fix(rectification): share decideFromDossier across projections and treat a sole candidate as a close, not a tie

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/lib/rectification-agentic/core/candidate-separation.ts

@@ -1,11 +1,12 @@
 /**
  * Candidate separation is not event-fit and not method coverage.
  * 34/33/33 is a tie. A 1-point engine lead is not a winner.
+ * One remaining candidate is a sole candidate, not a parallel range.
  */
 
 export const MIN_SEPARATION_LEAD = 8;
 
-export type SeparationStatus = "not_separated" | "weak_lead" | "separated";
+export type SeparationStatus = "not_separated" | "weak_lead" | "separated" | "sole_candidate";
 
 export type CandidateScoreRow = Readonly<{
   id?: string;
@@ -35,14 +36,36 @@ export function evaluateCandidateSeparation(
   const top = ranked[0] ?? null;
   const runnerUp = ranked[1] ?? null;
   const total = ranked.reduce((sum, item) => sum + Math.max(item.score, 0), 0);
-  const lead = top && runnerUp ? top.score - runnerUp.score : (top ? MIN_SEPARATION_LEAD : 0);
-  const topShare = top && total > 0 ? Math.max(top.score, 0) / total : 0;
-  const status: SeparationStatus = !top || ranked.length < 2 || lead < MIN_SEPARATION_LEAD
+  if (!top) {
+    return {
+      sufficient: false,
+      status: "not_separated",
+      lead: 0,
+      topShare: 0,
+      representativeTime: null,
+      credibleRange: [],
+      ranked,
+    };
+  }
+  if (!runnerUp) {
+    return {
+      sufficient: true,
+      status: "sole_candidate",
+      lead: 0,
+      topShare: 1,
+      representativeTime: top.time,
+      credibleRange: [top.time],
+      ranked,
+    };
+  }
+  const lead = top.score - runnerUp.score;
+  const topShare = total > 0 ? Math.max(top.score, 0) / total : 0;
+  const status: SeparationStatus = lead < MIN_SEPARATION_LEAD
     ? "not_separated"
     : lead >= 20
       ? "separated"
       : "weak_lead";
-  const peak = top?.score ?? 0;
+  const peak = top.score;
   const credibleRange = ranked
     .filter((item) => peak - item.score < MIN_SEPARATION_LEAD)
     .map((item) => item.time);
@@ -51,8 +74,8 @@ export function evaluateCandidateSeparation(
     status,
     lead,
     topShare,
-    representativeTime: top?.time ?? null,
-    credibleRange: credibleRange.length > 0 ? credibleRange : (top ? [top.time] : []),
+    representativeTime: top.time,
+    credibleRange: credibleRange.length > 0 ? credibleRange : [top.time],
     ranked,
   };
 }

frontend/src/lib/rectification-agentic/core/rectification-decision.ts

@@ -141,6 +141,19 @@ export function decideRectification(input: DecideRectificationInput): Rectificat
     }
     return completeWithRange(separation, holdout, range, "exhausted");
   }
+  if (holdout === "unavailable") {
+    if (userStopped) {
+      return completeWithRange(separation, holdout, range, "user_stopped");
+    }
+    return finish("adopt_representative", {
+      input,
+      separation,
+      holdout,
+      range,
+      probe: null,
+      canConfirmExactMinute: false,
+    });
+  }
   if (userStopped && holdout !== "passed") {
     return completeWithRange(separation, holdout, range, "user_stopped");
   }
@@ -273,7 +286,7 @@ function completeWithRange(
 }
 
 function finish(
-  sessionOutcome: "adopt_representative" | "awaiting_confirmation" | "validated_range" | "exact_minute_confirmed",
+  fallbackOutcome: "adopt_representative" | "awaiting_confirmation" | "validated_range" | "exact_minute_confirmed",
   input: {
     input: DecideRectificationInput;
     separation: CandidateSeparation;
@@ -294,7 +307,7 @@ function finish(
     ? (input.input.accepted ? "exact_minute_confirmed" : "awaiting_confirmation")
     : input.holdout === "passed"
       ? "validated_range"
-      : sessionOutcome;
+      : fallbackOutcome;
   return {
     phase: "completed",
     nextAction: "ready_to_adopt",