feat: deliver module objects directly to browsers through opaque read URLs

ADR 0030 left exactly one way to get an image to a browser: read the
object into the module's process and write it back out of a module HTTP
route. Every byte of every asset travelled storage -> Ekklesia -> browser.
For the slideshow this platform exists to replace that means Ekklesia in
the path of every image on every display, permanently, for bytes that
never change — and it would make Ekklesia responsible for re-implementing
byte ranges, without which video seeking cannot work at all.

A module can now ask a logical bucket for a temporary browser URL:

    const { url, expiresAt } = await assets.createReadUrl("slides/welcome.png");

The contract names intent, not mechanism. There is no signing, expiry
format, endpoint, or bucket in it — a host with no S3 anywhere could
satisfy the same method, which is what keeps a future single-module
standalone host able to implement it. The URL is opaque to module code and
a bearer capability to whoever holds it, so a module authorizes the
request in its own route before asking: storage bounds reach, never
identity. Lifetimes run one minute to six hours, fifteen by default, and
out-of-range values are refused rather than clamped, so "expires forever"
is unreachable. Logical keys stay canonical state; URLs are generated on
demand and never persisted or logged.

The provider endpoint and the browser delivery origin are separated
because measurement showed they cannot be collapsed: an S3-compatible
signature covers the request Host, so a URL signed for one origin and
rewritten to another is rejected. The browser-facing origin is therefore a
signing input (S3_DELIVERY_ENDPOINT), defaulting to S3_ENDPOINT — so the
standard deployment configures nothing and delivery just works. The scheme
is not signed, so a reverse proxy may terminate TLS provided it passes the
original Host through; that is pinned by a test rather than described and
hoped for.

Read URLs are stable within a window of one third of their lifetime.
Signing is a pure function of the clock, so naive re-signing yields a new
URL per second — a guaranteed browser cache miss, and the reference client
keys its <img> by URL, so an unchanged image would be torn down and
re-downloaded continuously. Quantizing the signing timestamp makes
repeated calls byte-identical while leaving at least two-thirds of the
lifetime; Cache-Control is set at signing time to the guaranteed
remainder, because the pinned SeaweedFS image sends none of its own.

Verified against live SeaweedFS: byte ranges answered directly with 206
and a correct Content-Range, so no range proxy is needed in Core; signing
is local (200 URLs in 66ms), so no batch API is needed; unsigned requests
for the same object are refused, so delivery never depends on a public
bucket; tampered signatures, swapped keys, and swapped buckets all
rejected. Signed write and delete URLs are deliberately not built.

Co-Authored-By: Claude Opus 5 <[email protected]>

docs/architecture/decisions/0031-direct-object-delivery.md

@@ -0,0 +1,214 @@
+# 0031: Browsers fetch objects directly, through opaque temporary read URLs
+
+- Status: Accepted
+- Date: 2026-08-23
+- Extends: [0004](0004-replace-unmaintained-minio.md),
+  [0021](0021-modules-as-hostable-products.md),
+  [0028](0028-module-operational-lifecycle.md),
+  [0030](0030-host-provided-module-object-storage.md)
+
+## Context
+
+[ADR 0030](0030-host-provided-module-object-storage.md) gave a module a scoped `context.storage` and
+took every provider detail away from it. That is right for module code, but it left exactly one way
+to get an image to a browser: read the object into the module's process and write it back out of a
+module HTTP route. Every byte of every asset travels storage → Ekklesia → browser, and Ekklesia's
+event loop carries it.
+
+For the product this platform exists to replace that is not a hypothetical cost. `The_River/Announcements`
+(commit `9aab486`) is a slideshow: a display renders full-screen images for hours, rotating every
+seven seconds, and the server rebuilds its slide list every thirty. Proxying it would put Ekklesia in
+the path of every image on every display in the building, permanently, to deliver bytes that never
+change. Worse, it would make Ekklesia responsible for re-implementing what an object store already
+does — byte ranges above all, without which video seeking cannot work at all.
+
+The existing application solves this by making the bucket world-readable and hardcoding its address:
+
+```js
+slides = files.map((name) => `http://10.40.0.2:9000/announcements/${encode(name)}`);
+```
+
+Direct delivery, at the cost of a permanently public bucket, an origin compiled into the client, and
+no per-object control of any kind. We want the delivery path and none of the cost.
+
+## Decision
+
+A module can ask a logical bucket for a temporary, browser-usable URL for one object:
+
+```ts
+const assets = context.storage.bucket("announcement-assets");
+const { url, expiresAt } = await assets.createReadUrl("slides/welcome.png");
+```
+
+The browser then fetches the object from the host's storage service directly. Ekklesia is not in the
+data path.
+
+### The contract names intent, not mechanism
+
+`createReadUrl` is the whole surface. There is no `presign`, no expiry format, no signature, no
+region, no endpoint, and no bucket — a module names the key it already knows and receives something a
+browser can use. The first implementation is S3-compatible presigned `GET`, but nothing about that
+reaches the contract: a host with no S3 anywhere in it could satisfy the same method by minting its
+own opaque token, and no module would change. This is the same reasoning that keeps `ModuleStorage`
+free of provider vocabulary in ADR 0030, applied to delivery.
+
+The return value is `{ url, expiresAt }` and deliberately nothing else. `expiresAt` exists so that a
+caller can decide *when to ask again* without reading the URL, which is what makes "the URL is
+opaque" an honest rule rather than an aspiration.
+
+### A read URL is a bearer capability
+
+Anyone holding the URL can read that one object until it expires. It is not an authenticated
+request, and this ADR does not pretend otherwise.
+
+The division of responsibility is therefore explicit:
+
+- **Whether this person may have the URL** is the module's own authorization decision, made in its
+  route before it asks for one. Storage does not know about people, permissions, or principals.
+- **How far the URL reaches once issued** is the storage contract's guarantee: one object, in one
+  module's bucket, for a bounded time.
+
+Storage authorization does not replace domain authorization, and the contract deliberately offers no
+hook that would let it try.
+
+### Expiry is bounded, and the bounds come from the reference consumer
+
+- **Default 15 minutes.** Announcements rebuilds its slide list every 30 seconds and re-broadcasts
+  state every 7. Fifteen minutes is roughly thirty times that natural refresh, so a display that
+  loses its connection for ten minutes still renders every slide the moment it reconnects — without
+  anyone building a refresh mechanism.
+- **Floor of 1 minute.** Below that, ordinary clock skew between Ekklesia and the storage service
+  can expire a URL before a browser can spend it.
+- **Ceiling of 6 hours.** This bounds the damage when a URL leaks. It outlasts any single gathering
+  while staying nowhere near a durable credential, and it binds well before the seven-day maximum
+  S3-compatible signing itself permits — so the contract's limit is the one that applies.
+
+Out-of-range requests are **refused, not clamped**. Silently shortening a lifetime would surface
+later as URLs expiring for no visible reason; silently lengthening one would weaken a capability
+without telling anyone. "Expires forever" is unreachable rather than discouraged.
+
+### Logical keys are canonical state; URLs are not
+
+A module persists the object key. It generates a URL when something is about to be delivered and then
+forgets it. Storing a URL would be storing a credential with an expiry date embedded in it, and it
+would break the moment the deployment's delivery origin changed.
+
+### Read URLs are stable within a window
+
+Signing is a pure function of the request and the clock, so signing the same object twice a second
+apart produces two different URLs for identical bytes. That is not merely untidy. A browser caches by
+URL, so a changed query string is a guaranteed cache miss — and UI frameworks routinely key list
+items by URL. The reference client renders:
+
+```jsx
+<img key={`current-${currentImage}`} src={currentImage} />
+```
+
+A new URL for an unchanged image therefore tears the element down and re-downloads it. A slideshow
+rebuilding its state every few seconds would re-fetch every slide continuously, having gained a
+direct path to storage and lost the caching that made it worth having.
+
+So the signing timestamp is rounded down to a window of one third of the requested lifetime. Repeated
+calls within that window return a **byte-identical** URL, and at least two-thirds of the lifetime
+always remains when one is handed out. Ekklesia also sets `Cache-Control: private, max-age=N` at
+signing time, where `N` is the guaranteed remainder — the pinned SeaweedFS image returns no
+`Cache-Control` of its own, which would otherwise leave browsers guessing.
+
+### The provider endpoint and the browser delivery origin are different things
+
+They cannot be collapsed, and this was measured rather than assumed. An S3-compatible signature
+covers the request's **`Host` header**, so a URL signed for one origin and then re-pointed at another
+fails verification. Rewriting after signing is not available.
+
+The browser-facing origin is therefore a **signing input**. `S3_DELIVERY_ENDPOINT` sets it, and when
+unset it is the provider endpoint — which is the ordinary case and the reason a normal deployment
+configures nothing.
+
+What the signature does **not** cover is the scheme. Terminating TLS at a reverse proxy and
+forwarding plaintext to the storage service verifies correctly, **provided the proxy passes the
+original `Host` through unchanged**. That is the single configuration requirement direct delivery
+imposes on a deployment, and it is pinned by an integration test rather than described here and
+hoped for.
+
+### Zero configuration for an ordinary deployment
+
+The development stack publishes the storage service on loopback, so `S3_ENDPOINT` is already an
+origin a browser can reach and serves both roles. An operator running the standard stack configures
+no endpoint, no keys, no bucket, and no delivery origin; modules declare logical buckets, bindings
+provision themselves, and delivery URLs work. `S3_DELIVERY_ENDPOINT` exists for the deployment where
+Core reaches storage by a private service name — and only then.
+
+### What a browser sees
+
+A read URL reveals the storage origin, the physical bucket name, the object key, and signing query
+parameters. This is accepted and stated plainly rather than worked around.
+
+Physical bucket names are **implementation metadata, not secrets**. Nothing is authorized by knowing
+one: the bucket is not publicly readable, and a URL's signature covers its own path, so editing the
+bucket or key in a URL produces a rejection rather than another object. Hiding them would mean
+reintroducing a proxy layer and recreating the data hop this ADR exists to remove — a real cost for a
+cosmetic gain.
+
+The distinction that matters is between **module code**, which must never depend on these details and
+cannot reach them, and **the browser**, which inevitably sees the URL it is fetching.
+
+## Consequences
+
+### What this buys
+
+Byte ranges work directly against the storage service — verified, `206` with a correct
+`Content-Range` — so video seeking becomes the provider's job and needs no range proxy in Core. This
+was the single largest reason to prefer direct delivery over proxying, and it removes a whole
+subsystem from the platform's future.
+
+Signing is a local computation: 200 URLs took 66 ms with no network traffic. A slideshow can build
+forty delivery URLs as cheaply as it builds forty strings, so no batch API is needed and none is
+added.
+
+### What it costs
+
+A leaked URL is usable until it expires. That is the nature of the mechanism, and it is why the
+ceiling is 6 hours rather than a day and why URLs are never logged.
+
+`createReadUrl` does not check that the object exists. A URL for a missing key — or one deleted after
+signing — returns `404` when fetched, which is what a browser already handles. Verifying up front
+would add a round trip to every URL, and a module listing forty slides would pay forty of them for
+something it just read.
+
+### Logging and diagnostics
+
+A read URL is treated as a bearer token. Complete URLs are never logged and never printed by Doctor.
+Doctor reports the storage origin, and the delivery origin when it differs, and says explicitly that
+a separate delivery origin was **not** probed — reporting "reachable" without that caveat would let
+an operator conclude direct delivery works when only half of it was tested.
+
+### CORS
+
+The pinned SeaweedFS image reflects any `Origin` back in `Access-Control-Allow-Origin` and does not
+set `Access-Control-Allow-Credentials`. Read URLs carry no cookies and no browser credentials, so a
+reflected origin grants nothing beyond what possession of the URL already grants. Ekklesia therefore
+configures no CORS policy of its own in this pass and relies on the provider's default, which is
+sufficient for element loads (`<img>`, `<video>`) and for `fetch` without credentials. A deployment
+that wants a narrower policy sets it on the storage service or its reverse proxy. This is recorded as
+an observed default rather than an endorsement.
+
+### Lifecycle is unchanged
+
+Storage lifecycle semantics stay exactly as ADR 0030 set them. A signing failure is an operational
+error a module may retry; it never changes a module's runtime state. Nothing here makes a running
+module blocked.
+
+### Standalone-host compatibility
+
+Everything a module touches — `createReadUrl`, the bounds, the `{ url, expiresAt }` shape — lives
+above the provider seam. A future single-module standalone host implements `StorageProvider` and
+gets delivery for free. A module never asks which host is running it, and there is deliberately no
+value it could branch on.
+
+### Deferred
+
+Signed **write** and **delete** URLs are not built. Uploads still go through a module route, where
+the module can validate what it is accepting; handing a browser a capability to write into a
+module's bucket needs its own decision about size, type, and quota, and does not belong in the pass
+that established reads. Realtime URL refresh is not built either — ordinary API reloads are
+sufficient, and a future realtime pass can refresh state and URLs together when it exists.

docs/architecture/decisions/README.md

@@ -39,3 +39,4 @@ ADRs capture durable choices that affect more than one package or phase.
 - [0028: Module operational lifecycle — enablement, eligibility, and what "running" means](0028-module-operational-lifecycle.md) — Accepted
 - [0029: Module configuration is manifest-declared, host-resolved, and secret-free at rest](0029-module-configuration-and-secrets.md) — Accepted
 - [0030: Modules declare logical buckets; hosts provide object storage](0030-host-provided-module-object-storage.md) — Accepted
+- [0031: Browsers fetch objects directly, through opaque temporary read URLs](0031-direct-object-delivery.md) — Accepted