diff --git a/aborist/qa/inspect.py b/aborist/qa/inspect.py
index 0a5292a..8385ef0 100644
--- a/aborist/qa/inspect.py
+++ b/aborist/qa/inspect.py
@@ -424,6 +424,66 @@ def _question_is_numeric_or_cause_shape(question_text: str) -> bool:
     return any(q.startswith(lead) for lead in _DEFLECTION_NUMERIC_OR_CAUSE_LEADERS)
 
 
+def diagnose_title_relevance(
+    claim_text: str,
+    cited_source_titles: list[str],
+) -> dict[str, Any]:
+    """Soft signal: do the cited chunk's source titles overlap the
+    claim's content tokens?
+
+    Empirically observed 2026-05-01 on 'explain spin glass modeling,
+    tensors?' — verifier returned STRICT 1/1 on a claim 'Spin glass
+    modeling involves... mathematical tools such as tensors' cited
+    to a chunk from the *Quantum chromodynamics* article. The claim
+    has zero stemmed-token overlap with the source title 'Quantum
+    chromodynamics'. Token-coverage check inside the chunk passed
+    accidentally on shared physics vocabulary (spin/model/etc.), but
+    the article isn't about spin glasses.
+
+    This sidecar surfaces the mismatch without modifying the binary
+    verifier output. ``kind`` of ``TITLE_MISMATCH`` means the cited
+    source's topic is structurally unrelated to the claim's subject;
+    the claim is likely a retrieval-driven hallucination grounded
+    against an incidentally-overlapping chunk.
+
+    Returns:
+        {
+            "kind": "title_match" | "title_mismatch" | "no_claim_tokens" | "no_titles",
+            "claim_tokens": [...],
+            "title_tokens": [...],   # union across all cited titles
+            "overlap": [...],
+        }
+
+    Sidecar-only — never enters the binary verifier output. Title
+    underscores in titles ('Quantum_chromodynamics' / 'Lois_Lane')
+    are normalized to spaces before tokenization."""
+    claim_set = set(_content_tokens_in_order(claim_text or ""))
+    if not claim_set:
+        return {
+            "kind": "no_claim_tokens",
+            "claim_tokens": [],
+            "title_tokens": [],
+            "overlap": [],
+        }
+    if not cited_source_titles:
+        return {
+            "kind": "no_titles",
+            "claim_tokens": sorted(claim_set),
+            "title_tokens": [],
+            "overlap": [],
+        }
+    title_set: set[str] = set()
+    for t in cited_source_titles:
+        title_set |= set(_content_tokens_in_order((t or "").replace("_", " ")))
+    overlap = claim_set & title_set
+    return {
+        "kind": "title_match" if overlap else "title_mismatch",
+        "claim_tokens": sorted(claim_set),
+        "title_tokens": sorted(title_set),
+        "overlap": sorted(overlap),
+    }
+
+
 def diagnose_deflection(question_text: str, answer_text: str) -> dict[str, Any]:
     """Soft signal: did the answer change topic?
 
diff --git a/tests/test_inspect.py b/tests/test_inspect.py
index 9c273f5..52170f3 100644
--- a/tests/test_inspect.py
+++ b/tests/test_inspect.py
@@ -22,6 +22,7 @@ from aborist.qa.inspect import (
     _classify_span,
     _normalize,
     diagnose_deflection,
+    diagnose_title_relevance,
     inspect_cache_key,
 )
 from aborist.store import append_audit, connect, transaction
@@ -538,3 +539,68 @@ def test_deflection_not_suppressed_for_who_questions():
     assert d["shape_suppressed"] is False
     assert d["kind"] == "deflection"
     assert d["subject_anchor"] == "mars"
+
+
+# ---------------------------------------------------------------------------
+# title-relevance sidecar
+# ---------------------------------------------------------------------------
+
+
+def test_title_mismatch_on_qcd_cited_for_spin_glass_claim():
+    """Empirical 2026-05-01: 'explain spin glass modeling, tensors?'
+    returned STRICT 1/1 with claim 'Spin glass modeling involves...
+    mathematical tools such as tensors' cited to a chunk from
+    Quantum_chromodynamics. Claim tokens have zero overlap with QCD
+    title — sidecar should flag TITLE_MISMATCH so an operator can
+    see the retrieval-driven hallucination signature."""
+    d = diagnose_title_relevance(
+        "Spin glass modeling involves using the concept of spin glasses, "
+        "which are disordered magnetic systems, to study complex systems "
+        "and phenomena in physics and other fields. Spin glasses are "
+        "characterized by random interactions. Tensors are used to "
+        "represent the interactions between spins.",
+        ["Quantum_chromodynamics"],
+    )
+    assert d["kind"] == "title_mismatch"
+    assert d["overlap"] == []
+    # Claim has 'spin', 'glass', 'modeling', etc. — title has 'quantum',
+    # 'chromodynamics'. Zero stem overlap.
+    assert "spin" in d["claim_tokens"]
+    assert "quantum" in d["title_tokens"]
+
+
+def test_title_match_on_lois_lane_cited_for_supermans_girlfriend():
+    """Sanity: legit citation (Lois Lane article cited for Lois-Lane
+    claim) passes title-relevance even though Superman isn't in the
+    title."""
+    d = diagnose_title_relevance(
+        "Lois Lane is the longtime love interest of Superman.",
+        ["Lois_Lane"],
+    )
+    assert d["kind"] == "title_match"
+    assert "lois" in d["overlap"]
+    assert "lane" in d["overlap"]
+
+
+def test_title_match_underscores_normalized():
+    """Wikipedia titles use underscores; normalization to spaces lets
+    multi-word titles tokenize correctly."""
+    d = diagnose_title_relevance(
+        "The Berlin Wall fell in 1989.",
+        ["Berlin_Wall"],
+    )
+    assert d["kind"] == "title_match"
+    assert "berlin" in d["overlap"]
+    assert "wall" in d["overlap"]
+
+
+def test_title_mismatch_no_titles():
+    """Defensive: empty title list returns no_titles."""
+    d = diagnose_title_relevance("Some claim.", [])
+    assert d["kind"] == "no_titles"
+
+
+def test_title_mismatch_no_claim_tokens():
+    """Defensive: empty/stopword-only claim returns no_claim_tokens."""
+    d = diagnose_title_relevance("the a an", ["Anything"])
+    assert d["kind"] == "no_claim_tokens"