feat(learning-harness): aggregation, noise handling and honest denominators

Task 2.4. Per family, and per slice when asked: outcome counts, recall, silence,
Youden, a directional-bias index and recall at a fixed false-positive ceiling.
Rows that cannot be scored are listed by reason and leave every denominator, and
a family with nothing scorable reports no rate rather than a perfect one.

Two numbers exist because Youden cannot tell apart a detector that flags
everything from one that says everything is safe: the directional-bias index
separates them, and recall at a fixed ceiling is forfeited entirely once a
family leaks more than the budget allows.

Change against a baseline is not a difference of means. Flips are counted per
pair in both directions and a two-sided exact sign test decides whether the
change is bigger than the noise, so one flip in ten reads as noise and six reads
as a real regression.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01T7XD7x5KonMdmGRkp63EQG

.kiro/specs/learning-harness/spec.json

@@ -1,9 +1,9 @@
 {
   "feature_name": "learning-harness",
   "created_at": "2026-09-06T06:32:41Z",
-  "updated_at": "2026-09-06T06:57:33Z",
+  "updated_at": "2026-09-06T07:00:52Z",
   "language": "en",
-  "phase": "tasks-generated",
+  "phase": "implementation",
   "approvals": {
     "requirements": {
       "generated": true,
@@ -15,10 +15,10 @@
     },
     "tasks": {
       "generated": true,
-      "approved": false
+      "approved": true
     }
   },
-  "ready_for_implementation": false,
+  "ready_for_implementation": true,
   "depends_on": [
     "pair-corpus-honesty",
     "corpus-seeded-mechanisms",
@@ -26,5 +26,5 @@
     "tree-sitter-overlay-extra",
     "harnessx-self-improving-rulesets"
   ],
-  "approval_note": "2026-09-06 requirements approved by the maintainer in session ('approve the requirements and run the design phase'); 2026-09-06 design approved by the maintainer in session ('approve the design and generate the tasks')"
+  "approval_note": "2026-09-06 requirements approved by the maintainer in session ('approve the requirements and run the design phase'); 2026-09-06 design approved by the maintainer in session ('approve the design and generate the tasks'); 2026-09-06 tasks approved by the maintainer in session ('approve the tasks and go on with the implementation')"
 }