docs(cli): correct the stated cause of a bootstrap that never returns

src/config/env.sh

@@ -949,9 +949,9 @@ function bashunit::env::cleanup_run_output_dir() {
 # subshells never inherit EXIT traps, so a parallel worker cannot remove the
 # directory mid-run.
 # Set while a bootstrap file is being sourced, cleared immediately after. A
-# `source` that never returns -- special-builtin semantics on a syntax error or
-# a bare `exit` -- leaves it set, which is the only trace such a failure leaves
-# (#1179).
+# `source` that never returns -- a syntax error while `set -e` is active, or a
+# bare `exit` in the file -- leaves it set, which is the only trace such a
+# failure leaves (#1179).
 _BASHUNIT_LOADING_BOOTSTRAP=""
 
 function bashunit::env::report_unfinished_bootstrap() {

src/main/bench.sh

@@ -87,9 +87,11 @@ function bashunit::main::cmd_bench() {
       # Export all variables from the env file so they're available in subshells
       # (e.g., process substitution used in load_test_files)
       set -o allexport
-      # `source` is a special builtin: a syntax error in the file, or a bare
-      # `exit`, ends this shell here and nothing below runs. The marker is what
-      # the EXIT trap reports when it was never cleared (#1181).
+      # Two ways this never returns: a syntax error makes `source` return
+      # non-zero, which ends the shell because `set -e` is active here, and a
+      # bare `exit` in the file ends it regardless. Either way nothing below
+      # runs, so the marker is what the EXIT trap reports when it was never
+      # cleared (#1181).
       _BASHUNIT_LOADING_BOOTSTRAP="$boot_file"
       # shellcheck disable=SC1090,SC2086
       source "$boot_file" ${BASHUNIT_BOOTSTRAP_ARGS:-}
@@ -145,12 +147,11 @@ function bashunit::main::cmd_bench() {
   # error left the run with no tests, no summary and exit 0, and CI passed
   # having executed nothing (#1179).
   if [ -f "${BASHUNIT_BOOTSTRAP:-}" ]; then
-    # `source` is a POSIX special builtin: a syntax error in the file, or a
-    # bare `exit`, terminates this shell right here -- so nothing after the
-    # call can report it, and the run ended with no tests, no summary and
-    # exit 0 (#1179). Pre-validating with `bash -n` would cost an interpreter
-    # fork on every invocation, which the cold-start budget forbids, so leave
-    # a marker instead and let the EXIT trap notice it was never cleared.
+    # Two ways this never returns: a syntax error makes `source` return
+    # non-zero, which ends the shell because `set -e` is active here, and a
+    # bare `exit` in the file ends it regardless. Either way nothing below
+    # runs, so the marker is what the EXIT trap reports when it was never
+    # cleared (#1179).
     _BASHUNIT_LOADING_BOOTSTRAP="$BASHUNIT_BOOTSTRAP"
     # shellcheck disable=SC1090,SC2086
     source "$BASHUNIT_BOOTSTRAP" ${BASHUNIT_BOOTSTRAP_ARGS:-}

src/main/subcommands.sh

@@ -43,9 +43,11 @@ function bashunit::main::cmd_doc() {
         exit 1
       fi
     else
-      # `source` is a special builtin: a syntax error in the file, or a bare
-      # `exit`, ends this shell here and nothing below runs. The marker is what
-      # the EXIT trap reports when it was never cleared (#1181).
+      # Two ways this never returns: a syntax error makes `source` return
+      # non-zero, which ends the shell because `set -e` is active here, and a
+      # bare `exit` in the file ends it regardless. Either way nothing below
+      # runs, so the marker is what the EXIT trap reports when it was never
+      # cleared (#1181).
       _BASHUNIT_LOADING_BOOTSTRAP="$boot_file"
       # shellcheck disable=SC1090,SC2086
       source "$boot_file" ${BASHUNIT_BOOTSTRAP_ARGS:-}

src/main/test.sh

@@ -326,9 +326,11 @@ function bashunit::main::cmd_test() {
       # Export all variables from the env file so they're available in subshells
       # (e.g., process substitution used in load_test_files)
       set -o allexport
-      # `source` is a special builtin: a syntax error in the file, or a bare
-      # `exit`, ends this shell here and nothing below runs. The marker is what
-      # the EXIT trap reports when it was never cleared (#1181).
+      # Two ways this never returns: a syntax error makes `source` return
+      # non-zero, which ends the shell because `set -e` is active here, and a
+      # bare `exit` in the file ends it regardless. Either way nothing below
+      # runs, so the marker is what the EXIT trap reports when it was never
+      # cleared (#1181).
       _BASHUNIT_LOADING_BOOTSTRAP="$boot_file"
       # shellcheck disable=SC1090,SC2086
       source "$boot_file" ${BASHUNIT_BOOTSTRAP_ARGS:-}
@@ -666,12 +668,14 @@ function bashunit::main::cmd_test() {
   # error left the run with no tests, no summary and exit 0, and CI passed
   # having executed nothing (#1179).
   if [ -f "${BASHUNIT_BOOTSTRAP:-}" ]; then
-    # `source` is a POSIX special builtin: a syntax error in the file, or a
-    # bare `exit`, terminates this shell right here -- so nothing after the
-    # call can report it, and the run ended with no tests, no summary and
-    # exit 0 (#1179). Pre-validating with `bash -n` would cost an interpreter
-    # fork on every invocation, which the cold-start budget forbids, so leave
-    # a marker instead and let the EXIT trap notice it was never cleared.
+    # Two ways this never returns: a syntax error makes `source` return
+    # non-zero, which ends the shell because `set -e` is active here, and a
+    # bare `exit` in the file ends it regardless of `set -e`. Either way
+    # nothing after the call runs, and the run ended with no tests, no summary
+    # and exit 0 (#1179). Pre-validating with `bash -n` would cost an
+    # interpreter fork on every invocation, which the cold-start budget
+    # forbids, so leave a marker and let the EXIT trap notice it was never
+    # cleared.
     _BASHUNIT_LOADING_BOOTSTRAP="$BASHUNIT_BOOTSTRAP"
     # shellcheck disable=SC1090,SC2086
     source "$BASHUNIT_BOOTSTRAP" ${BASHUNIT_BOOTSTRAP_ARGS:-}