diff --git a/backend/src/agents/main_agent/session/compaction_summary.py b/backend/src/agents/main_agent/session/compaction_summary.py
index 23f668a88..5d7c51384 100644
--- a/backend/src/agents/main_agent/session/compaction_summary.py
+++ b/backend/src/agents/main_agent/session/compaction_summary.py
@@ -84,6 +84,12 @@
 # cap (half the budget) is 4k, so this is what binds; it is the figure the
 # harness screen ran with.
 _EXTRACTION_MAX_OUTPUT_TOKENS = 3_000
+# A generation is used only on a positive completion signal. ``max_tokens``
+# is the one exception, because it is salvaged (see the module docstring).
+# Anything else (a guardrail stop, a content-filter refusal, an unknown
+# reason) could be the refusal text itself, and a summary persists into the
+# cacheable history until the next cut, so it falls back instead.
+_ACCEPTED_STOP_REASONS = frozenset({"end_turn", "max_tokens"})
 
 _COMPRESSION_SYSTEM_PROMPT = """You maintain the running summary of a long conversation between a user and an AI assistant. You are given the existing summary notes (oldest first). Rewrite them into ONE compact summary the assistant can continue the conversation from.
 
@@ -240,8 +246,14 @@ async def _compress(
                 "maxTokens": min(_max_output_tokens(model_id), max(256, int(budget_tokens))),
             },
         )
+        stop_reason = response.get("stopReason")
+        if stop_reason not in _ACCEPTED_STOP_REASONS:
+            logger.info(
+                "compaction_summary_model_refused: stopReason=%s; falling back to truncation", stop_reason,
+            )
+            return None, False
         out = response["output"]["message"]["content"][0]["text"].strip()
-        if response.get("stopReason") == "max_tokens":
+        if stop_reason == "max_tokens":
             salvaged = _salvage(out, budget_tokens)
             logger.info(
                 "compaction_summary_model_truncated: generation hit the token ceiling; kept %d of %d chars",
@@ -305,8 +317,14 @@ async def extract_with_model(
             messages=[{"role": "user", "content": [{"text": "Summary notes, oldest first:\n\n" + text}]}],
             inferenceConfig={"temperature": 0.0, "maxTokens": max(256, int(max_tokens))},
         )
+        stop_reason = response.get("stopReason")
+        if stop_reason not in _ACCEPTED_STOP_REASONS:
+            logger.info(
+                "compaction_summary_extract_refused: stopReason=%s; falling back to plain compression", stop_reason,
+            )
+            return None
         out = response["output"]["message"]["content"][0]["text"].strip()
-        if response.get("stopReason") == "max_tokens":
+        if stop_reason == "max_tokens":
             logger.info("compaction_summary_extract_truncated: keeping the complete lines")
             cut = out.rfind("\n")
             out = out[:cut].rstrip() if cut > 0 else ""
diff --git a/backend/src/apis/inference_api/chat/service.py b/backend/src/apis/inference_api/chat/service.py
index 76851b8d7..cb5ad0f27 100644
--- a/backend/src/apis/inference_api/chat/service.py
+++ b/backend/src/apis/inference_api/chat/service.py
@@ -664,6 +664,14 @@ async def generate_conversation_title(
             inferenceConfig=request_body["inferenceConfig"],
         )
 
+        # A guardrail or content-filter stop may carry the refusal as its
+        # text, which must not become the sidebar title. `max_tokens` is
+        # still accepted: the 50-char clip below already handles an overrun.
+        stop_reason = response.get("stopReason")
+        if stop_reason not in ("end_turn", "max_tokens"):
+            logger.warning("Title generation stopped with stopReason=%s; keeping the placeholder", stop_reason)
+            return "New Conversation"
+
         # Extract generated title from response
         title = response["output"]["message"]["content"][0]["text"].strip()
 
diff --git a/backend/src/apis/shared/files/document_digest.py b/backend/src/apis/shared/files/document_digest.py
index 5abea1059..fdb7a78a5 100644
--- a/backend/src/apis/shared/files/document_digest.py
+++ b/backend/src/apis/shared/files/document_digest.py
@@ -277,9 +277,15 @@ async def generate_abstract(outline: DocumentDigest, sample: str, model_id: str
             # silently drop every abstract.
             inferenceConfig={"temperature": 0.2, "maxTokens": _ABSTRACT_MAX_OUTPUT_TOKENS},
         )
-        if response.get("stopReason") == "max_tokens":
+        stop_reason = response.get("stopReason")
+        if stop_reason == "max_tokens":
             logger.debug("Document abstract hit the token ceiling; discarding")
             return None
+        # A guardrail or content-filter stop may carry the refusal as its
+        # text; only a finished generation is an abstract.
+        if stop_reason != "end_turn":
+            logger.debug("Document abstract stopped with stopReason=%s; discarding", stop_reason)
+            return None
         text = response["output"]["message"]["content"][0]["text"].strip()
         return re.sub(r"\s+", " ", text) or None
     except Exception:  # noqa: BLE001 - an abstract is never worth a failed upload
diff --git a/backend/src/apis/shared/tool_summaries/summarizer.py b/backend/src/apis/shared/tool_summaries/summarizer.py
index e677dbe71..34a37d448 100644
--- a/backend/src/apis/shared/tool_summaries/summarizer.py
+++ b/backend/src/apis/shared/tool_summaries/summarizer.py
@@ -187,9 +187,16 @@ async def summarize_tool_batch(calls: List[Dict[str, Any]]) -> Optional[str]:
         # deterministic formatter speak. (Defensive: the dangling quotes seen
         # on dev turned out to be `_unwrap_quotes`, not truncation, but
         # nothing guarded this boundary and a fragment must never persist.)
-        if response.get("stopReason") == "max_tokens":
+        # Any other non-`end_turn` stop (a guardrail or content-filter
+        # refusal, an unknown reason) is dropped too: its text may be the
+        # refusal itself, which is no summary of the batch.
+        stop_reason = response.get("stopReason")
+        if stop_reason == "max_tokens":
             logger.debug("Tool-batch summary hit the token ceiling; discarding")
             return None
+        if stop_reason != "end_turn":
+            logger.debug("Tool-batch summary stopped with stopReason=%s; discarding", stop_reason)
+            return None
 
         summary = _clean(response["output"]["message"]["content"][0]["text"])
         if not summary:
diff --git a/backend/tests/agents/main_agent/session/test_compaction_summary.py b/backend/tests/agents/main_agent/session/test_compaction_summary.py
index 242ba08b1..344f6bc89 100644
--- a/backend/tests/agents/main_agent/session/test_compaction_summary.py
+++ b/backend/tests/agents/main_agent/session/test_compaction_summary.py
@@ -90,6 +90,21 @@ async def test_model_ceiling_hit_with_no_complete_line_falls_back(self, bedrock)
         assert result.outcome == "truncated_after_model"
         assert approx_tokens(result.text) <= BUDGET
 
+    @pytest.mark.asyncio
+    @pytest.mark.parametrize("stop", ["guardrail_intervened", "content_filtered", "tool_use", "something_new", None])
+    async def test_a_refused_generation_falls_back_and_is_never_the_summary(self, bedrock, stop):
+        """Only a completed (or salvageable) generation becomes the checkpoint.
+
+        A refusal persisted as the summary would sit in the cacheable history
+        until the next cut.
+        """
+        bedrock.return_value = _model_reply("Sorry, the model cannot answer this.", stop=stop)
+        records = ["old " * 100, "new " * 50]
+        result = await bound_summary(records, BUDGET, model_enabled=True, model_id="m")
+        assert result.outcome == "truncated_after_model"
+        assert "Sorry" not in result.text and result.text.startswith("new")
+        assert await compress_with_model(records, BUDGET, model_id="m") is None
+
     @pytest.mark.asyncio
     async def test_model_overshoot_is_tail_trimmed(self, bedrock):
         bedrock.return_value = _model_reply("y" * 2000 + "END")
@@ -390,6 +405,27 @@ async def test_extraction_ceiling_hit_keeps_the_complete_lines(self, bedrock):
         assert result.outcome == "extract_then_compress"
         assert "- PRJ-4417" in result.text and "- PRJ-44\n" not in result.text
 
+    @pytest.mark.asyncio
+    async def test_refused_extraction_keeps_the_narrative_without_a_third_call(self, bedrock):
+        bedrock.side_effect = _route(
+            _model_reply("Sorry, the model cannot answer this.", stop="guardrail_intervened"),
+            _model_reply("plain compressed summary"),
+        )
+        result = await _extract(["r" * 2000])
+        assert result.outcome == "model"
+        assert result.text == "plain compressed summary"
+        assert bedrock.call_count == 2
+
+    @pytest.mark.asyncio
+    async def test_refused_narrative_keeps_the_pinned_block_and_truncates(self, bedrock):
+        bedrock.side_effect = _route(
+            _model_reply(PINNED),
+            _model_reply("Sorry, the model cannot answer this.", stop="guardrail_intervened"),
+        )
+        result = await _extract(["old " * 300, "newest record"])
+        assert result.outcome == "extract_then_truncate"
+        assert "Sorry" not in result.text and result.text.endswith("newest record")
+
     @pytest.mark.asyncio
     async def test_narrative_ceiling_hit_keeps_its_complete_lines(self, bedrock):
         """A cut-off narrative is salvaged, not swapped for raw records (extract_then_truncate)."""
diff --git a/backend/tests/apis/shared/tool_summaries/test_summarizer.py b/backend/tests/apis/shared/tool_summaries/test_summarizer.py
index 4d116975b..40e9f13c8 100644
--- a/backend/tests/apis/shared/tool_summaries/test_summarizer.py
+++ b/backend/tests/apis/shared/tool_summaries/test_summarizer.py
@@ -92,6 +92,27 @@ async def test_truncation_is_judged_by_stop_reason_not_by_length(bedrock):
     assert await summarize_tool_batch(_calls()) == long_but_finished
 
 
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("stop_reason", ["guardrail_intervened", "content_filtered", "tool_use", "something_new"])
+async def test_any_stop_other_than_end_turn_is_discarded(bedrock, stop_reason):
+    """A guardrail or content-filter stop can carry the refusal as its text.
+
+    Only `end_turn` says the model finished a summary; anything else must
+    leave the deterministic line in place.
+    """
+    bedrock.converse.return_value = _response("Sorry, the model cannot answer this.", stop_reason=stop_reason)
+
+    assert await summarize_tool_batch(_calls()) is None
+
+
+@pytest.mark.asyncio
+async def test_a_missing_stop_reason_is_discarded(bedrock):
+    bedrock.converse.return_value = {"output": {"message": {"content": [{"text": "Found 3 active courses"}]}}}
+
+    assert await summarize_tool_batch(_calls()) is None
+
 # -- every other failure is also a None -----------------------------------
 
 
diff --git a/backend/tests/shared/test_document_digest.py b/backend/tests/shared/test_document_digest.py
index b0f9a0b87..49b426af2 100644
--- a/backend/tests/shared/test_document_digest.py
+++ b/backend/tests/shared/test_document_digest.py
@@ -146,6 +146,13 @@ async def test_truncated_or_failed_generations_are_none(self, monkeypatch):
         assert await dd.generate_abstract(dd.DocumentDigest(), "text") is None
         assert await dd.generate_abstract(dd.DocumentDigest(), "   ") is None
 
+    @pytest.mark.asyncio
+    @pytest.mark.parametrize("stop", ["guardrail_intervened", "content_filtered", "something_new", None])
+    async def test_a_refused_generation_is_none(self, monkeypatch, stop):
+        """Only a finished generation is an abstract; a refusal's text is not."""
+        _bedrock(monkeypatch, text="Sorry, the model cannot answer this.", stop=stop)
+        assert await dd.generate_abstract(dd.DocumentDigest(), "text") is None
+
 
 class TestBuild:
     @pytest.mark.asyncio
diff --git a/backend/tests/shared/test_side_channel_inference_config.py b/backend/tests/shared/test_side_channel_inference_config.py
index c01f86076..5d241fe7c 100644
--- a/backend/tests/shared/test_side_channel_inference_config.py
+++ b/backend/tests/shared/test_side_channel_inference_config.py
@@ -17,12 +17,12 @@
 from apis.shared.tool_summaries.summarizer import summarize_tool_batch
 
 
-def _client(text: str) -> MagicMock:
+def _client(text: str, stop_reason: str = "end_turn") -> MagicMock:
     def converse(**kwargs):
         config = kwargs.get("inferenceConfig", {})
         if "temperature" in config and "topP" in config:
             raise RuntimeError("ValidationException: `temperature` and `top_p` cannot both be specified")
-        return {"stopReason": "end_turn", "output": {"message": {"content": [{"text": text}]}}}
+        return {"stopReason": stop_reason, "output": {"message": {"content": [{"text": text}]}}}
 
     client = MagicMock()
     client.converse.side_effect = converse
@@ -64,3 +64,25 @@ async def test_conversation_title(monkeypatch):
     title = await chat_service.generate_conversation_title(session_id="s", user_id="u", user_input="hi")
     assert title == "Planning a biology syllabus"
     assert "topP" not in client.converse.call_args.kwargs["inferenceConfig"]
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("stop_reason", ["guardrail_intervened", "content_filtered", None])
+async def test_conversation_title_refusal_keeps_the_placeholder(monkeypatch, stop_reason):
+    """A guardrail stop's text is the refusal; it must never become the title."""
+    client = _client("Sorry, the model cannot answer this.", stop_reason=stop_reason)
+    monkeypatch.setattr(chat_service.boto3, "client", MagicMock(return_value=client))
+    update = AsyncMock()
+    monkeypatch.setattr(chat_service, "update_session_title", update)
+    title = await chat_service.generate_conversation_title(session_id="s", user_id="u", user_input="hi")
+    assert title == "New Conversation"
+    update.assert_not_awaited()
+
+
+@pytest.mark.asyncio
+async def test_conversation_title_at_the_token_ceiling_is_still_clipped(monkeypatch):
+    client = _client("A" * 80, stop_reason="max_tokens")
+    monkeypatch.setattr(chat_service.boto3, "client", MagicMock(return_value=client))
+    monkeypatch.setattr(chat_service, "update_session_title", AsyncMock())
+    title = await chat_service.generate_conversation_title(session_id="s", user_id="u", user_input="hi")
+    assert title == "A" * 47 + "..."