Port onto libakstdlib 2b79aca and convert the eight bool predicates

akbasic's src/ now calls libakstdlib 313 times and raw libc 7 -- 2.2%
bypassed, against 86.4% on the same tree before this. The submodule bump
669b2b3 -> 2b79aca needed no source change of its own: the release is
drop-in for what akbasic already used.

Seven of the eight sites the earlier port left on raw libc change their own
signature rather than swallowing an error, per andrew's ruling on
libakstdlib#38. word_is, the is_waiting_for pair, the scanner's is_at_end,
peek, peek_next and match_next_char, format.c's overflow, and sink_akgl's
scroll/newline/putchar_at/echo_line/edit_key chain all return an
akerr_ErrorContext * and hand the answer back through an out parameter.
is_waiting_for and is_waiting_for_any are a public header change; every
call site that used one as a term in a condition hoists it into a
statement first.

verb_compare is the eighth and stays on strcmp. bsearch(3) fixes the
comparator's signature, so there is no out parameter to report through --
which is what libakstdlib#38 concluded. It carries a comment saying so and
saying why the bypass is safe there.

Six snprintf sites stay raw because they want truncation as an answer
rather than an error, and aksl_snprintf cannot express that until
libakstdlib#34 hands the required length back. Each of the six says so at
the site. Two of them, in host.c, are a latent defect rather than a
decision: a host type name over 31 characters truncates silently and two
sharing a prefix then collide, where structtype.c refuses the same case.

DLOAD leaked a file descriptor. Its read loop sat inside an ATTEMPT and the
PASS in it returned past CLEANUP, so a scan error left the file open.
Hoisting the loop into its own helper to convert fgets fixes it.

Refs libakstdlib#26, libakstdlib#38

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

include/akbasic/environment.h

@@ -156,18 +156,32 @@ akerr_ErrorContext AKERR_NOIGNORE *akbasic_environment_new_leaf(akbasic_Environm
  */
 akerr_ErrorContext AKERR_NOIGNORE *akbasic_environment_wait_for_command(akbasic_Environment *obj, const char *command);
 /**
- * @brief True when this scope or any enclosing one is skipping forward.
+ * @brief Whether this scope or any enclosing one is skipping forward.
+ *
+ * The answer leaves through @p dest rather than the return value. Deciding it
+ * reads a recorded verb name, that read can fail, and a `bool` return has
+ * nowhere to report the failure -- so the signature changes rather than the
+ * error being swallowed. libakstdlib #38 is the ruling; `probe` in `symtab.c`
+ * and `loop_continues` in `runtime_structure.c` are the same shape.
+ *
  * @param obj Scope to inspect; NULL is not waiting.
- * @return `true` when execution is currently suppressed.
+ * @param[out] dest `true` when execution is currently suppressed. Required.
+ * @return `NULL` on success, otherwise an error context owned by the caller.
+ * @throws AKERR_NULLPOINTER When dest is NULL.
  */
-bool akbasic_environment_is_waiting_for_any(akbasic_Environment *obj);
+akerr_ErrorContext AKERR_NOIGNORE *akbasic_environment_is_waiting_for_any(akbasic_Environment *obj, bool *dest);
 /**
- * @brief True when this scope or an enclosing one is waiting for a given verb.
+ * @brief Whether this scope or an enclosing one is waiting for a given verb.
+ *
+ * Reports through @p dest for the same reason its sibling above does.
+ *
  * @param obj Scope to inspect; NULL is not waiting.
- * @param command Verb to test for.
- * @return `true` when that verb is what execution is waiting on.
+ * @param command Verb to test for; NULL is not waiting.
+ * @param[out] dest `true` when that verb is what execution is waiting on. Required.
+ * @return `NULL` on success, otherwise an error context owned by the caller.
+ * @throws AKERR_NULLPOINTER When dest is NULL.
  */
-bool akbasic_environment_is_waiting_for(akbasic_Environment *obj, const char *command);
+akerr_ErrorContext AKERR_NOIGNORE *akbasic_environment_is_waiting_for(akbasic_Environment *obj, const char *command, bool *dest);
 /**
  * @brief Clear a pending wait, searching the parent chain for it.
  *