feat(signals): add queue burden score breakdown with weighted contributors and top lever

src/services/queue-burden-breakdown.ts

@@ -0,0 +1,284 @@
+import { sanitizePublicComment } from "../github/commands";
+import type { QueueHealth } from "../signals/engine";
+
+// ─── Queue burden breakdown (explanation family) ─────────────────────────────────────────────────
+// A pure projection over a computed {@link QueueHealth} that decomposes the otherwise-opaque
+// `burdenScore` into its weighted, observable contributors and names the single highest-leverage lever
+// a maintainer can pull to bring queue pressure down fastest. Sibling of `score-breakdown.ts`,
+// `miner-dashboard-recommendations.ts`, and `agent-action-explanation-card.ts`: deterministic, no I/O,
+// no GitHub fetch. Public-safe by construction — it reports observable counts, relative shares, and
+// bands only, and routes every rendered string through `sanitizePublicComment`.
+
+export type QueueBurdenBand = "credit" | "none" | "low" | "moderate" | "high";
+
+export type QueueBurdenComponent = {
+  /** The QueueHealth signal this contribution is derived from. */
+  component: string;
+  /** Observable signal count (open PRs, unlinked PRs, collision clusters, …). */
+  count: number;
+  /** Signed per-unit weight this signal carries in the burden formula (the reviewable credit is negative). */
+  weightPerUnit: number;
+  /** `count * weightPerUnit` — positive for a penalty, negative for the reviewable credit. */
+  contribution: number;
+  /** Share of total positive penalty (0–100). For the credit it is the percentage of penalty it offsets. */
+  sharePercent: number;
+  band: QueueBurdenBand;
+  summary: string;
+  lever: string;
+  /** 0–100 ranking weight used to pick the single highest-leverage improvement lever. */
+  leverageScore: number;
+};
+
+export type QueueBurdenBreakdown = {
+  repoFullName: string;
+  generatedAt: string;
+  /** The authoritative (already clamped) burden score carried on the QueueHealth. */
+  burdenScore: number;
+  level: QueueHealth["level"];
+  /** Pre-clamp signed sum of every contribution (penalties minus the reviewable credit). */
+  rawBurden: number;
+  /** True when the raw sum fell outside the 0–100 band and the engine clamped it. */
+  clamped: boolean;
+  /** Sum of the positive penalty contributions. */
+  totalPenalty: number;
+  /** Absolute size of the reviewable credit that offsets the penalties. */
+  totalCredit: number;
+  components: QueueBurdenComponent[];
+  highestLeverageLever: { component: string; lever: string; reason: string };
+  summary: string;
+};
+
+// These per-unit weights MIRROR buildQueueHealth() in src/signals/engine.ts. A drift-guard test rebuilds a
+// QueueHealth through buildQueueHealth and asserts this module recomposes the same burdenScore, so any change
+// to the engine weights fails the suite instead of silently producing a wrong breakdown.
+const PENALTY_DESCRIPTORS: ReadonlyArray<{
+  component: string;
+  weightPerUnit: number;
+  count: (health: QueueHealth) => number;
+  describe: (count: number) => { summary: string; lever: string };
+}> = [
+  {
+    component: "unlinkedPullRequests",
+    weightPerUnit: 8,
+    count: (health) => health.signals.unlinkedPullRequests,
+    describe: (count) =>
+      count > 0
+        ? {
+            summary: `${count} open pull request(s) lack a linked issue, the heaviest per-PR burden factor.`,
+            lever: "Ask contributors to link a closing issue or state explicit no-issue intent so unlinked PRs stop driving burden.",
+          }
+        : {
+            summary: "Every open pull request carries linked-issue context, so this factor adds no burden.",
+            lever: "Keep requiring a linked issue or a clear no-issue rationale so this factor stays at zero.",
+          },
+  },
+  {
+    component: "collisionClusters",
+    weightPerUnit: 10,
+    count: (health) => health.signals.collisionClusters,
+    describe: (count) =>
+      count > 0
+        ? {
+            summary: `${count} duplicate or overlapping work cluster(s) carry the highest per-unit burden weight.`,
+            lever: "Resolve overlapping submissions before spending detailed review time to cut collision burden fastest.",
+          }
+        : {
+            summary: "No duplicate or overlapping work clusters were detected, so this factor adds no burden.",
+            lever: "Keep deduplicating incoming work early so collision burden stays at zero.",
+          },
+  },
+  {
+    component: "openPullRequests",
+    weightPerUnit: 6,
+    count: (health) => health.signals.openPullRequests,
+    describe: (count) =>
+      count > 0
+        ? {
+            summary: `${count} open pull request(s) contribute baseline review load.`,
+            lever: "Land or close open pull requests to reduce the baseline queue load.",
+          }
+        : {
+            summary: "There are no open pull requests adding baseline load.",
+            lever: "No action needed; baseline pull-request load is already at zero.",
+          },
+  },
+  {
+    component: "stalePullRequests",
+    weightPerUnit: 6,
+    count: (health) => health.signals.stalePullRequests,
+    describe: (count) =>
+      count > 0
+        ? {
+            summary: `${count} open pull request(s) have stalled without an update for at least 14 days.`,
+            lever: "Review, nudge, or close stale pull requests so they stop accruing burden.",
+          }
+        : {
+            summary: "No open pull requests have stalled past the 14-day staleness threshold.",
+            lever: "Keep pull requests moving so none cross the staleness threshold.",
+          },
+  },
+  {
+    component: "over30DayPullRequests",
+    weightPerUnit: 4,
+    count: (health) => health.signals.ageBuckets.over30Days,
+    describe: (count) =>
+      count > 0
+        ? {
+            summary: `${count} open pull request(s) have aged past 30 days.`,
+            lever: "Resolve the long-aged pull requests to clear the oldest backlog in the queue.",
+          }
+        : {
+            summary: "No open pull requests have aged past 30 days.",
+            lever: "Keep clearing aged work so none crosses the 30-day mark.",
+          },
+  },
+  {
+    component: "openIssues",
+    weightPerUnit: 1,
+    count: (health) => health.signals.openIssues,
+    describe: (count) =>
+      count > 0
+        ? {
+            summary: `${count} open issue(s) add minor triage load.`,
+            lever: "Triage or close resolved open issues to trim residual queue load.",
+          }
+        : {
+            summary: "There are no open issues adding triage load.",
+            lever: "No action needed; open-issue triage load is already at zero.",
+          },
+  },
+];
+
+const REVIEWABLE_CREDIT_PER_UNIT = -2;
+
+function penaltyBand(count: number, sharePercent: number): QueueBurdenBand {
+  if (count <= 0) return "none";
+  if (sharePercent >= 40) return "high";
+  if (sharePercent >= 15) return "moderate";
+  return "low";
+}
+
+function shareOf(contribution: number, totalPenalty: number): number {
+  if (totalPenalty <= 0) return 0;
+  return Math.round((Math.abs(contribution) / totalPenalty) * 100);
+}
+
+function creditComponent(health: QueueHealth, totalPenalty: number): QueueBurdenComponent {
+  const count = health.signals.likelyReviewablePullRequests;
+  const contribution = count * REVIEWABLE_CREDIT_PER_UNIT;
+  const sharePercent = shareOf(contribution, totalPenalty);
+  return {
+    component: "likelyReviewablePullRequests",
+    count,
+    weightPerUnit: REVIEWABLE_CREDIT_PER_UNIT,
+    contribution,
+    sharePercent,
+    band: "credit",
+    summary:
+      count > 0
+        ? `${count} open pull request(s) look readily reviewable and reduce net queue burden.`
+        : "No open pull requests are currently counted as readily reviewable, so nothing is offsetting burden.",
+    lever:
+      count > 0
+        ? "Keep pull requests linked and fresh so they stay readily reviewable and keep offsetting burden."
+        : "Help open pull requests become linked and fresh so they start offsetting queue burden.",
+    // The credit is already helping; it is never the lever a maintainer pulls to REDUCE burden, so it stays
+    // out of the highest-leverage ranking.
+    leverageScore: 0,
+  };
+}
+
+function pickHighestLeverage(components: QueueBurdenComponent[]): QueueBurdenBreakdown["highestLeverageLever"] {
+  // Rank by share of burden, then break ties toward the heavier per-unit weight (reducing one high-weight item
+  // removes more burden per action, so it is the better lever), and finally by name purely for determinism.
+  const ranked = [...components].sort(
+    (left, right) =>
+      right.leverageScore - left.leverageScore ||
+      right.weightPerUnit - left.weightPerUnit ||
+      left.component.localeCompare(right.component),
+  );
+  const top = ranked[0]!;
+  // When no penalty is active (every leverageScore is 0), the sort tie-break would otherwise surface an
+  // arbitrary alphabetically-first component as "the lever" — which is misleading because there is nothing to
+  // reduce. Return an explicit no-op lever instead so the breakdown stays honest for a healthy queue.
+  if (top.leverageScore <= 0) {
+    return {
+      component: "none",
+      lever: sanitizePublicComment("No queue-burden lever needs attention; there are no active contributors to reduce."),
+      reason: sanitizePublicComment("Queue burden has no active penalty contributors right now, so there is no pressing lever to pull."),
+    };
+  }
+  const reason =
+    top.band === "high"
+      ? `${top.component} is the dominant queue-burden contributor right now.`
+      : `${top.component} is the largest remaining queue-burden contributor.`;
+  return {
+    component: top.component,
+    lever: top.lever,
+    reason: sanitizePublicComment(reason),
+  };
+}
+
+/**
+ * Pure projection over a {@link QueueHealth} that explains how the queue `burdenScore` breaks down into its
+ * weighted, observable contributors and names the single highest-leverage lever to reduce queue pressure.
+ */
+export function explainQueueBurden(health: QueueHealth): QueueBurdenBreakdown {
+  const penalties = PENALTY_DESCRIPTORS.map((descriptor) => {
+    const count = descriptor.count(health);
+    const contribution = count * descriptor.weightPerUnit;
+    return { descriptor, count, contribution };
+  });
+  const totalPenalty = penalties.reduce((sum, entry) => sum + entry.contribution, 0);
+
+  const penaltyComponents: QueueBurdenComponent[] = penalties.map(({ descriptor, count, contribution }) => {
+    const sharePercent = shareOf(contribution, totalPenalty);
+    const copy = descriptor.describe(count);
+    return {
+      component: descriptor.component,
+      count,
+      weightPerUnit: descriptor.weightPerUnit,
+      contribution,
+      sharePercent,
+      band: penaltyBand(count, sharePercent),
+      summary: copy.summary,
+      lever: copy.lever,
+      // A penalty's leverage is exactly its share of the burden — the biggest contributor is the best lever.
+      leverageScore: sharePercent,
+    };
+  });
+
+  const credit = creditComponent(health, totalPenalty);
+  const totalCredit = Math.abs(credit.contribution);
+  const rawBurden = totalPenalty + credit.contribution;
+  // The engine clamps burden to 0–100. The lower bound is unreachable in practice: every open PR adds 6 to the
+  // penalty while its reviewable credit only subtracts 2 (and reviewable PRs never exceed open PRs), so the
+  // penalties always dominate the credit. Only the upper clamp is observable here.
+  const clamped = rawBurden > 100;
+
+  const components = [...penaltyComponents, credit].map((entry) => ({
+    ...entry,
+    summary: sanitizePublicComment(entry.summary),
+    lever: sanitizePublicComment(entry.lever),
+  }));
+
+  const highestLeverageLever = pickHighestLeverage(components);
+  const summary =
+    highestLeverageLever.component === "none"
+      ? `Queue burden is ${health.level} with no active contributors to address.`
+      : `Queue burden is ${health.level}; ${highestLeverageLever.component} is the leading factor to address.`;
+
+  return {
+    repoFullName: health.repoFullName,
+    generatedAt: health.generatedAt,
+    burdenScore: health.burdenScore,
+    level: health.level,
+    rawBurden,
+    clamped,
+    totalPenalty,
+    totalCredit,
+    components,
+    highestLeverageLever,
+    summary: sanitizePublicComment(summary),
+  };
+}