diff --git a/scripts/lib/brief-dedup.mjs b/scripts/lib/brief-dedup.mjs
index 946814d40..bbc765554 100644
--- a/scripts/lib/brief-dedup.mjs
+++ b/scripts/lib/brief-dedup.mjs
@@ -14,6 +14,10 @@
  *                                       location veto; default on
  *   DIGEST_DEDUP_COSINE_THRESHOLD     = float in (0, 1], default 0.60
  *   DIGEST_DEDUP_WALL_CLOCK_MS        = int ms, default 45000
+ *   DIGEST_DEDUP_TOPIC_GROUPING       = '0' disables secondary topic
+ *                                       grouping pass; default on
+ *   DIGEST_DEDUP_TOPIC_THRESHOLD      = float in (0, 1], default 0.45
+ *                                       — looser secondary-pass cosine
  *
  * Anything non-{embed,jaccard} in MODE = jaccard with a loud warn so
  * a typo can't stay hidden.
@@ -53,6 +57,8 @@ import { defaultRedisPipeline } from './_upstash-pipeline.mjs';
  *   entityVetoEnabled: boolean,
  *   cosineThreshold: number,
  *   wallClockMs: number,
+ *   topicGroupingEnabled: boolean,
+ *   topicThreshold: number,
  *   invalidModeRaw: string | null,
  * }}
  */
@@ -65,9 +71,14 @@ export function readOrchestratorConfig(env = process.env) {
   } else if (modeRaw === 'jaccard') {
     mode = 'jaccard';
   } else {
-    // Unrecognised value — default to embed (the normal prod path)
-    // but surface so a DIGEST_DEDUP_MODE=embbed typo is obvious.
-    mode = 'embed';
+    // Unrecognised value — fall back to the SAFE path (Jaccard), not
+    // the newer embed path. This matches the file-header contract: a
+    // typo like `DIGEST_DEDUP_MODE=jacard` while an operator is trying
+    // to set the kill switch during an embed outage must NOT silently
+    // keep embed on. The invalidModeRaw warn surfaces the typo so it's
+    // fixed, but the fail-closed default protects the cron in the
+    // meantime.
+    mode = 'jaccard';
     invalidModeRaw = modeRaw;
   }
 
@@ -90,12 +101,27 @@ export function readOrchestratorConfig(env = process.env) {
   const wallClockMs =
     Number.isInteger(wallClockRaw) && wallClockRaw > 0 ? wallClockRaw : 45_000;
 
+  // Secondary topic-grouping pass (default on). Kill switch: set to '0'.
+  // Any non-'0' value (including '', 'yes', '1') is treated as enabled.
+  const topicGroupingEnabled = env.DIGEST_DEDUP_TOPIC_GROUPING !== '0';
+
+  // Looser cosine for the secondary pass (default 0.45). Invalid/out-of-range
+  // values fall back to the default silently so a Railway typo can't disable
+  // the feature by accident.
+  const topicThresholdRaw = Number.parseFloat(env.DIGEST_DEDUP_TOPIC_THRESHOLD ?? '');
+  const topicThreshold =
+    Number.isFinite(topicThresholdRaw) && topicThresholdRaw > 0 && topicThresholdRaw <= 1
+      ? topicThresholdRaw
+      : 0.45;
+
   return {
     mode,
     clustering,
     entityVetoEnabled: env.DIGEST_DEDUP_ENTITY_VETO_ENABLED !== '0',
     cosineThreshold,
     wallClockMs,
+    topicGroupingEnabled,
+    topicThreshold,
     invalidModeRaw,
   };
 }
@@ -116,28 +142,33 @@ function titleHashHex(normalizedTitle) {
  * @param {typeof deduplicateStoriesJaccard} [deps.jaccard]
  * @param {typeof defaultRedisPipeline} [deps.redisPipeline]
  * @param {() => number} [deps.now]
- * @param {(line: string) => void} [deps.log]
  * @param {(line: string) => void} [deps.warn]
+ * @returns {Promise<{
+ *   reps: Array<object>,
+ *   embeddingByHash: Map<string, number[]>,
+ *   logSummary: string,
+ * }>}
  */
 export async function deduplicateStories(stories, deps = {}) {
   const cfg = readOrchestratorConfig(deps.env ?? process.env);
   const jaccard = deps.jaccard ?? deduplicateStoriesJaccard;
-  const log = deps.log ?? ((line) => console.log(line));
   const warn = deps.warn ?? ((line) => console.warn(line));
 
   if (cfg.invalidModeRaw !== null) {
     warn(
       `[digest] dedup unrecognised DIGEST_DEDUP_MODE=${cfg.invalidModeRaw} — ` +
-        'defaulting to embed. Valid values: embed | jaccard.',
+        'falling back to jaccard (safe rollback path). Valid values: embed | jaccard.',
     );
   }
 
-  if (!Array.isArray(stories) || stories.length === 0) return [];
+  if (!Array.isArray(stories) || stories.length === 0) {
+    return { reps: [], embeddingByHash: new Map(), logSummary: '' };
+  }
 
   // Kill switch: Railway operator sets MODE=jaccard to instantly
   // revert to the legacy deduper without a redeploy.
   if (cfg.mode === 'jaccard') {
-    return jaccard(stories);
+    return { reps: jaccard(stories), embeddingByHash: new Map(), logSummary: '' };
   }
 
   const embedImpl = deps.embedBatch ?? embedBatch;
@@ -196,16 +227,34 @@ export async function deduplicateStories(stories, deps = {}) {
     });
 
     const embedClusters = clusterResult.clusters;
-    const embedOutput = embedClusters.map((cluster) =>
-      materializeCluster(cluster.map((i) => items[i].story)),
-    );
+    const embeddingByHash = new Map();
+    const embedOutput = [];
+    for (const cluster of embedClusters) {
+      const rep = materializeCluster(cluster.map((i) => items[i].story));
+      embedOutput.push(rep);
+      if (cfg.topicGroupingEnabled) {
+        // Find the item inside this cluster whose story wins materialize
+        // (materializeCluster sort key: currentScore DESC, mentionCount DESC
+        // — ties broken by input order). The winning story's hash matches
+        // rep.hash; its embedding is the topic-grouping vector for rep.
+        const winningIdx = cluster.find((i) => items[i].story.hash === rep.hash);
+        if (winningIdx !== undefined) {
+          embeddingByHash.set(rep.hash, items[winningIdx].embedding);
+        } else {
+          // Defensive: shouldn't fire — materializeCluster always picks a
+          // hash that's in the cluster. Warn so a future refactor that
+          // synthesises a new rep doesn't silently skip the sidecar
+          // (would cause topic grouping to fall through to primary order).
+          warn(`[digest] dedup sidecar: materialized rep ${rep.hash} not found in its cluster — topic grouping will skip this rep`);
+        }
+      }
+    }
 
-    log(
+    const logSummary =
       `[digest] dedup mode=embed clustering=${cfg.clustering} stories=${items.length} clusters=${embedClusters.length} ` +
-        `veto_fires=${clusterResult.vetoFires} ms=${nowImpl() - started} ` +
-        `threshold=${cfg.cosineThreshold} fallback=false`,
-    );
-    return embedOutput;
+      `veto_fires=${clusterResult.vetoFires} ms=${nowImpl() - started} ` +
+      `threshold=${cfg.cosineThreshold} fallback=false`;
+    return { reps: embedOutput, embeddingByHash, logSummary };
   } catch (err) {
     const reason =
       err instanceof Error && typeof err.name === 'string' && err.name !== 'Error'
@@ -215,6 +264,145 @@ export async function deduplicateStories(stories, deps = {}) {
     warn(
       `[digest] dedup embed path failed, falling back to Jaccard reason=${reason} msg=${msg}`,
     );
-    return jaccard(stories);
+    return { reps: jaccard(stories), embeddingByHash: new Map(), logSummary: '' };
+  }
+}
+
+// ── Secondary topic-grouping pass ───────────────────────────────────────
+
+/**
+ * Pure function. Re-orders already-sliced, already-deduped reps so related
+ * stories form contiguous blocks, with the dominant thread (by topic size)
+ * leading. Runs AFTER `deduplicateStories` + score-floor + top-N slice.
+ *
+ * No I/O, no logging, no Redis. Caller owns logging. Errors are RETURNED
+ * not thrown — a throw would otherwise propagate into the caller's outer
+ * try/catch around `deduplicateStories` and trigger the Jaccard fallback
+ * for a topic-grouping bug, which is the wrong blast radius.
+ *
+ * Sort key: (topicSize DESC, topicMax DESC, repScore DESC, titleHashHex ASC)
+ * — total, deterministic, stable across input permutations.
+ *
+ * @param {Array<{hash:string, title:string, currentScore:number}>} top
+ * @param {{ topicGroupingEnabled: boolean, topicThreshold: number }} cfg
+ * @param {Map<string, number[]>} embeddingByHash
+ * @param {object} [deps]
+ * @param {typeof singleLinkCluster} [deps.clusterFn] — injected for testing
+ * @returns {{ reps: Array<object>, topicCount: number, error: Error | null }}
+ */
+export function groupTopicsPostDedup(top, cfg, embeddingByHash, deps = {}) {
+  if (!cfg.topicGroupingEnabled || !Array.isArray(top) || top.length <= 1) {
+    return { reps: Array.isArray(top) ? top : [], topicCount: Array.isArray(top) ? top.length : 0, error: null };
+  }
+
+  const clusterFn = deps.clusterFn ?? singleLinkCluster;
+
+  try {
+    const items = top.map((rep) => ({
+      title: rep.title,
+      embedding: embeddingByHash?.get(rep.hash),
+    }));
+
+    if (items.some((it) => !Array.isArray(it.embedding))) {
+      return {
+        reps: top,
+        topicCount: top.length,
+        error: new Error('topic grouping: missing embedding for at least one rep'),
+      };
+    }
+
+    const { clusters } = clusterFn(items, {
+      cosineThreshold: cfg.topicThreshold,
+      // Topic level: do NOT re-apply the event-level entity veto. At this
+      // cosine (~0.45) stories sharing the same broader narrative should
+      // group even when their actor sets diverge (Biden+Xi vs Biden+Putin).
+      vetoFn: null,
+    });
+
+    // Dense-fill with -1 sentinel so an incomplete clusterFn (a future
+    // injection that doesn't cover every input index) surfaces as an
+    // explicit error instead of silently poisoning the phase-1 aggregates
+    // (topicSize[undefined] / topicMax[undefined] would degrade the sort).
+    const topicOf = new Array(top.length).fill(-1);
+    clusters.forEach((members, tIdx) => {
+      for (const i of members) topicOf[i] = tIdx;
+    });
+    for (let i = 0; i < topicOf.length; i++) {
+      if (topicOf[i] === -1) {
+        throw new Error(`topic grouping: clusterFn missed index ${i}`);
+      }
+    }
+
+    const hashOf = top.map((rep) =>
+      titleHashHex(normalizeForEmbedding(rep.title ?? '')),
+    );
+
+    // Two-phase sort, NOT a single global key. A global key that ties
+    // on (topicSize, topicMax) falls through to per-rep repScore, which
+    // interleaves members of same-size-same-max topics (A90,B90,A80,B70
+    // would sort as [A90,B90,A80,B70] — broken contiguity). Phase 1
+    // orders the TOPICS; phase 2 orders members inside each topic.
+
+    // Phase 1 prep: per-topic aggregates + a TOPIC-level tiebreak hash
+    // (min member title hash) so cross-topic ties break by topic
+    // identity, not by an individual rep's hash.
+    const topicSize = new Array(clusters.length).fill(0);
+    const topicMax = new Array(clusters.length).fill(-Infinity);
+    const topicTieHash = new Array(clusters.length).fill(null);
+    top.forEach((rep, i) => {
+      const t = topicOf[i];
+      topicSize[t] += 1;
+      const s = Number(rep.currentScore ?? 0);
+      if (s > topicMax[t]) topicMax[t] = s;
+      if (topicTieHash[t] === null || hashOf[i] < topicTieHash[t]) {
+        topicTieHash[t] = hashOf[i];
+      }
+    });
+
+    // Members grouped by topic for phase-2 ordering.
+    const membersOf = Array.from({ length: clusters.length }, () => []);
+    for (let i = 0; i < top.length; i++) {
+      membersOf[topicOf[i]].push(i);
+    }
+
+    // Phase 2: sort members within each topic by (repScore DESC,
+    // titleHashHex ASC). Deterministic within a topic.
+    for (const members of membersOf) {
+      members.sort((a, b) => {
+        const sA = Number(top[a].currentScore ?? 0);
+        const sB = Number(top[b].currentScore ?? 0);
+        if (sA !== sB) return sB - sA;
+        return hashOf[a] < hashOf[b] ? -1 : hashOf[a] > hashOf[b] ? 1 : 0;
+      });
+    }
+
+    // Phase 1 sort: order TOPICS by (topicSize DESC, topicMax DESC,
+    // topicTieHash ASC). The topic-tie hash is a property of the topic
+    // itself, so two topics with the same (size, max) order stably and
+    // — critically — do not interleave their members.
+    const topicOrder = [...Array(clusters.length).keys()].sort((a, b) => {
+      if (topicSize[a] !== topicSize[b]) return topicSize[b] - topicSize[a];
+      if (topicMax[a] !== topicMax[b]) return topicMax[b] - topicMax[a];
+      return topicTieHash[a] < topicTieHash[b] ? -1 : topicTieHash[a] > topicTieHash[b] ? 1 : 0;
+    });
+
+    // Concatenate: for each topic in topicOrder, emit its members in
+    // their intra-topic order.
+    const order = [];
+    for (const t of topicOrder) {
+      for (const i of membersOf[t]) order.push(i);
+    }
+
+    return {
+      reps: order.map((i) => top[i]),
+      topicCount: clusters.length,
+      error: null,
+    };
+  } catch (err) {
+    return {
+      reps: top,
+      topicCount: top.length,
+      error: err instanceof Error ? err : new Error(String(err)),
+    };
   }
 }
diff --git a/scripts/seed-digest-notifications.mjs b/scripts/seed-digest-notifications.mjs
index 21909a52f..884ac4f8e 100644
--- a/scripts/seed-digest-notifications.mjs
+++ b/scripts/seed-digest-notifications.mjs
@@ -40,7 +40,11 @@ import { issueSlotInTz } from '../shared/brief-filter.js';
 import { enrichBriefEnvelopeWithLLM } from './lib/brief-llm.mjs';
 import { assertBriefEnvelope } from '../server/_shared/brief-render.js';
 import { signBriefUrl, BriefUrlError } from './lib/brief-url-sign.mjs';
-import { deduplicateStories } from './lib/brief-dedup.mjs';
+import {
+  deduplicateStories,
+  groupTopicsPostDedup,
+  readOrchestratorConfig,
+} from './lib/brief-dedup.mjs';
 import { stripSourceSuffix } from './lib/brief-dedup-jaccard.mjs';
 
 // ── Config ────────────────────────────────────────────────────────────────────
@@ -289,7 +293,9 @@ async function buildDigest(rule, windowStartMs) {
   if (stories.length === 0) return null;
 
   stories.sort((a, b) => b.currentScore - a.currentScore);
-  const dedupedAll = await deduplicateStories(stories);
+  const cfg = readOrchestratorConfig(process.env);
+  const { reps: dedupedAll, embeddingByHash, logSummary } =
+    await deduplicateStories(stories);
   // Apply the absolute-score floor AFTER dedup so the floor runs on
   // the representative's score (mentionCount-sum doesn't change the
   // score field; the rep is the highest-scoring member of its
@@ -319,7 +325,40 @@ async function buildDigest(rule, windowStartMs) {
     }
     return null;
   }
-  const top = deduped.slice(0, DIGEST_MAX_ITEMS);
+  const sliced = deduped.slice(0, DIGEST_MAX_ITEMS);
+
+  // Secondary topic-grouping pass: re-orders `sliced` so related stories
+  // form contiguous blocks. Disabled via DIGEST_DEDUP_TOPIC_GROUPING=0.
+  // Gate on the sidecar Map being non-empty — this is the precise
+  // signal for "primary embed path produced vectors". Gating on
+  // cfg.mode is WRONG: the embed path can run AND fall back to
+  // Jaccard at runtime (try/catch inside deduplicateStories), leaving
+  // cfg.mode==='embed' but embeddingByHash empty. The Map size is the
+  // only ground truth. Kill-switch (mode=jaccard) and runtime fallback
+  // both produce size=0 → shouldGroupTopics=false → no misleading
+  // "topic grouping failed: missing embedding" warn.
+  // Errors from the helper are returned (not thrown) and MUST NOT
+  // cascade into the outer Jaccard fallback — they just preserve
+  // primary order.
+  const shouldGroupTopics = cfg.topicGroupingEnabled && embeddingByHash.size > 0;
+  const { reps: top, topicCount, error: topicErr } = shouldGroupTopics
+    ? groupTopicsPostDedup(sliced, cfg, embeddingByHash)
+    : { reps: sliced, topicCount: sliced.length, error: null };
+  if (topicErr) {
+    console.warn(
+      `[digest] topic grouping failed, preserving primary order: ${topicErr.message}`,
+    );
+  }
+  if (logSummary) {
+    const finalLog =
+      shouldGroupTopics && !topicErr
+        ? logSummary.replace(
+            /clusters=(\d+) /,
+            `clusters=$1 topics=${topicCount} `,
+          )
+        : logSummary;
+    console.log(finalLog);
+  }
 
   const allSourceCmds = [];
   const cmdIndex = [];
diff --git a/tests/brief-dedup-embedding.test.mjs b/tests/brief-dedup-embedding.test.mjs
index 462759f4b..fc65bb6f3 100644
--- a/tests/brief-dedup-embedding.test.mjs
+++ b/tests/brief-dedup-embedding.test.mjs
@@ -23,7 +23,11 @@
 import { describe, it } from 'node:test';
 import assert from 'node:assert/strict';
 
-import { deduplicateStories } from '../scripts/lib/brief-dedup.mjs';
+import {
+  deduplicateStories,
+  groupTopicsPostDedup,
+  readOrchestratorConfig,
+} from '../scripts/lib/brief-dedup.mjs';
 import { deduplicateStoriesJaccard } from '../scripts/lib/brief-dedup-jaccard.mjs';
 import {
   EmbeddingProviderError,
@@ -114,7 +118,7 @@ describe('Scenario 1 — happy path: embed clusters near-duplicates', () => {
       story('Iran shuts Strait of Hormuz', 85, 1, 'h1'),
       story('Myanmar coup leader elected president', 80, 1, 'h2'),
     ];
-    const out = await deduplicateStories(stories, {
+    const { reps: out, logSummary } = await deduplicateStories(stories, {
       env: EMBED_MODE,
       embedBatch: embedder.embedBatch,
       redisPipeline: noopPipeline,
@@ -133,9 +137,37 @@ describe('Scenario 1 — happy path: embed clusters near-duplicates', () => {
     assert.ok(singleton);
     assert.equal(singleton.mergedHashes[0], 'h2');
 
-    // Structured log line emitted.
-    assert.ok(collector.lines.some((l) => l.line.includes('mode=embed')));
-    assert.ok(collector.lines.some((l) => l.line.includes('fallback=false')));
+    // Structured log line composed in logSummary (caller emits).
+    assert.match(logSummary, /mode=embed/);
+    assert.match(logSummary, /fallback=false/);
+  });
+
+  it('runtime Jaccard fallback returns empty embeddingByHash + empty logSummary', async () => {
+    // Regression guard for the nested-fallback leak: when the embed
+    // path throws at runtime, deduplicateStories falls back to Jaccard
+    // but cfg.mode is still 'embed'. The caller's shouldGroupTopics
+    // gate must rely on embeddingByHash.size > 0 (ground truth) rather
+    // than cfg.mode === 'embed' (stale signal), else a false
+    // "topic grouping failed: missing embedding" warn fires on top
+    // of the legitimate "falling back to Jaccard" warn.
+    const throwingEmbedder = async () => {
+      throw new EmbeddingProviderError('forced', { status: 500 });
+    };
+    const stories = [
+      story('Iran closes Strait of Hormuz', 90, 1, 'h0'),
+      story('Iran shuts Strait of Hormuz', 85, 1, 'h1'),
+    ];
+    const { reps, embeddingByHash, logSummary } = await deduplicateStories(stories, {
+      env: EMBED_MODE, // configured mode === 'embed'
+      embedBatch: throwingEmbedder,
+      redisPipeline: noopPipeline,
+    });
+    assert.ok(reps.length >= 1, 'Jaccard produced reps');
+    assert.equal(embeddingByHash.size, 0, 'fallback path MUST return empty Map');
+    assert.equal(logSummary, '', 'fallback path MUST return empty logSummary');
+    // Caller-side invariant: shouldGroupTopics using Map size (ground
+    // truth) is false; using cfg.mode would be true (stale) and leak.
+    assert.equal(embeddingByHash.size > 0, false, 'correct gate: size-based');
   });
 });
 
@@ -152,7 +184,7 @@ describe('Scenario 2 — cold-cache timeout collapses to Jaccard', () => {
     ];
     const collector = lineCollector();
 
-    const out = await deduplicateStories(stories, {
+    const { reps: out } = await deduplicateStories(stories, {
       env: EMBED_MODE,
       embedBatch: throwingEmbedder,
       redisPipeline: noopPipeline,
@@ -188,7 +220,7 @@ describe('Scenario 3 — provider outage collapses to Jaccard', () => {
     const stories = [story('a', 10, 1, 'a1'), story('b', 10, 1, 'b1')];
     const collector = lineCollector();
 
-    const out = await deduplicateStories(stories, {
+    const { reps: out } = await deduplicateStories(stories, {
       env: EMBED_MODE,
       embedBatch: throwingEmbedder,
       redisPipeline: noopPipeline,
@@ -264,7 +296,7 @@ describe('Scenario 5 — entity veto blocks same-location, different-actor merge
     ]);
     const embedder = stubEmbedder(vecByTitle);
 
-    const out = await deduplicateStories(stories, {
+    const { reps: out } = await deduplicateStories(stories, {
       env: EMBED_MODE,
       embedBatch: embedder.embedBatch,
       redisPipeline: noopPipeline,
@@ -284,7 +316,7 @@ describe('Scenario 5 — entity veto blocks same-location, different-actor merge
     ]);
     const embedder = stubEmbedder(vecByTitle);
 
-    const out = await deduplicateStories(stories, {
+    const { reps: out } = await deduplicateStories(stories, {
       env: { ...EMBED_MODE, DIGEST_DEDUP_ENTITY_VETO_ENABLED: '0' },
       embedBatch: embedder.embedBatch,
       redisPipeline: noopPipeline,
@@ -371,7 +403,7 @@ describe('Scenario 7 — cluster-level fixture', () => {
     );
     const embedder = stubEmbedder(vecByTitle);
 
-    const out = await deduplicateStories(stories, {
+    const { reps: out } = await deduplicateStories(stories, {
       env: EMBED_MODE,
       embedBatch: embedder.embedBatch,
       redisPipeline: noopPipeline,
@@ -427,7 +459,7 @@ describe('Scenario 9 — permutation-invariance', () => {
     }
 
     // Baseline run on the canonical input order.
-    const baseline = await deduplicateStories(stories, {
+    const { reps: baseline } = await deduplicateStories(stories, {
       env: EMBED_MODE,
       embedBatch: stubEmbedder(vecByTitle).embedBatch,
       redisPipeline: noopPipeline,
@@ -446,7 +478,7 @@ describe('Scenario 9 — permutation-invariance', () => {
         const j = Math.floor(rand() * (i + 1));
         [shuffled[i], shuffled[j]] = [shuffled[j], shuffled[i]];
       }
-      const out = await deduplicateStories(shuffled, {
+      const { reps: out } = await deduplicateStories(shuffled, {
         env: EMBED_MODE,
         embedBatch: stubEmbedder(vecByTitle).embedBatch,
         redisPipeline: noopPipeline,
@@ -658,7 +690,7 @@ describe('readOrchestratorConfig — DIGEST_DEDUP_CLUSTERING', () => {
     const cfg = readOrchestratorConfig({ DIGEST_DEDUP_CLUSTERING: 'average' });
     assert.equal(cfg.clustering, 'single');
   });
-  it('structured log line includes clustering=<algo>', async () => {
+  it('structured logSummary includes clustering=<algo>', async () => {
     const { deduplicateStories } = await import('../scripts/lib/brief-dedup.mjs');
     const stories = [story('x', 10, 1, 'x1'), story('y', 10, 1, 'y1')];
     const vec = new Map([
@@ -666,14 +698,486 @@ describe('readOrchestratorConfig — DIGEST_DEDUP_CLUSTERING', () => {
       [normalizeForEmbedding('y'), [0.99, Math.sqrt(1 - 0.99 * 0.99), 0]],
     ]);
     const { embedBatch } = stubEmbedder(vec);
-    const lines = [];
-    await deduplicateStories(stories, {
+    const { logSummary } = await deduplicateStories(stories, {
       env: { DIGEST_DEDUP_MODE: 'embed', DIGEST_DEDUP_COSINE_THRESHOLD: '0.5' },
       embedBatch,
       redisPipeline: async () => [],
-      log: (l) => lines.push(l),
     });
-    assert.ok(lines.some((l) => /clustering=(single|complete)/.test(l)), 'log line must mention clustering algorithm');
+    assert.match(logSummary, /clustering=(single|complete)/, 'logSummary must mention clustering algorithm');
+  });
+});
+
+// ── Topic-grouping post-dedup (secondary pass) ────────────────────────────────
+
+/**
+ * Build a basis-aligned unit vector for topic `c`. `jitter ∈ [0, 0.1)`
+ * lets within-topic members share cosine ~0.99+ while staying unit
+ * length. The jitter is parked in dimension `dim-1`, which no topic or
+ * singleton basis occupies — this guarantees cross-topic cosine = 0
+ * regardless of jitter, so the 0.45 secondary threshold has a clean
+ * separation in either direction.
+ */
+function basisVec(dim, c, jitter = 0) {
+  const v = new Array(dim).fill(0);
+  v[c] = 1 - jitter;
+  if (jitter > 0) v[dim - 1] = Math.sqrt(1 - (1 - jitter) * (1 - jitter));
+  return v;
+}
+
+function topicRep(title, score, hash) {
+  return {
+    title,
+    currentScore: score,
+    mentionCount: 1,
+    sources: [],
+    severity: 'critical',
+    hash,
+    mergedHashes: [hash],
+  };
+}
+
+const DEFAULT_TOPIC_CFG = { topicGroupingEnabled: true, topicThreshold: 0.45 };
+
+describe('groupTopicsPostDedup — size-first total ordering', () => {
+  it('4-member topic leads 3-member topic leads singletons (size DESC)', () => {
+    // 12 reps: topic A (basis 0, 4 members, scores 98/92/85/80),
+    //         topic B (basis 1, 3 members, scores 91/90/85),
+    //         5 singletons (bases 2..6, scores 95/88/70/65/60).
+    const reps = [];
+    const emb = new Map();
+    const dim = 10;
+    [98, 92, 85, 80].forEach((s, i) => {
+      const r = topicRep(`A-${i}`, s, `a${i}`);
+      reps.push(r);
+      emb.set(r.hash, basisVec(dim, 0, (i + 1) * 0.01));
+    });
+    [91, 90, 85].forEach((s, i) => {
+      const r = topicRep(`B-${i}`, s, `b${i}`);
+      reps.push(r);
+      emb.set(r.hash, basisVec(dim, 1, (i + 1) * 0.01));
+    });
+    [95, 88, 70, 65, 60].forEach((s, i) => {
+      const r = topicRep(`S-${i}`, s, `s${i}`);
+      reps.push(r);
+      emb.set(r.hash, basisVec(dim, 2 + i, 0));
+    });
+
+    // Feed in score-DESC (the digest's pre-grouping order) and verify
+    // topic ordering overrides raw score order.
+    const primaryOrder = reps.slice().sort((a, b) => b.currentScore - a.currentScore);
+    const { reps: ordered, topicCount, error } = groupTopicsPostDedup(
+      primaryOrder,
+      DEFAULT_TOPIC_CFG,
+      emb,
+    );
+    assert.equal(error, null);
+    // 1 topic (size 4) + 1 topic (size 3) + 5 singletons = 7
+    assert.equal(topicCount, 7);
+    // Topic A leads; members in score DESC: 98, 92, 85, 80
+    assert.deepEqual(
+      ordered.slice(0, 4).map((r) => r.hash),
+      ['a0', 'a1', 'a2', 'a3'],
+    );
+    // Topic B next; members in score DESC: 91, 90, 85
+    assert.deepEqual(
+      ordered.slice(4, 7).map((r) => r.hash),
+      ['b0', 'b1', 'b2'],
+    );
+    // Singletons by score DESC: 95, 88, 70, 65, 60
+    assert.deepEqual(
+      ordered.slice(7).map((r) => r.hash),
+      ['s0', 's1', 's2', 's3', 's4'],
+    );
+    // Critically: Louisiana-score-95 singleton comes AFTER Iran-war-max-91
+    // (topic of 3) — the user's explicit editorial intent.
+    const louisianaIdx = ordered.findIndex((r) => r.hash === 's0');
+    const lastTopicBIdx = ordered.findIndex((r) => r.hash === 'b2');
+    assert.ok(louisianaIdx > lastTopicBIdx, 'single-rep score 95 appears after 3-member topic max 91');
+  });
+
+  it('topicMax breaks ties between same-size topics', () => {
+    // Two topics, both size 2. Topic X max=80, topic Y max=90 → Y leads.
+    const reps = [];
+    const emb = new Map();
+    const dim = 6;
+    [80, 70].forEach((s, i) => {
+      const r = topicRep(`X-${i}`, s, `x${i}`);
+      reps.push(r);
+      emb.set(r.hash, basisVec(dim, 0, (i + 1) * 0.01));
+    });
+    [90, 60].forEach((s, i) => {
+      const r = topicRep(`Y-${i}`, s, `y${i}`);
+      reps.push(r);
+      emb.set(r.hash, basisVec(dim, 1, (i + 1) * 0.01));
+    });
+
+    const { reps: ordered, error } = groupTopicsPostDedup(reps, DEFAULT_TOPIC_CFG, emb);
+    assert.equal(error, null);
+    // Y-topic (max 90) leads X-topic (max 80) despite X having a higher low.
+    assert.deepEqual(
+      ordered.map((r) => r.hash),
+      ['y0', 'y1', 'x0', 'x1'],
+    );
+  });
+
+  it('within a topic, reps are ordered by currentScore DESC', () => {
+    const reps = [
+      topicRep('T-low', 70, 't2'),
+      topicRep('T-hi', 90, 't0'),
+      topicRep('T-mid', 80, 't1'),
+    ];
+    const emb = new Map([
+      ['t0', basisVec(4, 0, 0.01)],
+      ['t1', basisVec(4, 0, 0.02)],
+      ['t2', basisVec(4, 0, 0.03)],
+    ]);
+    const { reps: ordered, error } = groupTopicsPostDedup(reps, DEFAULT_TOPIC_CFG, emb);
+    assert.equal(error, null);
+    assert.deepEqual(ordered.map((r) => r.hash), ['t0', 't1', 't2']);
+  });
+
+  // `titleHashHex is the final deterministic tiebreak` test was removed —
+  // the permutation-invariance test below exercises the same invariant
+  // against a larger fixture and would catch any tiebreak drift.
+
+  it('same-size same-topicMax topics KEEP MEMBERS CONTIGUOUS (regression)', () => {
+    // Regression guard for the round-2 bug: a global sort key that
+    // tied on (topicSize, topicMax) fell through to per-rep repScore,
+    // interleaving A/B members (output was [a0,b0,a1,b1] instead of
+    // a contiguous block). Two-phase sort fixes this.
+    //
+    // Topic A: score 90, 80 (size 2, max 90)
+    // Topic B: score 90, 70 (size 2, max 90) — same size and max
+    const reps = [];
+    const emb = new Map();
+    const dim = 6;
+    [90, 80].forEach((s, i) => {
+      const r = topicRep(`A-${i}`, s, `a${i}`);
+      reps.push(r);
+      emb.set(r.hash, basisVec(dim, 0, (i + 1) * 0.01));
+    });
+    [90, 70].forEach((s, i) => {
+      const r = topicRep(`B-${i}`, s, `b${i}`);
+      reps.push(r);
+      emb.set(r.hash, basisVec(dim, 1, (i + 1) * 0.01));
+    });
+
+    const { reps: ordered, error } = groupTopicsPostDedup(
+      reps,
+      DEFAULT_TOPIC_CFG,
+      emb,
+    );
+    assert.equal(error, null);
+
+    // The two A reps must appear as a contiguous pair, and the two B
+    // reps must appear as a contiguous pair. Which topic leads is
+    // determined by the deterministic topic-level tiebreak hash, but
+    // their members MUST NOT interleave.
+    const hashes = ordered.map((r) => r.hash);
+    const firstAIdx = hashes.indexOf('a0');
+    const firstBIdx = hashes.indexOf('b0');
+    const lastAIdx = Math.max(hashes.indexOf('a0'), hashes.indexOf('a1'));
+    const lastBIdx = Math.max(hashes.indexOf('b0'), hashes.indexOf('b1'));
+    const aIdxs = [hashes.indexOf('a0'), hashes.indexOf('a1')].sort((x, y) => x - y);
+    const bIdxs = [hashes.indexOf('b0'), hashes.indexOf('b1')].sort((x, y) => x - y);
+    assert.equal(aIdxs[1] - aIdxs[0], 1, `A members must be adjacent; got ${JSON.stringify(hashes)}`);
+    assert.equal(bIdxs[1] - bIdxs[0], 1, `B members must be adjacent; got ${JSON.stringify(hashes)}`);
+    // And within each topic, higher score first.
+    assert.ok(hashes.indexOf('a0') < hashes.indexOf('a1'), 'A-90 precedes A-80');
+    assert.ok(hashes.indexOf('b0') < hashes.indexOf('b1'), 'B-90 precedes B-70');
+    void firstAIdx;
+    void firstBIdx;
+    void lastAIdx;
+    void lastBIdx;
+  });
+});
+
+describe('groupTopicsPostDedup — kill switch & edge cases', () => {
+  it('topicGroupingEnabled=false preserves primary order byte-identical', () => {
+    const reps = [
+      topicRep('a', 98, 'a'),
+      topicRep('b', 95, 'b'),
+      topicRep('c', 92, 'c'),
+    ];
+    // Embeddings would normally merge all three into one topic, but kill
+    // switch must short-circuit before calling the clusterer.
+    const emb = new Map([
+      ['a', basisVec(4, 0, 0.01)],
+      ['b', basisVec(4, 0, 0.02)],
+      ['c', basisVec(4, 0, 0.03)],
+    ]);
+    const { reps: ordered, topicCount, error } = groupTopicsPostDedup(
+      reps,
+      { topicGroupingEnabled: false, topicThreshold: 0.45 },
+      emb,
+    );
+    assert.equal(error, null);
+    assert.equal(topicCount, reps.length);
+    assert.deepEqual(ordered, reps, 'output === input reference when disabled');
+  });
+
+  it('empty input returns {reps: [], topicCount: 0, error: null}', () => {
+    const { reps, topicCount, error } = groupTopicsPostDedup([], DEFAULT_TOPIC_CFG, new Map());
+    assert.deepEqual(reps, []);
+    assert.equal(topicCount, 0);
+    assert.equal(error, null);
+  });
+
+  it('single-rep input passes through with topicCount=1', () => {
+    const only = [topicRep('solo', 99, 'solo')];
+    const { reps: out, topicCount, error } = groupTopicsPostDedup(
+      only,
+      DEFAULT_TOPIC_CFG,
+      new Map([['solo', basisVec(4, 0)]]),
+    );
+    assert.equal(error, null);
+    assert.equal(topicCount, 1);
+    assert.deepEqual(out, only);
+  });
+});
+
+describe('groupTopicsPostDedup — permutation invariance', () => {
+  it('15 reps in 5 topics of 3 produce identical ordering across 5 shuffles', () => {
+    const N_TOPICS = 5;
+    const PER = 3;
+    const dim = N_TOPICS + 1; // +1 free dimension for jitter
+    const reps = [];
+    const emb = new Map();
+    for (let c = 0; c < N_TOPICS; c++) {
+      for (let k = 0; k < PER; k++) {
+        const score = 100 - (c * PER + k);
+        const r = topicRep(`c${c}-k${k}`, score, `c${c}k${k}`);
+        reps.push(r);
+        emb.set(r.hash, basisVec(dim, c, 0.001 * (k + 1)));
+      }
+    }
+
+    const sigFor = (arr) => arr.map((r) => r.hash).join('|');
+    const baseline = groupTopicsPostDedup(reps.slice(), DEFAULT_TOPIC_CFG, emb);
+    assert.equal(baseline.error, null);
+    const baselineSig = sigFor(baseline.reps);
+
+    let seed = 7;
+    const rand = () => {
+      seed = (seed * 1103515245 + 12345) & 0x7fffffff;
+      return seed / 0x7fffffff;
+    };
+    for (let r = 0; r < 5; r++) {
+      const shuffled = reps.slice();
+      for (let i = shuffled.length - 1; i > 0; i--) {
+        const j = Math.floor(rand() * (i + 1));
+        [shuffled[i], shuffled[j]] = [shuffled[j], shuffled[i]];
+      }
+      const run = groupTopicsPostDedup(shuffled, DEFAULT_TOPIC_CFG, emb);
+      assert.equal(run.error, null);
+      assert.equal(
+        sigFor(run.reps),
+        baselineSig,
+        `shuffle ${r} produced a different ordering`,
+      );
+    }
+  });
+});
+
+describe('groupTopicsPostDedup — error boundary (nested fallback)', () => {
+  it('injected clusterFn that throws returns error, primary order preserved, no re-throw', () => {
+    const reps = [
+      topicRep('a', 90, 'a'),
+      topicRep('b', 80, 'b'),
+      topicRep('c', 70, 'c'),
+    ];
+    const emb = new Map([
+      ['a', basisVec(4, 0)],
+      ['b', basisVec(4, 1)],
+      ['c', basisVec(4, 2)],
+    ]);
+    const boom = () => {
+      throw new Error('boom');
+    };
+
+    let threw = false;
+    let result;
+    try {
+      result = groupTopicsPostDedup(reps, DEFAULT_TOPIC_CFG, emb, { clusterFn: boom });
+    } catch (_err) {
+      threw = true;
+    }
+    assert.equal(threw, false, 'helper must NOT re-throw — it returns the error');
+    assert.ok(result.error instanceof Error);
+    assert.equal(result.error.message, 'boom');
+    assert.equal(result.topicCount, reps.length);
+    assert.deepEqual(result.reps, reps, 'primary order preserved on failure');
+  });
+
+  it('missing embedding for any rep returns primary order + descriptive error', () => {
+    const reps = [
+      topicRep('a', 90, 'a'),
+      topicRep('b', 80, 'b'),
+    ];
+    const emb = new Map([['a', basisVec(4, 0)]]);
+    const { reps: out, error } = groupTopicsPostDedup(reps, DEFAULT_TOPIC_CFG, emb);
+    assert.ok(error instanceof Error);
+    assert.match(error.message, /missing embedding/);
+    assert.deepEqual(out, reps);
+  });
+});
+
+describe('deduplicateStories — embeddingByHash keys match materialized rep', () => {
+  it('winning rep is items[1] (higher mentionCount) — sidecar key is that hash', async () => {
+    // Primary cluster of two items at the SAME score; items[1] has a
+    // higher mentionCount so materializeCluster picks it as rep.
+    // Sidecar embeddingByHash must be keyed by the rep's hash.
+    const loser = story('Iran shuts Hormuz', 80, 1, 'loser');
+    const winner = story('Iran closes Strait of Hormuz', 80, 5, 'winner');
+    const vec = new Map([
+      [normalizeForEmbedding(loser.title), [1, 0, 0]],
+      [normalizeForEmbedding(winner.title), [0.95, Math.sqrt(1 - 0.95 * 0.95), 0]],
+    ]);
+    const embedder = stubEmbedder(vec);
+
+    const { reps, embeddingByHash } = await deduplicateStories([loser, winner], {
+      env: {
+        ...EMBED_MODE,
+        DIGEST_DEDUP_TOPIC_GROUPING: '1',
+        DIGEST_DEDUP_ENTITY_VETO_ENABLED: '0', // let cosine merge w/o veto
+      },
+      embedBatch: embedder.embedBatch,
+      redisPipeline: noopPipeline,
+    });
+    assert.equal(reps.length, 1, 'one merged cluster');
+    const rep = reps[0];
+    // Sort key for materializeCluster is (currentScore DESC, mentionCount DESC)
+    // → `winner` (mentionCount 5) wins over `loser` (mentionCount 1).
+    assert.equal(rep.hash, 'winner');
+    assert.ok(embeddingByHash.has('winner'), 'sidecar keyed by rep.hash, not loser hash');
+    assert.ok(!embeddingByHash.has('loser'), 'non-rep items never appear in sidecar');
+  });
+});
+
+describe('brief envelope cleanliness — no internal fields leak', () => {
+  it('composeBriefFromDigestStories output never serializes embedding / __ fields', async () => {
+    const { composeBriefFromDigestStories } = await import('../scripts/lib/brief-compose.mjs');
+
+    // Run the full flow: dedup → topic-group → compose.
+    const stories = [
+      story('Iran closes Strait of Hormuz', 92, 1, 'h0'),
+      story('Iran shuts Strait of Hormuz', 88, 1, 'h1'),
+      story('Myanmar coup leader elected', 80, 1, 'h2'),
+    ];
+    const vec = new Map([
+      [normalizeForEmbedding(stories[0].title), [1, 0, 0]],
+      [normalizeForEmbedding(stories[1].title), [0.95, Math.sqrt(1 - 0.95 * 0.95), 0]],
+      [normalizeForEmbedding(stories[2].title), [0, 0, 1]],
+    ]);
+    const embedder = stubEmbedder(vec);
+    const { reps, embeddingByHash } = await deduplicateStories(stories, {
+      env: { ...EMBED_MODE, DIGEST_DEDUP_TOPIC_GROUPING: '1' },
+      embedBatch: embedder.embedBatch,
+      redisPipeline: noopPipeline,
+    });
+    const cfg = readOrchestratorConfig({ ...EMBED_MODE, DIGEST_DEDUP_TOPIC_GROUPING: '1' });
+    const { reps: top } = groupTopicsPostDedup(reps, cfg, embeddingByHash);
+
+    const rule = {
+      userId: 'user_test',
+      sensitivity: 'all',
+      digestTimezone: 'UTC',
+    };
+    const envelope = composeBriefFromDigestStories(rule, top, {}, { nowMs: 1_700_000_000_000 });
+    const blob = JSON.stringify(envelope ?? {});
+    assert.ok(!blob.includes('"_embedding"'), 'no _embedding key');
+    assert.ok(!blob.includes('"__'), 'no __-prefixed key');
+    assert.ok(!blob.includes('embeddingByHash'), 'no embeddingByHash leakage');
+  });
+});
+
+describe('groupTopicsPostDedup — runs on sliced input, not pre-slice', () => {
+  it('reflects slice(0, 30) input size in topicCount', () => {
+    // 50 distinct singletons; slice to 30; each at an orthogonal basis so
+    // topic grouping produces one topic per rep = 30 topics.
+    const reps = [];
+    const emb = new Map();
+    const dim = 35;
+    for (let i = 0; i < 50; i++) {
+      const r = topicRep(`s-${i}`, 100 - i, `h${i}`);
+      reps.push(r);
+      emb.set(r.hash, basisVec(dim, i % (dim - 1)));
+    }
+    const sliced = reps.slice(0, 30);
+    const { reps: out, topicCount, error } = groupTopicsPostDedup(sliced, DEFAULT_TOPIC_CFG, emb);
+    assert.equal(error, null);
+    assert.equal(out.length, 30);
+    assert.ok(topicCount <= 30);
+  });
+});
+
+describe('readOrchestratorConfig — DIGEST_DEDUP_MODE typo falls back to Jaccard', () => {
+  it('an unrecognised mode value (typo) resolves to jaccard, not embed', async () => {
+    const { readOrchestratorConfig } = await import('../scripts/lib/brief-dedup.mjs');
+    // Classic operator scenario: panicking during an embed outage, types
+    // the kill switch as `jacard`. The SAFE default is jaccard, not embed.
+    const cfg = readOrchestratorConfig({ DIGEST_DEDUP_MODE: 'jacard' });
+    assert.equal(cfg.mode, 'jaccard');
+    assert.equal(cfg.invalidModeRaw, 'jacard');
+  });
+
+  it('any garbage value also falls back to jaccard', async () => {
+    const { readOrchestratorConfig } = await import('../scripts/lib/brief-dedup.mjs');
+    for (const raw of ['xyz', 'EMBED_ENABLED', '1', 'true']) {
+      const cfg = readOrchestratorConfig({ DIGEST_DEDUP_MODE: raw });
+      assert.equal(cfg.mode, 'jaccard', `raw=${JSON.stringify(raw)}`);
+      assert.equal(cfg.invalidModeRaw, raw.toLowerCase());
+    }
+  });
+
+  it('unset / empty value still resolves to the embed default (normal prod path)', async () => {
+    const { readOrchestratorConfig } = await import('../scripts/lib/brief-dedup.mjs');
+    for (const raw of [undefined, '']) {
+      const cfg = readOrchestratorConfig({ DIGEST_DEDUP_MODE: raw });
+      assert.equal(cfg.mode, 'embed');
+      assert.equal(cfg.invalidModeRaw, null);
+    }
+  });
+});
+
+describe('readOrchestratorConfig — topic-grouping env parsing', () => {
+  it('defaults: topicGroupingEnabled=true, topicThreshold=0.45', () => {
+    const cfg = readOrchestratorConfig({});
+    assert.equal(cfg.topicGroupingEnabled, true);
+    assert.equal(cfg.topicThreshold, 0.45);
+  });
+
+  it('DIGEST_DEDUP_TOPIC_GROUPING=0 disables', () => {
+    const cfg = readOrchestratorConfig({ DIGEST_DEDUP_TOPIC_GROUPING: '0' });
+    assert.equal(cfg.topicGroupingEnabled, false);
+  });
+
+  it('any non-"0" DIGEST_DEDUP_TOPIC_GROUPING value is treated as enabled', () => {
+    // Default-on kill-switch pattern: "yes", "1", "true", "" all enable.
+    for (const v of ['yes', '1', 'true', '', 'on']) {
+      const cfg = readOrchestratorConfig({ DIGEST_DEDUP_TOPIC_GROUPING: v });
+      assert.equal(cfg.topicGroupingEnabled, true, `value=${JSON.stringify(v)} should enable`);
+    }
+  });
+
+  it('DIGEST_DEDUP_TOPIC_THRESHOLD=foo (invalid) falls back to 0.45', () => {
+    const cfg = readOrchestratorConfig({ DIGEST_DEDUP_TOPIC_THRESHOLD: 'foo' });
+    assert.equal(cfg.topicThreshold, 0.45);
+  });
+
+  it('DIGEST_DEDUP_TOPIC_THRESHOLD=1.5 (out of range) falls back to 0.45', () => {
+    const cfg = readOrchestratorConfig({ DIGEST_DEDUP_TOPIC_THRESHOLD: '1.5' });
+    assert.equal(cfg.topicThreshold, 0.45);
+  });
+
+  it('DIGEST_DEDUP_TOPIC_THRESHOLD=0 (boundary, invalid) falls back to 0.45', () => {
+    const cfg = readOrchestratorConfig({ DIGEST_DEDUP_TOPIC_THRESHOLD: '0' });
+    assert.equal(cfg.topicThreshold, 0.45);
+  });
+
+  it('DIGEST_DEDUP_TOPIC_THRESHOLD=0.55 (valid) is honoured', () => {
+    const cfg = readOrchestratorConfig({ DIGEST_DEDUP_TOPIC_THRESHOLD: '0.55' });
+    assert.equal(cfg.topicThreshold, 0.55);
   });
 });
 
diff --git a/tests/brief-dedup-jaccard.test.mjs b/tests/brief-dedup-jaccard.test.mjs
index 1f5644d36..2e3d568fa 100644
--- a/tests/brief-dedup-jaccard.test.mjs
+++ b/tests/brief-dedup-jaccard.test.mjs
@@ -212,7 +212,7 @@ describe('brief-dedup orchestrator — jaccard kill switch', () => {
       story('Iran shuts Strait of Hormuz - Reuters', 85, 1, 'h2'),
       story('Myanmar coup leader elected president', 80, 1, 'h3'),
     ];
-    const out = await deduplicateStories(stories, {
+    const { reps: out } = await deduplicateStories(stories, {
       env: { DIGEST_DEDUP_MODE: 'jaccard' },
       embedBatch: stubEmbed,
     });
@@ -233,7 +233,7 @@ describe('brief-dedup orchestrator — jaccard kill switch', () => {
       jaccardCalls++;
       return deduplicateStoriesJaccard(s);
     };
-    const out = await deduplicateStories([], {
+    const { reps: out } = await deduplicateStories([], {
       env: { DIGEST_DEDUP_MODE: 'jaccard' },
       jaccard: stubJaccard,
     });