Fixed command substitution behavior in shell expansion:

packages/bare-os-booter/lib/shell.js
$(...)/backticks are now enabled by default unless explicitly disabled via BARE_OS_SHELL_CMDSUBST=0|false|off.
Fixed sh -c exit/status propagation:

packages/bare-os-booter/lib/shell.js
Syncs BARE_OS_EXIT_STATUS after each executed statement so later commands in the same line (like echo $?) see the immediately previous status.
packages/bare-os-coreutils/src/sh.js
In -c mode, reads final BARE_OS_EXIT_STATUS back into ctx.exitCode for consistent result propagation.
Implemented trap behavior for requested scope (EXIT, INT, TERM):

packages/bare-os-booter/lib/shell.js
exit builtin now runs EXIT trap handler before requesting booter exit.
packages/bare-os-booter/index.js
Signal delivery for shell PID now triggers trap dispatch for INT/TERM.
Hardened ulimit -f invalid diagnostics:

packages/bare-os-coreutils/src/ulimit.js
Explicit invalid-value error for malformed -f setter input, with nonzero exit.
Supported-but-unimplemented setter values still return explicit unsupported-setter error.

packages/bare-os-seeder/kernel/etc/bare-os/posix_utilities.json

@@ -1,7 +1,7 @@
 {
   "schema": 2,
   "profileId": "bare-os-posix-like",
-  "generatedAt": "2026-04-27T12:30:48.768Z",
+  "generatedAt": "2026-04-27T12:41:02.630Z",
   "note": "Sparse POSIX Issue 7 coverage hints for /bin utilities. Omitted command names are not yet profiled here.",
   "commandIndex": [
     {