From a104f98dcaea6705122246280171009b118417e8 Mon Sep 17 00:00:00 2001
From: Masa <98894508+Masashi-Ono0611@users.noreply.github.com>
Date: Wed, 29 Jul 2026 03:44:17 +0900
Subject: [PATCH] fix(cycle): extract_facts guard counts only active legacy
 rows; reconcile preserves forget records (#2646) (#3474)
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master's empty-fence guard counts soft-expired legacy rows
(row_num IS NULL, expired_at set), so forget_fact — the sanctioned
removal path, which soft-expires rather than deletes — can never drain
the backlog: apply-migrations no-ops (already marked applied) and the
guard stays triggered forever, jamming extract_facts.

Narrowed re-send of #3252-sibling #3234, scoped to exactly what the
maintainer named reviewable: "one predicate plus the
reconcile-preservation guard."

- Guard predicate: the legacy COUNT adds `AND f.expired_at IS NULL`,
  so each forget_fact visibly drains the pending counter.
- Reconcile preservation: listExistingFactsForPage excludes soft-expired
  legacy rows (they are never fence-owned, so they must neither read as
  perpetually stale nor mask a fence row), and the two wipe call sites
  pass `preserveExpiredLegacy: true` so deleteFactsForPage keeps the
  forget record. The option is the minimal seam for that guard —
  implemented identically in both engines (~6 lines each).

Explicitly NOT included from #3234 (per the close review): the
drift-repair lane, the re-runnable migration orchestrator path, and the
race-accounting layer.

Fence-is-canonical semantics are preserved and pinned by test: if the
fence still carries an expired legacy row's claim, the reconcile
reinserts it as a fresh active fence-owned row (legacy DB-only forgets
are documented non-durable; the expired row survives as the audit
record of the forget).

Co-authored-by: Time Attakc <89218912+time-attack@users.noreply.github.com>
---
 src/core/cycle/extract-facts.ts               |  62 ++++--
 src/core/engine.ts                            |  13 +-
 src/core/pglite-engine.ts                     |  12 +-
 src/core/postgres-engine.ts                   |  11 +-
 .../facts-fence-reconcile-postgres.test.ts    |  87 +++++++++
 test/extract-facts-phase.test.ts              | 180 ++++++++++++++++++
 6 files changed, 345 insertions(+), 20 deletions(-)

diff --git a/src/core/cycle/extract-facts.ts b/src/core/cycle/extract-facts.ts
index 04ee53cea..94995539a 100644
--- a/src/core/cycle/extract-facts.ts
+++ b/src/core/cycle/extract-facts.ts
@@ -23,11 +23,12 @@
  * page coordinate only; legacy NULL-source_markdown_slug rows survive
  * because deleteFactsForPage targets source_markdown_slug = slug only.
  *
- * Empty-fence guard (Codex R2-#7; #2484): the phase refuses to do its
- * destructive reconciliation pass when genuinely-backfillable legacy
+ * Empty-fence guard (Codex R2-#7; #2484; #2646): the phase refuses to do
+ * its destructive reconciliation pass when genuinely-backfillable legacy
  * rows still exist — `row_num IS NULL` (never fenced) AND `entity_slug`
  * resolves to a live page in this source (so the v0_32_2 migration's
- * Phase B could fence them). Status returns `warn` with a hint to run
+ * Phase B could fence them) AND the row is not soft-expired
+ * (`expired_at IS NULL`). Status returns `warn` with a hint to run
  * `gbrain apply-migrations --yes`. Without the guard, an interrupted
  * upgrade where v0_32_2 hasn't run could leave the cycle silently
  * misreporting "0 facts on people/alice" while legacy rows linger.
@@ -41,6 +42,10 @@
  * the phase jams forever (~16/day observed). Requiring a backing page
  * keeps genuine pre-v0.32.2 rows (whose entity page exists) gating
  * while excluding the inline-writer's permanent-unfenceable rows.
+ *
+ * Soft-expired rows don't count either (#2646): they're what
+ * `forget_fact` produces, so excluding them lets operators drain the
+ * backlog through the sanctioned removal path instead of raw SQL.
  */
 
 import type { BrainEngine } from '../engine.ts';
@@ -88,6 +93,24 @@ function dedupeFactsByContentKey(facts: FenceExtractedFact[]): FenceExtractedFac
  * neither count as "stale" (which would force a wipe every cycle) nor
  * be compared against the fence's row set. Mirrors the
  * excludeSourcePrefixes filter deleteFactsForPage applies on the wipe.
+ *
+ * Also excludes soft-expired legacy rows (#2646: `row_num IS NULL AND
+ * expired_at IS NOT NULL`) — rows that `forget_fact` expired via its
+ * legacy DB-only path. They are not fence-owned (fence rows always
+ * carry a row_num), so they must neither count as "stale" (forcing a
+ * wipe every cycle) nor mask a fence row from insertion. Mirrors the
+ * preserveExpiredLegacy filter deleteFactsForPage applies on the wipe.
+ *
+ * Deliberate consequence: if the fence still carries the same
+ * (claim, source) as an expired legacy row, the reconcile inserts it
+ * as a fresh ACTIVE fence-owned row. That is the fence-is-canonical
+ * contract working as documented — legacy DB-only forgets "DO NOT
+ * survive rebuild" (see forget.ts header); suppressing the insert
+ * would instead create silent fence↔DB divergence, the exact failure
+ * mode the empty-fence guard exists to prevent. To durably forget
+ * such a claim, forget the fence-owned row (forget_fact now takes the
+ * fence path, which strikes the row through in markdown). The expired
+ * legacy row survives alongside as the record of the earlier forget.
  */
 async function listExistingFactsForPage(
   engine: BrainEngine,
@@ -100,6 +123,7 @@ async function listExistingFactsForPage(
       WHERE source_id = $1
         AND source_markdown_slug = $2
         AND COALESCE(source, '') NOT LIKE 'cli:%'
+        AND NOT (row_num IS NULL AND expired_at IS NOT NULL)
       ORDER BY row_num ASC, id ASC`,
     [sourceId, slug],
   );
@@ -173,7 +197,7 @@ export async function runExtractFacts(
     phantomsMorePending: false,
   };
 
-  // ── Empty-fence guard (Codex R2-#7; #2484) ─────────────────────
+  // ── Empty-fence guard (Codex R2-#7; #2484; #2646) ──────────────
   // Pre-check: if any genuinely-backfillable legacy fact rows exist,
   // refuse to run the destructive reconciliation pass — the v0_32_2
   // orchestrator must fence them first.
@@ -181,12 +205,13 @@ export async function runExtractFacts(
   // A row is a real backfill candidate only when `row_num IS NULL`
   // (never fenced) AND its `entity_slug` resolves to a LIVE page in
   // this source (the migration's Phase B only fences rows whose
-  // entity_slug maps to a writable page). #2484: the original
-  // predicate was just `row_num IS NULL AND entity_slug IS NOT NULL`,
-  // which ALSO matched structurally-unfenceable hot-memory rows the
-  // inline writer keeps producing post-migration: the legacy DB-only
-  // fallback (backstop.ts) writes `entity_slug` (a resolved slug, e.g.
-  // a slugify-floor or stub-guard-blocked unprefixed slug like
+  // entity_slug maps to a writable page) AND it is not soft-expired.
+  // #2484: the original predicate was just `row_num IS NULL AND
+  // entity_slug IS NOT NULL`, which ALSO matched
+  // structurally-unfenceable hot-memory rows the inline writer keeps
+  // producing post-migration: the legacy DB-only fallback
+  // (backstop.ts) writes `entity_slug` (a resolved slug, e.g. a
+  // slugify-floor or stub-guard-blocked unprefixed slug like
   // `people-jane-doe`) with `row_num` NULL whenever the slug has no
   // fenceable page. Those rows can never satisfy the migration's exit
   // condition (no page to fence onto, and `apply-migrations` is a
@@ -194,12 +219,17 @@ export async function runExtractFacts(
   // — ~16/day, mislabeled "v0.31 pending backfill." We now require a
   // live backing page, which both genuine pre-v0.32.2 rows (their
   // entity page exists) satisfy and inline-writer unfenceable rows do
-  // not.
+  // not. #2646: soft-expired rows (`expired_at IS NOT NULL`) are also
+  // excluded — `forget_fact`, the officially sanctioned removal path,
+  // soft-expires legacy rows rather than deleting them, so counting
+  // expired rows would leave the guard permanently stuck with no
+  // supported way to drain the backlog.
   const legacy = await engine.executeRaw<{ n: string }>(
     `SELECT COUNT(*) AS n
        FROM facts f
       WHERE f.row_num IS NULL
         AND f.entity_slug IS NOT NULL
+        AND f.expired_at IS NULL
         AND EXISTS (
           SELECT 1 FROM pages p
            WHERE p.source_id = f.source_id
@@ -334,9 +364,12 @@ export async function runExtractFacts(
         // partial-UNIQUE-index keyspace). #1928: `cli:`-origin facts
         // (conversation facts from extract-conversation-facts) are NOT
         // fence-owned — the page carries no `## Facts` fence to recreate
-        // them — so they MUST survive this reconcile.
+        // them — so they MUST survive this reconcile. #2646: soft-expired
+        // legacy rows (forget_fact's record of the forget) likewise
+        // survive via preserveExpiredLegacy.
         const deleted = await engine.deleteFactsForPage(slug, sourceId, {
           excludeSourcePrefixes: ['cli:'],
+          preserveExpiredLegacy: true,
         });
         result.factsDeleted += deleted.deleted;
       }
@@ -363,10 +396,11 @@ export async function runExtractFacts(
     if (hasStaleExisting || hasDuplicateExisting || hasRowNumDrift) {
       // Fall back to the legacy page-level reconcile when old DB rows must
       // be removed. Same delete scoping as above: legacy
-      // NULL-source_markdown_slug rows and `cli:`-origin conversation
-      // facts (#1928) survive.
+      // NULL-source_markdown_slug rows, `cli:`-origin conversation
+      // facts (#1928), and soft-expired legacy rows (#2646) survive.
       const deleted = await engine.deleteFactsForPage(slug, sourceId, {
         excludeSourcePrefixes: ['cli:'],
+        preserveExpiredLegacy: true,
       });
       result.factsDeleted += deleted.deleted;
       toInsert = extracted;
diff --git a/src/core/engine.ts b/src/core/engine.ts
index e7c7b62a7..871e031b0 100644
--- a/src/core/engine.ts
+++ b/src/core/engine.ts
@@ -1815,11 +1815,22 @@ export interface BrainEngine {
    * never recreate them (the page has no `## Facts` fence). Omitted ⇒ legacy
    * behavior (delete every fact on the page coordinate). NULL/empty `source`
    * rows are always deletable (fence default).
+   *
+   * #2646: `preserveExpiredLegacy` protects soft-expired legacy rows
+   * (`row_num IS NULL AND expired_at IS NOT NULL`) — the record left by
+   * `forget_fact`'s legacy DB-only path. Fence rows always carry a
+   * `row_num`, so these rows are never fence-owned and a wipe would
+   * destroy the forget record (the audit trail of the forget). Note what
+   * this does NOT promise: it protects the record, not the forget itself —
+   * if the fence still carries the same claim, fence canonicality
+   * independently reinserts it as a fresh active row (legacy DB-only
+   * forgets are documented as non-durable; see extract-facts.ts). Omitted
+   * ⇒ legacy behavior.
    */
   deleteFactsForPage(
     slug: string,
     source_id: string,
-    opts?: { excludeSourcePrefixes?: string[] },
+    opts?: { excludeSourcePrefixes?: string[]; preserveExpiredLegacy?: boolean },
   ): Promise<{ deleted: number }>;
 
   /**
diff --git a/src/core/pglite-engine.ts b/src/core/pglite-engine.ts
index f3a4f924c..ab562db23 100644
--- a/src/core/pglite-engine.ts
+++ b/src/core/pglite-engine.ts
@@ -4281,9 +4281,15 @@ export class PGLiteEngine implements BrainEngine {
   async deleteFactsForPage(
     slug: string,
     source_id: string,
-    opts?: { excludeSourcePrefixes?: string[] },
+    opts?: { excludeSourcePrefixes?: string[]; preserveExpiredLegacy?: boolean },
   ): Promise<{ deleted: number }> {
     const prefixes = opts?.excludeSourcePrefixes;
+    // #2646: keep soft-expired legacy rows (row_num NULL — never
+    // fence-owned) so a fence reconcile can't destroy forget_fact's
+    // legacy DB-only forget record.
+    const expiredLegacyFilter = opts?.preserveExpiredLegacy
+      ? ` AND NOT (row_num IS NULL AND expired_at IS NOT NULL)`
+      : '';
     if (prefixes && prefixes.length > 0) {
       // #1928: keep rows whose `source` matches an excluded prefix (e.g.
       // `cli:` conversation facts). COALESCE so NULL/empty-source fence rows
@@ -4292,13 +4298,13 @@ export class PGLiteEngine implements BrainEngine {
       const result = await this.db.query(
         `DELETE FROM facts
            WHERE source_id = $1 AND source_markdown_slug = $2
-             AND NOT (COALESCE(source, '') LIKE ANY($3::text[]))`,
+             AND NOT (COALESCE(source, '') LIKE ANY($3::text[]))${expiredLegacyFilter}`,
         [source_id, slug, patterns],
       );
       return { deleted: result.affectedRows ?? 0 };
     }
     const result = await this.db.query(
-      `DELETE FROM facts WHERE source_id = $1 AND source_markdown_slug = $2`,
+      `DELETE FROM facts WHERE source_id = $1 AND source_markdown_slug = $2${expiredLegacyFilter}`,
       [source_id, slug],
     );
     return { deleted: result.affectedRows ?? 0 };
diff --git a/src/core/postgres-engine.ts b/src/core/postgres-engine.ts
index 11ba60c9a..07608f3a4 100644
--- a/src/core/postgres-engine.ts
+++ b/src/core/postgres-engine.ts
@@ -4438,10 +4438,16 @@ export class PostgresEngine implements BrainEngine {
   async deleteFactsForPage(
     slug: string,
     source_id: string,
-    opts?: { excludeSourcePrefixes?: string[] },
+    opts?: { excludeSourcePrefixes?: string[]; preserveExpiredLegacy?: boolean },
   ): Promise<{ deleted: number }> {
     const sql = this.sql;
     const prefixes = opts?.excludeSourcePrefixes;
+    // #2646: keep soft-expired legacy rows (row_num NULL — never
+    // fence-owned) so a fence reconcile can't destroy forget_fact's
+    // legacy DB-only forget record.
+    const expiredLegacyFilter = opts?.preserveExpiredLegacy
+      ? sql`AND NOT (row_num IS NULL AND expired_at IS NOT NULL)`
+      : sql``;
     if (prefixes && prefixes.length > 0) {
       // #1928: keep rows whose `source` matches an excluded prefix (e.g.
       // `cli:` conversation facts). COALESCE so NULL/empty-source fence rows
@@ -4452,11 +4458,12 @@ export class PostgresEngine implements BrainEngine {
         WHERE source_id = ${source_id}
           AND source_markdown_slug = ${slug}
           AND NOT (COALESCE(source, '') LIKE ANY(${patterns}))
+          ${expiredLegacyFilter}
       `;
       return { deleted: result.count ?? 0 };
     }
     const result = await sql`
-      DELETE FROM facts WHERE source_id = ${source_id} AND source_markdown_slug = ${slug}
+      DELETE FROM facts WHERE source_id = ${source_id} AND source_markdown_slug = ${slug} ${expiredLegacyFilter}
     `;
     return { deleted: result.count ?? 0 };
   }
diff --git a/test/e2e/facts-fence-reconcile-postgres.test.ts b/test/e2e/facts-fence-reconcile-postgres.test.ts
index 774b55f44..d57e80620 100644
--- a/test/e2e/facts-fence-reconcile-postgres.test.ts
+++ b/test/e2e/facts-fence-reconcile-postgres.test.ts
@@ -73,3 +73,90 @@ describe.skipIf(skip)('facts-fence escaped-pipe reconciliation on Postgres', ()
     ]);
   }, 30_000);
 });
+
+describe.skipIf(skip)('deleteFactsForPage preserveExpiredLegacy on Postgres (#2646)', () => {
+  // The PGLite side of this contract is pinned by
+  // test/extract-facts-phase.test.ts; this pins the postgres.js
+  // tagged-fragment SQL (the two branches interpolate `expiredLegacyFilter`
+  // differently) AND the returned delete count on a real Postgres.
+  const slug = 'people/expired-legacy-preserve-example';
+  let engine: PostgresEngine;
+
+  beforeAll(async () => {
+    engine = new PostgresEngine();
+    await engine.connect({ database_url: databaseUrl! });
+    await engine.initSchema();
+  });
+
+  afterAll(async () => {
+    if (engine) {
+      await engine.executeRaw('DELETE FROM facts WHERE source_markdown_slug = $1', [slug]);
+      await engine.executeRaw('DELETE FROM pages WHERE slug = $1', [slug]);
+      await engine.disconnect();
+    }
+  });
+
+  async function seedRows(): Promise<void> {
+    await engine.executeRaw('DELETE FROM facts WHERE source_markdown_slug = $1', [slug]);
+    // One fence-owned active row (deletable) + one soft-expired legacy row
+    // (row_num NULL, expired_at set — forget_fact's record, must survive).
+    await engine.executeRaw(
+      `INSERT INTO facts (source_id, entity_slug, fact, kind, visibility, notability,
+                          valid_from, source, confidence, row_num, expired_at, source_markdown_slug)
+       VALUES
+         ('default', $1, 'fence-owned active fact', 'fact', 'world', 'high',
+          now(), 'fence:reconcile', 1.0, 1, NULL, $1),
+         ('default', $1, 'forgotten legacy claim', 'fact', 'private', 'medium',
+          now(), 'mcp:put_page', 1.0, NULL, now(), $1)`,
+      [slug],
+    );
+  }
+
+  test('no-prefix branch: expired legacy row survives, count reflects only real deletions', async () => {
+    await seedRows();
+    const { deleted } = await engine.deleteFactsForPage(slug, 'default', {
+      preserveExpiredLegacy: true,
+    });
+    expect(deleted).toBe(1); // only the fence-owned row
+
+    const rows = await engine.executeRaw<{ fact: string }>(
+      'SELECT fact FROM facts WHERE source_markdown_slug = $1', [slug],
+    );
+    expect(Array.from(rows).map(r => r.fact)).toEqual(['forgotten legacy claim']);
+  }, 30_000);
+
+  test('prefix branch: excludeSourcePrefixes and preserveExpiredLegacy compose', async () => {
+    await seedRows();
+    // Add a cli:-origin row that the prefix exclusion must protect.
+    await engine.executeRaw(
+      `INSERT INTO facts (source_id, entity_slug, fact, kind, visibility, notability,
+                          valid_from, source, confidence, row_num, expired_at, source_markdown_slug)
+       VALUES ('default', $1, 'conversation fact', 'fact', 'private', 'medium',
+               now(), 'cli:extract-conversation-facts', 1.0, NULL, NULL, $1)`,
+      [slug],
+    );
+    const { deleted } = await engine.deleteFactsForPage(slug, 'default', {
+      excludeSourcePrefixes: ['cli:'],
+      preserveExpiredLegacy: true,
+    });
+    expect(deleted).toBe(1); // only the fence-owned row
+
+    const rows = await engine.executeRaw<{ fact: string }>(
+      'SELECT fact FROM facts WHERE source_markdown_slug = $1 ORDER BY id', [slug],
+    );
+    expect(Array.from(rows).map(r => r.fact)).toEqual([
+      'forgotten legacy claim',
+      'conversation fact',
+    ]);
+  }, 30_000);
+
+  test('omitted option keeps legacy wipe behavior (expired row IS deleted)', async () => {
+    await seedRows();
+    const { deleted } = await engine.deleteFactsForPage(slug, 'default');
+    expect(deleted).toBe(2);
+    const rows = await engine.executeRaw<{ fact: string }>(
+      'SELECT fact FROM facts WHERE source_markdown_slug = $1', [slug],
+    );
+    expect(Array.from(rows)).toHaveLength(0);
+  }, 30_000);
+});
diff --git a/test/extract-facts-phase.test.ts b/test/extract-facts-phase.test.ts
index 5f046dfdf..d45900ee1 100644
--- a/test/extract-facts-phase.test.ts
+++ b/test/extract-facts-phase.test.ts
@@ -334,6 +334,186 @@ describe('runExtractFacts — empty-fence guard (Codex R2-#7)', () => {
     expect(r.factsInserted).toBe(1);
   });
 
+  test('soft-expired legacy rows do NOT trigger the guard (#2646 — forget_fact drains the backlog)', async () => {
+    // A legacy row that forget_fact already soft-expired. Before #2646
+    // the guard counted it forever: apply-migrations no-ops (migration
+    // marked applied) and forget_fact only sets expired_at, so the
+    // phase was permanently blocked with no sanctioned way out.
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    await (engine as any).db.query(
+      `INSERT INTO facts (source_id, entity_slug, fact, kind, visibility, notability,
+                          valid_from, source, confidence, expired_at)
+       VALUES ('default', 'people/alice', 'forgotten legacy claim', 'fact', 'private', 'medium',
+               now(), 'mcp:put_page', 1.0, now())`,
+    );
+
+    await putPage('people/alice', FACT_FENCE(
+      `| 1 | new fact | fact | 1.0 | world | high | 2026-01-01 |  | s |  |`,
+    ));
+
+    const r = await runExtractFacts(engine, { slugs: ['people/alice'] });
+
+    expect(r.guardTriggered).toBe(false);
+    expect(r.legacyRowsPending).toBe(0);
+    expect(r.factsInserted).toBe(1);
+
+    // The expired legacy row itself is untouched (soft-expire is the
+    // record of the forget; the phase must not hard-delete it).
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const rows = await (engine as any).db.query(
+      `SELECT fact FROM facts WHERE row_num IS NULL AND expired_at IS NOT NULL`,
+    );
+    expect(rows.rows).toHaveLength(1);
+    expect(rows.rows[0].fact).toBe('forgotten legacy claim');
+  });
+
+  test('expired legacy row WITH source_markdown_slug set survives reconcile untouched (#2646 codex P2)', async () => {
+    // Hybrid shape: row_num NULL (legacy — never fence-owned) but
+    // source_markdown_slug matching a live page. Without the
+    // preserveExpiredLegacy filter, the reconcile pass would count it
+    // as "stale", trigger a wipe, hard-delete the forget record, and
+    // reinsert the fence's rows fresh — reviving a forgotten claim as
+    // an active fact.
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    await (engine as any).db.query(
+      `INSERT INTO facts (source_id, entity_slug, fact, kind, visibility, notability,
+                          valid_from, source, confidence, expired_at, source_markdown_slug)
+       VALUES ('default', 'people/alice', 'forgotten hybrid claim', 'fact', 'private', 'medium',
+               now(), 'mcp:put_page', 1.0, now(), 'people/alice')`,
+    );
+
+    await putPage('people/alice', FACT_FENCE(
+      `| 1 | fence fact | fact | 1.0 | world | high | 2026-01-01 |  | s |  |`,
+    ));
+
+    const r1 = await runExtractFacts(engine, { slugs: ['people/alice'] });
+    const r2 = await runExtractFacts(engine, { slugs: ['people/alice'] });
+
+    expect(r1.guardTriggered).toBe(false);
+    // The expired hybrid row is invisible to the reconcile: the fence
+    // fact inserts normally, nothing is wiped, and re-running stays
+    // idempotent (the hybrid row must not read as perpetually stale).
+    expect(r1.factsInserted).toBe(1);
+    expect(r1.factsDeleted).toBe(0);
+    expect(r2.factsInserted).toBe(0);
+    expect(r2.factsDeleted).toBe(0);
+
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const rows = await (engine as any).db.query(
+      `SELECT fact, expired_at FROM facts WHERE source_markdown_slug = 'people/alice' ORDER BY id`,
+    );
+    expect(rows.rows).toHaveLength(2);
+    expect(rows.rows[0].fact).toBe('forgotten hybrid claim');
+    expect(rows.rows[0].expired_at).not.toBeNull();
+    expect(rows.rows[1].fact).toBe('fence fact');
+    expect(rows.rows[1].expired_at).toBeNull();
+  });
+
+  test('expired legacy hybrid row survives even a stale-row wipe on the same page (#2646 codex P2)', async () => {
+    // Force the wipe path: seed a fence, reconcile, then change the
+    // fence so the old DB row goes stale. The wipe must delete the
+    // stale fence-owned row but preserve the expired legacy hybrid.
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    await (engine as any).db.query(
+      `INSERT INTO facts (source_id, entity_slug, fact, kind, visibility, notability,
+                          valid_from, source, confidence, expired_at, source_markdown_slug)
+       VALUES ('default', 'people/alice', 'forgotten hybrid claim', 'fact', 'private', 'medium',
+               now(), 'mcp:put_page', 1.0, now(), 'people/alice')`,
+    );
+
+    await putPage('people/alice', FACT_FENCE(
+      `| 1 | old fact | fact | 1.0 | world | high | 2026-01-01 |  | s |  |`,
+    ));
+    await runExtractFacts(engine, { slugs: ['people/alice'] });
+
+    // Replace the fence content — 'old fact' is now stale in the DB.
+    await putPage('people/alice', FACT_FENCE(
+      `| 1 | replacement fact | fact | 1.0 | world | high | 2026-01-01 |  | s |  |`,
+    ));
+    const r = await runExtractFacts(engine, { slugs: ['people/alice'] });
+
+    expect(r.factsDeleted).toBe(1); // only the stale fence-owned row
+    expect(r.factsInserted).toBe(1);
+
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const rows = await (engine as any).db.query(
+      `SELECT fact FROM facts WHERE source_markdown_slug = 'people/alice' ORDER BY id`,
+    );
+    expect(rows.rows.map((row: { fact: string }) => row.fact))
+      .toEqual(['forgotten hybrid claim', 'replacement fact']);
+  });
+
+  test('fence claim matching an expired legacy row is inserted active — fence is canonical (#2646)', async () => {
+    // Deliberate semantics, pinned: legacy DB-only forgets are
+    // documented NOT to survive rebuild (forget.ts header — the
+    // explicit DB-only exception). When the fence still carries the
+    // same (claim, source), the reconcile inserts a fresh active
+    // fence-owned row; the expired legacy row survives alongside as
+    // the record of the earlier forget. Suppressing the insert would
+    // create silent fence↔DB divergence ("0 facts" while the fence
+    // says otherwise) — the exact failure mode the guard prevents.
+    // To durably forget, forget the fence-owned row (fence path).
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    await (engine as any).db.query(
+      `INSERT INTO facts (source_id, entity_slug, fact, kind, visibility, notability,
+                          valid_from, source, confidence, expired_at, source_markdown_slug)
+       VALUES ('default', 'people/alice', 'shared claim', 'fact', 'private', 'medium',
+               now(), 's', 1.0, now(), 'people/alice')`,
+    );
+
+    await putPage('people/alice', FACT_FENCE(
+      `| 1 | shared claim | fact | 1.0 | world | high | 2026-01-01 |  | s |  |`,
+    ));
+
+    const r1 = await runExtractFacts(engine, { slugs: ['people/alice'] });
+    const r2 = await runExtractFacts(engine, { slugs: ['people/alice'] });
+
+    expect(r1.factsInserted).toBe(1);
+    expect(r1.factsDeleted).toBe(0);
+    // Idempotent thereafter — the coexisting pair is stable state.
+    expect(r2.factsInserted).toBe(0);
+    expect(r2.factsDeleted).toBe(0);
+
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const rows = await (engine as any).db.query(
+      `SELECT fact, row_num, expired_at FROM facts
+        WHERE source_markdown_slug = 'people/alice' ORDER BY id`,
+    );
+    expect(rows.rows).toHaveLength(2);
+    expect(rows.rows[0]).toMatchObject({ fact: 'shared claim', row_num: null });
+    expect(rows.rows[0].expired_at).not.toBeNull();   // forget record preserved
+    expect(rows.rows[1]).toMatchObject({ fact: 'shared claim', row_num: 1 });
+    expect(rows.rows[1].expired_at).toBeNull();       // fence-canonical active row
+  });
+
+  test('mixed active + expired legacy rows: guard counts only the active ones (#2646)', async () => {
+    // One active legacy row + one soft-expired legacy row. The guard
+    // must still trigger (an active row is pending backfill) but the
+    // pending count must exclude the expired row — so each forget_fact
+    // visibly drains the counter toward release.
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    await (engine as any).db.query(
+      `INSERT INTO facts (source_id, entity_slug, fact, kind, visibility, notability,
+                          valid_from, source, confidence, expired_at)
+       VALUES
+         ('default', 'people/alice', 'active legacy claim', 'fact', 'private', 'medium',
+          now(), 'mcp:put_page', 1.0, NULL),
+         ('default', 'people/alice', 'expired legacy claim', 'fact', 'private', 'medium',
+          now(), 'mcp:put_page', 1.0, now())`,
+    );
+
+    await putPage('people/alice', FACT_FENCE(
+      `| 1 | new fact | fact | 1.0 | world | high | 2026-01-01 |  | s |  |`,
+    ));
+
+    const r = await runExtractFacts(engine, { slugs: ['people/alice'] });
+
+    expect(r.guardTriggered).toBe(true);
+    expect(r.legacyRowsPending).toBe(1);
+    expect(r.factsInserted).toBe(0);
+    expect(r.factsDeleted).toBe(0);
+  });
+
   test('NULL entity_slug legacy rows do NOT trigger the guard (they are structurally unfenceable)', async () => {
     // eslint-disable-next-line @typescript-eslint/no-explicit-any
     await (engine as any).db.query(