fix: Unit 6 — convention + doc cleanup (C-09, C-20-rem, C-22-rem, C-24, P-10, P-11)

Conventions satisfied, `cargo doc` clean, no actively-wrong comments,
producer/consumer naming consistent in the call/registry docs.

P-10 — `pump_sink` matched the string literals "call.published",
"call.completed", "call.aborted" (dispatch.rs) instead of the
EVENT_PUBLISHED / EVENT_COMPLETED / EVENT_ABORTED constants the rest
of the file imports. Replaced with the constants — pure refactor
hazard, no behavior change.

C-20 remainder — the wrong "SAFETY:" comment at from_call.rs:271
marked no `unsafe` block and was factually wrong (described a `'static`
return that isn't what `derive_alpn_from_op_name` does — it returns
`Option<String>`; the leak happens in `leak_alpn`). Reworded to a
plain note about the `'static` lifetime requirement. Also reworded
the abort-cancels claims in the `pump_sink` and `pump_stream` doc
comments (dispatch.rs): both claimed `call.aborted` "cancels the task
and drops the handler future" — the handler is actually `join!`-ed to
completion and not yet cancelled (the abort-cancels-Pub mechanism is
review 001 Unit 9). Trimmed step-numbered narration comments in
adapter.rs / client.rs that restated what the code does, keeping the
ordering-constraint and REQ-CH comments. The big reassembly.rs
deliberation landed with Unit 4; this finishes the remainder.

C-09 — fixed the 2 remaining `cargo doc` warnings (was 4; the
register_openable links were fixed in Unit 3):
- `unresolved link to default_policy` (operations.rs:50) — the
  [`default_policy`] intra-doc link resolves to
  super::policy::default_policy; used the full path.
- `env is both a module and a macro` (channels/mod.rs:30) — the
  [`env`] link collided with the std `env!` macro; qualified as
  [`self::env`].
`cargo doc --no-deps` now emits 0 warnings.

C-22 remainder — removed the filler `PhantomData` test at client.rs
(`let _ = std::marker::PhantomData::<ChannelClient>;` — asserts
nothing). The env.rs tautology was already removed in Unit 3.

C-24 — replaced "client→server streaming" with "producer→consumer
streaming" in call-protocol.md, operation-registry.md, README.md, and
open-questions.md (4 occurrences). Per AGENTS.md §8 the convention is
producer/consumer, not server/client. The remaining "client→server"
references in channels ADRs 034/037 are in stream_type table contexts
that Unit 10 (C-26) will handle as part of the spec-doc renumbering.

P-11 — amended ADR-046 §3's SinkHandler type so the stream item type
matches §6. §3 declared `Pin<Box<dyn Stream<Item = Value> + Send>>`;
§6 declared `Pin<Box<dyn Stream<Item = Result<Value, CallError>> +
Send>>`. The code uses §6's shape uniformly (registration.rs:32-40,
aliased as PublishStream). §3's text and the Door-type section are
amended to match §6; the Door-type section already marked the concrete
stream item type a two-way-door detail, so this is a text correction,
not a design change. Added an amendment note dated 2026-08-13.

Verification:
- cargo test --lib         → 449 passed, 0 failed (was 450; -1 removed filler test)
- cargo clippy --all-targets -- -D warnings → clean
- cargo fmt --check        → clean
- cargo doc --no-deps      → 0 warnings (was 2)

src/channels/client.rs

@@ -68,9 +68,7 @@ impl ChannelClient {
 
         // Spawn the mux runner BEFORE installing channel 0 —
         // `install_channel_zero` calls `mux.register(0).await` which
-        // sends a `Registration` to the runner and waits for the
-        // response. The runner must be draining `new_pumps` for the
-        // registration to complete.
+        // needs the runner to be draining `new_pumps`.
         let _mux_task = tokio::spawn(async move {
             if let Err(e) = mux_runner.run().await {
                 tracing::warn!(error = %e, "channel client: mux runner ended with error");
@@ -85,20 +83,14 @@ impl ChannelClient {
             ChannelSide::Connect,
         );
 
-        // Install channel 0 — the call adapter's read/write halves.
         let (channel0_send, channel0_recv) = manager
             .install_channel_zero(None)
             .await
             .map_err(|_| StreamError::StreamClosed)?;
 
-        // Join channel 0's reassembled read half + mux write half into
-        // a `BiStream` (via `channel_source`), wrap as a `Connection`
-        // (for ALPN/addr/identity), then yield the `BiStream` once via
-        // `accept_bi` and split it into a `SharedFrameWriter` (the
-        // framed write half for `call.requested` etc.) + a raw read
-        // half (for the read pump). This is the single-stream call
-        // mode (ADR-036 amendment): all `EventEnvelope` frames are
-        // multiplexed on channel 0's one `BiStream`.
+        // Single-stream call mode (ADR-036 amendment): channel 0's
+        // read+write halves are split into a `SharedFrameWriter`
+        // (for `call.requested`) and a read pump (for responses).
         let channel0_source =
             super::source::channel_source(channel0_recv, channel0_send, remote_addr);
         let channel0_conn = Connection::from_source(channel0_source, b"alknet/call".to_vec());
@@ -109,12 +101,6 @@ impl ChannelClient {
         let call_connection =
             CallConnection::new_single_stream(channel0_conn, single_stream_writer);
 
-        // Spawn the read pump for channel 0's response frames. Reads
-        // `EventEnvelope` frames off channel 0's reassembled read half
-        // (fed by the demux) and routes them into the
-        // `PendingRequestMap` via `dispatch_envelope`, resolving
-        // pending calls. This is the single-stream analogue of
-        // `read_stream_until_closed` in stream-per-request mode.
         let pending_map = Arc::clone(call_connection.pending());
         let _read_pump = tokio::spawn(async move {
             crate::protocol::connection::read_single_stream_until_closed(
@@ -124,9 +110,9 @@ impl ChannelClient {
             .await;
         });
 
-        // Spawn the demux loop (read side). The loop reads 8-byte
-        // chunk headers and routes payloads to the manager. It ends
-        // on transport EOF, clearing the channel map (REQ-CH-02).
+        // The demux loop ends on transport EOF, clearing the channel
+        // map (REQ-CH-02). The connect side passes `policy: None` (it
+        // does not enforce the per-identity cap).
         let demux_manager = manager.clone();
         let _demux_task = tokio::spawn(async move {
             super::adapter::ChannelsAdapter::run_demux_loop_for_client(
@@ -288,11 +274,6 @@ mod tests {
         })
     }
 
-    #[test]
-    fn channel_client_is_not_send_safe_across_await_by_default() {
-        let _ = std::marker::PhantomData::<ChannelClient>;
-    }
-
     /// C-25 #1 — the end-to-end acceptance gate for Unit 2 (channel 0
     /// single-stream call mode, ADR-036 amendment). Wires
     /// `ChannelClient` (connect side) ↔ `ChannelsAdapter` (accept