diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f25c4ba..afff891 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -38,6 +38,14 @@ jobs:
       - name: Run tests
         run: pnpm run test:ci
 
+      # Runs the leanWorkerBundle generateBundle assertion: fails if a
+      # denylisted package (dataforseo-client, autumn-js, ...) re-enters the
+      # worker's eager startup graph. See vite-plugin-lean-worker-bundle.ts.
+      - name: Build worker (eager-bundle guard)
+        run: pnpm vite build
+        env:
+          NODE_OPTIONS: --max-old-space-size=4096
+
       - name: Install website dependencies
         run: pnpm --dir web install --frozen-lockfile
 
diff --git a/knip.jsonc b/knip.jsonc
index e9df798..9ccb98d 100644
--- a/knip.jsonc
+++ b/knip.jsonc
@@ -18,6 +18,10 @@
     "src/db/pg/schema.ts",
     // Standalone CLI/dev scripts, invoked via package.json scripts
     "scripts/**",
+    // DataForSEO section barrel — consumed via the dynamic import in
+    // client.ts (loadDataforseoSections) + property access, which knip
+    // can't trace
+    "src/server/lib/dataforseo/sections.ts",
   ],
   "project": ["**/*.{js,mjs,ts,tsx}", "!src/routeTree.gen.ts", "!web/**"],
   "ignore": ["drizzle-prod.config.ts"],
diff --git a/scripts/brand-lookup-cost-profile.ts b/scripts/brand-lookup-cost-profile.ts
index 7de8ea7..fc2dae2 100644
--- a/scripts/brand-lookup-cost-profile.ts
+++ b/scripts/brand-lookup-cost-profile.ts
@@ -1,14 +1,16 @@
 import process from "node:process";
 import {
-  buildLlmTarget,
-  CHATGPT_LANGUAGE_CODE,
-  CHATGPT_LOCATION_CODE,
   fetchLlmAggregatedMetrics,
   fetchLlmCrossAggregatedMetrics,
   fetchLlmMentionsSearch,
   fetchLlmTopPages,
-  type LlmPlatform,
 } from "@/server/lib/dataforseo/ai";
+import {
+  buildLlmTarget,
+  CHATGPT_LANGUAGE_CODE,
+  CHATGPT_LOCATION_CODE,
+  type LlmPlatform,
+} from "@/server/lib/dataforseo/shared";
 import { applyBillingMarkupUsd } from "@/shared/billing";
 import { resolveCompetitorGroups } from "@/server/features/ai-search/services/shareOfVoice";
 import { parseCompetitorList } from "@/types/schemas/ai-search";
diff --git a/src/routes/api/autumn/$.ts b/src/routes/api/autumn/$.ts
index d794578..47aaaff 100644
--- a/src/routes/api/autumn/$.ts
+++ b/src/routes/api/autumn/$.ts
@@ -1,27 +1,36 @@
 import { createFileRoute } from "@tanstack/react-router";
-import { autumnHandler } from "autumn-js/fetch";
+import type { autumnHandler } from "autumn-js/fetch";
 import { env } from "cloudflare:workers";
 import { isHostedAuthMode } from "@/lib/auth-mode";
 import { resolveHostedContext } from "@/middleware/ensure-user/hosted";
 
-const handler = autumnHandler({
-  identify: async (request) => {
-    const context = await resolveHostedContext(request.headers);
+let handlerPromise: Promise<ReturnType<typeof autumnHandler>> | undefined;
 
-    return {
-      customerId: context.organizationId,
-    };
-  },
-});
+// Lazy: keeps autumn-js/fetch out of the eager isolate startup graph;
+// resolves instantly after the first request.
+function loadHandler() {
+  return (handlerPromise ??= import("autumn-js/fetch").then(
+    ({ autumnHandler }) =>
+      autumnHandler({
+        identify: async (request) => {
+          const context = await resolveHostedContext(request.headers);
 
-function handleAutumnRequest(request: Request) {
+          return {
+            customerId: context.organizationId,
+          };
+        },
+      }),
+  ));
+}
+
+async function handleAutumnRequest(request: Request) {
   if (!isHostedAuthMode(env.AUTH_MODE)) {
     return new Response("Not found", {
       status: 404,
     });
   }
 
-  return handler(request);
+  return (await loadHandler())(request);
 }
 
 export const Route = createFileRoute("/api/autumn/$")({
diff --git a/src/server/billing/autumn.ts b/src/server/billing/autumn.ts
index be9dbe6..b92119f 100644
--- a/src/server/billing/autumn.ts
+++ b/src/server/billing/autumn.ts
@@ -1,29 +1,53 @@
-import { Autumn } from "autumn-js";
+import type { Autumn } from "autumn-js";
 import { getRequiredEnvValue } from "@/server/lib/runtime-env";
 
-export const autumn = new Autumn({
-  secretKey: () => getRequiredEnvValue("AUTUMN_SECRET_KEY"),
-  // Retries 429/500/502/503/504 (per-operation retryCodes) plus connection
-  // errors. Cloudflare 52x statuses are not in the SDK's retry list, so those
-  // still surface immediately.
-  //
-  // These reads/gates (customers.getOrCreate, check) sit on the request hot
-  // path, so keep the total retry window short: when Autumn is rate-limiting or
-  // slow, an 8s backoff window held the isolate open for seconds on every
-  // request and cascaded into region-wide congestion (incident 2026-07-06).
-  // Fail fast instead — a caller that can't gate surfaces an error rather than
-  // hanging.
-  retryConfig: {
-    strategy: "backoff",
-    backoff: {
-      initialInterval: 250,
-      maxInterval: 1000,
-      exponent: 1.5,
-      maxElapsedTime: 2500,
-    },
-    retryConnectionErrors: true,
+let autumnPromise: Promise<Autumn> | undefined;
+
+// Lazy: keeps the ~450 kB autumn-js SDK out of the eager isolate startup
+// graph (self-hosted deployments never load it at all); resolves instantly
+// after the first call.
+function loadAutumn(): Promise<Autumn> {
+  return (autumnPromise ??= import("autumn-js").then(
+    ({ Autumn }) =>
+      new Autumn({
+        secretKey: () => getRequiredEnvValue("AUTUMN_SECRET_KEY"),
+        // Retries 429/500/502/503/504 (per-operation retryCodes) plus
+        // connection errors. Cloudflare 52x statuses are not in the SDK's
+        // retry list, so those still surface immediately.
+        //
+        // These reads/gates (customers.getOrCreate, check) sit on the request
+        // hot path, so keep the total retry window short: when Autumn is
+        // rate-limiting or slow, an 8s backoff window held the isolate open
+        // for seconds on every request and cascaded into region-wide
+        // congestion (incident 2026-07-06). Fail fast instead — a caller that
+        // can't gate surfaces an error rather than hanging.
+        retryConfig: {
+          strategy: "backoff",
+          backoff: {
+            initialInterval: 250,
+            maxInterval: 1000,
+            exponent: 1.5,
+            maxElapsedTime: 2500,
+          },
+          retryConnectionErrors: true,
+        },
+      }),
+  ));
+}
+
+/** Shape-preserving lazy facade over the SDK client: call sites keep the
+ *  plain `autumn.check(...)` form. Covers only the methods we use — add a
+ *  line here when adopting a new one. */
+export const autumn = {
+  check: (...args: Parameters<Autumn["check"]>) =>
+    loadAutumn().then((client) => client.check(...args)),
+  track: (...args: Parameters<Autumn["track"]>) =>
+    loadAutumn().then((client) => client.track(...args)),
+  customers: {
+    getOrCreate: (...args: Parameters<Autumn["customers"]["getOrCreate"]>) =>
+      loadAutumn().then((client) => client.customers.getOrCreate(...args)),
   },
-});
+};
 
 // track() has no idempotency key, so replaying a deduction Autumn already
 // processed (5xx after a successful write, dropped connection) would
diff --git a/src/server/features/ai-search/services/brandLookupShaping.ts b/src/server/features/ai-search/services/brandLookupShaping.ts
index 236a99f..2aee9c1 100644
--- a/src/server/features/ai-search/services/brandLookupShaping.ts
+++ b/src/server/features/ai-search/services/brandLookupShaping.ts
@@ -3,7 +3,7 @@ import {
   CHATGPT_LANGUAGE_CODE,
   CHATGPT_LOCATION_CODE,
   type LlmPlatform,
-} from "@/server/lib/dataforseo/ai";
+} from "@/server/lib/dataforseo/shared";
 import type {
   LlmAggregatedTotal,
   LlmMentionItem,
diff --git a/src/server/lib/dataforseo/ai.ts b/src/server/lib/dataforseo/ai.ts
index 657024f..21675ea 100644
--- a/src/server/lib/dataforseo/ai.ts
+++ b/src/server/lib/dataforseo/ai.ts
@@ -28,6 +28,7 @@ import {
 import { createDataforseoBillingClassifier } from "@/server/lib/dataforseoBillingClassification";
 import { AppError } from "@/server/lib/errors";
 import { aiOptimizationApi } from "@/server/lib/dataforseo/core";
+import type { LlmPlatform, LlmTarget } from "@/server/lib/dataforseo/shared";
 import {
   assertOk,
   buildTaskBilling,
@@ -36,12 +37,6 @@ import {
   type DataforseoTaskLike,
 } from "@/server/lib/dataforseo/envelope";
 
-// ChatGPT mention/response data is only available for US/en per DataForSEO docs.
-export const CHATGPT_LOCATION_CODE = 2840;
-export const CHATGPT_LANGUAGE_CODE = "en";
-
-export type LlmPlatform = "chat_gpt" | "google";
-
 const classifyAiSearchError = createDataforseoBillingClassifier({
   pathPrefix: "/ai_optimization/",
   billingIssueCode: "AI_SEARCH_BILLING_ISSUE",
@@ -52,45 +47,6 @@ const classifyAiSearchError = createDataforseoBillingClassifier({
 const assertOptions = (path: string) =>
   ({ classify: classifyAiSearchError, classifyPath: path }) as const;
 
-// ---------------------------------------------------------------------------
-// Target builders — DataForSEO's `target` array accepts domain OR keyword
-// entries. We always pass exactly one target per call.
-// ---------------------------------------------------------------------------
-
-type LlmTarget =
-  | {
-      domain: string;
-      include_subdomains?: boolean;
-      search_filter?: "include" | "exclude";
-      search_scope?: string[];
-    }
-  | {
-      keyword: string;
-      search_filter?: "include" | "exclude";
-      search_scope?: string[];
-      match_type?: "word_match" | "partial_match";
-    };
-
-export function buildLlmTarget(input: {
-  type: "domain" | "keyword";
-  value: string;
-}): LlmTarget {
-  if (input.type === "domain") {
-    return {
-      domain: input.value,
-      include_subdomains: true,
-      search_filter: "include",
-      search_scope: ["any"],
-    };
-  }
-  return {
-    keyword: input.value,
-    search_filter: "include",
-    search_scope: ["any", "brand_entities"],
-    match_type: "word_match",
-  };
-}
-
 function clampLimit(value: number, min: number, max: number): number {
   return Math.min(max, Math.max(min, Math.floor(value)));
 }
diff --git a/src/server/lib/dataforseo/backlinks.test.ts b/src/server/lib/dataforseo/backlinks.test.ts
index 1c7294d..949f365 100644
--- a/src/server/lib/dataforseo/backlinks.test.ts
+++ b/src/server/lib/dataforseo/backlinks.test.ts
@@ -19,8 +19,8 @@ import {
   fetchBacklinksHistory,
   fetchBacklinksRows,
   fetchBacklinksSummary,
-  normalizeBacklinksTarget,
 } from "@/server/lib/dataforseo/backlinks";
+import { normalizeBacklinksTarget } from "@/server/lib/dataforseoBacklinksTarget";
 
 // A successful DataForSEO task always carries billing metadata (path + cost).
 const billed = {
diff --git a/src/server/lib/dataforseo/backlinks.ts b/src/server/lib/dataforseo/backlinks.ts
index c4b30d6..a57ed82 100644
--- a/src/server/lib/dataforseo/backlinks.ts
+++ b/src/server/lib/dataforseo/backlinks.ts
@@ -21,8 +21,6 @@ import {
   type DataforseoApiResponse,
 } from "@/server/lib/dataforseo/envelope";
 
-export { normalizeBacklinksTarget } from "@/server/lib/dataforseoBacklinksTarget";
-
 type BacklinksRequest = { target: string };
 type BacklinksListRequest = BacklinksRequest &
   BacklinksSpamFilterOptions & {
diff --git a/src/server/lib/dataforseo/client.ts b/src/server/lib/dataforseo/client.ts
index 8b272fe..8065ad9 100644
--- a/src/server/lib/dataforseo/client.ts
+++ b/src/server/lib/dataforseo/client.ts
@@ -8,45 +8,9 @@ import {
   trackUsageCreditSpend,
 } from "@/server/billing/subscription";
 import type { BillingCustomerContext } from "@/server/billing/subscription";
-import {
-  fetchBusinessListingsSearch,
-  fetchQuestionsAnswers,
-} from "@/server/lib/dataforseo/business";
-import {
-  fetchBacklinksHistory,
-  fetchBacklinksRows,
-  fetchBacklinksSummary,
-  fetchDomainPagesSummary,
-  fetchReferringDomains,
-} from "@/server/lib/dataforseo/backlinks";
-import {
-  fetchDomainRankOverview,
-  fetchKeywordIdeas,
-  fetchKeywordOverview,
-  fetchKeywordSuggestions,
-  fetchRankedKeywords,
-  fetchRelatedKeywords,
-  fetchRelevantPages,
-  fetchSerpCompetitors,
-} from "@/server/lib/dataforseo/labs";
-import {
-  fetchAdsKeywordIdeas,
-  fetchAdsSearchVolume,
-} from "@/server/lib/dataforseo/google-ads";
-import {
-  fetchLiveSerp,
-  fetchLocalSerp,
-  fetchRankCheckSerp,
-  postRankCheckTasks,
-} from "@/server/lib/dataforseo/serp";
-import { fetchLighthouseResult } from "@/server/lib/dataforseo/lighthouse";
-import {
-  fetchLlmAggregatedMetrics,
-  fetchLlmCrossAggregatedMetrics,
-  fetchLlmMentionsSearch,
-  fetchLlmResponse,
-  fetchLlmTopPages,
-} from "@/server/lib/dataforseo/ai";
+// Type-only namespace import: erased at compile, so the section modules (and
+// the SDK they pull in) still only load through loadDataforseoSections below.
+import type * as sections from "@/server/lib/dataforseo/sections";
 import {
   DataforseoChargedTaskError,
   type DataforseoApiCallCost,
@@ -57,10 +21,24 @@ import { AppError } from "@/server/lib/errors";
 
 export { mapDataforseoPathToCreditFeature };
 
+/** The section-fetcher barrel (sections.ts), as a type for `meter` pickers. */
+export type DataforseoSections = typeof sections;
+
+let sectionsPromise: Promise<DataforseoSections> | undefined;
+
+/** Single lazy boundary for the DataForSEO subtree: the section fetchers and
+ * the ~3 MB dataforseo-client SDK they statically import stay out of the
+ * eager isolate startup graph and load once, on the first API call. */
+export function loadDataforseoSections(): Promise<DataforseoSections> {
+  return (sectionsPromise ??= import("@/server/lib/dataforseo/sections"));
+}
+
 /**
  * Wraps a section fetcher with billing metering. Each entry on the client is
- * `meter(customer, fetcher, defaultFeature?)`, which returns a function with the
- * fetcher's own input type and resolves to its unwrapped `.data`.
+ * `meter(customer, (s) => s.fetchX, defaultFeature?)`, which returns a function
+ * with the fetcher's own input type and resolves to its unwrapped `.data`. The
+ * picker indirection (rather than the fetcher itself) keeps the section
+ * modules behind loadDataforseoSections.
  *
  * `defaultFeature` is the fallback credit feature; a caller can override it per
  * call by passing `creditFeature` in the input (e.g. an MCP tool attributing
@@ -69,13 +47,15 @@ export { mapDataforseoPathToCreditFeature };
  */
 function meter<I, T>(
   customer: BillingCustomerContext,
-  fetcher: (input: I) => Promise<DataforseoApiResponse<T>>,
+  pick: (
+    sections: DataforseoSections,
+  ) => (input: I) => Promise<DataforseoApiResponse<T>>,
   defaultFeature?: CreditFeature,
 ): (input: I & { creditFeature?: CreditFeature }) => Promise<T> {
   return (input) =>
     meterDataforseoCall(
       customer,
-      () => fetcher(input),
+      async () => pick(await loadDataforseoSections())(input),
       input.creditFeature ?? defaultFeature,
     );
 }
@@ -85,56 +65,71 @@ export function createDataforseoClient(customer: BillingCustomerContext) {
     business: {
       businessListings: meter(
         customer,
-        fetchBusinessListingsSearch,
+        (s) => s.fetchBusinessListingsSearch,
+        "local_seo",
+      ),
+      questionsAnswers: meter(
+        customer,
+        (s) => s.fetchQuestionsAnswers,
         "local_seo",
       ),
-      questionsAnswers: meter(customer, fetchQuestionsAnswers, "local_seo"),
     },
     backlinks: {
-      summary: meter(customer, fetchBacklinksSummary),
-      rows: meter(customer, fetchBacklinksRows),
-      referringDomains: meter(customer, fetchReferringDomains),
-      domainPages: meter(customer, fetchDomainPagesSummary),
-      history: meter(customer, fetchBacklinksHistory),
+      summary: meter(customer, (s) => s.fetchBacklinksSummary),
+      rows: meter(customer, (s) => s.fetchBacklinksRows),
+      referringDomains: meter(customer, (s) => s.fetchReferringDomains),
+      domainPages: meter(customer, (s) => s.fetchDomainPagesSummary),
+      history: meter(customer, (s) => s.fetchBacklinksHistory),
     },
     keywords: {
-      related: meter(customer, fetchRelatedKeywords),
-      suggestions: meter(customer, fetchKeywordSuggestions),
-      ideas: meter(customer, fetchKeywordIdeas),
+      related: meter(customer, (s) => s.fetchRelatedKeywords),
+      suggestions: meter(customer, (s) => s.fetchKeywordSuggestions),
+      ideas: meter(customer, (s) => s.fetchKeywordIdeas),
       // Google Ads endpoints for countries Labs doesn't support.
-      adsIdeas: meter(customer, fetchAdsKeywordIdeas),
-      adsSearchVolume: meter(customer, fetchAdsSearchVolume),
+      adsIdeas: meter(customer, (s) => s.fetchAdsKeywordIdeas),
+      adsSearchVolume: meter(customer, (s) => s.fetchAdsSearchVolume),
     },
     domain: {
-      rankOverview: meter(customer, fetchDomainRankOverview),
-      rankedKeywords: meter(customer, fetchRankedKeywords),
-      relevantPages: meter(customer, fetchRelevantPages),
+      rankOverview: meter(customer, (s) => s.fetchDomainRankOverview),
+      rankedKeywords: meter(customer, (s) => s.fetchRankedKeywords),
+      relevantPages: meter(customer, (s) => s.fetchRelevantPages),
     },
     serp: {
-      live: meter(customer, fetchLiveSerp),
-      rankCheck: meter(customer, fetchRankCheckSerp, "rank_tracking"),
+      live: meter(customer, (s) => s.fetchLiveSerp),
+      rankCheck: meter(customer, (s) => s.fetchRankCheckSerp, "rank_tracking"),
       // Posts up to 100 queued rank check tasks; one metered charge covers the
       // whole batch (DataForSEO bills task_post at post time, collection is
       // free).
-      rankCheckTaskPost: meter(customer, postRankCheckTasks, "rank_tracking"),
-      local: meter(customer, fetchLocalSerp, "local_seo"),
+      rankCheckTaskPost: meter(
+        customer,
+        (s) => s.postRankCheckTasks,
+        "rank_tracking",
+      ),
+      local: meter(customer, (s) => s.fetchLocalSerp, "local_seo"),
     },
     labs: {
       // Callers (e.g. the keyword-metrics MCP tool) can attribute the spend to
       // their own feature by passing `creditFeature` in the input; defaults to
       // rank_tracking when omitted.
-      keywordOverview: meter(customer, fetchKeywordOverview, "rank_tracking"),
-      serpCompetitors: meter(customer, fetchSerpCompetitors),
+      keywordOverview: meter(
+        customer,
+        (s) => s.fetchKeywordOverview,
+        "rank_tracking",
+      ),
+      serpCompetitors: meter(customer, (s) => s.fetchSerpCompetitors),
     },
     lighthouse: {
-      live: meter(customer, fetchLighthouseResult),
+      live: meter(customer, (s) => s.fetchLighthouseResult),
     },
     aiSearch: {
-      mentionsSearch: meter(customer, fetchLlmMentionsSearch),
-      aggregatedMetrics: meter(customer, fetchLlmAggregatedMetrics),
-      topPages: meter(customer, fetchLlmTopPages),
-      crossAggregatedMetrics: meter(customer, fetchLlmCrossAggregatedMetrics),
-      llmResponse: meter(customer, fetchLlmResponse),
+      mentionsSearch: meter(customer, (s) => s.fetchLlmMentionsSearch),
+      aggregatedMetrics: meter(customer, (s) => s.fetchLlmAggregatedMetrics),
+      topPages: meter(customer, (s) => s.fetchLlmTopPages),
+      crossAggregatedMetrics: meter(
+        customer,
+        (s) => s.fetchLlmCrossAggregatedMetrics,
+      ),
+      llmResponse: meter(customer, (s) => s.fetchLlmResponse),
     },
   } as const;
 }
diff --git a/src/server/lib/dataforseo/endpoints.test.ts b/src/server/lib/dataforseo/endpoints.test.ts
index 47b4974..3046ce9 100644
--- a/src/server/lib/dataforseo/endpoints.test.ts
+++ b/src/server/lib/dataforseo/endpoints.test.ts
@@ -6,13 +6,13 @@ vi.mock("@/server/lib/runtime-env", () => ({
 
 import { fetchQuestionsAnswers } from "@/server/lib/dataforseo/business";
 import {
-  buildLlmTarget,
   fetchLlmAggregatedMetrics,
   fetchLlmCrossAggregatedMetrics,
   fetchLlmMentionsSearch,
   fetchLlmResponse,
   fetchLlmTopPages,
 } from "@/server/lib/dataforseo/ai";
+import { buildLlmTarget } from "@/server/lib/dataforseo/shared";
 
 function parseDataforseoRequestBody(init: RequestInit | undefined): unknown {
   const body = init?.body;
diff --git a/src/server/lib/dataforseo/index.ts b/src/server/lib/dataforseo/index.ts
index 2fe98ac..7258fa2 100644
--- a/src/server/lib/dataforseo/index.ts
+++ b/src/server/lib/dataforseo/index.ts
@@ -1,7 +1,15 @@
 // Public surface of the DataForSEO integration. Internals live in the
-// per-section files (labs / serp / business / backlinks / ai /
-// lighthouse); everything funnels through envelope.ts (status + billing) and is
-// metered in client.ts.
+// per-section files (labs / serp / business / backlinks / ai / lighthouse),
+// which sit behind the single dynamic import in client.ts so the ~3 MB SDK
+// loads lazily; everything funnels through envelope.ts (status + billing) and
+// is metered in client.ts. Runtime values re-exported here must be SDK-free
+// (shared.ts) or lazy — a static value re-export from a section file would
+// drag the SDK back into the eager isolate startup graph.
+
+import {
+  loadDataforseoSections,
+  type DataforseoSections,
+} from "@/server/lib/dataforseo/client";
 
 export { createDataforseoClient } from "@/server/lib/dataforseo/client";
 
@@ -10,35 +18,41 @@ export {
   type KeywordMetricRow,
 } from "@/server/lib/dataforseo/keyword-metrics";
 
-export {
-  type LabsKeywordDataItem,
-  type DomainRankedKeywordItem,
-  type RelevantPagesItem,
-} from "@/server/lib/dataforseo/labs";
-
-export { type AdsKeywordIdeaItem } from "@/server/lib/dataforseo/google-ads";
-
-export {
-  fetchRankCheckTaskResult,
-  MAX_TASKS_PER_POST,
-  type SerpLiveItem,
-  type RankCheckResult,
-  type RankCheckTaskInput,
-  type PostedRankCheckTask,
-} from "@/server/lib/dataforseo/serp";
-
-export {
-  normalizeBacklinksTarget,
-  type BacklinksSummaryItem,
-  type BacklinksItem,
-  type ReferringDomainItem,
-  type DomainPageSummaryItem,
-  type BacklinksHistoryItem,
-} from "@/server/lib/dataforseo/backlinks";
-
 export {
   buildLlmTarget,
   CHATGPT_LANGUAGE_CODE,
   CHATGPT_LOCATION_CODE,
+  MAX_TASKS_PER_POST,
   type LlmPlatform,
-} from "@/server/lib/dataforseo/ai";
+} from "@/server/lib/dataforseo/shared";
+
+export { normalizeBacklinksTarget } from "@/server/lib/dataforseoBacklinksTarget";
+
+/** Lazy wrapper for the one section fetcher called outside the metered client
+ * (rank-check task collection is free at DataForSEO, so it skips metering). */
+export const fetchRankCheckTaskResult: DataforseoSections["fetchRankCheckTaskResult"] =
+  async (input) =>
+    (await loadDataforseoSections()).fetchRankCheckTaskResult(input);
+
+export type {
+  LabsKeywordDataItem,
+  DomainRankedKeywordItem,
+  RelevantPagesItem,
+} from "@/server/lib/dataforseo/labs";
+
+export type { AdsKeywordIdeaItem } from "@/server/lib/dataforseo/google-ads";
+
+export type {
+  SerpLiveItem,
+  RankCheckResult,
+  RankCheckTaskInput,
+  PostedRankCheckTask,
+} from "@/server/lib/dataforseo/serp";
+
+export type {
+  BacklinksSummaryItem,
+  BacklinksItem,
+  ReferringDomainItem,
+  DomainPageSummaryItem,
+  BacklinksHistoryItem,
+} from "@/server/lib/dataforseo/backlinks";
diff --git a/src/server/lib/dataforseo/sections.ts b/src/server/lib/dataforseo/sections.ts
new file mode 100644
index 0000000..987ce6c
--- /dev/null
+++ b/src/server/lib/dataforseo/sections.ts
@@ -0,0 +1,54 @@
+// Root of the lazily loaded DataForSEO subtree. The section fetchers — and
+// the ~3 MB dataforseo-client SDK they statically import — are reached only
+// through the single dynamic import in client.ts (loadDataforseoSections), so
+// the whole subtree lands in one lazy chunk outside the eager isolate startup
+// graph. Never import this barrel or a section file statically from eager
+// server code; the leanWorkerBundle vite plugin fails the build if the SDK
+// re-enters the eager graph. SDK-free values live in shared.ts instead.
+
+export {
+  fetchBusinessListingsSearch,
+  fetchQuestionsAnswers,
+} from "@/server/lib/dataforseo/business";
+
+export {
+  fetchBacklinksHistory,
+  fetchBacklinksRows,
+  fetchBacklinksSummary,
+  fetchDomainPagesSummary,
+  fetchReferringDomains,
+} from "@/server/lib/dataforseo/backlinks";
+
+export {
+  fetchDomainRankOverview,
+  fetchKeywordIdeas,
+  fetchKeywordOverview,
+  fetchKeywordSuggestions,
+  fetchRankedKeywords,
+  fetchRelatedKeywords,
+  fetchRelevantPages,
+  fetchSerpCompetitors,
+} from "@/server/lib/dataforseo/labs";
+
+export {
+  fetchAdsKeywordIdeas,
+  fetchAdsSearchVolume,
+} from "@/server/lib/dataforseo/google-ads";
+
+export {
+  fetchLiveSerp,
+  fetchLocalSerp,
+  fetchRankCheckSerp,
+  fetchRankCheckTaskResult,
+  postRankCheckTasks,
+} from "@/server/lib/dataforseo/serp";
+
+export { fetchLighthouseResult } from "@/server/lib/dataforseo/lighthouse";
+
+export {
+  fetchLlmAggregatedMetrics,
+  fetchLlmCrossAggregatedMetrics,
+  fetchLlmMentionsSearch,
+  fetchLlmResponse,
+  fetchLlmTopPages,
+} from "@/server/lib/dataforseo/ai";
diff --git a/src/server/lib/dataforseo/serp.ts b/src/server/lib/dataforseo/serp.ts
index 8bae7ba..9ed6908 100644
--- a/src/server/lib/dataforseo/serp.ts
+++ b/src/server/lib/dataforseo/serp.ts
@@ -7,6 +7,7 @@ import {
   SerpGoogleOrganicTaskPostRequestInfo,
 } from "dataforseo-client";
 import { serpApi } from "@/server/lib/dataforseo/core";
+import { MAX_TASKS_PER_POST } from "@/server/lib/dataforseo/shared";
 import {
   assertOk,
   buildTaskBilling,
@@ -184,9 +185,6 @@ export async function fetchRankCheckSerp(input: {
 // stragglers, orchestrated by the rank check workflow.
 // ---------------------------------------------------------------------------
 
-/** Max tasks DataForSEO accepts in a single task_post request. */
-export const MAX_TASKS_PER_POST = 100;
-
 export interface RankCheckTaskInput {
   keyword: string;
   keywordId: string;
diff --git a/src/server/lib/dataforseo/shared.ts b/src/server/lib/dataforseo/shared.ts
new file mode 100644
index 0000000..b692eea
--- /dev/null
+++ b/src/server/lib/dataforseo/shared.ts
@@ -0,0 +1,50 @@
+// SDK-free constants and target builders shared between eager server code
+// (features, workflows, MCP tools) and the lazily loaded section fetchers.
+// Keep this module free of dataforseo-client and section-file imports —
+// anything imported from here must be safe to evaluate in the eager isolate
+// startup graph.
+
+// ChatGPT mention/response data is only available for US/en per DataForSEO docs.
+export const CHATGPT_LOCATION_CODE = 2840;
+export const CHATGPT_LANGUAGE_CODE = "en";
+
+export type LlmPlatform = "chat_gpt" | "google";
+
+/** Max tasks DataForSEO accepts in a single task_post request. */
+export const MAX_TASKS_PER_POST = 100;
+
+// DataForSEO's LLM-mentions `target` array accepts domain OR keyword entries.
+// We always pass exactly one target per call.
+export type LlmTarget =
+  | {
+      domain: string;
+      include_subdomains?: boolean;
+      search_filter?: "include" | "exclude";
+      search_scope?: string[];
+    }
+  | {
+      keyword: string;
+      search_filter?: "include" | "exclude";
+      search_scope?: string[];
+      match_type?: "word_match" | "partial_match";
+    };
+
+export function buildLlmTarget(input: {
+  type: "domain" | "keyword";
+  value: string;
+}): LlmTarget {
+  if (input.type === "domain") {
+    return {
+      domain: input.value,
+      include_subdomains: true,
+      search_filter: "include",
+      search_scope: ["any"],
+    };
+  }
+  return {
+    keyword: input.value,
+    search_filter: "include",
+    search_scope: ["any", "brand_entities"],
+    match_type: "word_match",
+  };
+}
diff --git a/src/server/lib/just-bash-stub.ts b/src/server/lib/just-bash-stub.ts
index 22325a8..a5007dc 100644
--- a/src/server/lib/just-bash-stub.ts
+++ b/src/server/lib/just-bash-stub.ts
@@ -1,5 +1,6 @@
 /**
- * Build-time stand-in for `just-bash`, wired up via the vite.config.ts alias.
+ * Build-time stand-in for `just-bash`, wired up via the leanWorkerBundle
+ * plugin's alias (vite-plugin-lean-worker-bundle.ts).
  *
  * `@cloudflare/think` eagerly imports just-bash (~21 MB of source, plus
  * turndown and the 8.6 MB @mixmark-io/domino DOM implementation) at module
@@ -14,7 +15,8 @@
  * @cloudflare/think loads just-bash lazily.
  */
 const STUBBED_MESSAGE =
-  "just-bash is stubbed out of the worker bundle (see vite.config.ts); " +
+  "just-bash is stubbed out of the worker bundle (see " +
+  "vite-plugin-lean-worker-bundle.ts); " +
   "the workspace bash tool is disabled for this deployment";
 
 // Covers every named import in the dependency graph: `Bash` (Think's
diff --git a/src/server/lib/workers-ai-provider-stub.ts b/src/server/lib/workers-ai-provider-stub.ts
new file mode 100644
index 0000000..de14bd7
--- /dev/null
+++ b/src/server/lib/workers-ai-provider-stub.ts
@@ -0,0 +1,30 @@
+/**
+ * Build-time stand-in for `workers-ai-provider` (and its /anthropic and
+ * /openai subpaths), wired up via the leanWorkerBundle vite plugin.
+ *
+ * `@cloudflare/think` eagerly imports all three (~540 kB with the @ai-sdk/
+ * openai + @ai-sdk/anthropic providers they pull in) solely to build its lazy
+ * default provider in `resolveModel()` — which only runs when `getModel()`
+ * returns a bare model-id string. Both our chat agents (SamChatAgent,
+ * OnboardingChatAgent) return a constructed OpenRouter LanguageModel instead,
+ * so the default provider is dead code; this stub keeps it out of the eager
+ * worker bundle. Same pattern as just-bash-stub.ts.
+ */
+const STUBBED_MESSAGE =
+  "workers-ai-provider is stubbed out of the worker bundle to keep it out of " +
+  "the eager isolate startup graph (see vite-plugin-lean-worker-bundle.ts); " +
+  "SamChatAgent/OnboardingChatAgent override getModel with OpenRouter";
+
+// Covers every named import in the dependency graph: `createWorkersAI` (root),
+// `anthropic` (/anthropic) and `openai` (/openai).
+export function createWorkersAI(): never {
+  throw new Error(STUBBED_MESSAGE);
+}
+
+export function anthropic(): never {
+  throw new Error(STUBBED_MESSAGE);
+}
+
+export function openai(): never {
+  throw new Error(STUBBED_MESSAGE);
+}
diff --git a/vite-plugin-lean-worker-bundle.ts b/vite-plugin-lean-worker-bundle.ts
new file mode 100644
index 0000000..271fa8d
--- /dev/null
+++ b/vite-plugin-lean-worker-bundle.ts
@@ -0,0 +1,168 @@
+import { fileURLToPath } from "node:url";
+import type { Plugin } from "vite";
+
+// Literal `new URL(..., import.meta.url)` per stub (rather than a path
+// helper) so knip sees the stub files as used.
+const JUST_BASH_STUB = fileURLToPath(
+  new URL("./src/server/lib/just-bash-stub.ts", import.meta.url),
+);
+const WORKERS_AI_PROVIDER_STUB = fileURLToPath(
+  new URL("./src/server/lib/workers-ai-provider-stub.ts", import.meta.url),
+);
+/**
+ * Dependencies that must never be reachable from the worker's eager startup
+ * module graph. The 128 MB isolate limit is shared by everything evaluated at
+ * startup (production OOM bursts trace back to baseline heap, not leaks), so
+ * each of these is either loaded lazily behind a dynamic import or stubbed
+ * out. `generateBundle` below fails the build if one sneaks back in via a
+ * static import chain — e.g. an eager `import { fetchLiveSerp } from
+ * "@/server/lib/dataforseo/serp"` instead of going through the metered client.
+ */
+const EAGER_DENYLIST: Array<{ pattern: RegExp; expected: string }> = [
+  {
+    pattern: /node_modules\/dataforseo-client\//,
+    expected:
+      "lazy-loaded behind loadDataforseoSections() — eager code must go " +
+      "through the metered client or src/server/lib/dataforseo/shared.ts",
+  },
+  {
+    pattern: /node_modules\/autumn-js\//,
+    expected:
+      "lazy-loaded behind the facade in src/server/billing/autumn.ts and " +
+      "the /api/autumn route's lazy handler",
+  },
+  {
+    pattern:
+      /node_modules\/(workers-ai-provider|@ai-sdk\/(openai|anthropic))\//,
+    expected:
+      "aliased to workers-ai-provider-stub.ts (@cloudflare/think's default " +
+      "provider path is dead code — our agents construct OpenRouter models)",
+  },
+  {
+    pattern: /node_modules\/just-bash\//,
+    expected:
+      "aliased to just-bash-stub.ts (Think's workspace bash tool is disabled)",
+  },
+  {
+    // The barrel (index.*) is allowed — the load hook rewrites its content to
+    // re-export English only — as is en.* itself. Every other locale module
+    // must stay out; if the load-hook swap ever regresses, the real barrel
+    // pulls the individual locale files back in and they match here.
+    pattern: /node_modules\/zod\/v4\/locales\/(?!en\.|index\.)/,
+    expected:
+      "replaced with an en-only barrel via the load hook below (we never " +
+      "localize zod errors)",
+  },
+  {
+    // Pre-existing boundary from the site-audit engine, guarded here too.
+    pattern: /node_modules\/cheerio\//,
+    expected:
+      "lazy-loaded behind the page-analyzer dynamic import " +
+      "(site-audit-workflow-helpers.ts)",
+  },
+];
+
+/**
+ * Keeps the worker's eager server bundle lean, in three parts:
+ *
+ * 1. `resolve.alias` stubs for packages that are pure dead weight (dead code
+ *    paths in @cloudflare/think).
+ * 2. A `load`-hook swap of zod v4's all-languages locales barrel for an
+ *    en-only barrel (the barrel is imported via relative specifiers inside
+ *    zod itself, and pre-enforced resolvers in this plugin stack win the
+ *    resolveId race, so matching the resolved file path in `load` is the
+ *    reliable seam).
+ * 3. A `generateBundle` assertion that walks the static-import closure of the
+ *    worker entry chunk and fails the build if any EAGER_DENYLIST module is
+ *    reachable — turning "we verified the chunk by grepping a sourcemap once"
+ *    into a permanent regression test.
+ */
+export function leanWorkerBundle(): Plugin {
+  return {
+    name: "lean-worker-bundle",
+    config() {
+      return {
+        resolve: {
+          alias: {
+            // Rationale for each stub lives in its docblock. TODO: remove the
+            // just-bash workaround once @cloudflare/think stops eagerly
+            // importing it (https://github.com/cloudflare/agents/issues/1673).
+            "just-bash": JUST_BASH_STUB,
+            // Subpaths must precede the bare specifier, which would otherwise
+            // prefix-match them.
+            "workers-ai-provider/anthropic": WORKERS_AI_PROVIDER_STUB,
+            "workers-ai-provider/openai": WORKERS_AI_PROVIDER_STUB,
+            "workers-ai-provider": WORKERS_AI_PROVIDER_STUB,
+          },
+        },
+      };
+    },
+    load(id) {
+      // zod v4's core/classic entrypoints re-export the full locales barrel
+      // (`export * as locales from "../locales/index.js"`, every language,
+      // ~208 kB) into the eager bundle. Zod's default English error map
+      // imports `../locales/en.js` directly and bypasses the barrel, so only
+      // `z.locales.<lang>` consumers need it — and we never localize zod
+      // errors. Serve an en-only barrel in its place so `z.locales.en` keeps
+      // working and the other ~40 languages tree-shake away. (`./en.js`
+      // resolves relative to the real barrel path, so no stub file needed.)
+      const barrel = id.match(
+        /node_modules\/zod\/v4\/locales\/index\.(js|cjs)$/,
+      );
+      if (barrel) {
+        return `export { default as en } from "./en.${barrel[1]}";`;
+      }
+    },
+    generateBundle(_options, bundle) {
+      // Only the worker build matters for isolate memory; the client bundle
+      // never contains these packages (and the zod swap applies everywhere).
+      if (this.environment.name !== "ssr") return;
+
+      // Bundle keys are chunk fileNames already.
+      const chunkAt = (fileName: string) => {
+        const output = bundle[fileName];
+        return output?.type === "chunk" ? output : undefined;
+      };
+
+      // Static-import closure from the entry chunks: everything here is
+      // evaluated at isolate startup. Dynamic imports are excluded — landing
+      // there is the point of the lazy boundaries.
+      const eager = new Set<string>();
+      const queue = Object.values(bundle)
+        .filter((output) => output.type === "chunk" && output.isEntry)
+        .map((chunk) => chunk.fileName);
+      while (queue.length > 0) {
+        const fileName = queue.pop();
+        if (fileName === undefined || eager.has(fileName)) continue;
+        eager.add(fileName);
+        queue.push(...(chunkAt(fileName)?.imports ?? []));
+      }
+
+      const violations: string[] = [];
+      for (const rule of EAGER_DENYLIST) {
+        for (const fileName of eager) {
+          const hits =
+            chunkAt(fileName)?.moduleIds.filter((id) =>
+              rule.pattern.test(id),
+            ) ?? [];
+          if (hits.length > 0) {
+            violations.push(
+              `${hits[0]}${hits.length > 1 ? ` (+${hits.length - 1} more modules)` : ""}\n` +
+                `  reached the eager startup graph via chunk ${fileName}\n` +
+                `  expected: ${rule.expected}`,
+            );
+          }
+        }
+      }
+
+      if (violations.length > 0) {
+        this.error(
+          `[lean-worker-bundle] denylisted module(s) in the worker's eager ` +
+            `startup graph:\n\n${violations.join("\n\n")}\n\nRestore the ` +
+            `lazy/stub boundary, or update EAGER_DENYLIST in ` +
+            `vite-plugin-lean-worker-bundle.ts if this is intentional.`,
+        );
+      }
+    },
+  };
+}
diff --git a/vite.config.ts b/vite.config.ts
index 26856d1..c5221eb 100644
--- a/vite.config.ts
+++ b/vite.config.ts
@@ -1,4 +1,3 @@
-import { fileURLToPath } from "node:url";
 import { tanstackStart } from "@tanstack/react-start/plugin/vite";
 import { defineConfig, loadEnv } from "vite";
 import tsConfigPaths from "vite-tsconfig-paths";
@@ -6,6 +5,7 @@ import viteReact from "@vitejs/plugin-react";
 import tailwindcss from "@tailwindcss/vite";
 import { cloudflare } from "@cloudflare/vite-plugin";
 import { devtools } from "@tanstack/devtools-vite";
+import { leanWorkerBundle } from "./vite-plugin-lean-worker-bundle";
 
 export default defineConfig(({ mode }) => {
   const env = loadEnv(mode, process.cwd(), "");
@@ -22,23 +22,6 @@ export default defineConfig(({ mode }) => {
   const emitSourcemaps = env.POSTHOG_SOURCEMAPS === "true";
 
   return {
-    resolve: {
-      alias: {
-        // TODO: Remove this workaround once @cloudflare/think stops eagerly
-        // importing just-bash at module init
-        // (https://github.com/cloudflare/agents/issues/1673).
-        //
-        // just-bash (plus its turndown → @mixmark-io/domino chain, ~30 MB of
-        // source) is only used by Think's workspace bash tool, which SAM
-        // disables — but the eager import drags it into the main worker's
-        // startup module graph, inflating every isolate's baseline heap
-        // toward the 128 MB limit (production OOM bursts on unrelated
-        // routes). Alias it to a throwing stub so it never ships.
-        "just-bash": fileURLToPath(
-          new URL("./src/server/lib/just-bash-stub.ts", import.meta.url),
-        ),
-      },
-    },
     envPrefix: [
       "VITE_",
       "AUTH_MODE",
@@ -60,6 +43,7 @@ export default defineConfig(({ mode }) => {
       outDir: emitSourcemaps ? "dist-sourcemaps" : "dist",
     },
     plugins: [
+      leanWorkerBundle(),
       showDevtools
         ? devtools({
             consolePiping: {