diff --git a/src/__tests__/dashboard-tile-eligibility-bucket-guard.test.ts b/src/__tests__/dashboard-tile-eligibility-bucket-guard.test.ts
new file mode 100644
index 000000000..2fc4e3a07
--- /dev/null
+++ b/src/__tests__/dashboard-tile-eligibility-bucket-guard.test.ts
@@ -0,0 +1,197 @@
+/**
+ * Structural guard — a dashboard tile may not be gated on a closed enum
+ * whose column is nullable.
+ *
+ * The Blood Glucose tile decided whether to paint by filtering the four
+ * `GlucoseContext` members against a per-context summary record and asking
+ * whether any of them held readings. Every named context is a legal value of
+ * the column, so the list read as exhaustive — but `glucose_context` is
+ * nullable, and a meter synced through Apple Health writes no meal-time
+ * metadata at all. An account with one hundred percent untagged readings
+ * therefore matched no bucket, and the tile was omitted with the module on,
+ * the layout toggle on, and a reading from today. Nothing warned: every
+ * behavioural test in the suite seeded a tagged reading, so the missing arm
+ * was invisible from the outside (#943).
+ *
+ * What the guard asserts: wherever a dashboard tile surface derives presence
+ * from a list of enum buckets, the list must carry a null / unknown arm — or
+ * the call site must write down why it cannot. It matches on the list
+ * EXPRESSION, following one hop through a named constant, because the fix for
+ * this class is always the same: the untagged bucket joins the list the
+ * eligibility loop already walks.
+ *
+ * Its limits, written down so a later reader does not over-trust it: it sees
+ * presence tests spelled with `count`, and a bucket list that is either an
+ * inline literal or a single named constant. An eligibility gate that counted
+ * rows some other way, or assembled its bucket list at runtime, would slip
+ * past. The `detect()` self-controls below exist so a refactor that silently
+ * stops matching anything fails here rather than going quiet.
+ */
+import { describe, it, expect } from "vitest";
+import { readFileSync, readdirSync, statSync } from "node:fs";
+import { join } from "node:path";
+
+/**
+ * A bucket list that carries one of these tokens has an arm for rows the
+ * enum cannot name. Matched against the list expression's source text, so a
+ * shared constant (`GLUCOSE_CONTEXT_BUCKETS = [...NAMED, UNSPECIFIED]`)
+ * satisfies it through its own name.
+ */
+const UNTAGGED_ARM = /UNSPECIFIED|UNKNOWN|UNTAGGED|OTHER|NONE/;
+
+/** The written-reason escape hatch, with a non-empty reason after it. */
+const WRITTEN_REASON = /tile-eligibility-exempt:\s*\S/;
+
+/** Dashboard surfaces that decide whether a tile paints. */
+const SURFACES = [
+  "src/app/page-client.tsx",
+  ...listSourceFiles("src/components/dashboard"),
+  ...listSourceFiles("src/lib/dashboard"),
+];
+
+function listSourceFiles(dir: string): string[] {
+  const abs = join(process.cwd(), dir);
+  return readdirSync(abs)
+    .filter((name) => /\.tsx?$/.test(name))
+    .map((name) => join(dir, name))
+    .filter((rel) => statSync(join(process.cwd(), rel)).isFile());
+}
+
+interface Finding {
+  /** The bucket-list expression as written at the eligibility site. */
+  list: string;
+  /** 1-based line of the eligibility site. */
+  line: number;
+}
+
+/**
+ * Iteration over a bucket list: `for (const x of LIST)` or
+ * `LIST.filter(…)` / `.some(…)`. The list is either an inline array literal
+ * or an identifier.
+ */
+const ITERATION =
+  /(?:for\s*\(\s*(?:const|let)\s+[^)]*?\bof\s+(\[[^\]]*\]|[A-Za-z_$][\w$]*)\s*\))|(?:(\[[^\]]*\]|[A-Za-z_$][\w$]*)\s*\.\s*(?:filter|some|flatMap)\s*\()/g;
+
+/** A presence test — "does this bucket hold any readings". */
+const PRESENCE = /\bcount\b/;
+
+/** How far past the iteration head a presence test still belongs to it. */
+const BODY_WINDOW = 500;
+
+/**
+ * Every eligibility site in `source` whose bucket list has no untagged arm
+ * and no written reason. `resolve` supplies the initializer text of a named
+ * constant so the guard can follow one hop out of the file.
+ */
+export function detect(
+  source: string,
+  resolve: (name: string) => string | null,
+): Finding[] {
+  const findings: Finding[] = [];
+  ITERATION.lastIndex = 0;
+  let match: RegExpExecArray | null;
+  while ((match = ITERATION.exec(source)) !== null) {
+    const list = match[1] ?? match[2];
+    if (!list) continue;
+    const body = source.slice(match.index, match.index + BODY_WINDOW);
+    if (!PRESENCE.test(body)) continue;
+    // Only enum-shaped lists are in scope: an inline literal of UPPER_SNAKE
+    // members, or an UPPER_SNAKE constant name.
+    const inline = list.startsWith("[");
+    const members = inline ? list.match(/"[A-Z][A-Z0-9_]*"/g) : null;
+    if (inline && (members?.length ?? 0) < 2) continue;
+    if (!inline && !/^[A-Z][A-Z0-9_]*$/.test(list)) continue;
+    const expression = inline ? list : (resolve(list) ?? list);
+    if (UNTAGGED_ARM.test(expression)) continue;
+    const before = source.slice(Math.max(0, match.index - 400), match.index);
+    if (WRITTEN_REASON.test(before)) continue;
+    findings.push({
+      list,
+      line: source.slice(0, match.index).split("\n").length,
+    });
+  }
+  return findings;
+}
+
+/** Initializer text of `export const NAME = …` / `const NAME = …` in `src/`. */
+function resolveConstant(name: string): string | null {
+  for (const file of CONSTANT_SOURCES) {
+    const source = readFileSync(join(process.cwd(), file), "utf8");
+    const declaration = new RegExp(
+      `(?:export\\s+)?const\\s+${name}\\s*(?::[^=]+)?=\\s*(\\[[\\s\\S]*?\\])`,
+    ).exec(source);
+    if (declaration) return declaration[1];
+  }
+  return null;
+}
+
+/** Files a dashboard surface may import a bucket list from. */
+const CONSTANT_SOURCES = ["src/lib/glucose.ts", ...SURFACES];
+
+describe("detect() — the matcher itself", () => {
+  it("flags the shape that shipped: four enum members, no null arm", () => {
+    const shipped = `
+      const contexts = ["FASTING", "POSTPRANDIAL", "RANDOM", "BEDTIME"];
+      const present = ["FASTING", "POSTPRANDIAL", "RANDOM", "BEDTIME"].filter(
+        (ctx) => (byContext[ctx]?.count ?? 0) > 0,
+      );
+    `;
+    const findings = detect(shipped, () => null);
+    expect(findings).toHaveLength(1);
+    expect(findings[0].list).toContain("FASTING");
+  });
+
+  it("accepts a list that carries an untagged arm", () => {
+    const fixed = `
+      for (const bucket of GLUCOSE_CONTEXT_BUCKETS) {
+        const summary = byContext?.[bucket];
+        if (!summary || summary.count <= 0) continue;
+      }
+    `;
+    const resolve = () => '["FASTING", "BEDTIME", GLUCOSE_CONTEXT_UNSPECIFIED]';
+    expect(detect(fixed, resolve)).toEqual([]);
+    // …and rejects the same site when the constant has no arm, so the pass
+    // above is the arm's doing and not the resolver's.
+    expect(detect(fixed, () => '["FASTING", "BEDTIME"]')).toHaveLength(1);
+  });
+
+  it("accepts a written reason", () => {
+    const exempt = `
+      // tile-eligibility-exempt: sleep stages are never null on this path.
+      for (const stage of ["DEEP", "REM"]) {
+        if (byStage[stage].count > 0) return true;
+      }
+    `;
+    expect(detect(exempt, () => null)).toEqual([]);
+  });
+
+  it("ignores lists that are not presence tests", () => {
+    const unrelated = `
+      const labels = ["WEIGHT", "PULSE"].map((type) => LABELS[type]);
+    `;
+    expect(detect(unrelated, () => null)).toEqual([]);
+  });
+});
+
+describe("dashboard tile eligibility", () => {
+  it("scans the surfaces it claims to scan", () => {
+    // An empty match set must fail rather than read as clean: the guard is
+    // worthless the day its matchers stop finding the real call sites.
+    expect(SURFACES.length).toBeGreaterThan(5);
+    const sited = SURFACES.filter((file) =>
+      PRESENCE.test(readFileSync(join(process.cwd(), file), "utf8")),
+    );
+    expect(sited.length).toBeGreaterThan(0);
+  });
+
+  it("computes no tile's eligibility from an enum without a null arm", () => {
+    const offenders: string[] = [];
+    for (const file of SURFACES) {
+      const source = readFileSync(join(process.cwd(), file), "utf8");
+      for (const finding of detect(source, resolveConstant)) {
+        offenders.push(`${file}:${finding.line} — ${finding.list}`);
+      }
+    }
+    expect(offenders).toEqual([]);
+  });
+});
diff --git a/tests/integration/dashboard-glucose-untagged.test.ts b/tests/integration/dashboard-glucose-untagged.test.ts
new file mode 100644
index 000000000..810696cac
--- /dev/null
+++ b/tests/integration/dashboard-glucose-untagged.test.ts
@@ -0,0 +1,165 @@
+/**
+ * #943 — untagged glucose readings light the dashboard tile.
+ *
+ * A reporter's meter syncs through Apple Health and never writes HealthKit's
+ * blood-glucose meal-time metadata, so all of their readings carry a NULL
+ * `glucose_context`. The tile strip filtered the four named contexts against
+ * the per-context summaries, matched none, and omitted the tile — module on,
+ * layout toggle on, a reading from today, and no warning anywhere.
+ *
+ * A real Postgres is what makes this convincing: the summaries are built from
+ * rows the database actually holds, with the column genuinely NULL, and the
+ * tile gate is the same pure resolver the page renders through.
+ */
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+import { cookieJar, headerJar } from "./mock-next-headers";
+import { getPrismaClient, truncateAllTables } from "./setup";
+
+import { resolveGlucoseTiles } from "@/components/dashboard/dashboard-gates";
+import type { DataSummary } from "@/lib/analytics/trends";
+
+vi.mock("next/headers", async () => {
+  const { cookieJar, headerJar } = await import("./mock-next-headers");
+  return {
+    headers: vi.fn(async () => ({
+      get: (name: string) => headerJar.get(name.toLowerCase()) ?? null,
+    })),
+    cookies: vi.fn(async () => ({
+      get: (name: string) => {
+        const value = cookieJar.get(name);
+        return value ? { name, value } : undefined;
+      },
+      set: (name: string, value: string) => {
+        cookieJar.set(name, value);
+      },
+      delete: (name: string) => {
+        cookieJar.delete(name);
+      },
+    })),
+  };
+});
+
+vi.mock("@/lib/db-compat", () => ({
+  ensureDbCompatibility: vi.fn().mockResolvedValue(undefined),
+}));
+
+interface AnalyticsEnvelope {
+  data: {
+    glucoseByContext: Record<string, DataSummary> | null;
+  };
+  error: null;
+}
+
+const DAY_MS = 24 * 60 * 60 * 1000;
+const READINGS = 20;
+
+beforeEach(async () => {
+  await truncateAllTables(getPrismaClient());
+  cookieJar.clear();
+  headerJar.clear();
+});
+
+async function seedUntaggedGlucose() {
+  const prisma = getPrismaClient();
+  const user = await prisma.user.create({
+    data: {
+      username: "glucose-untagged",
+      email: "glucose-untagged@example.test",
+      role: "USER",
+      timezone: "Europe/Berlin",
+    },
+  });
+  const session = await prisma.session.create({
+    data: { userId: user.id, expiresAt: new Date(Date.now() + 60_000) },
+  });
+  cookieJar.set("healthlog_session", session.id);
+
+  // 20 readings, one per day, newest first at 104 mg/dL. Every one of them
+  // arrives exactly as the reporter's sync writes them: no meal-time context.
+  const now = Date.now();
+  await prisma.measurement.createMany({
+    data: Array.from({ length: READINGS }, (_, i) => ({
+      userId: user.id,
+      type: "BLOOD_GLUCOSE" as const,
+      value: 104 + i,
+      unit: "mg/dL",
+      source: "APPLE_HEALTH" as const,
+      measuredAt: new Date(now - i * DAY_MS),
+      glucoseContext: null,
+    })),
+  });
+  return user;
+}
+
+async function readAnalytics(): Promise<AnalyticsEnvelope> {
+  const { GET } = await import("@/app/api/analytics/route");
+  const response = await (
+    GET as unknown as (req: Request) => Promise<Response>
+  )(new Request("http://localhost/api/analytics"));
+  expect(response.status).toBe(200);
+  return (await response.json()) as AnalyticsEnvelope;
+}
+
+describe("dashboard glucose tile with untagged readings (#943)", () => {
+  it("stores the readings with a NULL context", async () => {
+    const user = await seedUntaggedGlucose();
+    const rows = await getPrismaClient().measurement.findMany({
+      where: { userId: user.id, type: "BLOOD_GLUCOSE" },
+      select: { glucoseContext: true },
+    });
+
+    expect(rows).toHaveLength(READINGS);
+    expect(rows.every((row) => row.glucoseContext === null)).toBe(true);
+  });
+
+  it("reports the tile as eligible and carries the latest value", async () => {
+    await seedUntaggedGlucose();
+
+    const envelope = await readAnalytics();
+    const byContext = envelope.data.glucoseByContext;
+    expect(byContext).not.toBeNull();
+
+    // The summaries carry the untagged bucket, and nothing else.
+    expect(Object.keys(byContext ?? {})).toEqual(["UNSPECIFIED"]);
+    const summary = byContext!.UNSPECIFIED;
+    expect(summary.count).toBe(READINGS);
+    expect(summary.latest).toBe(104);
+    expect(summary.avg30).not.toBeNull();
+
+    // …and the tile gate the dashboard renders through says "paint it".
+    const tiles = resolveGlucoseTiles(byContext ?? undefined);
+    expect(tiles).toHaveLength(1);
+    expect(tiles[0]).toMatchObject({
+      bucket: "UNSPECIFIED",
+      labelKey: "targets.glucoseUnspecified",
+    });
+    expect(tiles[0].summary.latest).toBe(104);
+  });
+
+  it("keeps a tagged reading in its own bucket beside the untagged ones", async () => {
+    const user = await seedUntaggedGlucose();
+    await getPrismaClient().measurement.create({
+      data: {
+        userId: user.id,
+        type: "BLOOD_GLUCOSE",
+        value: 92,
+        unit: "mg/dL",
+        source: "MANUAL",
+        measuredAt: new Date(),
+        glucoseContext: "FASTING",
+      },
+    });
+
+    const envelope = await readAnalytics();
+    const byContext = envelope.data.glucoseByContext ?? {};
+
+    expect(Object.keys(byContext).sort()).toEqual(["FASTING", "UNSPECIFIED"]);
+    expect(byContext.FASTING.count).toBe(1);
+    expect(byContext.UNSPECIFIED.count).toBe(READINGS);
+    expect(resolveGlucoseTiles(byContext).map((tile) => tile.bucket)).toEqual([
+      "FASTING",
+      "UNSPECIFIED",
+    ]);
+  });
+});