diff --git a/app/services/diagnose/__init__.py b/app/services/diagnose/__init__.py
index 51613cf..80d8a0f 100644
--- a/app/services/diagnose/__init__.py
+++ b/app/services/diagnose/__init__.py
@@ -227,7 +227,6 @@ async def diagnose_stream(
 
     yield {"type": "status", "message": "Loading environment context…"}
     ctx = await asyncio.to_thread(lambda: retrieve_context(db_path, query))
-    context_block = format_context_block(ctx)
     yield {
         "type": "context",
         "facts": ctx.facts,
@@ -320,6 +319,8 @@ async def diagnose_stream(
         return  # pipeline emits its own "done" event
 
     if llm_url and llm_model and combined:
+        # Only compute context_block in the legacy path — pipeline uses ctx directly.
+        context_block = format_context_block(ctx)
         yield {"type": "status", "message": "Analyzing with LLM…"}
         reasoning = await asyncio.to_thread(
             lambda: summarize(
diff --git a/app/services/diagnose/_llm_client.py b/app/services/diagnose/_llm_client.py
new file mode 100644
index 0000000..a9e1481
--- /dev/null
+++ b/app/services/diagnose/_llm_client.py
@@ -0,0 +1,116 @@
+"""Shared LLM client for the multi-agent diagnose pipeline.
+
+Both Stage 3 (RootCauseHypothesizer) and Stage 5 (SummarySynthesizer) send
+messages to the same LLM backend using the same two-step pattern:
+  1. Try the cf-orch task endpoint  → product-scoped inference routing.
+  2. Fall back to OpenAI-compat     → direct model call by name.
+
+Centralising here means changes to auth headers, timeouts, retry logic, or
+cf-orch payload structure only need to be made once.
+"""
+from __future__ import annotations
+
+import logging
+import re
+
+import httpx
+
+logger = logging.getLogger(__name__)
+
+# Regex that strips ```json … ``` or ``` … ``` fences from LLM output.
+_JSON_FENCE_RE = re.compile(
+    r"^```(?:json)?\s*|\s*```$",
+    re.MULTILINE,
+)
+
+
+def extract_content(resp_json: dict) -> str | None:
+    """Pull text content from an OpenAI-compat chat completion response.
+
+    Returns None when the response has no choices or empty content.
+    """
+    choices = resp_json.get("choices") or []
+    if not choices:
+        return None
+    return (choices[0].get("message", {}).get("content") or "").strip() or None
+
+
+def strip_json_fences(raw: str) -> str:
+    """Remove markdown code fences that some LLMs wrap around JSON output.
+
+    Example: '```json\\n[...]\\n```' → '[...]'
+    """
+    return _JSON_FENCE_RE.sub("", raw).strip()
+
+
+def call_llm(
+    llm_url: str,
+    llm_model: str,
+    llm_api_key: str | None,
+    messages: list[dict],
+    task_name: str = "log_analysis",
+    timeout: float = 120.0,
+) -> str | None:
+    """Send messages to the LLM; return raw text or None on failure.
+
+    Tries the cf-orch task endpoint first (product-routed inference).
+    Falls back to a direct OpenAI-compat ``/v1/chat/completions`` call when:
+      - The task endpoint returns 404 (no assignment for this task).
+      - The task endpoint is unreachable (connection error, timeout, etc.).
+
+    Args:
+        llm_url:     Base URL of the LLM backend (e.g. ``http://10.1.10.71:7700``).
+        llm_model:   Model identifier used in the OpenAI-compat fallback call.
+        llm_api_key: Optional bearer token for authenticated endpoints.
+        messages:    OpenAI-style message list (system + user turns).
+        task_name:   cf-orch task name for product-routed inference (default: ``log_analysis``).
+        timeout:     Request timeout in seconds (default: 120).
+
+    Returns:
+        Raw text content string, or None if both paths fail.
+    """
+    headers: dict[str, str] = {}
+    if llm_api_key:
+        headers["Authorization"] = f"Bearer {llm_api_key}"
+
+    # --- Path 1: cf-orch task endpoint ---
+    task_url = f"{llm_url.rstrip('/')}/api/inference/task"
+    try:
+        resp = httpx.post(
+            task_url,
+            json={
+                "product": "turnstone",
+                "task": task_name,
+                "payload": {"messages": messages, "stream": False},
+            },
+            headers=headers,
+            timeout=timeout,
+        )
+        if resp.status_code == 200:
+            return extract_content(resp.json())
+        if resp.status_code != 404:
+            resp.raise_for_status()
+        logger.debug(
+            "No task assignment for turnstone.%s — falling back to direct model",
+            task_name,
+        )
+    except Exception as exc:  # noqa: BLE001
+        # Broad catch is intentional: captures network errors, timeouts, and
+        # any backend-specific exceptions so the pipeline can fall back.
+        logger.debug(
+            "Task endpoint unavailable (%s) — falling back to direct model", exc
+        )
+
+    # --- Path 2: OpenAI-compat fallback ---
+    try:
+        resp = httpx.post(
+            f"{llm_url.rstrip('/')}/v1/chat/completions",
+            json={"model": llm_model, "messages": messages, "stream": False},
+            headers=headers,
+            timeout=timeout,
+        )
+        resp.raise_for_status()
+        return extract_content(resp.json())
+    except Exception as exc:  # noqa: BLE001
+        logger.warning("LLM call failed (%s): %s", type(exc).__name__, exc)
+        return None
diff --git a/app/services/diagnose/classifier.py b/app/services/diagnose/classifier.py
index b7aa8ed..b340c39 100644
--- a/app/services/diagnose/classifier.py
+++ b/app/services/diagnose/classifier.py
@@ -19,6 +19,8 @@ import os
 from pathlib import Path
 from typing import Any
 
+from types import MappingProxyType
+
 from app.services.diagnose.models import (
     ClassifiedTimeline,
     EventCluster,
@@ -243,7 +245,7 @@ class SeverityClassifier:
 
         return ClassifiedTimeline(
             timeline=timeline,
-            cluster_severities=cluster_severities,
+            cluster_severities=MappingProxyType(cluster_severities),
             classifier_used=classifier_used,  # type: ignore[arg-type]
             model_id=self._model_id if ml_available else None,
         )
diff --git a/app/services/diagnose/hypothesizer.py b/app/services/diagnose/hypothesizer.py
index 7c5c3e6..827332f 100644
--- a/app/services/diagnose/hypothesizer.py
+++ b/app/services/diagnose/hypothesizer.py
@@ -5,9 +5,8 @@ import json
 import logging
 from uuid import uuid4
 
-import httpx
-
 from app.context.retriever import RetrievedContext
+from app.services.diagnose._llm_client import call_llm, strip_json_fences
 from app.services.diagnose.models import (
     ClassifiedTimeline,
     EventCluster,
@@ -60,14 +59,6 @@ def _cluster_summary(cluster: EventCluster, severity: str) -> str:
     return summary
 
 
-def _extract_content(resp_json: dict) -> str | None:
-    """Pull text content from an OpenAI-compat chat completion response."""
-    choices = resp_json.get("choices") or []
-    if not choices:
-        return None
-    return (choices[0].get("message", {}).get("content") or "").strip() or None
-
-
 class RootCauseHypothesizer:
     """Generate ranked root-cause hypotheses from a classified log timeline."""
 
@@ -120,7 +111,7 @@ class RootCauseHypothesizer:
             {"role": "user", "content": user_message},
         ]
 
-        raw_response = self._call_llm(
+        raw_response = call_llm(
             llm_url=llm_url,
             llm_model=llm_model,
             llm_api_key=llm_api_key,
@@ -131,59 +122,14 @@ class RootCauseHypothesizer:
 
         return self._parse_response(raw_response)
 
-    def _call_llm(
-        self,
-        llm_url: str,
-        llm_model: str,
-        llm_api_key: str | None,
-        messages: list[dict],
-    ) -> str | None:
-        """Send messages to the LLM and return raw text content."""
-        headers = {"Authorization": f"Bearer {llm_api_key}"} if llm_api_key else {}
-
-        # Try cf-orch task-based endpoint first.
-        task_url = f"{llm_url.rstrip('/')}/api/inference/task"
-        try:
-            resp = httpx.post(
-                task_url,
-                json={
-                    "product": "turnstone",
-                    "task": "log_analysis",
-                    "payload": {"messages": messages, "stream": False},
-                },
-                headers=headers,
-                timeout=120.0,
-            )
-            if resp.status_code == 200:
-                return _extract_content(resp.json())
-            if resp.status_code != 404:
-                resp.raise_for_status()
-            logger.debug(
-                "No task assignment for turnstone.log_analysis — falling back to direct model"
-            )
-        except Exception as exc:
-            logger.debug("Task endpoint unavailable (%s) — falling back to direct model", exc)
-
-        # Fallback: OpenAI-compat endpoint with explicit model name.
-        try:
-            resp = httpx.post(
-                f"{llm_url.rstrip('/')}/v1/chat/completions",
-                json={"model": llm_model, "messages": messages, "stream": False},
-                headers=headers,
-                timeout=120.0,
-            )
-            resp.raise_for_status()
-            return _extract_content(resp.json())
-        except Exception as exc:
-            logger.warning(
-                "LLM hypothesizer failed (%s): %s", type(exc).__name__, exc
-            )
-            return None
-
     def _parse_response(self, raw: str) -> list[Hypothesis]:
-        """Parse the LLM JSON response into a list of Hypothesis objects."""
+        """Parse the LLM JSON response into a list of Hypothesis objects.
+
+        Strips markdown code fences before parsing — some LLMs wrap JSON in
+        triple-backtick fences despite being instructed not to.
+        """
         try:
-            data = json.loads(raw.strip())
+            data = json.loads(strip_json_fences(raw))
         except json.JSONDecodeError:
             logger.warning(
                 "Hypothesizer: invalid JSON from LLM (truncated): %.120s", raw
@@ -207,7 +153,9 @@ class RootCauseHypothesizer:
                 title=str(item.get("title", "Unknown"))[:80],
                 description=str(item.get("description", "")),
                 confidence=_coerce_float(item.get("confidence"), 0.5),
-                supporting_cluster_ids=tuple(item.get("supporting_clusters") or []),
+                supporting_cluster_ids=tuple(
+                    str(x) for x in (item.get("supporting_clusters") or [])
+                ),
                 runbook_refs=(),
                 severity=severity,
             )
diff --git a/app/services/diagnose/models.py b/app/services/diagnose/models.py
index 2831d30..ed454d1 100644
--- a/app/services/diagnose/models.py
+++ b/app/services/diagnose/models.py
@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 from dataclasses import dataclass
+from types import MappingProxyType
 from typing import Literal
 
 SeverityLabel = Literal["CRITICAL", "ERROR", "WARN", "INFO", "DEBUG", "UNKNOWN"]
@@ -40,10 +41,14 @@ class TimelineResult:
 
 @dataclass(frozen=True)
 class ClassifiedTimeline:
-    """Timeline annotated with ML-assigned severity per cluster."""
+    """Timeline annotated with ML-assigned severity per cluster.
+
+    ``cluster_severities`` is a ``MappingProxyType`` so the mapping is
+    fully immutable — consistent with the ``frozen=True`` intent.
+    """
 
     timeline: TimelineResult
-    cluster_severities: dict[str, SeverityLabel]
+    cluster_severities: MappingProxyType  # MappingProxyType[str, SeverityLabel]
     classifier_used: Literal["ml", "pattern_tags", "regex"]
     model_id: str | None
 
diff --git a/app/services/diagnose/pipeline.py b/app/services/diagnose/pipeline.py
index f902610..a60952f 100644
--- a/app/services/diagnose/pipeline.py
+++ b/app/services/diagnose/pipeline.py
@@ -53,9 +53,15 @@ async def run_pipeline(
     """
     # Stage 1: Timeline reconstruction
     yield {"type": "status", "message": "Building timeline…"}
-    timeline = await asyncio.to_thread(
-        TimelineReconstructor().reconstruct, entries
-    )
+    try:
+        timeline = await asyncio.to_thread(
+            TimelineReconstructor().reconstruct, entries
+        )
+    except Exception as exc:
+        logger.exception("Stage 1 (timeline) failed: %s", exc)
+        yield {"type": "error", "message": "Pipeline error in stage 1 (timeline)"}
+        yield {"type": "done"}
+        return
     n_clusters = len(timeline.clusters)
     burst = timeline.burst_count
     yield {
@@ -66,9 +72,15 @@ async def run_pipeline(
     }
 
     # Stage 2: Severity classification
-    classified = await asyncio.to_thread(
-        SeverityClassifier().classify, timeline
-    )
+    try:
+        classified = await asyncio.to_thread(
+            SeverityClassifier().classify, timeline
+        )
+    except Exception as exc:
+        logger.exception("Stage 2 (classifier) failed: %s", exc)
+        yield {"type": "error", "message": "Pipeline error in stage 2 (classifier)"}
+        yield {"type": "done"}
+        return
     sev_counts: dict[str, int] = {}
     for sev in classified.cluster_severities.values():
         sev_counts[sev] = sev_counts.get(sev, 0) + 1
@@ -81,15 +93,21 @@ async def run_pipeline(
     }
 
     # Stage 3: Root-cause hypotheses
-    hypotheses = await asyncio.to_thread(
-        RootCauseHypothesizer().hypothesize,
-        classified,
-        ctx,
-        query,
-        llm_url,
-        llm_model,
-        llm_api_key,
-    )
+    try:
+        hypotheses = await asyncio.to_thread(
+            RootCauseHypothesizer().hypothesize,
+            classified,
+            ctx,
+            query,
+            llm_url,
+            llm_model,
+            llm_api_key,
+        )
+    except Exception as exc:
+        logger.exception("Stage 3 (hypothesizer) failed: %s", exc)
+        yield {"type": "error", "message": "Pipeline error in stage 3 (hypothesizer)"}
+        yield {"type": "done"}
+        return
     yield {
         "type": "pipeline_stage",
         "stage": 3,
@@ -98,9 +116,15 @@ async def run_pipeline(
     }
 
     # Stage 4: False-positive suppression
-    ranked = await asyncio.to_thread(
-        FalsePositiveSuppressor().suppress, hypotheses, db_path
-    )
+    try:
+        ranked = await asyncio.to_thread(
+            FalsePositiveSuppressor().suppress, hypotheses, db_path
+        )
+    except Exception as exc:
+        logger.exception("Stage 4 (suppressor) failed: %s", exc)
+        yield {"type": "error", "message": "Pipeline error in stage 4 (suppressor)"}
+        yield {"type": "done"}
+        return
     suppressed = sum(1 for rh in ranked if rh.suppress)
     active = len(ranked) - suppressed
     yield {
@@ -116,16 +140,22 @@ async def run_pipeline(
 
     # Stage 5: Summary synthesis
     yield {"type": "status", "message": "Synthesizing…"}
-    synthesis_text = await asyncio.to_thread(
-        SummarySynthesizer().synthesize,
-        ranked,
-        timeline,
-        ctx,
-        query,
-        llm_url,
-        llm_model,
-        llm_api_key,
-    )
+    try:
+        synthesis_text = await asyncio.to_thread(
+            SummarySynthesizer().synthesize,
+            ranked,
+            timeline,
+            ctx,
+            query,
+            llm_url,
+            llm_model,
+            llm_api_key,
+        )
+    except Exception as exc:
+        logger.exception("Stage 5 (synthesizer) failed: %s", exc)
+        yield {"type": "error", "message": "Pipeline error in stage 5 (synthesizer)"}
+        yield {"type": "done"}
+        return
     if synthesis_text:
         yield {"type": "reasoning", "text": synthesis_text}
 
diff --git a/app/services/diagnose/synthesizer.py b/app/services/diagnose/synthesizer.py
index ce07625..edbf29a 100644
--- a/app/services/diagnose/synthesizer.py
+++ b/app/services/diagnose/synthesizer.py
@@ -7,9 +7,8 @@ from __future__ import annotations
 
 import logging
 
-import httpx
-
 from app.context.retriever import RetrievedContext
+from app.services.diagnose._llm_client import call_llm
 from app.services.diagnose.models import RankedHypothesis, TimelineResult
 
 logger = logging.getLogger(__name__)
@@ -29,14 +28,6 @@ _SYSTEM_PROMPT = (
 )
 
 
-def _extract_content(resp_json: dict) -> str | None:
-    """Pull text content from an OpenAI-compat chat completion response."""
-    choices = resp_json.get("choices") or []
-    if not choices:
-        return None
-    return (choices[0].get("message", {}).get("content") or "").strip() or None
-
-
 def _build_hypothesis_block(ranked: list[RankedHypothesis]) -> str:
     """Build the hypothesis block for the prompt (non-suppressed only, top 3)."""
     active = [rh for rh in ranked if not rh.suppress][:3]
@@ -46,15 +37,10 @@ def _build_hypothesis_block(ranked: list[RankedHypothesis]) -> str:
     for rh in active:
         h = rh.hypothesis
         conf_pct = int(h.confidence * 100)
-        similar = (
-            f"Yes — suppressed, {rh.suppression_reason}"
-            if rh.suppress and rh.suppression_reason
-            else "No"
-        )
         novelty = f"{rh.novelty_score:.2f}"
         lines.append(
             f"- [{h.severity}, {conf_pct}%] {h.title}\n"
-            f"  Similar resolved incident? {similar} (novelty {novelty})"
+            f"  Novelty: {novelty}"
         )
     return "\n".join(lines)
 
@@ -149,62 +135,10 @@ class SummarySynthesizer:
             {"role": "user", "content": user_message},
         ]
 
-        result = self._call_llm(
+        result = call_llm(
             llm_url=llm_url,
             llm_model=llm_model,
             llm_api_key=llm_api_key,
             messages=messages,
         )
         return result if result else fallback
-
-    def _call_llm(
-        self,
-        llm_url: str,
-        llm_model: str,
-        llm_api_key: str | None,
-        messages: list[dict],
-    ) -> str | None:
-        """Send messages to the LLM and return raw text content.
-
-        Tries the cf-orch task endpoint first, falls back to direct OpenAI-compat.
-        """
-        headers = {"Authorization": f"Bearer {llm_api_key}"} if llm_api_key else {}
-
-        task_url = f"{llm_url.rstrip('/')}/api/inference/task"
-        try:
-            resp = httpx.post(
-                task_url,
-                json={
-                    "product": "turnstone",
-                    "task": "log_analysis",
-                    "payload": {"messages": messages, "stream": False},
-                },
-                headers=headers,
-                timeout=120.0,
-            )
-            if resp.status_code == 200:
-                return _extract_content(resp.json())
-            if resp.status_code != 404:
-                resp.raise_for_status()
-            logger.debug(
-                "No task assignment for turnstone.log_analysis — falling back to direct model"
-            )
-        except Exception as exc:
-            logger.debug(
-                "Task endpoint unavailable (%s) — falling back to direct model", exc
-            )
-
-        try:
-            resp = httpx.post(
-                f"{llm_url.rstrip('/')}/v1/chat/completions",
-                json={"model": llm_model, "messages": messages, "stream": False},
-                headers=headers,
-                timeout=120.0,
-            )
-            resp.raise_for_status()
-            return _extract_content(resp.json())
-        except Exception as exc:
-            logger.warning(
-                "LLM synthesizer failed (%s): %s", type(exc).__name__, exc
-            )
-            return None