diff --git a/src/db/retention.ts b/src/db/retention.ts
index 78033f38d5..1b69018f8b 100644
--- a/src/db/retention.ts
+++ b/src/db/retention.ts
@@ -118,6 +118,18 @@ export const LATEST_ONLY_SIGNAL_SNAPSHOT_TYPES = [
   "contributor-evidence-graph",
   "contributor-outcome-history",
   "contributor-strategy",
+  // #8900: these eight writers also INSERT a fresh row every run (persistSignalSnapshot is not an
+  // upsert) while every consumer reads only index [0] / the latest row — same latest-only contract as
+  // the repo-* and contributor-intelligence types above. queue-health stays EXCLUDED (feeds
+  // buildQueueTrendReport as a real series).
+  "config-quality",
+  "label-audit",
+  "maintainer-lane",
+  "maintainer-cut-readiness",
+  "contributor-intake-health",
+  "issue-quality",
+  "repo-outcome-patterns",
+  "pr-reviewability",
 ] as const;
 
 /**
diff --git a/test/unit/retention.test.ts b/test/unit/retention.test.ts
index 7797b9a7d9..2d40c0f300 100644
--- a/test/unit/retention.test.ts
+++ b/test/unit/retention.test.ts
@@ -201,6 +201,39 @@ describe("dedupeSignalSnapshots", () => {
     expect(ids).toContain("pack-2");
   });
 
+  it("dedupes the eight latest-only signal types added in #8900 to one row per repo", async () => {
+    const env = createTestEnv();
+    const types = [
+      "config-quality",
+      "label-audit",
+      "maintainer-lane",
+      "maintainer-cut-readiness",
+      "contributor-intake-health",
+      "issue-quality",
+      "repo-outcome-patterns",
+      "pr-reviewability",
+    ] as const;
+    for (const signalType of types) {
+      await insertSignalSnapshot(env, `${signalType}-old`, signalType, "JSONbored/loopover", "2026-07-01T00:00:00.000Z");
+      await insertSignalSnapshot(env, `${signalType}-mid`, signalType, "JSONbored/loopover", "2026-07-02T00:00:00.000Z");
+      await insertSignalSnapshot(env, `${signalType}-new`, signalType, "JSONbored/loopover", "2026-07-03T00:00:00.000Z");
+      await insertSignalSnapshot(env, `${signalType}-other`, signalType, "other/repo", "2026-07-03T00:00:00.000Z");
+    }
+
+    const results = await dedupeSignalSnapshots(env);
+    const byType = Object.fromEntries(results.map((r) => [r.signalType, r.deleted]));
+    for (const signalType of types) {
+      expect(byType[signalType]).toBe(2); // old + mid deleted; new kept; other/repo untouched
+      expect(await countSignalSnapshots(env, signalType)).toBe(2); // latest for loopover + other/repo
+    }
+    const remaining = await env.DB.prepare("SELECT id FROM signal_snapshots ORDER BY id").all<{ id: string }>();
+    const ids = (remaining.results ?? []).map((row) => row.id);
+    expect(ids).toContain("pr-reviewability-new");
+    expect(ids).toContain("pr-reviewability-other");
+    expect(ids).not.toContain("pr-reviewability-old");
+    expect(ids).not.toContain("pr-reviewability-mid");
+  });
+
   it("dedupes private and public focus-manifest cache snapshots (regression for storage exhaustion)", async () => {
     const env = createTestEnv();
     await insertSignalSnapshot(env, "private-old", REPO_FOCUS_MANIFEST_SIGNAL, "JSONbored/loopover", "2026-06-01T00:00:00.000Z");