without one."
+--
+-- Listed for every platform because a platform table describes availability
+-- rather than applicability. A project selects this implementation with a
+-- conditional dependency on cfg(os = "emscripten"); one that selects it
+-- elsewhere fails at compile time, which is the correct place for that
+-- failure.
+--
+-- IT PROVIDES TWELVE OF THE FIFTEEN INTERFACES, and the absence is the report.
+-- `openkal.process`, `openkal.exec` and `openkal.space` are not there: no
+-- fork, no exec, no writable-then-executable memory, no second address space.
+-- A program that uses one of those seventeen names fails at LINK naming the
+-- symbol, which is clause 6.2's second time -- the mechanism rather than a
+-- defect. Measured:
+--
+--   wasm-ld: error: obj/main.o: undefined symbol: kal_process_spawn
+--
+-- `openkal.task` is behind the `threads` feature, because `-pthread` selects a
+-- different C library build, memory model and loader contract on this
+-- platform. Without the feature its translation unit is empty and the eight
+-- symbols do not exist, which is the same treatment the three absent
+-- interfaces get.
+--
+-- Conformance, measured with emsdk 6.0.9 under node: 86 held, 0 did not hold,
+-- 13 not observed.
+package = {
+    spec        = "1",
+    namespace   = "mcpplibs",
+    name        = "openkal-emscripten",
+    description = "An implementation of openkal for Emscripten, written above a C library rather than beneath one",
+    licenses    = {"Apache-2.0"},
+    repo        = "https://github.com/mcpplibs/openkal-emscripten",
+    type        = "package",
+
+    xpm = {
+        linux = {
+            ["0.1.0"] = {
+                url    = {
+                    GLOBAL = "https://github.com/mcpplibs/openkal-emscripten/archive/refs/tags/0.1.0.tar.gz",
+                    CN     = "https://gitcode.com/mcpp-res/openkal-emscripten/releases/download/0.1.0/openkal-emscripten-0.1.0.tar.gz",
+                },
+                sha256 = "9c5ca4ae4c3bb22b127e2fbf6ca5bd4ecbdd80eac4a28018e3deb0c7ebd07b6d",
+            },
+        },
+        macosx = {
+            ["0.1.0"] = {
+                url    = {
+                    GLOBAL = "https://github.com/mcpplibs/openkal-emscripten/archive/refs/tags/0.1.0.tar.gz",
+                    CN     = "https://gitcode.com/mcpp-res/openkal-emscripten/releases/download/0.1.0/openkal-emscripten-0.1.0.tar.gz",
+                },
+                sha256 = "9c5ca4ae4c3bb22b127e2fbf6ca5bd4ecbdd80eac4a28018e3deb0c7ebd07b6d",
+            },
+        },
+        windows = {
+            ["0.1.0"] = {
+                url    = {
+                    GLOBAL = "https://github.com/mcpplibs/openkal-emscripten/archive/refs/tags/0.1.0.tar.gz",
+                    CN     = "https://gitcode.com/mcpp-res/openkal-emscripten/releases/download/0.1.0/openkal-emscripten-0.1.0.tar.gz",
+                },
+                sha256 = "9c5ca4ae4c3bb22b127e2fbf6ca5bd4ecbdd80eac4a28018e3deb0c7ebd07b6d",
+            },
+        },
+    },
+
+    -- The package's own manifest, inside the tarball's wrap directory.
+    mcpp = "*/mcpp.toml",
+}