diff --git a/src/lib/insights/__tests__/status-shared.test.ts b/src/lib/insights/__tests__/status-shared.test.ts
index 6b3ce1f84..1a0e9f309 100644
--- a/src/lib/insights/__tests__/status-shared.test.ts
+++ b/src/lib/insights/__tests__/status-shared.test.ts
@@ -1,9 +1,20 @@
 import { describe, expect, it } from "vitest";
 import {
+  extractAssessmentSummary,
   parseSummaryFromContent,
   stripJsonFences,
 } from "@/lib/insights/status-shared";
 
+/**
+ * The exact malformed shape reported against the resting-pulse Assessment
+ * (HealthLog#608): a truncated `{ "summary": "…` — an OPEN brace, the property
+ * name, quotes and an unclosed string, with no closing `}`. Before the fix this
+ * fell through the parser and rendered raw (braces, `"summary"`, quotes, literal
+ * `\n`) in the Assessment card. It must resolve to the controlled fallback.
+ */
+const TRUNCATED_PULSE_ENVELOPE =
+  '{ "summary": "Your resting pulse has been running lower than the last check';
+
 /**
  * The Anthropic + local providers have no native JSON mode, so a compliant
  * model still routinely wraps its `{ "summary": … }` reply in a ```json
@@ -59,4 +70,69 @@ describe("parseSummaryFromContent", () => {
       "just prose, no json",
     );
   });
+
+  it("returns empty string for a truncated envelope (never the raw JSON)", () => {
+    const out = parseSummaryFromContent(TRUNCATED_PULSE_ENVELOPE);
+    expect(out).toBe("");
+    expect(out).not.toContain('"summary"');
+    expect(out).not.toContain("{");
+  });
+});
+
+describe("extractAssessmentSummary", () => {
+  it("classifies a structured object with a valid summary", () => {
+    const out = extractAssessmentSummary('{"summary":"hello"}');
+    expect(out).toEqual({ kind: "summary", text: "hello" });
+  });
+
+  it("parses a JSON STRING that carries a top-level summary", () => {
+    // A provider handed back the envelope as a serialized string. It parses to
+    // the same summary as an inline object — not treated as prose.
+    const jsonString = JSON.stringify({
+      summary: "resting pulse steady at 58",
+    });
+    const out = extractAssessmentSummary(jsonString);
+    expect(out).toEqual({
+      kind: "summary",
+      text: "resting pulse steady at 58",
+    });
+  });
+
+  it("classifies a fenced envelope as summary (no native JSON mode)", () => {
+    const out = extractAssessmentSummary('```json\n{"summary":"hello"}\n```');
+    expect(out).toEqual({ kind: "summary", text: "hello" });
+  });
+
+  it("preserves a plain-text reply as prose, verbatim", () => {
+    const prose =
+      "Your resting pulse is averaging 58 bpm, in line with baseline.";
+    expect(extractAssessmentSummary(prose)).toEqual({
+      kind: "prose",
+      text: prose,
+    });
+  });
+
+  it("does not treat a plain sentence containing a brace as JSON", () => {
+    const prose = "Your resting pulse sits around 58 bpm {your usual range}.";
+    expect(extractAssessmentSummary(prose)).toEqual({
+      kind: "prose",
+      text: prose,
+    });
+  });
+
+  it("resolves a truncated envelope to unparseable (regression: #608)", () => {
+    expect(extractAssessmentSummary(TRUNCATED_PULSE_ENVELOPE)).toEqual({
+      kind: "unparseable",
+    });
+  });
+
+  it("resolves a summary-less object to unparseable", () => {
+    expect(extractAssessmentSummary("{}")).toEqual({ kind: "unparseable" });
+  });
+
+  it("resolves an empty-summary object to unparseable", () => {
+    expect(extractAssessmentSummary('{"summary":""}')).toEqual({
+      kind: "unparseable",
+    });
+  });
 });
diff --git a/src/lib/insights/__tests__/status-summary-screen.test.ts b/src/lib/insights/__tests__/status-summary-screen.test.ts
index d466bf259..c7c669f64 100644
--- a/src/lib/insights/__tests__/status-summary-screen.test.ts
+++ b/src/lib/insights/__tests__/status-summary-screen.test.ts
@@ -92,3 +92,37 @@ describe("finalizeStatusSummary — clean assessments pass untouched", () => {
     expect(out.ok).toBe(true);
   });
 });
+
+/**
+ * HealthLog#608 — a truncated `{ "summary": "…` (unclosed, no `}`) used to fall
+ * through the parser and render raw (braces, `"summary"`, quotes, literal `\n`)
+ * in the resting-pulse Assessment card. It must now resolve to the withhold
+ * state so the caller serves its deterministic stub, never the raw envelope.
+ */
+describe("finalizeStatusSummary — malformed structured output is withheld", () => {
+  const TRUNCATED =
+    '{ "summary": "Your resting pulse has been running lower than the last check';
+
+  it("withholds a truncated envelope instead of surfacing raw JSON", () => {
+    const out = finalizeStatusSummary(TRUNCATED, "en");
+    expect(out.ok).toBe(false);
+    if (!out.ok) expect(out.reason).toBe("unparseable_output");
+    // Nothing about the raw envelope can leak on the ok:false branch.
+    if (out.ok) {
+      expect(out.text).not.toContain('"summary"');
+      expect(out.text).not.toContain("{");
+    }
+  });
+
+  it("withholds a summary-less object", () => {
+    const out = finalizeStatusSummary("{}", "en");
+    expect(out.ok).toBe(false);
+    if (!out.ok) expect(out.reason).toBe("unparseable_output");
+  });
+
+  it("still renders a valid object summary", () => {
+    const out = finalizeStatusSummary('{"summary":"Steady at 58 bpm."}', "en");
+    expect(out.ok).toBe(true);
+    if (out.ok) expect(out.text).toBe("Steady at 58 bpm.");
+  });
+});
diff --git a/src/lib/insights/derived/derived-assessment-ai.ts b/src/lib/insights/derived/derived-assessment-ai.ts
index 3b142ef60..f17eba298 100644
--- a/src/lib/insights/derived/derived-assessment-ai.ts
+++ b/src/lib/insights/derived/derived-assessment-ai.ts
@@ -31,9 +31,9 @@ import {
   withOutputLanguage,
 } from "@/lib/ai/prompts/output-language";
 import {
+  extractAssessmentSummary,
   normalizeLocale,
   normalizeSummaryText,
-  parseSummaryFromContent,
   persistStatusInsight,
 } from "@/lib/insights/status-shared";
 import { runStatusCompletion } from "@/lib/insights/status-provider";
@@ -311,7 +311,19 @@ export async function generateDerivedScoreAssessment(args: {
     return;
   }
 
-  const text = normalizeSummaryText(parseSummaryFromContent(outcome.content));
+  // A malformed / truncated / summary-less structured envelope must never
+  // persist as the derived-score assessment (the raw-JSON class of bug). On an
+  // unparseable envelope persist nothing — the route keeps serving the
+  // always-grounded deterministic fallback, so the field stays honest.
+  const extracted = extractAssessmentSummary(outcome.content);
+  if (extracted.kind === "unparseable") {
+    annotate({
+      action: { name: "insights.derived-assessment.unparseable" },
+      meta: { metric: args.metric },
+    });
+    return;
+  }
+  const text = normalizeSummaryText(extracted.text);
   if (!text) return;
 
   // v1.22 (W6) — score number-grounding gate. The only numbers the prose may
diff --git a/src/lib/insights/medication-compliance-status.ts b/src/lib/insights/medication-compliance-status.ts
index 1b5b4f9a1..5fc2ba088 100644
--- a/src/lib/insights/medication-compliance-status.ts
+++ b/src/lib/insights/medication-compliance-status.ts
@@ -30,9 +30,9 @@ import { buildMetricSignal } from "@/lib/insights/metric-signal";
 import { degradeStatusSnapshotToBudget } from "@/lib/insights/graded-series";
 import {
   type SupportedLocale,
+  extractAssessmentSummary,
   normalizeLocale,
   normalizeSummaryText,
-  parseSummaryFromContent,
   round,
 } from "@/lib/insights/status-shared";
 import {
@@ -577,9 +577,32 @@ export async function prepareMedicationComplianceStatusForUser(
       // does not emit per-medication text. The per-medication cards carry a
       // placeholder so the UI surfaces a row per active medication; the
       // overall `summary` is the model-authored assessment.
-      const summary = normalizeSummaryText(
-        parseSummaryFromContent(outcome.content),
-      );
+      // A malformed / truncated / summary-less structured envelope must never
+      // persist as the day's assessment (the raw-JSON class of bug). WITHHOLD:
+      // serve the deterministic no-key line, write a short negative stub, and
+      // persist no model text. The per-medication rows still render.
+      const extracted = extractAssessmentSummary(outcome.content);
+      if (extracted.kind === "unparseable") {
+        annotate({
+          action: { name: "insights.status.outbound_blocked" },
+          meta: { cacheAction, reason: "unparseable_output" },
+        });
+        returnTimeoutFallback({
+          cacheAction,
+          reason: "screened",
+          userId,
+          todayKey,
+          stubText: getNoKeyMedicationComplianceStatusText(locale),
+        });
+        return {
+          hasProvider: true,
+          summary: getNoKeyMedicationComplianceStatusText(locale),
+          medications: medicationSummaries,
+          cached: true,
+          updatedAt: null,
+        };
+      }
+      const summary = normalizeSummaryText(extracted.text);
       if (!summary) {
         throw new Error(
           "Medication-compliance-status summary was empty after normalization",
diff --git a/src/lib/insights/status-shared.ts b/src/lib/insights/status-shared.ts
index 454ead431..3bda3ab05 100644
--- a/src/lib/insights/status-shared.ts
+++ b/src/lib/insights/status-shared.ts
@@ -145,30 +145,120 @@ export function stripJsonFences(content: string): string {
 }
 
 /**
- * Pull the `summary` string out of a model completion. The status
- * prompts return a `{ "summary": "…" }` envelope; a model that ignores
- * the contract and returns bare prose falls back to the raw content.
+ * Outcome of reading a status completion for its user-facing summary.
+ *
+ *   - `summary` — a `{ "summary": "…" }` envelope parsed to a non-empty
+ *     string. Render it.
+ *   - `prose`   — the model ignored the JSON contract and returned a plain
+ *     sentence. Render it verbatim (back-compat with non-JSON-mode providers).
+ *   - `unparseable` — the model ATTEMPTED the structured envelope but it came
+ *     back malformed, truncated, or summary-less. There is NO safe text to
+ *     render: the caller must fall back to its deterministic stub. This is the
+ *     state that stops a partial `{ "summary": "…` (braces, property name,
+ *     quotes, literal `\n`) from ever reaching the card — the class of bug
+ *     reported against the resting-pulse Assessment.
+ */
+export type SummaryExtraction =
+  | { kind: "summary"; text: string }
+  | { kind: "prose"; text: string }
+  | { kind: "unparseable" };
+
+/**
+ * Parse a candidate string as a `{ summary }` object. Reports whether the
+ * string was valid JSON *object* at all (`parsed`) separately from whether it
+ * carried a usable non-empty `summary` — so the caller can tell a malformed /
+ * truncated envelope apart from a well-formed object that simply lacks the
+ * field.
+ */
+function parseSummaryObject(candidate: string): {
+  parsed: boolean;
+  summary: string | null;
+} {
+  try {
+    const obj = JSON.parse(candidate) as unknown;
+    if (obj !== null && typeof obj === "object" && !Array.isArray(obj)) {
+      const value = (obj as { summary?: unknown }).summary;
+      if (typeof value === "string" && value.trim().length > 0) {
+        return { parsed: true, summary: value };
+      }
+      // Well-formed object, but no usable summary (e.g. `{}` or `{summary:""}`).
+      return { parsed: true, summary: null };
+    }
+    // Valid JSON, but not a summary object (array / number / bare string).
+    return { parsed: false, summary: null };
+  } catch {
+    return { parsed: false, summary: null };
+  }
+}
+
+/**
+ * Did the completion OPEN like a JSON object? A genuine prose sentence never
+ * starts with `{` (a stray brace mid-sentence does not count), so a `{`-led
+ * payload that failed both parse attempts above is a malformed / truncated
+ * envelope — never surfaced raw. Strips a leading code fence first so a
+ * fenced-but-truncated object is caught too.
+ */
+function looksLikeJsonObjectAttempt(content: string): boolean {
+  const afterFence = content.replace(/^```(?:json)?\s*/i, "").trimStart();
+  return afterFence.startsWith("{");
+}
+
+/**
+ * Read a model completion for its user-facing summary and classify the result.
  *
  * Tries the content as-is first (the common, fence-free case), then a
- * fence-stripped retry for providers without a native JSON mode.
+ * fence-stripped retry for providers without a native JSON mode. A completion
+ * that attempted the `{ summary }` envelope but came back malformed / truncated
+ * / summary-less resolves to `unparseable` rather than falling through as raw
+ * text — the caller then serves its deterministic fallback. Only a completion
+ * that never attempted the envelope (genuine prose) passes through verbatim.
+ */
+export function extractAssessmentSummary(content: string): SummaryExtraction {
+  const trimmed = content.trim();
+
+  // Attempt 1 — the content is itself a JSON object.
+  const direct = parseSummaryObject(trimmed);
+  if (direct.parsed) {
+    return direct.summary
+      ? { kind: "summary", text: direct.summary }
+      : { kind: "unparseable" };
+  }
+
+  // Attempt 2 — strip a code fence / surrounding prose and retry.
+  const stripped = stripJsonFences(trimmed);
+  if (stripped !== trimmed) {
+    const viaFence = parseSummaryObject(stripped);
+    if (viaFence.parsed) {
+      return viaFence.summary
+        ? { kind: "summary", text: viaFence.summary }
+        : { kind: "unparseable" };
+    }
+  }
+
+  // Neither parse produced a summary object. If the payload OPENED like an
+  // object, the model attempted the envelope and it came back malformed or
+  // truncated — resolve to the controlled fallback, never the raw braces /
+  // property name / quotes / literal `\n`. Genuine prose falls through.
+  if (looksLikeJsonObjectAttempt(trimmed)) {
+    return { kind: "unparseable" };
+  }
+  return { kind: "prose", text: content };
+}
+
+/**
+ * Pull the `summary` string out of a model completion. The status prompts
+ * return a `{ "summary": "…" }` envelope; a model that ignores the contract and
+ * returns bare prose falls back to the raw content. A malformed / truncated /
+ * summary-less structured envelope resolves to an EMPTY string (never the raw
+ * JSON) so no caller can surface partial structured output.
+ *
+ * Prefer `extractAssessmentSummary` in new code: it distinguishes an
+ * unparseable envelope from genuinely empty prose, which this thin wrapper
+ * collapses to `""`.
  */
 export function parseSummaryFromContent(content: string): string {
-  try {
-    const parsed = JSON.parse(content) as { summary?: string };
-    if (typeof parsed.summary === "string") return parsed.summary;
-  } catch {
-    // not directly parseable — try a fence-stripped retry below
-  }
-  try {
-    const stripped = stripJsonFences(content);
-    if (stripped !== content) {
-      const parsed = JSON.parse(stripped) as { summary?: string };
-      if (typeof parsed.summary === "string") return parsed.summary;
-    }
-  } catch {
-    // still not JSON — fall through to the raw content
-  }
-  return content;
+  const extracted = extractAssessmentSummary(content);
+  return extracted.kind === "unparseable" ? "" : extracted.text;
 }
 
 /**
@@ -230,7 +320,8 @@ export async function persistStatusInsight(args: {
  * withholds.
  */
 export type StatusSummaryOutcome =
-  { ok: true; text: string } | { ok: false; reason: OutboundReason };
+  | { ok: true; text: string }
+  | { ok: false; reason: OutboundReason | "unparseable_output" };
 
 /**
  * The single finalize step every per-metric / biomarker / derived-score status
@@ -263,7 +354,14 @@ export function finalizeStatusSummary(
   content: string,
   locale: SupportedLocale,
 ): StatusSummaryOutcome {
-  const text = normalizeSummaryText(parseSummaryFromContent(content));
+  const extracted = extractAssessmentSummary(content);
+  // A malformed / truncated / summary-less structured envelope has no safe
+  // text to render. WITHHOLD — the caller serves its deterministic stub. Only
+  // the `unparseable` discriminator is logged, never the assessment content.
+  if (extracted.kind === "unparseable") {
+    return { ok: false, reason: "unparseable_output" };
+  }
+  const text = normalizeSummaryText(extracted.text);
   if (!text) return { ok: true, text: "" };
   const decision = screenModelOutput(text, locale, INSIGHTS_CONTRACTS);
   if (decision.block && decision.reason) {