diff --git a/lib/domain_assigner.py b/lib/domain_assigner.py
new file mode 100644
index 0000000..c00894f
--- /dev/null
+++ b/lib/domain_assigner.py
@@ -0,0 +1,284 @@
+"""
+RECON Domain Assigner
+
+Computes per-video domain assignments from concept extraction results.
+Two functions, two execution modes:
+
+  compute_assignment() — pass 1, inline from post-embed hook
+  run_tiebreaker_pass() — batch, resolves ties via channel concept scan
+
+Status values written to documents.recon_domain_status:
+  assigned       — clear winner from pass 1 concept count
+  tied_pass_1    — concept tie, awaiting channel tiebreaker
+  tied_pass_2    — resolved by channel tiebreaker
+  tied_manual    — needs human review (dashboard)
+  needs_reprocess — missing concepts or only legacy domains
+  manual_assigned — human override from dashboard
+"""
+import json
+import os
+from collections import Counter
+
+from .recon_domains import VALID_DOMAINS, DOMAIN_CATEGORY_MAP
+from .utils import setup_logging
+
+logger = setup_logging('recon.domain_assigner')
+
+# Channels with more than this many videos skip channel tiebreaking entirely
+MEGA_CHANNEL_THRESHOLD = 500
+
+
+def _count_concept_domains(concepts_dir, file_hash):
+    """Read concept files and count valid domain occurrences.
+
+    Args:
+        concepts_dir: Base concepts directory (e.g. /opt/recon/data/concepts)
+        file_hash: Document hash
+
+    Returns:
+        Counter of {domain_name: count} for valid domains only,
+        or None if no concept directory exists.
+    """
+    doc_concepts_dir = os.path.join(concepts_dir, file_hash)
+    if not os.path.isdir(doc_concepts_dir):
+        return None
+
+    domain_counter = Counter()
+
+    for fname in os.listdir(doc_concepts_dir):
+        if not fname.startswith('window_') or not fname.endswith('.json'):
+            continue
+        fpath = os.path.join(doc_concepts_dir, fname)
+        try:
+            with open(fpath, 'r') as f:
+                concepts = json.load(f)
+        except (json.JSONDecodeError, OSError):
+            continue
+
+        if not isinstance(concepts, list):
+            continue
+
+        for concept in concepts:
+            if not isinstance(concept, dict):
+                continue
+            dom = concept.get('domain')
+            if isinstance(dom, str) and dom in VALID_DOMAINS:
+                domain_counter[dom] += 1
+            elif isinstance(dom, list):
+                for d in dom:
+                    if isinstance(d, str) and d in VALID_DOMAINS:
+                        domain_counter[d] += 1
+
+    return domain_counter
+
+
+def compute_assignment(file_hash, db, config):
+    """Compute domain assignment for a single document (pass 1).
+
+    Counts domain occurrences across all concepts. If a single domain
+    wins, assigns it. If tied, defers to batch tiebreaker.
+
+    Args:
+        file_hash: Document hash
+        db: StatusDB instance
+        config: RECON config dict
+
+    Returns:
+        (domain, status) tuple where domain is a string or None,
+        and status is one of: 'assigned', 'tied_pass_1', 'needs_reprocess'
+    """
+    concepts_dir = config['paths']['concepts']
+    domain_counter = _count_concept_domains(concepts_dir, file_hash)
+
+    if domain_counter is None or len(domain_counter) == 0:
+        return (None, 'needs_reprocess')
+
+    top = domain_counter.most_common(2)
+    top_domain = top[0][0]
+    top_count = top[0][1]
+
+    if len(top) == 1 or top[1][1] < top_count:
+        return (top_domain, 'assigned')
+
+    # Tie — defer to tiebreaker pass
+    return (None, 'tied_pass_1')
+
+
+def _get_tied_domains(concepts_dir, file_hash):
+    """Get the set of domains tied for first place in a document's concepts."""
+    domain_counter = _count_concept_domains(concepts_dir, file_hash)
+    if not domain_counter:
+        return []
+
+    top = domain_counter.most_common()
+    if not top:
+        return []
+
+    max_count = top[0][1]
+    return [dom for dom, cnt in top if cnt == max_count]
+
+
+def _channel_video_hashes(db, channel_name, exclude_hash=None):
+    """Get all document hashes belonging to a PeerTube channel.
+
+    Args:
+        db: StatusDB instance
+        channel_name: catalogue.category (channel actor name)
+        exclude_hash: Hash to exclude (the document being resolved)
+
+    Returns:
+        List of document hashes
+    """
+    conn = db._get_conn()
+    rows = conn.execute(
+        "SELECT hash FROM catalogue WHERE category = ? AND source = 'stream.echo6.co'",
+        (channel_name,)
+    ).fetchall()
+    hashes = [r['hash'] for r in rows]
+    if exclude_hash:
+        hashes = [h for h in hashes if h != exclude_hash]
+    return hashes
+
+
+def _channel_video_count(db, channel_name):
+    """Count total videos in a channel."""
+    conn = db._get_conn()
+    row = conn.execute(
+        "SELECT COUNT(*) as cnt FROM catalogue WHERE category = ? AND source = 'stream.echo6.co'",
+        (channel_name,)
+    ).fetchone()
+    return row['cnt'] if row else 0
+
+
+def run_tiebreaker_pass(db, config):
+    """Resolve tied domain assignments using channel-level concept analysis.
+
+    Processes all documents where recon_domain_status = 'tied_pass_1'.
+
+    Pass 2: For each tied document, reads concept files from all other
+    videos in the same channel and picks the tied domain with the highest
+    channel-wide count.
+
+    Pass 3 (defensive re-run): Re-reads the same channel concept files a
+    second time with identical logic. This catches concept-file changes
+    that occurred mid-run (e.g. concurrent enrichment writing new windows).
+    In steady state pass 3 produces the same result as pass 2, but under
+    concurrent writes it can resolve a tie that pass 2 missed.
+
+    Mega-channels (>500 videos) skip both passes and go straight to
+    'tied_manual' for dashboard review.
+
+    Args:
+        db: StatusDB instance
+        config: RECON config dict
+
+    Returns:
+        Dict with counts: resolved, manual, skipped, errors
+    """
+    concepts_dir = config['paths']['concepts']
+    tied_items = db.get_items_by_domain_status('tied_pass_1')
+
+    stats = {'resolved': 0, 'manual': 0, 'skipped': 0, 'errors': 0, 'total': len(tied_items)}
+    logger.info(f"Tiebreaker pass: {len(tied_items)} items to resolve")
+
+    # Cache channel sizes to avoid repeated queries
+    channel_size_cache = {}
+
+    for item in tied_items:
+        file_hash = item['hash']
+        channel = item.get('category', '')
+
+        try:
+            tied_domains = _get_tied_domains(concepts_dir, file_hash)
+            if not tied_domains:
+                db.set_domain_assignment(file_hash, None, 'needs_reprocess')
+                stats['skipped'] += 1
+                continue
+
+            if len(tied_domains) == 1:
+                # No longer tied (possibly re-enriched since pass 1)
+                db.set_domain_assignment(file_hash, tied_domains[0], 'assigned')
+                stats['resolved'] += 1
+                continue
+
+            # Check mega-channel rule
+            if channel not in channel_size_cache:
+                channel_size_cache[channel] = _channel_video_count(db, channel)
+
+            if channel_size_cache[channel] > MEGA_CHANNEL_THRESHOLD:
+                fallback = sorted(tied_domains)[0]
+                db.set_domain_assignment(file_hash, fallback, 'tied_manual')
+                stats['manual'] += 1
+                logger.debug(f"  {file_hash[:12]}: mega-channel '{channel}' "
+                             f"({channel_size_cache[channel]} videos), → tied_manual")
+                continue
+
+            # Channel tiebreaker: count domains across all other videos in channel
+            other_hashes = _channel_video_hashes(db, channel, exclude_hash=file_hash)
+            channel_domain_counts = Counter()
+
+            for other_hash in other_hashes:
+                other_counts = _count_concept_domains(concepts_dir, other_hash)
+                if other_counts:
+                    channel_domain_counts.update(other_counts)
+
+            # Among tied domains only, pick highest channel-wide count
+            best_domain = None
+            best_count = -1
+            for dom in tied_domains:
+                c = channel_domain_counts.get(dom, 0)
+                if c > best_count:
+                    best_count = c
+                    best_domain = dom
+
+            # Pass 2: check if channel tiebreaker resolved it
+            tied_at_channel = [d for d in tied_domains
+                               if channel_domain_counts.get(d, 0) == best_count]
+
+            if len(tied_at_channel) == 1:
+                db.set_domain_assignment(file_hash, best_domain, 'tied_pass_2')
+                stats['resolved'] += 1
+                logger.debug(f"  {file_hash[:12]}: resolved → {best_domain} (pass 2 channel tiebreaker)")
+                continue
+
+            # Pass 3: defensive re-run — re-count channel concepts to catch
+            # concept-file changes that occurred mid-run. Identical logic to
+            # pass 2; resolves races where files were written between the
+            # two reads.
+            channel_domain_counts_p3 = Counter()
+            for other_hash in other_hashes:
+                other_counts = _count_concept_domains(concepts_dir, other_hash)
+                if other_counts:
+                    channel_domain_counts_p3.update(other_counts)
+
+            best_domain_p3 = None
+            best_count_p3 = -1
+            for dom in tied_domains:
+                c = channel_domain_counts_p3.get(dom, 0)
+                if c > best_count_p3:
+                    best_count_p3 = c
+                    best_domain_p3 = dom
+
+            tied_at_p3 = [d for d in tied_domains
+                          if channel_domain_counts_p3.get(d, 0) == best_count_p3]
+
+            if len(tied_at_p3) == 1:
+                db.set_domain_assignment(file_hash, best_domain_p3, 'tied_pass_2')
+                stats['resolved'] += 1
+                logger.debug(f"  {file_hash[:12]}: resolved → {best_domain_p3} (pass 3 defensive re-run)")
+                continue
+
+            # Still tied after pass 3 — mark for manual review
+            fallback = sorted(tied_domains)[0]
+            db.set_domain_assignment(file_hash, fallback, 'tied_manual')
+            stats['manual'] += 1
+            logger.debug(f"  {file_hash[:12]}: still tied after pass 3, → tied_manual")
+
+        except Exception as e:
+            logger.warning(f"  Tiebreaker error for {file_hash[:12]}: {e}")
+            stats['errors'] += 1
+
+    logger.info(f"Tiebreaker complete: {stats['resolved']} resolved, "
+                f"{stats['manual']} manual, {stats['skipped']} skipped, "
+                f"{stats['errors']} errors")
+    return stats