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+// Pure core for the phase-2 calibration backfill (#8170, epic #8082): the two GitHub-truth passes phase 1
+// (#8157, backfill-calibration-corpus-core.ts) deliberately deferred. The thin IO wrapper
+// (backfill-calibration-corpus-phase2.ts) does every DB/GitHub read and write; everything here is pure.
+//
+//   • Pass A — retro successor scan: run #8166's `evaluateSuccessorMatch` (imported, never re-implemented)
+//     over historical bot-close decisions vs the merged PRs that followed them. A confirmed match flips the
+//     phase-1 override row's verdict to `reversed` — the ledger's first organic-shaped negative labels.
+//   • Pass B — raw-context re-fetch: patch the phase-1 fired rows with the PR diff the live capture (#8130)
+//     would have recorded (`metadata.diff`, bounded to RAW_CONTEXT_MAX_DIFF_CHARS), public repos only.
+//   • Conservative + idempotent: borderline successor matches record NOTHING; both patchers return null on
+//     an already-patched row, so re-runs are no-ops; every patched row carries a distinct provenance tag.
+import { evaluateSuccessorMatch, SUPERSEDED_LOOKBACK_MS, type SupersededHeuristics } from "../src/review/reversal-superseded.js";
+import { RAW_CONTEXT_MAX_DIFF_CHARS } from "../src/rules/advisory.js";
+import { BACKFILL_RULE_ID } from "./backfill-calibration-corpus-core.js";
+
+/** Distinct provenance for pass A's retro labels — never confusable with phase 1's decision-level rows. */
+export const RETRO_SUCCESSOR_PROVENANCE = "github_successor_scan";
+/** Provenance for the strongest retro label: the close-verdict PR ITSELF later merged (the operator
+ *  reopened + merged it) — a definitive same-PR reversal needing no successor heuristics at all. */
+export const RETRO_SAME_PR_MERGED_PROVENANCE = "github_same_pr_merged";
+/** Distinct provenance for pass B's re-fetched raw context. */
+export const RAW_CONTEXT_REFETCH_PROVENANCE = "github_raw_context_refetch";
+
+/** A phase-1 backfilled close decision, hydrated with the GitHub truth the wrapper fetched. */
+export type HistoricalCloseSide = {
+  targetKey: string;
+  repo: string;
+  number: number;
+  /** ISO close time (phase 1's terminal_at) — successors must merge within the #8166 lookback AFTER it. */
+  closedAt: string;
+  authorLogin: string | null;
+  linkedIssues: readonly number[];
+  files: readonly string[];
+};
+
+/** A candidate successor: a PR in the same repo that actually merged. */
+export type SuccessorSide = {
+  number: number;
+  mergedAt: string;
+  authorLogin: string | null;
+  linkedIssues: readonly number[];
+  files: readonly string[];
+};
+
+export type RetroSuccessorMatch = {
+  targetKey: string;
+  supersededBy: number;
+  heuristics: SupersededHeuristics;
+};
+
+/**
+ * Decide which historical closes were superseded by a later merge. Pure: both sides arrive pre-fetched.
+ * The window is directional — a successor must merge AFTER the close and within {@link SUPERSEDED_LOOKBACK_MS}
+ * (#8166's own bound) — and the EARLIEST qualifying merge wins so re-runs with more candidates stay stable.
+ */
+export function matchRetroSuccessors(close: HistoricalCloseSide, successors: readonly SuccessorSide[]): RetroSuccessorMatch | null {
+  const closedAtMs = Date.parse(close.closedAt);
+  if (!Number.isFinite(closedAtMs)) return null;
+  const eligible = successors
+    .filter((successor) => {
+      if (successor.number === close.number) return false;
+      const mergedAtMs = Date.parse(successor.mergedAt);
+      return Number.isFinite(mergedAtMs) && mergedAtMs > closedAtMs && mergedAtMs - closedAtMs <= SUPERSEDED_LOOKBACK_MS;
+    })
+    .sort((a, b) => (a.mergedAt < b.mergedAt ? -1 : a.mergedAt > b.mergedAt ? 1 : a.number - b.number));
+  for (const successor of eligible) {
+    const heuristics = evaluateSuccessorMatch(
+      { authorLogin: successor.authorLogin, linkedIssues: successor.linkedIssues, files: successor.files },
+      { authorLogin: close.authorLogin, linkedIssues: close.linkedIssues, files: close.files },
+    );
+    if (heuristics) return { targetKey: close.targetKey, supersededBy: successor.number, heuristics };
+  }
+  return null;
+}
+
+/** The deterministic phase-1 row ids this pass is allowed to touch — live capture rows are never patched. */
+export function backfillOverrideId(targetKey: string): string {
+  return `backfill:${BACKFILL_RULE_ID}:${targetKey}:override`;
+}
+export function backfillFiredId(targetKey: string): string {
+  return `backfill:${BACKFILL_RULE_ID}:${targetKey}:fired`;
+}
+
+/**
+ * Patch a phase-1 override row's metadata to the retro `reversed` verdict. Returns the new JSON, or null
+ * when the row is already reversed (idempotent re-run) or does not parse as an object (never guess).
+ */
+export function patchOverrideMetadataToReversed(metadataJson: string, match: RetroSuccessorMatch): string | null {
+  const metadata = parseObject(metadataJson);
+  if (!metadata) return null;
+  if (metadata.verdict === "reversed") return null;
+  return JSON.stringify({
+    ...metadata,
+    verdict: "reversed",
+    retroLabel: {
+      provenance: RETRO_SUCCESSOR_PROVENANCE,
+      supersededBy: match.supersededBy,
+      heuristics: match.heuristics,
+    },
+  });
+}
+
+/**
+ * Patch a phase-1 override row for the same-PR reversal: GitHub says the close-verdict PR itself MERGED
+ * (the operator reopened + merged it) — the decision was overridden on its own target, no heuristics
+ * involved. Same idempotency contract as {@link patchOverrideMetadataToReversed}.
+ */
+export function patchOverrideMetadataToSamePrMerged(metadataJson: string, mergedAt: string): string | null {
+  const metadata = parseObject(metadataJson);
+  if (!metadata) return null;
+  if (metadata.verdict === "reversed") return null;
+  return JSON.stringify({
+    ...metadata,
+    verdict: "reversed",
+    retroLabel: { provenance: RETRO_SAME_PR_MERGED_PROVENANCE, mergedAt },
+  });
+}
+
+/**
+ * Patch a phase-1 fired row's metadata with the re-fetched PR diff — the field the live #8130 capture
+ * records for this rule (`metadata.diff`, same bound). Returns null when raw context is already present
+ * (either captured live or patched by an earlier run), when the diff is empty, or on unparseable metadata.
+ */
+export function patchFiredMetadataWithDiff(metadataJson: string, diff: string): string | null {
+  const metadata = parseObject(metadataJson);
+  if (!metadata) return null;
+  if (typeof metadata.diff === "string") return null;
+  const bounded = diff.slice(0, RAW_CONTEXT_MAX_DIFF_CHARS);
+  if (bounded === "") return null;
+  return JSON.stringify({ ...metadata, diff: bounded, rawContextProvenance: RAW_CONTEXT_REFETCH_PROVENANCE });
+}
+
+export type Phase2Report = {
+  pass: "successors" | "raw-context";
+  scanned: number;
+  patched: number;
+  alreadyPatched: number;
+  noMatch: number;
+  /** Pass-A heuristic breakdown (#8170's apply decision hinges on it): a SAME-AUTHOR rework merging is
+   *  strong bot-was-wrong evidence; a shared-issue match by a DIFFERENT author is routine duplicate
+   *  competition in this culture — the winner merging does not make closing the loser wrong. */
+  matchedSameAuthor: number;
+  matchedSharedIssueOnly: number;
+  /** The close-verdict PR itself later merged — definitive reversals, no heuristics (see the operator's
+   *  own reopen-and-merge history; the strongest label class this pass produces). */
+  matchedSamePrMerged: number;
+  requestsUsed: number;
+  exhaustedBudget: boolean;
+  resumeFrom: string | null;
+};
+
+/** Render the dry-run/apply report #8170 requires before any apply. */
+export function renderPhase2Report(report: Phase2Report, mode: "dry-run" | "apply"): string {
+  const lines = [
+    `Calibration corpus backfill phase 2 (${mode}) — pass ${report.pass}, provenance ${
+      report.pass === "successors" ? RETRO_SUCCESSOR_PROVENANCE : RAW_CONTEXT_REFETCH_PROVENANCE
+    }`,
+    `  scanned: ${report.scanned}  patched: ${report.patched}  already-patched: ${report.alreadyPatched}  no-match/skipped: ${report.noMatch}`,
+    ...(report.pass === "successors"
+      ? [
+          `  match classes: same-PR reopened+merged ${report.matchedSamePrMerged} (definitive), same-author rework ${report.matchedSameAuthor}, shared-issue-only (different author) ${report.matchedSharedIssueOnly}`,
+        ]
+      : []),
+    `  GitHub requests used: ${report.requestsUsed}${report.exhaustedBudget ? " (budget exhausted — resumable)" : ""}`,
+  ];
+  if (report.resumeFrom) lines.push(`  resume from: ${report.resumeFrom} (state file updated)`);
+  return lines.join("\n");
+}
+
+function parseObject(json: string): Record<string, unknown> | null {
+  try {
+    const parsed: unknown = JSON.parse(json);
+    if (parsed && typeof parsed === "object" && !Array.isArray(parsed)) return parsed as Record<string, unknown>;
+  } catch {
+    /* corrupt row -- treat as unpatchable, mirroring phase 1's fail-open metadata parse */
+  }
+  return null;
+}