docs(websocket): record WS-13 no-keepalive decision + progress semantics (WS-13)

Decides the WS-13 legitimate-silence question as option (b): 60s of no
chunk progress is an intentional eviction line even for silent
subscriptions; no WS ping/pong keepalive is added because a keepalive
can only rescue app-silence by re-arming the deadline, which reopens
the dribble hole the knob exists to seal. Documented in the byte_adapter
module doc, on DEFAULT_WS_IDLE_TIMEOUT, on the unchanged
HttpAdapter::with_ws_idle_timeout knob, and in websocket.md (new
'Idle-read timeout' section, including the FWD-15 SSE-keepalive
layering note). Deployment posture for long-lived silent sessions:
with_ws_idle_timeout(None) + WsSessions abort + write-side caps.

docs/architecture/websocket.md

@@ -1,6 +1,6 @@
 ---
 status: draft
-last_updated: 2026-08-27
+last_updated: 2026-08-30
 ---
 
 # WebSocket — the Browser Bidirectional Path (Channels over WS)
@@ -176,6 +176,49 @@ The adapter is shared with the `from_wss` consumer path
 ([ADR-070](decisions/070-from-wss-consumer-adapter.md)) — one
 implementation, both directions.
 
+#### Idle-read timeout: progress semantics + the no-keepalive decision (WS-01, WS-13)
+
+The WS pumps carry an **idle-read eviction knob**
+(`HttpAdapter::with_ws_idle_timeout`, default
+`DEFAULT_WS_IDLE_TIMEOUT` = 60 s, disable with `None`). Its semantics,
+decided in review-002 (WS-13), are **progress-based, deliberately
+strict**:
+
+- The deadline resets on **demux progress** — bytes actually forwarded
+  into the byte stream that *complete* an inbound chunk (a full
+  8-byte header + its declared payload). WS message arrival resets
+  nothing.
+- Therefore the dribble stall (declare a chunk, deliver its payload a
+  byte per message) hits the deadline and is evicted with a `1001`
+  (GoingAway) close — even though messages keep arriving — while a
+  peer delivering complete chunks, however slowly per message, re-arms
+  the window with each chunk and survives.
+- **There is no WS ping/pong keepalive, on purpose.** A keepalive
+  rescues app-silence only by re-arming the deadline — and a pong is
+  indistinguishable from the dribble's almost-invisible arrivals, so
+  adding one would reopen the stall it exists to seal. The recorded
+  decision (module doc of `src/websocket/byte_adapter.rs`, option (b)
+  of the two WS-13 alternatives): **60 s of no chunk progress is an
+  intentional eviction line, even for a silent subscription.**
+- A deployment running long-lived silent-but-alive sessions (quiet
+  subscriptions that outlast the window) disables the knob with
+  `with_ws_idle_timeout(None)` and leans on the remaining levers:
+  the session registry's forced-eviction
+  ([`WsSessions::abort`](#connection-local-overlay)), the
+  inbound caps (WS-06), and the write-side caps (WS-04/05/06). This is
+  the same deployment posture as `from_wss`'s drop monitor
+  ([ADR-070](decisions/070-from-wss-consumer-adapter.md)): the idle
+  knob bounds *demux parking*, not app liveness.
+- Layered note (the WS-13/FWD-15 interaction recorded here): the
+  *HTTP* SSE path (`/subscribe`) sends server-side keep-alive comment
+  frames every 15 s — see
+  [http-server.md](http-server.md)) — because its idle enemy is
+  LB/proxy timeouts, and its keep-alive does not reset any
+  progress deadline, it cannot reopen the WS-13 hole. The two live at
+  different layers: SSE keep-alive fights transport fires; the WS idle
+  knob bounds demux parking. Both documented in the same pass per
+  review-002 Unit-2 sequencing.
+
 ### Dispatch: channel 0 = the shared `Dispatcher`, unchanged
 
 Channel 0's session is the alknet design's native session, verbatim:

src/server/adapter.rs

@@ -218,11 +218,20 @@ impl HttpAdapter {
         self
     }
 
-    /// The WS idle-read timeout (WS-01): the read pump closes the
+    /// The WS idle-read timeout (WS-01, WS-13 semantics): the read
-    /// connection with a 1001 (GoingAway) close frame after this long
+    /// pump closes the connection with a 1001 (GoingAway) close frame
-    /// without an inbound WS message — bounding the demux stall a
+    /// after this long producing **no completed inbound chunk** — the
-    /// dribbling (or silently-stalled) peer can pin. `None` disables
+    /// deadline resets on demux progress (complete chunks forwarded
-    /// the knob (not recommended: the stall window is then unbounded).
+    /// into the byte stream), not on WS message arrival, so a
+    /// dribbling peer (slow message arrivals inside a declared chunk)
+    /// is bounded while productive-but-slow peers survive. This is an
+    /// intentional no-progress eviction line, not a transport-idle
+    /// bound: there is no WS ping/pong keepalive, and app-silence that
+    /// outlasts the window (a quiet subscription) is evicted by design
+    /// — see `websocket::byte_adapter`'s module doc. `None` disables
+    /// the knob (not recommended: the stall window is then unbounded;
+    /// long-lived silent subscriptions are the intended `None` case,
+    /// leaning on `WsSessions::abort` and the write-side caps).
     ///
     /// Default: [`crate::websocket::DEFAULT_WS_IDLE_TIMEOUT`] (60 s).
     pub fn with_ws_idle_timeout(mut self, idle_timeout: Option<Duration>) -> Self {

src/websocket/byte_adapter.rs

@@ -32,6 +32,32 @@
 //! Text WS messages are rejected with a protocol-level close (code
 //! 1002); all frames are binary (websocket.md §Framing).
 //!
+//! Idle-read timeout (WS-01, WS-13 semantics): the knob
+//! (`DEFAULT_WS_IDLE_TIMEOUT`, deployment-adjustable via
+//! `HttpAdapter::with_ws_idle_timeout`, disable via `None`) evicts a
+//! connection whose inbound stream produces **no completed chunk for
+//! the whole window** — the deadline resets on demux progress (bytes
+//! forwarded into `read_tx` that complete 8-byte-header-framed chunks),
+//! never on WS message arrival, so a forever-dribble inside a declared
+//! chunk hits the deadline even though messages keep arriving, while a
+//! peer delivering complete chunks — however slowly per-message —
+//! re-arms the window with each one.
+//!
+//! Legitimate silence (WS-13 decision, recorded — option (b)): there
+//! is deliberately **no WS ping/pong keepalive**. A keepalive can only
+//! rescue app-silence by re-arming the deadline, which would reopen the
+//! dribble hole it exists to seal (pong = traffic from the attacker's
+//! point of view); instead, 60 s of *no chunk progress* is an
+//! intentional eviction line even for a silent subscription — a
+//! long-lived quiet subscription that must survive past the window
+//! (with server-side pushes; see the keep-alive discussion in
+//! `websocket.md`) is exactly the deployment that dials
+//! `with_ws_idle_timeout(None)` and leans on the other bounds
+//! (`WsSessions::abort` eviction, the write-side caps). Read eviction
+//! closes with 1001 (Going Away) — a normal connection end from the
+//! demux's point of view (EOF → channels cleared, pendings failed),
+//! not a protocol error.
+//!
 //! Close mapping: WS close (either side) → read EOF → the demux clears
 //! all channels (REQ-CH-02) and the dispatch loop fails outstanding
 //! pendings. `AsyncWrite::shutdown` closes the WS sink after the queued
@@ -107,20 +133,27 @@ pub const WS_PROTOCOL_ERROR: u16 = 1002;
 /// violation it cannot recover from (WS-04/HY-09, WS-05).
 pub const WS_INTERNAL_ERROR: u16 = 1011;
 
-/// Idle-read close code (WS-01): a read side that stays silent past the
+/// Idle-read close code (WS-01/WS-13): a read side that produces no
-/// configured idle timeout is closed with 1001 (Going Away) — a normal
+/// demux progress (no completed inbound chunk) past the configured
-/// connection end from the demux's point of view (EOF → channels
+/// window is closed with 1001 (Going Away) — a normal connection end
-/// cleared, pendings failed), not a protocol error.
+/// from the demux's point of view (EOF → channels cleared, pendings
+/// failed), not a protocol error.
 pub const WS_GOING_AWAY: u16 = 1001;
 
-/// Default idle-read timeout for the WS pumps (WS-01): a peer whose
+/// Default idle-read timeout for the WS pumps (WS-01, WS-13): a
-/// inbound byte stream stops producing **complete chunks** cannot
+/// connection whose inbound stream completes **no chunk** within this
-/// park the single demux loop longer than this (WS-13 progress
+/// window is evicted — the deadline resets on demux progress (complete
-/// semantics — the deadline resets when a complete chunk's bytes are
+/// chunks forwarded into `read_tx`), not on WS message arrival, so a
-/// forwarded into `read_tx`, not when WS messages arrive, so a
+/// forever-dribble inside a declared chunk still hits it.
-/// forever-dribble inside a declared chunk still hits it). Zero-wait
+///
-/// is spelled `None`; this duration is the deployment default
+/// This is an intentional no-progress eviction line, *not* a
-/// (`HttpAdapter::with_ws_idle_timeout`).
+/// transport-idle bound: there is no WS ping/pong keepalive, and
+/// app-silence that outlasts the window (a quiet subscription) is
+/// evicted with 1001 by design — see the module doc's "Legitimate
+/// silence" decision. A deployment running long-lived silent
+/// subscriptions disables the knob with
+/// `HttpAdapter::with_ws_idle_timeout(None)` (`None`, not zero — zero
+/// is not a meaningful window).
 pub const DEFAULT_WS_IDLE_TIMEOUT: Duration = Duration::from_secs(60);
 
 /// Observes the inbound byte stream for chunk framing (WS-13): counts