diff --git a/e2e/mobile-route-overflow.spec.ts b/e2e/mobile-route-overflow.spec.ts
index a0d0397b8..127ad3a3c 100644
--- a/e2e/mobile-route-overflow.spec.ts
+++ b/e2e/mobile-route-overflow.spec.ts
@@ -5,7 +5,7 @@ import type { APIRequestContext } from "@playwright/test";
 
 import { ADMIN_SECTION_SLUGS } from "@/components/admin/section-slugs";
 import { MODULE_SETTINGS_PAGE_IDS } from "@/components/settings/module-settings-page-ids";
-import { SETTINGS_SECTION_SLUGS } from "@/components/settings/section-slugs";
+import { SETTINGS_SECTION_SLUGS } from "@/lib/settings/section-slugs";
 
 import { expect, test } from "./setup/test";
 import { MOBILE_ROUTES_STORAGE_STATE_PATH } from "./setup/global-setup";
diff --git a/eslint-plugins/healthlog/__tests__/import-boundaries.test.mjs b/eslint-plugins/healthlog/__tests__/import-boundaries.test.mjs
new file mode 100644
index 000000000..992691be5
--- /dev/null
+++ b/eslint-plugins/healthlog/__tests__/import-boundaries.test.mjs
@@ -0,0 +1,147 @@
+/**
+ * Unit tests for the `healthlog/import-boundaries` rule: src/lib never
+ * imports components or app, and a "use client" file never makes a value
+ * import of a server-only module. Covers alias and relative specifiers,
+ * type-only imports, dynamic imports, re-exports, the allow map and its
+ * stale-entry report.
+ */
+
+import { describe, it } from "vitest";
+import { RuleTester } from "eslint";
+import nextTs from "eslint-config-next/typescript";
+import rule from "../import-boundaries.js";
+
+// The TypeScript parser the app lints with, taken from the same config so
+// `import type` reaches the rule as it does in `pnpm lint`.
+const tsParser = nextTs.find((c) => c.languageOptions?.parser).languageOptions
+  .parser;
+
+RuleTester.describe = describe;
+RuleTester.it = it;
+RuleTester.itOnly = it.only;
+
+const ruleTester = new RuleTester({
+  languageOptions: {
+    parser: tsParser,
+    ecmaVersion: 2023,
+    sourceType: "module",
+    parserOptions: { ecmaFeatures: { jsx: true } },
+  },
+});
+
+const LIB_FILE = "/repo/src/lib/medications/example.ts";
+const CLIENT_FILE = "/repo/src/components/medications/example.tsx";
+
+ruleTester.run("import-boundaries", rule, {
+  valid: [
+    // lib importing lib, a package, and itself relatively.
+    { code: 'import { a } from "@/lib/x";', filename: LIB_FILE },
+    { code: 'import { z } from "zod";', filename: LIB_FILE },
+    { code: 'import { b } from "../y";', filename: LIB_FILE },
+    // components importing components and lib is the right direction.
+    {
+      code: 'import { C } from "@/components/ui/card";',
+      filename: CLIENT_FILE,
+    },
+    // Tests are out of scope.
+    {
+      code: 'import { C } from "@/components/ui/card";',
+      filename: "/repo/src/lib/medications/__tests__/x.test.ts",
+    },
+    // An allowed lib file that still imports upward.
+    {
+      code: 'import { C } from "@/components/ui/card";',
+      filename: LIB_FILE,
+      options: [{ allow: { "src/lib/medications/example.ts": "reason" } }],
+    },
+    // A server component (no directive) may import the database client.
+    {
+      code: 'import { prisma } from "@/lib/db";',
+      filename: "/repo/src/app/page.tsx",
+    },
+    // A client file may import types from server modules and the enums entry.
+    {
+      code: '"use client";\nimport type { MeasurementType } from "@/generated/prisma/client";',
+      filename: CLIENT_FILE,
+    },
+    {
+      code: '"use client";\nimport { type BackupRestoreJobView } from "@/lib/jobs/backup-restore";',
+      filename: CLIENT_FILE,
+    },
+    {
+      code: '"use client";\nimport { MeasurementType } from "@/generated/prisma/enums";',
+      filename: CLIENT_FILE,
+    },
+    // A string that only looks like the directive is not one.
+    {
+      code: 'const x = "use client";\nimport { prisma } from "@/lib/db";',
+      filename: CLIENT_FILE,
+    },
+  ],
+  invalid: [
+    {
+      code: 'import { C } from "@/components/ui/card";',
+      filename: LIB_FILE,
+      errors: [{ messageId: "libUpward" }],
+    },
+    {
+      code: 'import type { P } from "@/app/settings/page";',
+      filename: LIB_FILE,
+      errors: [{ messageId: "libUpward" }],
+    },
+    // Relative specifiers resolve to the same layer check.
+    {
+      code: 'import { C } from "../../components/ui/card";',
+      filename: LIB_FILE,
+      errors: [{ messageId: "libUpward" }],
+    },
+    {
+      code: 'export { C } from "@/components/ui/card";',
+      filename: LIB_FILE,
+      errors: [{ messageId: "libUpward" }],
+    },
+    {
+      code: 'const m = await import("@/components/ui/card");',
+      filename: LIB_FILE,
+      errors: [{ messageId: "libUpward" }],
+    },
+    // An allowed file that stopped importing upward must leave the list.
+    {
+      code: 'import { a } from "@/lib/x";',
+      filename: LIB_FILE,
+      options: [{ allow: { "src/lib/medications/example.ts": "reason" } }],
+      errors: [{ messageId: "staleAllow" }],
+    },
+    // Server-only modules in a client file.
+    {
+      code: '"use client";\nimport { prisma } from "@/lib/db";',
+      filename: CLIENT_FILE,
+      errors: [{ messageId: "clientServerOnly" }],
+    },
+    {
+      code: '"use client";\nimport { encrypt } from "@/lib/crypto";',
+      filename: CLIENT_FILE,
+      errors: [{ messageId: "clientServerOnly" }],
+    },
+    {
+      code: '"use client";\nimport { MeasurementType } from "@/generated/prisma/client";',
+      filename: CLIENT_FILE,
+      errors: [{ messageId: "clientServerOnly" }],
+    },
+    {
+      code: '"use client";\nimport { enqueue } from "@/lib/jobs/boss-instance";',
+      filename: CLIENT_FILE,
+      errors: [{ messageId: "clientServerOnly" }],
+    },
+    {
+      code: '"use client";\nimport { cookies } from "next/headers";',
+      filename: CLIENT_FILE,
+      errors: [{ messageId: "clientServerOnly" }],
+    },
+    {
+      code: '"use client";\nimport { Pool } from "pg";',
+      filename: CLIENT_FILE,
+      errors: [{ messageId: "clientServerOnly" }],
+    },
+  ],
+});
diff --git a/eslint-plugins/healthlog/import-boundaries.js b/eslint-plugins/healthlog/import-boundaries.js
new file mode 100644
index 000000000..09f6806bd
--- /dev/null
+++ b/eslint-plugins/healthlog/import-boundaries.js
@@ -0,0 +1,199 @@
+/**
+ * @fileoverview ESLint rule — import direction between the layers of `src`.
+ *
+ * Two boundaries, both checked per import statement so the mistake shows up
+ * in the editor rather than in a later sweep:
+ *
+ *   1. `src/lib/**` never imports from `src/components/**` or `src/app/**`.
+ *      The direction is `app → components → hooks → lib`. A lib module that
+ *      reaches upward drags a component folder into server jobs and makes
+ *      the layers impossible to split. Type-only imports count too: the
+ *      dependency is the same, only erased at build time.
+ *
+ *   2. A `"use client"` file never makes a value import of a server-only
+ *      module: the database client, the crypto module, the Prisma client
+ *      entry, the job queue, `pg`, `next/headers`. Type-only imports are
+ *      erased and stay legal, and the Prisma `enums` entry is browser-safe.
+ *      The transitive version of this check is
+ *      `src/__tests__/client-bundle-server-import-guard.test.ts`, which walks
+ *      the whole client graph; this rule is the direct, local half.
+ *
+ * Existing lib → components imports are listed in the `allow` option, file
+ * by file, each with the reason it has not moved yet. A listed file that no
+ * longer imports upward is reported too, so the list can only shrink.
+ *
+ * WHAT THIS DOES NOT CATCH
+ *
+ * A dependency through a re-export in a package outside `src`, and a
+ * `require()` call. Neither occurs in the tree today.
+ */
+
+"use strict";
+
+const path = require("node:path");
+
+function toPosix(filename) {
+  return filename.replace(/\\/g, "/");
+}
+
+function isTestFile(filename) {
+  return (
+    /\/__tests__\//.test(filename) ||
+    /\.(test|spec)\.[cm]?[jt]sx?$/.test(filename) ||
+    /\/__mocks__\//.test(filename)
+  );
+}
+
+/** Path of `filename` relative to the repository's `src/`, or null. */
+function srcRelative(filename) {
+  const idx = filename.lastIndexOf("/src/");
+  return idx === -1 ? null : filename.slice(idx + 1);
+}
+
+/** Where a specifier lands inside `src/`, or null for a package. */
+function targetInSrc(spec, filename) {
+  if (spec.startsWith("@/")) return `src/${spec.slice(2)}`;
+  if (spec.startsWith(".")) {
+    const abs = toPosix(path.resolve(path.dirname(filename), spec));
+    return srcRelative(abs);
+  }
+  return null;
+}
+
+const SERVER_ONLY_PACKAGES = [
+  /^pg$/,
+  /^pg-boss$/,
+  /^@prisma\//,
+  /^next\/headers$/,
+];
+
+const SERVER_ONLY_SRC = [
+  /^src\/lib\/db(-session)?$/,
+  /^src\/lib\/crypto(\/|$)/,
+  /^src\/lib\/jobs\//,
+  /^src\/generated\/prisma\/(client|internal|models)(\/|$)/,
+];
+
+function isServerOnly(spec, filename) {
+  if (SERVER_ONLY_PACKAGES.some((re) => re.test(spec))) return true;
+  const target = targetInSrc(spec, filename);
+  if (!target) return false;
+  const bare = target.replace(/\.(ts|tsx|js|mjs)$/, "");
+  return SERVER_ONLY_SRC.some((re) => re.test(bare));
+}
+
+function isTypeOnly(node) {
+  if (node.importKind === "type" || node.exportKind === "type") return true;
+  const specifiers = node.specifiers ?? [];
+  return (
+    specifiers.length > 0 &&
+    specifiers.every((s) => s.importKind === "type" || s.exportKind === "type")
+  );
+}
+
+function hasUseClient(program) {
+  for (const stmt of program.body) {
+    if (stmt.type !== "ExpressionStatement" || !stmt.directive) break;
+    if (stmt.directive === "use client") return true;
+  }
+  return false;
+}
+
+/** @type {import("eslint").Rule.RuleModule} */
+const importBoundariesRule = {
+  meta: {
+    type: "problem",
+    docs: {
+      description:
+        "Keep src/lib below components and app, and server-only modules out of client files.",
+    },
+    schema: [
+      {
+        type: "object",
+        properties: {
+          allow: {
+            type: "object",
+            additionalProperties: { type: "string", minLength: 1 },
+          },
+        },
+        additionalProperties: false,
+      },
+    ],
+    messages: {
+      libUpward:
+        "src/lib must not import {{target}}. Move the shared piece into src/lib (or the importer into the component folder); an exception goes into the rule's `allow` map in eslint.config.mjs with its reason.",
+      staleAllow:
+        "This file is in the import-boundaries `allow` map but no longer imports from src/components or src/app. Remove the entry so the list keeps shrinking.",
+      clientServerOnly:
+        'A "use client" file must not import {{spec}}: it is server-only and would ship to the browser. Import a type with `import type`, or move the call behind an API route or a server component.',
+    },
+  },
+
+  create(context) {
+    const filename = toPosix(context.filename ?? context.getFilename?.() ?? "");
+    const rel = srcRelative(filename);
+    if (!rel || isTestFile(filename)) return {};
+
+    const allow = (context.options[0] && context.options[0].allow) || {};
+    const inLib = rel.startsWith("src/lib/");
+    const allowed = inLib && Object.hasOwn(allow, rel);
+    let upwardSeen = false;
+    let isClient = false;
+
+    function check(node, source) {
+      if (!source || typeof source.value !== "string") return;
+      const spec = source.value;
+      if (inLib) {
+        const target = targetInSrc(spec, filename);
+        if (
+          target &&
+          (target.startsWith("src/components/") ||
+            target.startsWith("src/app/"))
+        ) {
+          upwardSeen = true;
+          if (!allowed) {
+            context.report({
+              node: source,
+              messageId: "libUpward",
+              data: { target: spec },
+            });
+          }
+        }
+      }
+      if (isClient && !isTypeOnly(node) && isServerOnly(spec, filename)) {
+        context.report({
+          node: source,
+          messageId: "clientServerOnly",
+          data: { spec },
+        });
+      }
+    }
+
+    return {
+      Program(program) {
+        isClient = hasUseClient(program);
+      },
+      ImportDeclaration(node) {
+        check(node, node.source);
+      },
+      ExportNamedDeclaration(node) {
+        if (node.source) check(node, node.source);
+      },
+      ExportAllDeclaration(node) {
+        check(node, node.source);
+      },
+      ImportExpression(node) {
+        if (node.source && node.source.type === "Literal") {
+          check(node, node.source);
+        }
+      },
+      "Program:exit"(program) {
+        if (allowed && !upwardSeen) {
+          context.report({ node: program, messageId: "staleAllow" });
+        }
+      },
+    };
+  },
+};
+
+module.exports = importBoundariesRule;
diff --git a/eslint-plugins/healthlog/index.js b/eslint-plugins/healthlog/index.js
index ef0b03df6..590d89d7e 100644
--- a/eslint-plugins/healthlog/index.js
+++ b/eslint-plugins/healthlog/index.js
@@ -21,6 +21,8 @@
  *                              toLocaleString().
  *   - `no-raw-card-shell`    — a card surface is a <Card> or a shell
  *                              primitive, not bg-card + border + rounded-xl.
+ *   - `import-boundaries`    — src/lib never imports components or app, and
+ *                              a "use client" file imports no server module.
  */
 
 "use strict";
@@ -36,6 +38,7 @@ const noUtcDayKey = require("./no-utc-day-key.js");
 const noPlanningTags = require("./no-planning-tags.js");
 const noUnlocalisedDecimal = require("./no-unlocalised-decimal.js");
 const noRawCardShell = require("./no-raw-card-shell.js");
+const importBoundaries = require("./import-boundaries.js");
 
 module.exports = {
   rules: {
@@ -55,5 +58,6 @@ module.exports = {
     "no-planning-tags": noPlanningTags,
     "no-unlocalised-decimal": noUnlocalisedDecimal,
     "no-raw-card-shell": noRawCardShell,
+    "import-boundaries": importBoundaries,
   },
 };
diff --git a/eslint.config.mjs b/eslint.config.mjs
index a6bf8aac0..ce53edc99 100644
--- a/eslint.config.mjs
+++ b/eslint.config.mjs
@@ -176,6 +176,27 @@ const eslintConfig = defineConfig([
           ],
         },
       ],
+      // Layer direction: src/lib never imports src/components or src/app, and
+      // a "use client" file makes no value import of the database client,
+      // crypto, the Prisma client entry, the job queue, pg or next/headers.
+      // The files below still import upward; each says why it has not moved.
+      // A listed file that stops importing upward fails until it is removed,
+      // so the map only shrinks. See the rule header.
+      "healthlog/import-boundaries": [
+        "error",
+        {
+          allow: {
+            "src/lib/insights/metric-catalog.ts":
+              "reads SUB_PAGE_TABS, which is declared inside the client tab strip component together with its labels and order",
+            "src/lib/insights/target-adjust-context.tsx":
+              "a React provider that renders TargetEditSheet; it belongs under components but has importers across 21 insight pages",
+            "src/lib/errors/error-toast.tsx":
+              "a React toast renderer that renders ErrorIdLine; it belongs under components but is imported by most client surfaces",
+            "src/lib/module-list-prefs.ts":
+              "a client hook module that raises the shared outcome toast; it moves with the module list settings surface",
+          },
+        },
+      ],
     },
   },
   // v1.28.17 — every recharts-rendering component funnels through the
diff --git a/src/__tests__/settings-legacy-routes.test.ts b/src/__tests__/settings-legacy-routes.test.ts
index c04cbe5ad..870b11045 100644
--- a/src/__tests__/settings-legacy-routes.test.ts
+++ b/src/__tests__/settings-legacy-routes.test.ts
@@ -19,7 +19,7 @@ import { dirname, join } from "node:path";
 import { describe, expect, it } from "vitest";
 
 import nextConfig from "../../next.config";
-import { SETTINGS_SECTION_SLUGS } from "@/components/settings/section-slugs";
+import { SETTINGS_SECTION_SLUGS } from "@/lib/settings/section-slugs";
 import { LAYOUT_GROUP_IDS } from "@/components/settings/layout-groups";
 import { MODULE_SETTINGS_PAGE_IDS } from "@/components/settings/module-settings-page-ids";
 import {
diff --git a/src/app/api/medications/[id]/glp1/route.ts b/src/app/api/medications/[id]/glp1/route.ts
index ffeff1384..eb5781d23 100644
--- a/src/app/api/medications/[id]/glp1/route.ts
+++ b/src/app/api/medications/[id]/glp1/route.ts
@@ -34,7 +34,7 @@ import {
   estimateRunwayDays,
   lowStockTriggerDays,
   type RunwaySchedule,
-} from "@/components/medications/detail/supply-runway";
+} from "@/lib/medications/supply-runway";
 import {
   resolveLowStockRunwayDays,
   resolveReorderLeadDays,
diff --git a/src/app/api/medications/[id]/route.ts b/src/app/api/medications/[id]/route.ts
index e711a713d..a85ee9561 100644
--- a/src/app/api/medications/[id]/route.ts
+++ b/src/app/api/medications/[id]/route.ts
@@ -54,7 +54,7 @@ import { assertMedicationOwnership } from "@/lib/medications/route-guards";
 import {
   effectiveUnitsPerDose,
   estimateUnitsRunwayDays,
-} from "@/components/medications/detail/supply-runway";
+} from "@/lib/medications/supply-runway";
 import { serializeScheduleUnitsPerDose } from "@/lib/medications/schedule-units-dto";
 import { hhmmToMinutesOrNull } from "@/lib/medications/scheduling/hhmm";
 import { getUserTodayBounds } from "@/lib/tz/local-day";
diff --git a/src/app/insights/sleep/__tests__/empty-state-href.test.ts b/src/app/insights/sleep/__tests__/empty-state-href.test.ts
index 58613b6ba..0e3d1f414 100644
--- a/src/app/insights/sleep/__tests__/empty-state-href.test.ts
+++ b/src/app/insights/sleep/__tests__/empty-state-href.test.ts
@@ -10,7 +10,7 @@ import { join } from "node:path";
 
 import { describe, expect, it } from "vitest";
 
-import { isSettingsSectionSlug } from "@/components/settings/section-slugs";
+import { isSettingsSectionSlug } from "@/lib/settings/section-slugs";
 
 describe("sleep empty-state CTA href", () => {
   it("links to /settings/integrations (a real settings slug)", () => {
diff --git a/src/app/settings/[section]/page.tsx b/src/app/settings/[section]/page.tsx
index c58be6aeb..5c17bd69f 100644
--- a/src/app/settings/[section]/page.tsx
+++ b/src/app/settings/[section]/page.tsx
@@ -3,7 +3,7 @@ import { notFound } from "next/navigation";
 import {
   SETTINGS_SECTION_SLUGS,
   isSettingsSectionSlug,
-} from "@/components/settings/section-slugs";
+} from "@/lib/settings/section-slugs";
 import { SettingsShell } from "@/components/settings/settings-shell";
 import {
   SettingsSectionLoader,
diff --git a/src/components/admin/section-slugs.ts b/src/components/admin/section-slugs.ts
index 55ac2e4f7..e9c61c703 100644
--- a/src/components/admin/section-slugs.ts
+++ b/src/components/admin/section-slugs.ts
@@ -1,6 +1,6 @@
 /**
  * Server-safe constants for the v1.5 admin split. Mirrors the pattern in
- * `src/components/settings/section-slugs.ts` so server-rendered code paths
+ * `src/lib/settings/section-slugs.ts` so server-rendered code paths
  * (`generateStaticParams()`, the page guard, route-existence tests) can
  * import the slug list without dragging the `<AdminShell>` client bundle
  * into the server graph.
diff --git a/src/lib/command-palette/__tests__/build-index.test.ts b/src/components/command-palette/__tests__/build-index.test.ts
similarity index 99%
rename from src/lib/command-palette/__tests__/build-index.test.ts
rename to src/components/command-palette/__tests__/build-index.test.ts
index 7540fd70b..0dfdf379b 100644
--- a/src/lib/command-palette/__tests__/build-index.test.ts
+++ b/src/components/command-palette/__tests__/build-index.test.ts
@@ -3,7 +3,7 @@ import { describe, expect, it } from "vitest";
 import {
   buildPaletteIndex,
   type PaletteIndexInput,
-} from "@/lib/command-palette/build-index";
+} from "@/components/command-palette/build-index";
 
 const t = (key: string) => key;
 
diff --git a/src/components/command-palette/__tests__/command-palette.test.tsx b/src/components/command-palette/__tests__/command-palette.test.tsx
index aeeb64b5f..c8c36fa01 100644
--- a/src/components/command-palette/__tests__/command-palette.test.tsx
+++ b/src/components/command-palette/__tests__/command-palette.test.tsx
@@ -3,7 +3,7 @@ import { renderToStaticMarkup } from "react-dom/server";
 import { Activity, Moon, Plus, Smile } from "lucide-react";
 
 import { I18nProvider } from "@/lib/i18n/context";
-import type { PaletteEntry } from "@/lib/command-palette/build-index";
+import type { PaletteEntry } from "@/components/command-palette/build-index";
 import type { SearchResponse } from "@/lib/search/contract";
 
 vi.mock("next/navigation", () => ({
diff --git a/src/lib/command-palette/build-index.ts b/src/components/command-palette/build-index.ts
similarity index 98%
rename from src/lib/command-palette/build-index.ts
rename to src/components/command-palette/build-index.ts
index 68e2bf471..112c8ac74 100644
--- a/src/lib/command-palette/build-index.ts
+++ b/src/components/command-palette/build-index.ts
@@ -24,8 +24,8 @@ import {
   SETTINGS_CARDS,
   SETTINGS_LAYOUT_PAGES,
   SETTINGS_MODULE_PAGES,
-} from "./settings-cards";
-import { PALETTE_SYNONYMS } from "./synonyms";
+} from "@/lib/command-palette/settings-cards";
+import { PALETTE_SYNONYMS } from "@/lib/command-palette/synonyms";
 
 /**
  * The command palette's index: every place and action this session may
diff --git a/src/components/command-palette/command-palette.tsx b/src/components/command-palette/command-palette.tsx
index 14b19727f..148492314 100644
--- a/src/components/command-palette/command-palette.tsx
+++ b/src/components/command-palette/command-palette.tsx
@@ -30,7 +30,7 @@ import {
   EMPTY_STATE_ACTIONS,
   type PaletteEntry,
   type PaletteGroup,
-} from "@/lib/command-palette/build-index";
+} from "@/components/command-palette/build-index";
 import { rankEntries } from "@/lib/command-palette/rank";
 import { pushRecent, readRecent } from "@/lib/command-palette/recent";
 import { scrollToAnchorWhenReady } from "@/lib/dom/scroll-to-anchor";
diff --git a/src/components/command-palette/use-palette-index.ts b/src/components/command-palette/use-palette-index.ts
index 3d98e2a0b..32eb9a68d 100644
--- a/src/components/command-palette/use-palette-index.ts
+++ b/src/components/command-palette/use-palette-index.ts
@@ -14,7 +14,7 @@ import { useRecordCapabilities } from "@/hooks/use-record-capabilities";
 import {
   buildPaletteIndex,
   type PaletteEntry,
-} from "@/lib/command-palette/build-index";
+} from "@/components/command-palette/build-index";
 import { useTranslations } from "@/lib/i18n/context";
 import {
   MODULE_REGISTRY,
diff --git a/src/components/insights/__tests__/sleep-overview-empty-href.test.ts b/src/components/insights/__tests__/sleep-overview-empty-href.test.ts
index 6a336abaa..441a7b5f2 100644
--- a/src/components/insights/__tests__/sleep-overview-empty-href.test.ts
+++ b/src/components/insights/__tests__/sleep-overview-empty-href.test.ts
@@ -11,7 +11,7 @@ import { join } from "node:path";
 
 import { describe, expect, it } from "vitest";
 
-import { isSettingsSectionSlug } from "@/components/settings/section-slugs";
+import { isSettingsSectionSlug } from "@/lib/settings/section-slugs";
 
 describe("sleep-overview empty-state CTA href", () => {
   it("links to /settings/integrations (a real settings slug)", () => {
diff --git a/src/components/medications/__tests__/medication-form-v15.test.tsx b/src/components/medications/__tests__/medication-form-v15.test.tsx
index c598921b7..f68d69598 100644
--- a/src/components/medications/__tests__/medication-form-v15.test.tsx
+++ b/src/components/medications/__tests__/medication-form-v15.test.tsx
@@ -24,10 +24,8 @@ import {
   weekdayIndexesToTokens,
   weekdayIndexToToken,
 } from "@/components/medications/scheduling/legacy-bridge";
-import {
-  DEFAULT_SUB_CONTROLS,
-  type WeekdayToken,
-} from "@/components/medications/scheduling/types";
+import { DEFAULT_SUB_CONTROLS } from "@/components/medications/scheduling/types";
+import { type WeekdayToken } from "@/lib/medications/scheduling/weekday-tokens";
 
 describe("weekdayIndexToToken", () => {
   it("maps Sunday-anchored 0..6 to SU/MO/TU/WE/TH/FR/SA", () => {
diff --git a/src/components/medications/detail/medication-detail-tabs.tsx b/src/components/medications/detail/medication-detail-tabs.tsx
index 140e60ab6..ff57868ce 100644
--- a/src/components/medications/detail/medication-detail-tabs.tsx
+++ b/src/components/medications/detail/medication-detail-tabs.tsx
@@ -88,7 +88,7 @@ import { PhaseConfigSheet } from "@/components/medications/sections/phase-config
 import { SideEffectsSection } from "@/components/medications/side-effects-section";
 import { ChartSkeleton } from "@/components/charts/chart-skeleton";
 import { TitrationTimeline } from "@/components/medications/titration-timeline";
-import { estimateRunwayDays } from "@/components/medications/detail/supply-runway";
+import { estimateRunwayDays } from "@/lib/medications/supply-runway";
 import type { SupplySummary } from "@/lib/medications/inventory/summary";
 import { MedicationWizardDialog } from "@/components/medications/wizard/medication-wizard-dialog";
 import { parseScheduleRecurrence } from "@/lib/medication-schedule";
diff --git a/src/components/medications/glp1-medication-card.tsx b/src/components/medications/glp1-medication-card.tsx
index 72a73b447..5024217cd 100644
--- a/src/components/medications/glp1-medication-card.tsx
+++ b/src/components/medications/glp1-medication-card.tsx
@@ -38,7 +38,7 @@ import {
   estimateDailyDoseCount,
   estimateRunwayDays,
   lowStockTriggerDays,
-} from "@/components/medications/detail/supply-runway";
+} from "@/lib/medications/supply-runway";
 import { useAuth } from "@/hooks/use-auth";
 import { useMedicationComplianceSummary } from "@/lib/queries/use-medication-compliance-summary";
 import { DEFAULT_TIMEZONE } from "@/lib/tz/format";
diff --git a/src/components/medications/medication-card.tsx b/src/components/medications/medication-card.tsx
index 7c7a1f5ed..d3033e08b 100644
--- a/src/components/medications/medication-card.tsx
+++ b/src/components/medications/medication-card.tsx
@@ -24,7 +24,7 @@ import {
   estimateDailyDoseCount,
   estimateRunwayDays,
   lowStockTriggerDays,
-} from "@/components/medications/detail/supply-runway";
+} from "@/lib/medications/supply-runway";
 import { useTranslations, useFormatters } from "@/lib/i18n/context";
 import {
   invalidateKeys,
diff --git a/src/components/medications/medication-table.tsx b/src/components/medications/medication-table.tsx
index 56f11405c..5795b6d3e 100644
--- a/src/components/medications/medication-table.tsx
+++ b/src/components/medications/medication-table.tsx
@@ -28,7 +28,7 @@ import { Skeleton } from "@/components/ui/skeleton";
 import { MedicationStatusPill } from "@/components/medications/card-parts/medication-status-pill";
 import { useWeekdayLabel } from "@/components/medications/card-parts/medication-next-last-slot";
 import { resolveDisplayedSlotInstant } from "@/components/medications/card-parts/displayed-slot-instant";
-import { estimateRunwayDays } from "@/components/medications/detail/supply-runway";
+import { estimateRunwayDays } from "@/lib/medications/supply-runway";
 import { useMedicationIntake } from "@/components/medications/use-medication-intake";
 import { reduceCurrentWindowStatus } from "@/lib/medications/window-status";
 import { resolveNextDueDayLabel } from "@/lib/medications/next-due-day-label";
diff --git a/src/components/medications/scheduling/cadence-picker.tsx b/src/components/medications/scheduling/cadence-picker.tsx
index 4a4271e0b..1ecff45bc 100644
--- a/src/components/medications/scheduling/cadence-picker.tsx
+++ b/src/components/medications/scheduling/cadence-picker.tsx
@@ -59,9 +59,11 @@ import {
   type CadenceSubControls,
   type CadenceValue,
   DEFAULT_SUB_CONTROLS,
+} from "./types";
+import {
   type WeekdayToken,
   WEEKDAY_TOKENS,
-} from "./types";
+} from "@/lib/medications/scheduling/weekday-tokens";
 
 export interface CadencePickerProps {
   value: CadenceValue;
diff --git a/src/components/medications/scheduling/legacy-bridge.ts b/src/components/medications/scheduling/legacy-bridge.ts
index 5af04db0f..7ce92cff9 100644
--- a/src/components/medications/scheduling/legacy-bridge.ts
+++ b/src/components/medications/scheduling/legacy-bridge.ts
@@ -17,9 +17,11 @@ import {
   type CadenceSubControls,
   type CadenceValue,
   DEFAULT_SUB_CONTROLS,
+} from "./types";
+import {
   type WeekdayToken,
   WEEKDAY_TOKENS,
-} from "./types";
+} from "@/lib/medications/scheduling/weekday-tokens";
 
 /**
  * Legacy schedule shape the page passes to the form. Sunday-anchored
diff --git a/src/components/medications/scheduling/types.ts b/src/components/medications/scheduling/types.ts
index 823e42a3f..5df6d4cea 100644
--- a/src/components/medications/scheduling/types.ts
+++ b/src/components/medications/scheduling/types.ts
@@ -17,6 +17,8 @@
  * structured values; the wizard / form maps them to the wire format.
  */
 
+import type { WeekdayToken } from "@/lib/medications/scheduling/weekday-tokens";
+
 /**
  * The eight cadence kinds the wizard exposes. Maps to the engine's
  * dispatch tiers in `src/lib/medications/scheduling/recurrence.ts`:
@@ -71,18 +73,6 @@ export interface CadenceSubControls {
   rollingDays: number;
 }
 
-/** RFC 5545 BYDAY tokens — the order the chip row renders. */
-export const WEEKDAY_TOKENS = [
-  "MO",
-  "TU",
-  "WE",
-  "TH",
-  "FR",
-  "SA",
-  "SU",
-] as const;
-export type WeekdayToken = (typeof WEEKDAY_TOKENS)[number];
-
 /** Sensible defaults so a brand-new picker has valid sub-controls. */
 export const DEFAULT_SUB_CONTROLS: CadenceSubControls = {
   weekdays: ["MO"],
diff --git a/src/components/medications/wizard/nl-bridge.ts b/src/components/medications/wizard/nl-bridge.ts
index 9279a2211..685473f9b 100644
--- a/src/components/medications/wizard/nl-bridge.ts
+++ b/src/components/medications/wizard/nl-bridge.ts
@@ -16,8 +16,8 @@ import { isoStringToDate } from "@/components/medications/scheduling/course-wind
 import {
   DEFAULT_SUB_CONTROLS,
   type CadenceSubControls,
-  type WeekdayToken,
 } from "@/components/medications/scheduling/types";
+import { type WeekdayToken } from "@/lib/medications/scheduling/weekday-tokens";
 import type { WizardPayload as ExtractorPayload } from "@/components/medications/scheduling/natural-language-extractor";
 
 import type { WizardPayload } from "./wizard-payload";
diff --git a/src/components/medications/wizard/steps/step6-sub-cadence.tsx b/src/components/medications/wizard/steps/step6-sub-cadence.tsx
index 259b0e499..e5816b6b9 100644
--- a/src/components/medications/wizard/steps/step6-sub-cadence.tsx
+++ b/src/components/medications/wizard/steps/step6-sub-cadence.tsx
@@ -5,11 +5,11 @@ import { useMemo } from "react";
 import { encodeCadence } from "@/components/medications/scheduling/cadence-picker";
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
+import { type CadenceSubControls } from "@/components/medications/scheduling/types";
 import {
-  type CadenceSubControls,
   type WeekdayToken,
   WEEKDAY_TOKENS,
-} from "@/components/medications/scheduling/types";
+} from "@/lib/medications/scheduling/weekday-tokens";
 import { useTranslations } from "@/lib/i18n/context";
 
 import type { StepProps } from "./step1-name";
diff --git a/src/components/settings/__tests__/sections-i18n-parity.test.ts b/src/components/settings/__tests__/sections-i18n-parity.test.ts
index 8b6be7cc0..60e0ae128 100644
--- a/src/components/settings/__tests__/sections-i18n-parity.test.ts
+++ b/src/components/settings/__tests__/sections-i18n-parity.test.ts
@@ -12,7 +12,7 @@
 import { describe, expect, it } from "vitest";
 import en from "../../../../messages/en.json" with { type: "json" };
 import de from "../../../../messages/de.json" with { type: "json" };
-import { SETTINGS_SECTION_SLUGS } from "../section-slugs";
+import { SETTINGS_SECTION_SLUGS } from "@/lib/settings/section-slugs";
 
 type Bag = Record<string, unknown>;
 
diff --git a/src/components/settings/__tests__/sections.test.tsx b/src/components/settings/__tests__/sections.test.tsx
index e6420d6a3..7433e2e73 100644
--- a/src/components/settings/__tests__/sections.test.tsx
+++ b/src/components/settings/__tests__/sections.test.tsx
@@ -112,7 +112,7 @@ vi.mock("@/components/settings/thresholds-editor-section", () => ({
 }));
 import { I18nProvider } from "@/lib/i18n/context";
 import { SettingsSectionFrame } from "./section-frame-harness";
-import type { SettingsSectionSlug } from "../section-slugs";
+import type { SettingsSectionSlug } from "@/lib/settings/section-slugs";
 import { AboutSection } from "../about-section";
 import { AccountSection } from "../account-section";
 import { AdvancedSection } from "../advanced-section";
diff --git a/src/components/settings/record-settings-section-gate.tsx b/src/components/settings/record-settings-section-gate.tsx
index 35d155064..a66a0a387 100644
--- a/src/components/settings/record-settings-section-gate.tsx
+++ b/src/components/settings/record-settings-section-gate.tsx
@@ -11,7 +11,7 @@ import { classifySettingsDestination } from "@/lib/record-settings/classificatio
 import { SettingsCardHeader } from "@/components/settings/_card-header";
 import { ManagedIntegrationStatus } from "@/components/settings/managed-integration-status";
 import { SettingsCard } from "@/components/settings/settings-card";
-import type { SettingsSectionSlug } from "@/components/settings/section-slugs";
+import type { SettingsSectionSlug } from "@/lib/settings/section-slugs";
 
 // The two record-scoped surfaces load on demand. Both are forms that validate
 // with Zod (the managed settings patch, the allergy and family-history
diff --git a/src/components/settings/settings-section-loader.tsx b/src/components/settings/settings-section-loader.tsx
index 41aecb597..2c0faae98 100644
--- a/src/components/settings/settings-section-loader.tsx
+++ b/src/components/settings/settings-section-loader.tsx
@@ -5,7 +5,7 @@ import { useEffect, type ComponentType } from "react";
 
 import { Skeleton } from "@/components/ui/skeleton";
 import { SettingsCard } from "@/components/settings/settings-card";
-import type { SettingsSectionSlug } from "@/components/settings/section-slugs";
+import type { SettingsSectionSlug } from "@/lib/settings/section-slugs";
 import type { IntegrationCallbackUrls } from "@/lib/integrations/callback-urls";
 
 /**
diff --git a/src/components/settings/settings-shell.tsx b/src/components/settings/settings-shell.tsx
index 29c8b1af2..1ddee6b15 100644
--- a/src/components/settings/settings-shell.tsx
+++ b/src/components/settings/settings-shell.tsx
@@ -55,7 +55,7 @@ import {
   SETTINGS_SECTION_SLUGS,
   isSettingsSectionSlug,
   type SettingsSectionSlug,
-} from "./section-slugs";
+} from "@/lib/settings/section-slugs";
 import { SettingsHubBackLink } from "./settings-hub-back-link";
 import { SettingsMobileNav } from "./settings-mobile-nav";
 import { SettingsAnchorForward } from "./settings-anchor-forward";
diff --git a/src/lib/ai/coach/medication-extract-prompt.ts b/src/lib/ai/coach/medication-extract-prompt.ts
index bbabd616c..09d735dbe 100644
--- a/src/lib/ai/coach/medication-extract-prompt.ts
+++ b/src/lib/ai/coach/medication-extract-prompt.ts
@@ -29,7 +29,7 @@
 
 import { z } from "zod/v4";
 
-import { WEEKDAY_TOKENS } from "@/components/medications/scheduling/types";
+import { WEEKDAY_TOKENS } from "@/lib/medications/scheduling/weekday-tokens";
 
 /** Closed list — matches the design-synthesis dose-unit dropdown. */
 export const DOSE_UNITS = [
diff --git a/src/lib/jobs/medication-low-stock.ts b/src/lib/jobs/medication-low-stock.ts
index ea44a842d..5c2e8af5c 100644
--- a/src/lib/jobs/medication-low-stock.ts
+++ b/src/lib/jobs/medication-low-stock.ts
@@ -69,7 +69,7 @@ import {
   lowStockTriggerDays,
   supplyRunwayDates,
   type RunwaySchedule,
-} from "@/components/medications/detail/supply-runway";
+} from "@/lib/medications/supply-runway";
 import {
   detectSupplyUnderflow,
   summariseSupply,
diff --git a/src/components/medications/__tests__/supply-runway.test.ts b/src/lib/medications/__tests__/supply-runway.test.ts
similarity index 99%
rename from src/components/medications/__tests__/supply-runway.test.ts
rename to src/lib/medications/__tests__/supply-runway.test.ts
index 25513acc4..40424820c 100644
--- a/src/components/medications/__tests__/supply-runway.test.ts
+++ b/src/lib/medications/__tests__/supply-runway.test.ts
@@ -16,7 +16,7 @@ import {
   lowStockTriggerDays,
   supplyRunwayDates,
   type RunwaySchedule,
-} from "@/components/medications/detail/supply-runway";
+} from "@/lib/medications/supply-runway";
 
 function schedule(partial: Partial<RunwaySchedule>): RunwaySchedule {
   return {
diff --git a/src/lib/medications/list-read.ts b/src/lib/medications/list-read.ts
index 72507873e..a931edb2a 100644
--- a/src/lib/medications/list-read.ts
+++ b/src/lib/medications/list-read.ts
@@ -24,7 +24,7 @@ import {
 import {
   effectiveUnitsPerDose,
   estimateUnitsRunwayDays,
-} from "@/components/medications/detail/supply-runway";
+} from "@/lib/medications/supply-runway";
 import { serializeScheduleUnitsPerDose } from "@/lib/medications/schedule-units-dto";
 import {
   computeDisplayDue,
diff --git a/src/lib/medications/scheduling/weekday-tokens.ts b/src/lib/medications/scheduling/weekday-tokens.ts
new file mode 100644
index 000000000..8a5166107
--- /dev/null
+++ b/src/lib/medications/scheduling/weekday-tokens.ts
@@ -0,0 +1,17 @@
+/**
+ * RFC 5545 BYDAY tokens in the order the weekday chip row renders them.
+ *
+ * Shared by the scheduling wizard and the server-side medication extraction
+ * prompt, so it lives beside the recurrence engine rather than in a
+ * component folder.
+ */
+export const WEEKDAY_TOKENS = [
+  "MO",
+  "TU",
+  "WE",
+  "TH",
+  "FR",
+  "SA",
+  "SU",
+] as const;
+export type WeekdayToken = (typeof WEEKDAY_TOKENS)[number];
diff --git a/src/components/medications/detail/supply-runway.ts b/src/lib/medications/supply-runway.ts
similarity index 100%
rename from src/components/medications/detail/supply-runway.ts
rename to src/lib/medications/supply-runway.ts
diff --git a/src/lib/record-settings/classification.ts b/src/lib/record-settings/classification.ts
index fbeda64b2..3512c8204 100644
--- a/src/lib/record-settings/classification.ts
+++ b/src/lib/record-settings/classification.ts
@@ -1,7 +1,7 @@
 import {
   SETTINGS_SECTION_SLUGS,
   type SettingsSectionSlug,
-} from "@/components/settings/section-slugs";
+} from "@/lib/settings/section-slugs";
 import type {
   AccountAccessLevel,
   AccountRecordKind,
diff --git a/src/components/settings/section-slugs.ts b/src/lib/settings/section-slugs.ts
similarity index 100%
rename from src/components/settings/section-slugs.ts
rename to src/lib/settings/section-slugs.ts