Count work only under a budget, and say why a view failed only then (017)

The work budget added about 26 instructions to every row of a table a
host shows (bank, a table of 10,000 rows: +3.0% instructions an ask),
which 017's one-app criterion allows at 1%. A sample put most of it in
show_given asking every cell why it failed, and the rest in evaluate
and the row lookup writing that reason and the count for every cell.

Now nothing is counted without a budget (PureApp.work stays), the
reason is written only when a view, a cell or a row has no value, and
pure-serve asks it only of a cell without one. The table: +0.94%; the
other bank queries within 0.4%. The tests that read the count set a
budget that is never reached.

1 files changed, 3 insertions, 3 deletions

diff --git a/core/module.h b/core/module.h
index c4919c9..2cc3109 100644
--- a/core/module.h
+++ b/core/module.h
@@ -554,11 +554,11 @@ size_t pure_app_state_bytes(const PureApp *);
  * item of its list (of its slice, when it takes one) it goes over, all
  * counted as the fold or walk begins. Past it the event fails with the fault
  * PURE_FAULT_WORK (PURE_LIMIT) and changes nothing, and a view has no value.
- * 0: no budget, at first. */
+ * 0: no budget, at first, and then nothing is counted (PureApp.work stays). */
 void pure_app_work(PureApp *, uint64_t instructions);
 /* Why the last view evaluated on this app (or a table's rows asked for)
- * had no value: PURE_FAULT_WORK past the work budget, another fault, or
- * PURE_FAULT_NONE when it had one. */
+ * had no value, once it had none: PURE_FAULT_WORK past the work budget,
+ * another fault, or PURE_FAULT_NONE. pure_app_rows always says. */
 PureFault pure_app_view_fault(const PureApp *);
 
 /* Readers on other threads. Right after a save an app can make a snapshot of