diff --git a/apps/api/src/body-limits.ts b/apps/api/src/body-limits.ts
index 12e4ea9..f4551f0 100644
--- a/apps/api/src/body-limits.ts
+++ b/apps/api/src/body-limits.ts
@@ -1,6 +1,10 @@
-import { MODULE_ROUTE_MAX_BODY_BYTES_CEILING } from "@ekklesia/contracts";
-import type { Context } from "hono";
-import { bodyLimit } from "hono/body-limit";
+import {
+  MODULE_ROUTE_ABSOLUTE_MAX_BODY_BYTES,
+  MODULE_ROUTE_MAX_BODY_BYTES_CEILING,
+  MODULE_ROUTE_STREAMED_MAX_BODY_BYTES_CEILING,
+  type ModuleRouteBodyMode,
+} from "@ekklesia/contracts";
+import type { Context, MiddlewareHandler } from "hono";
 
 /**
  * The platform's one request-body policy, centralized here rather than scattered as magic numbers
@@ -19,15 +23,20 @@ import { bodyLimit } from "hono/body-limit";
  *   field individually bounded well under 1 KiB combined; 16 KiB leaves headroom without inviting
  *   abuse.
  * - `MODULE_ROUTE_MAX_BODY_BYTES_CEILING` (1 MiB, re-exported from `@ekklesia/contracts` — the same
- *   constant a module's own route declaration is validated against at registration) is the hard
- *   ceiling no module route may exceed and doubles as the platform's overall request-body ceiling:
- *   nothing in this platform ever declares, or enforces, a larger single request body than this.
- *   Large media transfer is explicitly out of scope for ordinary module HTTP bodies — it belongs to
- *   a future dedicated storage design, not to widening this ceiling.
+ *   constant a module's own **buffered** route declaration is validated against at registration) is
+ *   the ceiling for every body the platform materializes before a handler runs. It has not moved.
+ * - `MODULE_ROUTE_STREAMED_MAX_BODY_BYTES_CEILING` (32 MiB) is what a route may declare when it
+ *   explicitly opts into `bodyMode: "streamed"` (ADR 0042), and doubles as
+ *   `MODULE_ROUTE_ABSOLUTE_MAX_BODY_BYTES`: no route, in any mode, may declare or accept a larger
+ *   single request body, and no unbounded option exists anywhere in the contract.
  */
 export const AUTH_REQUEST_MAX_BODY_BYTES = 8 * 1024;
 export const CORE_MUTATION_MAX_BODY_BYTES = 16 * 1024;
-export { MODULE_ROUTE_MAX_BODY_BYTES_CEILING };
+export {
+  MODULE_ROUTE_ABSOLUTE_MAX_BODY_BYTES,
+  MODULE_ROUTE_MAX_BODY_BYTES_CEILING,
+  MODULE_ROUTE_STREAMED_MAX_BODY_BYTES_CEILING,
+};
 
 /** The one stable, sanitized public contract for every request-body-size rejection across the
  * platform — auth, Core, and module routes alike. Never leaks the configured limit, the offending
@@ -37,12 +46,173 @@ export function requestBodyTooLargeResponse(c: Context): Response {
   return c.json({ code: "REQUEST_BODY_TOO_LARGE" }, 413);
 }
 
-/** A single shared `hono/body-limit` factory so every call site uses the identical sanitized 413
- * contract rather than redefining `onError` per route. Covers both a declared oversized
- * `Content-Length` and an oversized chunked/streamed body with no declared length — see
- * `hono/body-limit`'s pinned implementation, which checks `Content-Length` synchronously before
- * ever reading the stream, and otherwise reads and counts the stream incrementally, rejecting as
- * soon as the running total exceeds `maxSize` rather than buffering the whole body first. */
-export function platformBodyLimit(maxSize: number) {
-  return bodyLimit({ maxSize, onError: requestBodyTooLargeResponse });
+/**
+ * A declared `Content-Length`, or `undefined` when there is not exactly one well-formed one.
+ *
+ * A malformed or contradictory value is treated as *absent* rather than as a rejection, deliberately:
+ * the byte counting below bounds the request either way, so refusing here could only ever turn a
+ * legitimate request away without making an illegitimate one any less bounded. Node's own HTTP
+ * parser rejects genuinely malformed framing before this code sees the request at all.
+ */
+function declaredContentLength(request: Request): number | undefined {
+  const header = request.headers.get("content-length");
+  if (header === null || !/^\d{1,15}$/u.test(header.trim())) {
+    return undefined;
+  }
+  return Number.parseInt(header.trim(), 10);
+}
+
+/** Releases a body nothing consumed, so an abandoned or oversized upload does not hold a socket
+ * open waiting to be read. Safe on a stream that is locked, already drained, or already errored. */
+function releaseUnreadBody(request: Request): void {
+  const body = request.body;
+  if (!body || body.locked) {
+    return;
+  }
+  void body.cancel().catch(() => undefined);
+}
+
+/**
+ * Reads at most `maxSize` bytes, stopping and cancelling the source the moment the running total
+ * exceeds it. Never allocates beyond what it has already accepted, so an over-limit body costs one
+ * chunk past the limit rather than the whole upload.
+ */
+async function readBounded(
+  body: ReadableStream<Uint8Array>,
+  maxSize: number,
+): Promise<readonly Uint8Array[] | "over-limit"> {
+  const reader = body.getReader();
+  const chunks: Uint8Array[] = [];
+  let size = 0;
+  try {
+    for (;;) {
+      const { done, value } = await reader.read();
+      if (done) {
+        return chunks;
+      }
+      size += value.byteLength;
+      if (size > maxSize) {
+        await reader.cancel().catch(() => undefined);
+        return "over-limit";
+      }
+      chunks.push(value);
+    }
+  } finally {
+    reader.releaseLock();
+  }
+}
+
+function streamOf(chunks: readonly Uint8Array[]): ReadableStream<Uint8Array> {
+  return new ReadableStream<Uint8Array>({
+    start(controller) {
+      for (const chunk of chunks) {
+        controller.enqueue(chunk);
+      }
+      controller.close();
+    },
+  });
+}
+
+/**
+ * The platform's one request-body limiter, for every route in the application.
+ *
+ * ## Both modes reject a declared oversize before anything else happens
+ *
+ * A `Content-Length` above the limit is refused synchronously, before authorization, before the
+ * handler, and before a single body byte is read. That is the cheap rejection an ordinary
+ * too-large upload takes.
+ *
+ * ## `buffered` — the body is materialized, bounded, before the handler runs
+ *
+ * The exact behaviour every route had before streaming existed, now with the counting done here
+ * rather than by a dependency. Bytes are counted as they arrive and the request is rejected the
+ * moment the running total passes the limit, so a lying or absent `Content-Length` is bounded by
+ * what actually arrived rather than by what was claimed. The handler then receives a request whose
+ * body is fully available and provably within its declared allowance — which is what makes
+ * `await request.json()` safe in a module handler.
+ *
+ * The platform holds at most the route's own declared allowance in memory, and a buffered route may
+ * declare at most 1 MiB. That bound is the whole reason the buffered ceiling has not moved.
+ *
+ * ## `streamed` — the body is counted as the handler consumes it, and never materialized
+ *
+ * Nothing is buffered. The body is wrapped in a counting transform and handed to the handler, which
+ * reads it as a stream; the moment the running total passes the limit the stream errors, the source
+ * is cancelled, and the response is replaced with the same sanitized `413` — even if the handler
+ * caught the error and tried to answer anyway. That last part matters: a limit a handler can swallow
+ * is not a limit.
+ *
+ * The consequence a module author must know is that in this mode a `413` can arrive **after** the
+ * handler has started, so a handler that persists as it reads has to be prepared for a partially
+ * consumed upload. Writing to a temporary key and committing only after the read completes is the
+ * pattern; the platform cannot do it for you, because only the module knows what a partial write
+ * means to its own data.
+ *
+ * ## Ordering
+ *
+ * This runs before permission evaluation for both modes, so a request that is *declared* too large
+ * never reaches authorization work. In `streamed` mode no body byte is read until the handler reads
+ * it, and the handler only runs after authorization succeeds — so an unauthorized caller can never
+ * push a large upload through the platform at all.
+ *
+ * ## Timeouts
+ *
+ * Body reading is bounded in time by the server's own `headersTimeout`/`requestTimeout`
+ * (`apps/api/src/server.ts`), not by anything here. A slow upload is a slow *request*, and the
+ * platform already has one answer for that rather than a second per-route one.
+ */
+export function platformBodyLimit(
+  maxSize: number,
+  mode: ModuleRouteBodyMode = "buffered",
+): MiddlewareHandler {
+  return async function enforceBodyLimit(c, next) {
+    const request = c.req.raw;
+    const declared = declaredContentLength(request);
+    if (declared !== undefined && declared > maxSize) {
+      return requestBodyTooLargeResponse(c);
+    }
+    if (!request.body) {
+      return next();
+    }
+
+    if (mode === "buffered") {
+      const chunks = await readBounded(request.body, maxSize);
+      if (chunks === "over-limit") {
+        return requestBodyTooLargeResponse(c);
+      }
+      c.req.raw = new Request(request, {
+        body: streamOf(chunks),
+        // Required by undici whenever a `Request` is constructed from a stream.
+        duplex: "half",
+      } as RequestInit);
+      return next();
+    }
+
+    let overLimit = false;
+    let total = 0;
+    const counted = request.body.pipeThrough(
+      new TransformStream<Uint8Array, Uint8Array>({
+        transform(chunk, controller) {
+          total += chunk.byteLength;
+          if (total > maxSize) {
+            overLimit = true;
+            // Erroring the transform propagates back to the source and cancels it, so the socket is
+            // released rather than left draining an upload nobody will read.
+            controller.error(new Error("REQUEST_BODY_TOO_LARGE"));
+            return;
+          }
+          controller.enqueue(chunk);
+        },
+      }),
+    );
+    c.req.raw = new Request(request, { body: counted, duplex: "half" } as RequestInit);
+
+    await next();
+
+    if (overLimit) {
+      c.res = requestBodyTooLargeResponse(c);
+    }
+    releaseUnreadBody(c.req.raw);
+    return;
+  };
 }
diff --git a/apps/api/src/module-http-routes.ts b/apps/api/src/module-http-routes.ts
index d58253c..3bbd4bc 100644
--- a/apps/api/src/module-http-routes.ts
+++ b/apps/api/src/module-http-routes.ts
@@ -235,9 +235,12 @@ export function mountModuleHttpRoutes(
 
     const requireRoutePermission = requirePermission(middlewareOptions, route.permission);
     // The route's own conscious body contract (`route.maxBodyBytes` — 0 means no body accepted at
-    // all) is enforced before permission evaluation ever runs, so an oversized request never
-    // reaches authorization work, let alone the handler or the module database.
-    const routeBodyLimit = platformBodyLimit(route.maxBodyBytes);
+    // all) is enforced before permission evaluation ever runs, so a request *declared* oversized
+    // never reaches authorization work, let alone the handler or the module database. In
+    // `streamed` mode no body byte is read until the handler reads it, and the handler runs only
+    // after authorization succeeds, so an unauthorized caller can never push an upload through
+    // (ADR 0042).
+    const routeBodyLimit = platformBodyLimit(route.maxBodyBytes, route.bodyMode);
     const path = moduleRoutePath(route.moduleId, route.path);
     const finalHandler = async (c: Context): Promise<Response> => {
       const context: ModuleRouteHandlerContext = Object.freeze({
diff --git a/apps/api/tests/api-http.integration.ts b/apps/api/tests/api-http.integration.ts
index e509faf..7855e76 100644
--- a/apps/api/tests/api-http.integration.ts
+++ b/apps/api/tests/api-http.integration.ts
@@ -432,6 +432,39 @@ async function createFixtureModule(
                   async handler(request, context) {
                     return Response.json({ created: true, principal: context.principal }, { status: 201 });
                   },
+                });
+                // An image-sized streamed upload (ADR 0042). The handler counts bytes as they
+                // arrive and never materializes the body, which is exactly what a real module
+                // storing an upload would do.
+                http.route({
+                  method: "POST",
+                  path: "/uploads",
+                  permission: "calendar.events.read",
+                  maxBodyBytes: 33554432,
+                  bodyMode: "streamed",
+                  async handler(request) {
+                    let bytes = 0;
+                    if (request.body) {
+                      const reader = request.body.getReader();
+                      for (;;) {
+                        const chunk = await reader.read();
+                        if (chunk.done) { break; }
+                        bytes += chunk.value.byteLength;
+                      }
+                    }
+                    return Response.json({ bytes }, { status: 201 });
+                  },
+                });
+                http.route({
+                  method: "POST",
+                  path: "/small-uploads",
+                  permission: "calendar.events.read",
+                  maxBodyBytes: 64,
+                  bodyMode: "streamed",
+                  async handler(request) {
+                    await request.arrayBuffer().catch(() => undefined);
+                    return Response.json({ swallowed: true }, { status: 201 });
+                  },
                 });`
               : ""
           }
@@ -2685,6 +2718,73 @@ describe.sequential("live API — installed module permission end-to-end", () =>
     expect(await trustedResponse.json()).toMatchObject({ created: true });
   });
 
+  it("streams one image-sized upload end to end over real HTTP", async () => {
+    // 25 MiB — an ordinary photograph, and the size the streamed ceiling exists to accommodate. It
+    // travels through a real socket, a real Node server, and the platform's byte counter, and the
+    // platform holds none of it (ADR 0042).
+    const image = new Uint8Array(25 * 1024 * 1024).fill(0x41);
+
+    const response = await fetch(`${origin}/api/v1/modules/calendar/uploads`, {
+      body: image,
+      headers: {
+        "content-type": "application/octet-stream",
+        cookie: ownerCookie,
+        origin: dashboardOrigin,
+      },
+      method: "POST",
+    });
+
+    expect(response.status).toBe(201);
+    expect(await response.json()).toEqual({ bytes: image.byteLength });
+  }, 60_000);
+
+  it("refuses a declared oversize on a streamed route with a sanitized 413", async () => {
+    const response = await fetch(`${origin}/api/v1/modules/calendar/small-uploads`, {
+      body: "a".repeat(65),
+      headers: {
+        "content-type": "text/plain",
+        cookie: ownerCookie,
+        origin: dashboardOrigin,
+      },
+      method: "POST",
+    });
+
+    expect(response.status).toBe(413);
+    expect(await response.json()).toEqual({ code: "REQUEST_BODY_TOO_LARGE" });
+  });
+
+  it("terminates a chunked streamed body that exceeds the limit, even when the handler swallowed it", async () => {
+    // No declared `Content-Length`, so only the running byte count can bound this — and the
+    // handler deliberately ignores the stream error and answers `201`. The platform's `413` still
+    // wins: a limit a handler can swallow is not a limit.
+    const oversize = new ReadableStream<Uint8Array>({
+      pull(controller) {
+        controller.enqueue(new Uint8Array(512).fill(0x41));
+      },
+    });
+
+    const response = await fetch(`${origin}/api/v1/modules/calendar/small-uploads`, {
+      body: oversize,
+      duplex: "half",
+      headers: { cookie: ownerCookie, origin: dashboardOrigin },
+      method: "POST",
+    } as RequestInit);
+
+    expect(response.status).toBe(413);
+    expect(await response.json()).toEqual({ code: "REQUEST_BODY_TOO_LARGE" });
+  }, 30_000);
+
+  it("keeps the server healthy after an oversized upload", async () => {
+    // The socket was released rather than left draining, so the very next request is served
+    // normally.
+    const response = await fetch(`${origin}/api/v1/modules/calendar/events/evt-43`, {
+      headers: { cookie: ownerCookie },
+    });
+
+    expect(response.status).toBe(200);
+    expect(await response.json()).toMatchObject({ eventId: "evt-43" });
+  });
+
   it("rejects a well-formed permission absent from the composed registry, writing no grant or audit row", async () => {
     const admin = await openAdministrativeClient(database.url);
     try {
diff --git a/apps/api/tests/module-http-routes.test.ts b/apps/api/tests/module-http-routes.test.ts
index f892330..c7d1b3d 100644
--- a/apps/api/tests/module-http-routes.test.ts
+++ b/apps/api/tests/module-http-routes.test.ts
@@ -58,14 +58,17 @@ function fakeStore(): AuthorizationStore {
   };
 }
 
-/** Defaults `maxBodyBytes` to a generous value for tests that are not themselves exercising the
+/** Defaults `maxBodyBytes` and `bodyMode` for tests that are not themselves exercising the
  * body-size contract, so the many pre-existing routing/authorization/CORS scenarios below do not
  * each need to restate an unrelated body-size choice; the dedicated "module route body limits"
- * suite further down overrides it explicitly to prove the contract itself. */
+ * suite further down overrides them explicitly to prove the contract itself. */
 function moduleRoute(
-  fields: Omit<RegisteredModuleHttpRoute, "maxBodyBytes"> & { maxBodyBytes?: number },
+  fields: Omit<RegisteredModuleHttpRoute, "bodyMode" | "maxBodyBytes"> & {
+    bodyMode?: RegisteredModuleHttpRoute["bodyMode"];
+    maxBodyBytes?: number;
+  },
 ): RegisteredModuleHttpRoute {
-  return Object.freeze({ maxBodyBytes: 1024, ...fields });
+  return Object.freeze({ bodyMode: "buffered", maxBodyBytes: 1024, ...fields });
 }
 
 /** A small typed fake `ModuleRuntimeServices` — these tests exercise route mounting,
@@ -1634,3 +1637,375 @@ describe("module route overlap can never reach mounting", () => {
     expect(moduleRoutesOverlap(paramRoute, staticRoute)).toBe(true);
   });
 });
+
+/**
+ * Explicit, bounded streaming uploads (ADR 0042).
+ *
+ * The distinction being proven throughout is *when* the platform knows a body is too large, and what
+ * it holds while finding out. In `buffered` mode the answer is "before the handler runs, holding at
+ * most the route's own declared allowance". In `streamed` mode it is "as the handler consumes it,
+ * holding nothing" — and the `413` still wins, even when the handler tried to answer anyway.
+ */
+describe("module route streamed body limits", () => {
+  const oneMebibyte = 1024 * 1024;
+
+  /** A body of `size` bytes delivered in realistic chunks, with no declared `Content-Length` — the
+   * chunked-transfer shape a browser `fetch` of a `ReadableStream` actually produces. */
+  function chunkedBody(size: number, chunkSize = 64 * 1024): ReadableStream<Uint8Array> {
+    let sent = 0;
+    return new ReadableStream<Uint8Array>({
+      pull(controller) {
+        if (sent >= size) {
+          controller.close();
+          return;
+        }
+        const next = Math.min(chunkSize, size - sent);
+        sent += next;
+        controller.enqueue(new Uint8Array(next).fill(97));
+      },
+    });
+  }
+
+  function streamingApp(options: {
+    readonly handler: ModuleRouteHandler;
+    readonly maxBodyBytes: number;
+    readonly evaluator?: AuthorizationEvaluator;
+  }) {
+    return buildModuleApp({
+      ...(options.evaluator ? { evaluator: options.evaluator } : {}),
+      registry: permissionRegistry([{ id: writePermission, baseline: "public" }]),
+      routes: [
+        moduleRoute({
+          bodyMode: "streamed",
+          handler: options.handler,
+          maxBodyBytes: options.maxBodyBytes,
+          method: "POST",
+          moduleId: "calendar",
+          path: "/uploads",
+          permission: writePermission,
+        }),
+      ],
+    });
+  }
+
+  /** Counts what the handler actually received, which is the only honest way to tell "streamed" from
+   * "buffered then handed over". */
+  async function countingHandler(received: { bytes: number }): Promise<ModuleRouteHandler> {
+    return async (request) => {
+      const body = request.body;
+      if (!body) {
+        return Response.json({ bytes: 0 });
+      }
+      const reader = body.getReader();
+      for (;;) {
+        const { done, value } = await reader.read();
+        if (done) {
+          break;
+        }
+        received.bytes += value.byteLength;
+      }
+      return Response.json({ bytes: received.bytes });
+    };
+  }
+
+  it("accepts a body of exactly the declared limit", async () => {
+    const received = { bytes: 0 };
+    const { app } = streamingApp({
+      handler: await countingHandler(received),
+      maxBodyBytes: oneMebibyte,
+    });
+
+    const response = await app.request("/api/v1/modules/calendar/uploads", {
+      body: chunkedBody(oneMebibyte),
+      duplex: "half",
+      headers: { origin: trustedOrigin },
+      method: "POST",
+    } as RequestInit);
+
+    expect(response.status).toBe(200);
+    expect(await response.json()).toEqual({ bytes: oneMebibyte });
+  });
+
+  it("rejects a declared Content-Length over the limit before the handler runs", async () => {
+    const received = { bytes: 0 };
+    const counting = await countingHandler(received);
+    const handler = vi.fn<ModuleRouteHandler>(counting);
+    const { app } = streamingApp({ handler, maxBodyBytes: 1024 });
+
+    const response = await app.request("/api/v1/modules/calendar/uploads", {
+      body: chunkedBody(2048, 16),
+      duplex: "half",
+      headers: { "content-length": String(1025), origin: trustedOrigin },
+      method: "POST",
+    } as RequestInit);
+
+    expect(response.status).toBe(413);
+    expect(await response.json()).toEqual({ code: "REQUEST_BODY_TOO_LARGE" });
+    // The cheap rejection: the declared size alone decided it, so no handler work happened and no
+    // byte of the upload reached module code.
+    expect(handler).not.toHaveBeenCalled();
+    expect(received.bytes).toBe(0);
+  });
+
+  it("terminates a body whose actual size exceeds a smaller declared Content-Length", async () => {
+    // A misleading `Content-Length` buys nothing: the running byte count is what bounds the request,
+    // so a header claiming 8 bytes cannot smuggle a megabyte past the limit.
+    const received = { bytes: 0 };
+    const { app } = streamingApp({
+      handler: await countingHandler(received),
+      maxBodyBytes: 64,
+    });
+
+    const response = await app.request("/api/v1/modules/calendar/uploads", {
+      body: chunkedBody(4096, 32),
+      duplex: "half",
+      headers: { "content-length": "8", origin: trustedOrigin },
+      method: "POST",
+    } as RequestInit);
+
+    expect(response.status).toBe(413);
+    expect(await response.json()).toEqual({ code: "REQUEST_BODY_TOO_LARGE" });
+    // It stopped promptly rather than draining the whole upload first.
+    expect(received.bytes).toBeLessThanOrEqual(96);
+  });
+
+  it("answers 413 even when the handler swallowed the stream error and tried to respond", async () => {
+    // A limit a handler can swallow is not a limit.
+    const handler = vi.fn<ModuleRouteHandler>(async (request) => {
+      try {
+        await request.arrayBuffer();
+      } catch {
+        // Deliberately ignored, exactly as a careless module might.
+      }
+      return Response.json({ ok: "handler won" });
+    });
+    const { app } = streamingApp({ handler, maxBodyBytes: 64 });
+
+    const response = await app.request("/api/v1/modules/calendar/uploads", {
+      body: chunkedBody(4096, 32),
+      duplex: "half",
+      headers: { origin: trustedOrigin },
+      method: "POST",
+    } as RequestInit);
+
+    expect(handler).toHaveBeenCalledTimes(1);
+    expect(response.status).toBe(413);
+    expect(await response.json()).toEqual({ code: "REQUEST_BODY_TOO_LARGE" });
+  });
+
+  it("never buffers the body: the handler sees the first bytes before the last are sent", async () => {
+    let released: (() => void) | undefined;
+    const finished = new Promise<void>((resolve) => {
+      released = resolve;
+    });
+    let firstChunkSeen = false;
+    let secondChunkQueued = false;
+    const body = new ReadableStream<Uint8Array>({
+      async pull(controller) {
+        if (!secondChunkQueued) {
+          secondChunkQueued = true;
+          controller.enqueue(new Uint8Array(16).fill(97));
+          return;
+        }
+        // Only produce the rest once the handler has demonstrably consumed the first chunk. A
+        // buffering platform would deadlock here rather than reach the assertion below.
+        await finished;
+        controller.close();
+      },
+    });
+    const handler = vi.fn<ModuleRouteHandler>(async (request) => {
+      const reader = (request.body as ReadableStream<Uint8Array>).getReader();
+      const first = await reader.read();
+      firstChunkSeen = !first.done;
+      released?.();
+      for (;;) {
+        const next = await reader.read();
+        if (next.done) {
+          break;
+        }
+      }
+      return Response.json({ ok: true });
+    });
+    const { app } = streamingApp({ handler, maxBodyBytes: oneMebibyte });
+
+    const response = await app.request("/api/v1/modules/calendar/uploads", {
+      body,
+      duplex: "half",
+      headers: { origin: trustedOrigin },
+      method: "POST",
+    } as RequestInit);
+
+    expect(firstChunkSeen).toBe(true);
+    expect(response.status).toBe(200);
+  });
+
+  it("releases an aborted upload without taking the platform down", async () => {
+    const aborted = new ReadableStream<Uint8Array>({
+      start(controller) {
+        controller.enqueue(new Uint8Array(16).fill(97));
+        controller.error(new Error("client went away"));
+      },
+    });
+    const handler = vi.fn<ModuleRouteHandler>(async (request) => {
+      await request.arrayBuffer();
+      return Response.json({ ok: true });
+    });
+    const { app } = streamingApp({ handler, maxBodyBytes: oneMebibyte });
+
+    const response = await app.request("/api/v1/modules/calendar/uploads", {
+      body: aborted,
+      duplex: "half",
+      headers: { origin: trustedOrigin },
+      method: "POST",
+    } as RequestInit);
+
+    // An abort is a failed request, never an unhandled rejection or a 413: nothing exceeded a limit.
+    expect(response.status).toBe(500);
+    expect(await response.json()).toEqual({ code: "MODULE_HANDLER_FAILED" });
+  });
+
+  it("releases a body the handler never read", async () => {
+    let cancelled = false;
+    const body = new ReadableStream<Uint8Array>({
+      cancel() {
+        cancelled = true;
+      },
+      pull(controller) {
+        controller.enqueue(new Uint8Array(16).fill(97));
+      },
+    });
+    const { app } = streamingApp({
+      handler: async () => Response.json({ ok: true }),
+      maxBodyBytes: oneMebibyte,
+    });
+
+    const response = await app.request("/api/v1/modules/calendar/uploads", {
+      body,
+      duplex: "half",
+      headers: { origin: trustedOrigin },
+      method: "POST",
+    } as RequestInit);
+
+    expect(response.status).toBe(200);
+    expect(cancelled).toBe(true);
+  });
+
+  it("refuses a declared oversize before authorization, and never streams for a denied caller", async () => {
+    const evaluator: AuthorizationEvaluator = {
+      authorize: vi.fn().mockResolvedValue({ allowed: false }),
+    };
+    const handler = vi.fn<ModuleRouteHandler>(async () => Response.json({ ok: true }));
+    const { app } = buildModuleApp({
+      evaluator,
+      registry: permissionRegistry([{ id: writePermission, baseline: "restricted" }]),
+      routes: [
+        moduleRoute({
+          bodyMode: "streamed",
+          handler,
+          maxBodyBytes: 64,
+          method: "POST",
+          moduleId: "calendar",
+          path: "/uploads",
+          permission: writePermission,
+        }),
+      ],
+    });
+
+    const declaredOversize = await app.request("/api/v1/modules/calendar/uploads", {
+      body: "a".repeat(65),
+      headers: { "content-length": "65", origin: trustedOrigin },
+      method: "POST",
+    });
+    expect(declaredOversize.status).toBe(413);
+    expect(evaluator.authorize).not.toHaveBeenCalled();
+
+    // A within-limit body from a denied caller is refused by authorization, and the handler — the
+    // only thing that ever reads a byte in streamed mode — never runs.
+    const response = await app.request("/api/v1/modules/calendar/uploads", {
+      body: chunkedBody(32, 8),
+      duplex: "half",
+      headers: { origin: trustedOrigin },
+      method: "POST",
+    } as RequestInit);
+    expect(response.status).toBe(403);
+    expect(handler).not.toHaveBeenCalled();
+  });
+
+  it("still rejects an untrusted Origin before any body handling", async () => {
+    const handler = vi.fn<ModuleRouteHandler>(async () => Response.json({ ok: true }));
+    const { app } = streamingApp({ handler, maxBodyBytes: oneMebibyte });
+
+    const response = await app.request("/api/v1/modules/calendar/uploads", {
+      body: chunkedBody(4096),
+      duplex: "half",
+      headers: { origin: untrustedOrigin },
+      method: "POST",
+    } as RequestInit);
+
+    expect(response.status).toBe(403);
+    expect(await response.json()).toEqual({ code: "UNTRUSTED_ORIGIN" });
+    expect(handler).not.toHaveBeenCalled();
+  });
+
+  it("keeps every rejection sanitized, naming no limit, size, or body content", async () => {
+    const { app } = streamingApp({
+      handler: async () => Response.json({ ok: true }),
+      maxBodyBytes: 64,
+    });
+
+    const response = await app.request("/api/v1/modules/calendar/uploads", {
+      body: "secret-payload-".repeat(64),
+      headers: { "content-length": String(15 * 64), origin: trustedOrigin },
+      method: "POST",
+    });
+    const body = await response.text();
+
+    expect(response.status).toBe(413);
+    expect(body).toBe('{"code":"REQUEST_BODY_TOO_LARGE"}');
+    expect(body).not.toContain("secret-payload");
+    expect(body).not.toContain("64");
+    expect(response.headers.get("cache-control")).toBe("no-store");
+  });
+
+  it("still materializes a buffered body before the handler runs", async () => {
+    // The pre-existing promise, unchanged: a buffered handler may call `request.json()` and know the
+    // body is already there and already within its declared allowance.
+    const handler = vi.fn<ModuleRouteHandler>(async (request) => {
+      const text = await request.text();
+      return Response.json({ length: text.length });
+    });
+    const { app } = buildModuleApp({
+      registry: permissionRegistry([{ id: writePermission, baseline: "public" }]),
+      routes: [
+        moduleRoute({
+          bodyMode: "buffered",
+          handler,
+          maxBodyBytes: 128,
+          method: "POST",
+          moduleId: "calendar",
+          path: "/events",
+          permission: writePermission,
+        }),
+      ],
+    });
+
+    const withinLimit = await app.request("/api/v1/modules/calendar/events", {
+      body: chunkedBody(128, 16),
+      duplex: "half",
+      headers: { origin: trustedOrigin },
+      method: "POST",
+    } as RequestInit);
+    expect(withinLimit.status).toBe(200);
+    expect(await withinLimit.json()).toEqual({ length: 128 });
+
+    const overLimit = await app.request("/api/v1/modules/calendar/events", {
+      body: chunkedBody(129, 16),
+      duplex: "half",
+      headers: { origin: trustedOrigin },
+      method: "POST",
+    } as RequestInit);
+    expect(overLimit.status).toBe(413);
+    // A buffered route's handler never sees an over-limit request at all.
+    expect(handler).toHaveBeenCalledTimes(1);
+  });
+});
diff --git a/core/src/modules/runtime.ts b/core/src/modules/runtime.ts
index 93908ba..810caea 100644
--- a/core/src/modules/runtime.ts
+++ b/core/src/modules/runtime.ts
@@ -60,6 +60,7 @@ export type ModuleRuntimeIssueCode =
   | "MODULE_ROLLBACK_TIMEOUT"
   | "MODULE_ROUTE_DEFINITION_INVALID"
   | "MODULE_ROUTE_DUPLICATE"
+  | "MODULE_ROUTE_BODY_MODE_INVALID"
   | "MODULE_ROUTE_MAX_BODY_BYTES_INVALID"
   | "MODULE_ROUTE_METHOD_INVALID"
   | "MODULE_ROUTE_OVERLAP"
@@ -467,6 +468,7 @@ class StagedModuleHttpRoutes {
         shapes.add(shapeKey);
         local.push(
           Object.freeze({
+            bodyMode: parsed.data.bodyMode,
             handler: parsed.data.handler,
             maxBodyBytes: parsed.data.maxBodyBytes,
             method: parsed.data.method,
diff --git a/core/tests/module-runtime.test.ts b/core/tests/module-runtime.test.ts
index c731c99..00a3059 100644
--- a/core/tests/module-runtime.test.ts
+++ b/core/tests/module-runtime.test.ts
@@ -861,6 +861,7 @@ describe("module HTTP routes", () => {
     expect(runtime.routes).toHaveLength(3);
     for (const route of runtime.routes) {
       expect(Object.keys(route).sort()).toEqual([
+        "bodyMode",
         "handler",
         "maxBodyBytes",
         "method",
diff --git a/docs/architecture/decisions/0042-bounded-streaming-request-bodies.md b/docs/architecture/decisions/0042-bounded-streaming-request-bodies.md
new file mode 100644
index 0000000..95f218a
--- /dev/null
+++ b/docs/architecture/decisions/0042-bounded-streaming-request-bodies.md
@@ -0,0 +1,160 @@
+# 0042: Explicit, bounded streaming request bodies
+
+- Status: Accepted
+- Date: 2026-08-27
+- Supersedes: none
+- Related: [ADR 0015](0015-static-module-http-routing-and-runtime-lifecycle.md),
+  [ADR 0017](0017-public-request-perimeter-hardening.md),
+  [ADR 0030](0030-host-provided-module-object-storage.md),
+  [ADR 0031](0031-direct-object-delivery.md)
+
+## Context
+
+ADR 0017 gave every public route an enforced request-body ceiling and capped a module route at
+1 MiB, with an explicit note that "large media transfer belongs to a future dedicated storage
+design, never to widening this ceiling."
+
+The storage design arrived — ADR 0030 gave modules a scoped object store, ADR 0031 took Ekklesia out
+of the *read* path with signed delivery URLs — and it did not solve the *write* path. ADR 0031
+deliberately declined to offer signed write URLs, so the only way bytes reach a module's bucket is
+through that module's own HTTP route. That route is capped at 1 MiB, and an ordinary photograph is
+not 1 MiB. A church uploading a slide for a lobby screen cannot, today, get the file in.
+
+Two properties of the existing implementation also need naming, because they are what the change has
+to preserve and what it has to fix:
+
+- The pinned body-limit middleware **fully buffers** any body with no declared `Content-Length`
+  before deciding. At 1 MiB that is a bounded, acceptable cost. At image sizes it would mean the
+  platform holding every concurrent upload in memory.
+- With a declared `Content-Length` within the limit it *counts nothing at all*, trusting the header.
+  Node's HTTP framing makes that safe today, but it is trust the platform does not need to extend.
+
+## Decision
+
+Extend the existing route contract. There is no second HTTP system, no upload endpoint, no signed
+write URL, and no new middleware stack — one route declaration, one limiter, one `413`.
+
+### A route declares how its body reaches it
+
+`ModuleRouteDefinitionInput` gains one optional field:
+
+```ts
+http.route({
+  method: "POST",
+  path: "/uploads",
+  permission: "signage.slides.write",
+  maxBodyBytes: 33_554_432,
+  bodyMode: "streamed",
+  handler,
+});
+```
+
+- **`buffered`** (the default, and what every route written before this meant) — the platform reads
+  and counts the whole body **before** the handler runs, so the handler is promised a fully
+  available, bounded body and an oversized request is rejected before any authorization or handler
+  work happens. Ceiling: 1 MiB, unchanged.
+- **`streamed`** — the platform counts bytes **as the handler consumes them** and never materializes
+  the body. Ceiling: 32 MiB.
+
+The mode is **explicit rather than inferred from the size**. Inferring it — "over 1 MiB means
+streamed" — would mean an author who raised a limit silently changed how their own handler receives
+its body, and when a `413` can arrive relative to their own code. That is exactly the class of
+invisible change this repository refuses.
+
+Omitting the field means `buffered`, so no existing route changed behaviour, and the canonical parsed
+form always carries a mode so nothing downstream re-applies the default or disagrees about it.
+
+### The ceilings, and why 32 MiB
+
+`MODULE_ROUTE_MAX_BODY_BYTES_CEILING` stays at 1 MiB for buffered bodies: a body the platform
+materializes is a body the platform is holding, and 1 MiB is the most a JSON request has any business
+being.
+
+`MODULE_ROUTE_STREAMED_MAX_BODY_BYTES_CEILING` is 32 MiB, sized to hold one 25 MiB image plus bounded
+overhead — a multipart envelope, its boundaries and part headers, and room for a client that pads. It
+is also `MODULE_ROUTE_ABSOLUTE_MAX_BODY_BYTES`: **no route, in any mode, may declare or accept a
+larger single request body, and no unbounded option exists anywhere in the contract.** A route
+declaring more than its mode's ceiling fails registration, exactly as an over-ceiling value always
+has.
+
+The unit is deliberately **one file per request**. A UI offering twenty images issues twenty
+individually bounded requests, each of which the platform can reject cheaply and each of which fails
+alone; a 500 MiB aggregate request would make one bad byte waste everything already sent, and nothing
+in this contract can express one.
+
+### Enforcement, in one limiter
+
+The platform's own limiter replaces the buffering dependency. It is the same code for both modes and
+differs only in *when* it counts:
+
+1. A declared `Content-Length` above the limit is refused synchronously — before authorization,
+   before the handler, before a single body byte is read. That is the cheap rejection an ordinary
+   too-large upload takes. A malformed or contradictory header is treated as *absent* rather than as
+   a rejection, because the byte counting bounds the request either way and refusing could only turn
+   a legitimate request away.
+2. `buffered`: bytes are counted as they arrive and the request is rejected the moment the running
+   total passes the limit — so a lying or absent `Content-Length` is bounded by what actually
+   arrived rather than by what was claimed, which the previous implementation did not do. At most
+   the route's own declared allowance is ever held.
+3. `streamed`: the body is wrapped in a counting transform and handed to the handler. The moment the
+   total passes the limit the stream errors, the source is cancelled, and the response is replaced
+   with the same sanitized `413` — **even if the handler caught the error and answered anyway**. A
+   limit a handler can swallow is not a limit.
+
+A body no handler read is cancelled after the request, so an abandoned upload releases its socket
+rather than draining. An aborted upload surfaces as an ordinary failed request, never a `413`:
+nothing exceeded a limit.
+
+Ordering is unchanged and remains deliberate: trusted-origin check, then the body contract, then
+permission evaluation, then the handler. In `streamed` mode no body byte is read until the handler
+reads it and the handler runs only after authorization succeeds, so an unauthorized caller can never
+push an upload through the platform at all — strictly better than the buffered path.
+
+Timeouts stay where they were: the server's own `headersTimeout`/`requestTimeout`. A slow upload is a
+slow *request*, and the platform already has one answer for that rather than a second per-route one.
+
+### What a module author must know
+
+In `streamed` mode a `413` can arrive **after** the handler has started. A handler that persists as
+it reads must be prepared for a partially consumed upload — write to a temporary key and commit only
+after the read completes. The platform cannot do that for the module, because only the module knows
+what a partial write means to its own data.
+
+## Consequences
+
+- An ordinary image upload works, through the route contract a module already had, with the platform
+  holding none of it.
+- The buffered path now counts bytes it previously trusted a header for, closing a gap rather than
+  opening one.
+- Every existing route and every existing test is unchanged: the default is the old behaviour, and
+  the `413` contract, ordering, and sanitization are identical.
+- `apps/api` owns ~60 lines of stream plumbing it previously delegated. That is the price of a
+  limiter that neither buffers a large body nor can be swallowed by a handler, and it is enforced by
+  tests rather than by reading the dependency's source.
+- Media larger than 32 MiB — a video — still has no path in. That is deliberate and named below.
+
+## Alternatives
+
+- **Raise the single ceiling to 32 MiB.** Rejected: every existing route would silently gain the
+  ability to have 32 MiB buffered in memory on its behalf, and `await request.json()` in a module
+  handler would stop being a bounded operation.
+- **Infer streaming from `maxBodyBytes`.** Rejected: it makes a size change silently change delivery
+  semantics and error timing for the author's own code.
+- **A separate upload endpoint or second HTTP system.** Rejected: a second route table, a second
+  authorization path, a second CORS and origin policy, and a second failure vocabulary, to solve
+  something the existing route contract can express with one field.
+- **Signed write URLs to object storage.** Deliberately still deferred (ADR 0031). A signed write URL
+  is a bearer capability to *create* an object, which needs quota, content-type, and lifecycle
+  answers this pass does not have — and a module that wants to validate, transform, or authorize per
+  byte cannot use one anyway.
+- **Let the handler enforce its own limit.** Rejected: a limit enforced by the party being protected
+  against is not a limit, and every module would reimplement it slightly differently.
+- **Trust `Content-Length` in streamed mode.** Rejected: the running byte count costs nothing and
+  removes the need to reason about framing at all.
+
+## Deferred
+
+Signed write URLs, resumable or chunked multi-request uploads, per-module or per-installation upload
+quotas, content-type or magic-byte validation, virus scanning, image transformation, progress
+reporting, and any body larger than the absolute ceiling — a video pipeline is its own design, not a
+larger number here.
diff --git a/docs/architecture/decisions/README.md b/docs/architecture/decisions/README.md
index 625c34a..e87d890 100644
--- a/docs/architecture/decisions/README.md
+++ b/docs/architecture/decisions/README.md
@@ -50,3 +50,4 @@ ADRs capture durable choices that affect more than one package or phase.
 - [0039: Shared design tokens and foundational elements](0039-shared-design-tokens-and-elements.md) — Accepted
 - [0040: Module stylesheets, and every browser artifact gets an isolated root](0040-module-stylesheets-and-artifact-isolation.md) — Accepted
 - [0041: One module may contribute a browser renderer to another module's capability](0041-module-browser-contributions.md) — Accepted
+- [0042: Explicit, bounded streaming request bodies](0042-bounded-streaming-request-bodies.md) — Accepted
diff --git a/docs/development/api.md b/docs/development/api.md
index 29ade94..76c079d 100644
--- a/docs/development/api.md
+++ b/docs/development/api.md
@@ -408,16 +408,28 @@ protection across restarts or replicas.
 
 ## Request body limits
 
-Every public body-consuming route has an explicit, platform-enforced byte ceiling
-(`apps/api/src/body-limits.ts`, built on Hono's pinned `hono/body-limit` middleware — verified
-directly against its source to reject both an oversized declared `Content-Length` and an oversized
-declared-length-free streamed body without ever buffering the whole payload first):
+Every public body-consuming route has an explicit, platform-enforced byte ceiling, enforced by the
+platform's own limiter (`apps/api/src/body-limits.ts`):
 
 | Surface | Limit |
 | --- | --- |
 | `/api/auth/*` (every Better Auth route) | 8 KiB |
 | `POST /api/v1/grants`, `POST /api/v1/grants/:grantId/revoke` | 16 KiB |
-| A module route (`http.route(...)`'s own `maxBodyBytes`) | Up to 1 MiB, the platform ceiling (`MODULE_ROUTE_MAX_BODY_BYTES_CEILING`, `@ekklesia/contracts`) |
+| A module route declaring `bodyMode: "buffered"` (the default) | Up to 1 MiB (`MODULE_ROUTE_MAX_BODY_BYTES_CEILING`, `@ekklesia/contracts`) |
+| A module route declaring `bodyMode: "streamed"` | Up to 32 MiB (`MODULE_ROUTE_STREAMED_MAX_BODY_BYTES_CEILING`), which is also `MODULE_ROUTE_ABSOLUTE_MAX_BODY_BYTES` |
+
+A declared `Content-Length` over the limit is refused synchronously, before authorization and before
+a single body byte is read. Beyond that the two module modes differ only in *when* the platform
+counts ([ADR 0042](../architecture/decisions/0042-bounded-streaming-request-bodies.md)):
+
+- **`buffered`** materializes the body before the handler runs, counting as it arrives, so a lying or
+  absent `Content-Length` is bounded by what actually arrived. The handler is promised a fully
+  available body within its declared allowance, and the platform holds at most that allowance.
+- **`streamed`** never materializes the body: it is counted as the handler consumes it, and the
+  moment the total passes the limit the stream errors, the source is cancelled, and the response
+  becomes the same `413` — even if the handler caught the error and answered anyway. A `413` can
+  therefore arrive *after* a streamed handler has started, which is the one consequence a module
+  author must design for.
 
 An oversized request always receives the identical stable, sanitized contract —
 `413 {"code":"REQUEST_BODY_TOO_LARGE"}` with `Cache-Control: no-store` — and never invokes Better
@@ -425,10 +437,20 @@ Auth's business logic, a Core mutation, permission evaluation (where avoidable),
 or module database behavior. For a state-changing route the body limit is enforced after
 `requireTrustedOrigin` but before permission evaluation, so a rejected cross-origin mutation's body
 is never read for size at all, while an oversized same-origin request still fails before any
-authorization work runs. See [Module HTTP routes](#module-http-routes) for the module-route body
-contract itself, and [Module development](../module-development/README.md#http-routes) for the
-module-authoring side of it. Large media transfer is explicitly out of scope for ordinary module
-HTTP bodies — that belongs to a future dedicated storage design, never to widening this ceiling.
+authorization work runs. In `streamed` mode no body byte is read until the handler reads it, and the
+handler runs only after authorization succeeds, so an unauthorized caller can never push an upload
+through the platform at all.
+
+Body reading is bounded in time by the server's own `headersTimeout`/`requestTimeout` below, not by a
+second per-route timeout. A body no handler read is cancelled after the request, so an abandoned
+upload releases its socket rather than draining; an aborted upload surfaces as an ordinary failed
+request rather than a `413`, because nothing exceeded a limit.
+
+See [Module HTTP routes](#module-http-routes) for the module-route body contract itself, and
+[Module development](../module-development/README.md#http-routes) for the module-authoring side of
+it. The absolute ceiling is one image-sized file per request: aggregate uploads and anything larger
+than 32 MiB remain out of scope, and signed write URLs are still deliberately not offered
+([ADR 0031](../architecture/decisions/0031-direct-object-delivery.md)).
 
 ## Node request and header timeouts
 
diff --git a/docs/module-development/README.md b/docs/module-development/README.md
index a134bd9..cc637cc 100644
--- a/docs/module-development/README.md
+++ b/docs/module-development/README.md
@@ -1005,8 +1005,8 @@ export default defineModuleRuntime({
 });
 ```
 
-A route definition has exactly five fields — `method`, `path`, `permission`, `maxBodyBytes`,
-`handler` — and nothing else; an unknown field (a baseline, a mount prefix, CORS/origin policy,
+A route definition has exactly five required fields — `method`, `path`, `permission`,
+`maxBodyBytes`, `handler` — plus one optional `bodyMode`, and nothing else; an unknown field (a baseline, a mount prefix, CORS/origin policy,
 middleware, audit metadata, authentication behavior, or another module's namespace) fails
 registration outright rather than being ignored. `method` is one of `GET`, `POST`, `PUT`, `PATCH`,
 `DELETE`, always uppercase; there is no `OPTIONS` (the platform owns CORS preflight) and no
@@ -1071,15 +1071,61 @@ ones. The platform continues to own authentication, authorization, `Origin`, COR
 cache behavior, and uncaught-handler sanitization, and permission enforcement always completes
 before your handler runs — an unauthorized caller can never reach your validation at all.
 
+### Request bodies: `maxBodyBytes` and `bodyMode`
+
 `maxBodyBytes` is a conscious, required request-body contract, not an optional or defaulted field:
 `0` means the route accepts no body at all, and a non-empty declared (`Content-Length`) or streamed
 body is rejected before the handler ever runs; any other value is the exact maximum number of bytes
-accepted. It must be a non-negative integer no greater than the platform ceiling,
-`MODULE_ROUTE_MAX_BODY_BYTES_CEILING` (`@ekklesia/contracts`, currently 1 MiB) — a negative,
-non-integer, non-finite, or over-ceiling value fails registration with
-`MODULE_ROUTE_MAX_BODY_BYTES_INVALID`. The platform enforces this limit itself, ahead of permission
-evaluation and the handler, using the identical sanitized `413 {"code":"REQUEST_BODY_TOO_LARGE"}`
-contract every other body-consuming route in the platform uses — see
+accepted. A negative, non-integer, non-finite, or over-ceiling value fails registration with
+`MODULE_ROUTE_MAX_BODY_BYTES_INVALID`.
+
+`bodyMode` chooses how that body reaches you, and therefore which ceiling applies
+([ADR 0042](../architecture/decisions/0042-bounded-streaming-request-bodies.md)):
+
+| `bodyMode` | Ceiling | What the platform does |
+| --- | --- | --- |
+| `"buffered"` (default) | 1 MiB | Reads and counts the whole body **before** your handler runs |
+| `"streamed"` | 32 MiB | Counts bytes **as you consume them**, and never materializes the body |
+
+```ts
+http.route({
+  method: "POST",
+  path: "/slides",
+  permission: "signage.slides.write",
+  maxBodyBytes: 33_554_432,
+  bodyMode: "streamed",
+  async handler(request, context) { /* read request.body as a stream */ },
+});
+```
+
+Omitting `bodyMode` means `buffered`, which is what every route written before this existed meant.
+
+**Memory.** In `buffered` mode the platform holds at most your declared allowance, which is why that
+ceiling is small and why `await request.json()` is safe there. In `streamed` mode the platform holds
+nothing: read `request.body` as a stream. Calling `request.arrayBuffer()` on a streamed route works
+but throws away the entire point — you have just buffered 32 MiB yourself.
+
+**Streaming.** A declared `Content-Length` over your limit is refused synchronously, before
+authorization and before a byte is read. Otherwise the platform counts what actually arrives, so a
+misleading or absent `Content-Length` bounds nothing.
+
+**A `413` can arrive after your handler starts.** This is the one consequence of `streamed` mode you
+must design for. When the running total passes your limit the stream errors, the source is cancelled,
+and the platform replaces your response with the sanitized `413` — even if you caught the error and
+answered anyway. If you persist as you read, write to a temporary key and commit only once the read
+completes; the platform cannot do that for you, because only your module knows what a partial write
+means to its own data.
+
+**Timeouts.** Body reading is bounded by the server's own header and request timeouts, not by a
+per-route setting. A slow upload is a slow request, and the platform has one answer for that.
+
+**One file per request.** 32 MiB is the platform's absolute ceiling in every mode — there is no
+unbounded option anywhere in the contract. A UI uploading twenty images issues twenty individually
+bounded requests; nothing here can express a 500 MiB aggregate upload, deliberately, because one bad
+byte in one would waste everything already sent.
+
+Every rejection uses the identical sanitized `413 {"code":"REQUEST_BODY_TOO_LARGE"}` contract every
+other body-consuming route in the platform uses — see
 [API](../development/api.md#request-body-limits).
 
 `path` is local to the module, never the path a caller actually sends. The platform alone owns the
diff --git a/packages/contracts/src/module-http.ts b/packages/contracts/src/module-http.ts
index 8354be1..c1f9769 100644
--- a/packages/contracts/src/module-http.ts
+++ b/packages/contracts/src/module-http.ts
@@ -25,21 +25,72 @@ export function isModuleHttpMethod(value: unknown): value is ModuleHttpMethod {
 }
 
 /**
- * The platform-owned hard ceiling on any single module route's declared request-body allowance, in
- * bytes. No module route may declare a `maxBodyBytes` above this value — validated at registration
- * (`safeParseModuleRouteDefinition`, below), not merely documented. This is a security contract,
- * not a manifest capability: it does not gate on `manifestVersion` and is enforced identically for
- * every installed module regardless of its declared compatibility range. Large media transfer
- * belongs to a future dedicated storage design, never to widening this ceiling.
+ * How a route's request body reaches its handler, and therefore which ceiling applies to it
+ * (ADR 0042).
+ *
+ * - `buffered` (the default, and everything that existed before): the platform reads and counts the
+ *   whole body **before** the handler runs, so the handler is promised a fully available, bounded
+ *   body and an oversized request is rejected before any authorization or handler work happens.
+ *   Bounded by {@link MODULE_ROUTE_MAX_BODY_BYTES_CEILING}, deliberately small.
+ * - `streamed`: the platform counts bytes **as the handler consumes them** and never materializes
+ *   the body. That is what makes an ordinary image upload possible without the platform holding it
+ *   in memory, and it is the whole reason the larger ceiling exists.
+ *
+ * Selecting the mode is an explicit, conscious decision rather than something inferred from the size
+ * a route asked for. Inferring it would mean an author who raised a limit silently changed how their
+ * own handler receives its body — and when a `413` can arrive relative to their own code.
+ */
+export const MODULE_HTTP_BODY_MODES = ["buffered", "streamed"] as const;
+
+export type ModuleRouteBodyMode = (typeof MODULE_HTTP_BODY_MODES)[number];
+
+const moduleRouteBodyModes: ReadonlySet<string> = new Set(MODULE_HTTP_BODY_MODES);
+
+export function isModuleRouteBodyMode(value: unknown): value is ModuleRouteBodyMode {
+  return typeof value === "string" && moduleRouteBodyModes.has(value);
+}
+
+/**
+ * The platform-owned hard ceiling on a **buffered** module route's declared request-body allowance,
+ * in bytes. No buffered route may declare a `maxBodyBytes` above this value — validated at
+ * registration (`safeParseModuleRouteDefinition`, below), not merely documented. This is a security
+ * contract, not a manifest capability: it does not gate on `manifestVersion` and is enforced
+ * identically for every installed module regardless of its declared compatibility range.
+ *
+ * It stays exactly where it was. A body the platform materializes before a handler runs is a body
+ * the platform is holding in memory, and 1 MiB is the most a JSON request has any business being.
  */
 export const MODULE_ROUTE_MAX_BODY_BYTES_CEILING = 1_048_576;
 
+/**
+ * The platform-owned hard ceiling on a **streamed** module route's declared allowance, in bytes,
+ * and the platform's absolute request-body ceiling: nothing in Ekklesia may declare or accept a
+ * larger single request body, and there is no unbounded option anywhere in the contract.
+ *
+ * 32 MiB, chosen to hold one 25 MiB image plus bounded request overhead — a multipart envelope, its
+ * boundaries and part headers, and a modest allowance for a client that pads. The unit is
+ * deliberately *one file*: a UI offering twenty images issues twenty individually bounded requests,
+ * each of which the platform can reject cheaply, rather than one 500 MiB request whose failure
+ * wastes everything already sent. Nothing in this contract can express an aggregate upload.
+ */
+export const MODULE_ROUTE_STREAMED_MAX_BODY_BYTES_CEILING = 33_554_432;
+
+/** The largest body any module route may declare, in any mode. */
+export const MODULE_ROUTE_ABSOLUTE_MAX_BODY_BYTES = MODULE_ROUTE_STREAMED_MAX_BODY_BYTES_CEILING;
+
+/** The ceiling that applies to one delivery mode. */
+export function moduleRouteBodyCeiling(mode: ModuleRouteBodyMode): number {
+  return mode === "streamed"
+    ? MODULE_ROUTE_STREAMED_MAX_BODY_BYTES_CEILING
+    : MODULE_ROUTE_MAX_BODY_BYTES_CEILING;
+}
+
 const moduleRouteMaxBodyBytesSchema = z
   .number()
   .int()
   .finite()
   .min(0)
-  .max(MODULE_ROUTE_MAX_BODY_BYTES_CEILING);
+  .max(MODULE_ROUTE_ABSOLUTE_MAX_BODY_BYTES);
 
 const MODULE_ROUTE_PATH_MAX_LENGTH = 256;
 const staticSegmentPattern = /^[a-z0-9]+(?:-[a-z0-9]+)*$/u;
@@ -265,6 +316,12 @@ export interface ModuleRouteDefinitionInput {
   readonly path: string;
   readonly permission: string;
   readonly maxBodyBytes: number;
+  /**
+   * How the body reaches the handler, and therefore which ceiling `maxBodyBytes` is checked
+   * against (ADR 0042). Omitted means `buffered`, which is what every route written before this
+   * existed meant, so adding this field changed no existing route's behaviour.
+   */
+  readonly bodyMode?: ModuleRouteBodyMode;
   readonly handler: ModuleRouteHandler;
 }
 
@@ -275,6 +332,9 @@ export interface ModuleRouteDefinition {
   readonly path: ModuleRoutePath;
   readonly permission: PermissionId;
   readonly maxBodyBytes: number;
+  /** Always present in the canonical form, defaulted to `buffered`, so no consumer downstream has
+   * to re-apply the default and none of them can disagree about it. */
+  readonly bodyMode: ModuleRouteBodyMode;
   readonly handler: ModuleRouteHandler;
 }
 
@@ -294,10 +354,20 @@ export interface RegisteredModuleHttpRoute {
   readonly path: ModuleRoutePath;
   readonly permission: PermissionId;
   readonly maxBodyBytes: number;
+  readonly bodyMode: ModuleRouteBodyMode;
   readonly handler: ModuleRouteHandler;
 }
 
 const moduleRouteDefinitionKeys = new Set([
+  "method",
+  "path",
+  "permission",
+  "maxBodyBytes",
+  "bodyMode",
+  "handler",
+]);
+
+const requiredModuleRouteDefinitionKeys = new Set([
   "method",
   "path",
   "permission",
@@ -314,15 +384,18 @@ function hasModuleRouteDefinitionShape(value: unknown): value is {
   path: unknown;
   permission: unknown;
   maxBodyBytes: unknown;
+  bodyMode: unknown;
   handler: unknown;
 } {
   if (!isRecord(value)) {
     return false;
   }
   const keys = Object.keys(value);
+  // Every required field present, `bodyMode` optional, and nothing else at all: a route definition
+  // still cannot carry a baseline, a mount prefix, middleware, or another module's namespace.
   return (
-    keys.length === moduleRouteDefinitionKeys.size &&
     keys.every((key) => moduleRouteDefinitionKeys.has(key)) &&
+    [...requiredModuleRouteDefinitionKeys].every((key) => keys.includes(key)) &&
     typeof value.handler === "function"
   );
 }
@@ -332,6 +405,7 @@ export type ModuleRouteDefinitionIssueCode =
   | "MODULE_ROUTE_METHOD_INVALID"
   | "MODULE_ROUTE_PATH_INVALID"
   | "MODULE_ROUTE_PERMISSION_INVALID"
+  | "MODULE_ROUTE_BODY_MODE_INVALID"
   | "MODULE_ROUTE_MAX_BODY_BYTES_INVALID";
 
 export type ModuleRouteDefinitionParseResult =
@@ -360,13 +434,23 @@ export function safeParseModuleRouteDefinition(value: unknown): ModuleRouteDefin
   if (!parsedPermission.success) {
     return { success: false, code: "MODULE_ROUTE_PERMISSION_INVALID" };
   }
+  if (value.bodyMode !== undefined && !isModuleRouteBodyMode(value.bodyMode)) {
+    return { success: false, code: "MODULE_ROUTE_BODY_MODE_INVALID" };
+  }
+  const bodyMode: ModuleRouteBodyMode = isModuleRouteBodyMode(value.bodyMode)
+    ? value.bodyMode
+    : "buffered";
   const parsedMaxBodyBytes = moduleRouteMaxBodyBytesSchema.safeParse(value.maxBodyBytes);
-  if (!parsedMaxBodyBytes.success) {
+  // The ceiling is chosen by the declared mode, so a route asking for more than a buffered body may
+  // hold has to say `streamed` — and thereby accept that its handler consumes a stream and that a
+  // `413` can arrive after its own code has started running.
+  if (!parsedMaxBodyBytes.success || parsedMaxBodyBytes.data > moduleRouteBodyCeiling(bodyMode)) {
     return { success: false, code: "MODULE_ROUTE_MAX_BODY_BYTES_INVALID" };
   }
   return {
     success: true,
     data: Object.freeze({
+      bodyMode,
       method: value.method,
       path: parsedPath.data,
       permission: parsedPermission.data,
diff --git a/packages/contracts/tests/module-http.test.ts b/packages/contracts/tests/module-http.test.ts
index 4f2d3c2..533383b 100644
--- a/packages/contracts/tests/module-http.test.ts
+++ b/packages/contracts/tests/module-http.test.ts
@@ -2,7 +2,10 @@ import { describe, expect, it } from "vitest";
 import {
   isModuleHttpMethod,
   MODULE_HTTP_METHODS,
+  MODULE_ROUTE_ABSOLUTE_MAX_BODY_BYTES,
   MODULE_ROUTE_MAX_BODY_BYTES_CEILING,
+  MODULE_ROUTE_STREAMED_MAX_BODY_BYTES_CEILING,
+  moduleRouteBodyCeiling,
   type ModuleRouteDefinitionInput,
   moduleRoutePathSchema,
   moduleRouteShapeKey,
@@ -153,6 +156,7 @@ describe("safeParseModuleRouteDefinition", () => {
     expect(result.success).toBe(true);
     if (result.success) {
       expect(result.data).toEqual({
+        bodyMode: "buffered",
         method: "GET",
         path: "/events/:eventId",
         permission: "calendar.events.read",
@@ -258,6 +262,81 @@ describe("safeParseModuleRouteDefinition", () => {
     });
   });
 
+  it("defaults an omitted bodyMode to buffered, so an existing route means what it always meant", () => {
+    const parsed = safeParseModuleRouteDefinition(validDefinition());
+
+    expect(parsed.success && parsed.data.bodyMode).toBe("buffered");
+  });
+
+  it("accepts either declared body mode and carries it through", () => {
+    for (const bodyMode of ["buffered", "streamed"] as const) {
+      const parsed = safeParseModuleRouteDefinition({ ...validDefinition(), bodyMode });
+
+      expect(parsed.success && parsed.data.bodyMode).toBe(bodyMode);
+    }
+  });
+
+  it("rejects a body mode outside the closed set", () => {
+    for (const bodyMode of ["stream", "chunked", "", 1, null]) {
+      expect(safeParseModuleRouteDefinition({ ...validDefinition(), bodyMode })).toEqual({
+        success: false,
+        code: "MODULE_ROUTE_BODY_MODE_INVALID",
+      });
+    }
+  });
+
+  it("checks maxBodyBytes against the ceiling the declared mode selects", () => {
+    // A route asking for more than a buffered body may hold must say `streamed` — and thereby accept
+    // that its handler consumes a stream (ADR 0042).
+    expect(
+      safeParseModuleRouteDefinition(
+        validDefinition({ maxBodyBytes: MODULE_ROUTE_MAX_BODY_BYTES_CEILING + 1 }),
+      ),
+    ).toEqual({ success: false, code: "MODULE_ROUTE_MAX_BODY_BYTES_INVALID" });
+    expect(
+      safeParseModuleRouteDefinition({
+        ...validDefinition({ maxBodyBytes: MODULE_ROUTE_MAX_BODY_BYTES_CEILING + 1 }),
+        bodyMode: "streamed",
+      }).success,
+    ).toBe(true);
+  });
+
+  it("holds one 25 MiB image plus bounded overhead, and refuses one byte more", () => {
+    const image = 25 * 1024 * 1024;
+
+    expect(MODULE_ROUTE_STREAMED_MAX_BODY_BYTES_CEILING).toBeGreaterThan(image);
+    expect(
+      safeParseModuleRouteDefinition({
+        ...validDefinition({ maxBodyBytes: MODULE_ROUTE_STREAMED_MAX_BODY_BYTES_CEILING }),
+        bodyMode: "streamed",
+      }).success,
+    ).toBe(true);
+    expect(
+      safeParseModuleRouteDefinition({
+        ...validDefinition({ maxBodyBytes: MODULE_ROUTE_STREAMED_MAX_BODY_BYTES_CEILING + 1 }),
+        bodyMode: "streamed",
+      }),
+    ).toEqual({ success: false, code: "MODULE_ROUTE_MAX_BODY_BYTES_INVALID" });
+  });
+
+  it("has one absolute ceiling and no unbounded option in any mode", () => {
+    expect(MODULE_ROUTE_ABSOLUTE_MAX_BODY_BYTES).toBe(MODULE_ROUTE_STREAMED_MAX_BODY_BYTES_CEILING);
+    expect(moduleRouteBodyCeiling("buffered")).toBe(MODULE_ROUTE_MAX_BODY_BYTES_CEILING);
+    expect(moduleRouteBodyCeiling("streamed")).toBe(MODULE_ROUTE_ABSOLUTE_MAX_BODY_BYTES);
+    for (const bodyMode of ["buffered", "streamed"] as const) {
+      for (const maxBodyBytes of [
+        Number.POSITIVE_INFINITY,
+        Number.MAX_SAFE_INTEGER,
+        MODULE_ROUTE_ABSOLUTE_MAX_BODY_BYTES + 1,
+      ]) {
+        expect(
+          safeParseModuleRouteDefinition({ ...validDefinition({ maxBodyBytes }), bodyMode })
+            .success,
+        ).toBe(false);
+      }
+    }
+  });
+
   it("does not retain the caller's mutable definition object: mutating it afterward cannot change the parsed result", () => {
     const source = { ...validDefinition() };
     const result = safeParseModuleRouteDefinition(source);