cgen: single-binary native build via jolt cgen-build (jolt-a7ds) (#150)

Fuse an app's native-compiled numeric-leaf fns plus its source into one
static executable: no sidecar .so, no toolchain on the target. The AOT path
(#148) already produced a prebuilt module + manifest; this links them into
the jpm-built exe so the app ships as a single file.

`jolt cgen-build -m NS -o OUT` stages a build dir (src/jolt-core symlinks
into the jolt tree, a generated cg.c of the hot fns, an uberscript bundle of
the app, and an entry that bakes the runtime, installs the native fns as var
roots, and runs -main), then runs `jpm build` there — declare-native builds
cg.a and declare-executable static-links it (jpm's create-executable marshals
the module cfns and calls its static entry at startup).

Build needs cc + jpm; the result needs neither. Mechanics that bit, codified
in cgen_build.janet: stdlib_embed slurps .clj cwd-relative so the build runs
in a repo-mirroring dir; jpm hardcodes ./project.janet and sets syspath=modpath;
the executable's dofile imports cg and static-links cg.a, neither ordered nor
release-built by default, so deps are wired explicitly; cleanup must lstat (the
tree symlinks must not be followed); the inner build runs --workers=1 so it
doesn't starve siblings in the parallel gate.

test/integration/cgen-build-test.janet builds the mandelbrot fixture, runs it
from a clean dir with no src/ and no cg.so, and checks the total at native
speed. Closes jolt-a7ds.

Co-authored-by: Yogthos <yogthos@gmail.com>

test/integration/cgen-build-test.janet

@@ -0,0 +1,51 @@
+# Single-binary native build (jolt-a7ds): `jolt cgen-build` fuses an app's hot
+# numeric-leaf fns (compiled to C) + the app source into ONE static executable —
+# no sidecar .so, no toolchain on the target. This test builds the fixture app to
+# a binary, runs it from a CLEAN dir (no src/, no cg.so) to prove it's
+# self-contained, and checks the result + native fn count. Skips with no cc.
+(import ../../src/jolt/cgen :as cgen)
+(import ../../src/jolt/cgen_build :as cb)
+
+(print "Single-binary native build (jolt-a7ds)...")
+
+(var failures 0)
+(defn check [label ok] (if ok (print "  ok: " label) (do (++ failures) (eprintf "  FAIL: %s" label))))
+
+(def home (os/cwd))                                       # the repo (gate runs here)
+(def fixture-root (string home "/test/fixtures/cgen-build"))
+
+(if (cgen/toolchain-available?)
+  (do
+    (def out (string (or (os/getenv "TMPDIR") "/tmp") "/jolt-cgen-build-test/app"))
+    (def r (cb/build-app {:main "cgapp" :out out :jolt-home home
+                          :source-roots [fixture-root]}))
+    (check "build reported the single native leaf (count-point)" (= 1 (r :native-count)))
+    (check "binary exists at :out" (os/stat out))
+
+    # Run from a CLEAN dir with NO src/ and NO cg.so beside it — proves the binary
+    # is self-contained (runtime needs neither the jolt tree nor a sidecar .so).
+    (def rundir (string (or (os/getenv "TMPDIR") "/tmp") "/jolt-cgen-build-run"))
+    (when (os/stat rundir) (each e (os/dir rundir) (os/rm (string rundir "/" e))) (os/rmdir rundir))
+    (os/mkdir rundir)
+    (def bin (string rundir "/app"))
+    (spit bin (slurp out))
+    (os/chmod bin 8r755)
+
+    (defn run-app [&opt n]
+      (def tmp (string rundir "/out.txt"))
+      (def f (file/open tmp :w))
+      (def code (os/execute (if n [bin (string n)] [bin]) :px {:out f} ))
+      (file/close f)
+      {:code code :out (string/trim (slurp tmp))})
+
+    (def res (run-app))
+    (check "exits 0" (= 0 (res :code)))
+    (check "self-contained binary computes the right mandelbrot total (n=200)"
+           (= "3288753" (res :out)))
+    (check "passes through command-line args (n=400)"
+           (= "13162060" ((run-app 400) :out))))
+  (print "  (toolchain absent — skipping single-binary build)"))
+
+(if (= 0 failures)
+  (print "All tests passed.")
+  (do (eprintf "%d cgen-build check(s) failed" failures) (os/exit 1)))