FABRIC-3 XLVIII.6: #131 closed -- QEMU's capture doubled a byte, not our kernel [skip ci]

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GE3SDvQn5EoxdGufk84zz2

CHANGELOG.md

@@ -1,6 +1,14 @@
 # Changelog
 
-## 2026-11-07 — LithosAnanke v4.0.0-alpha.2: the first published alpha
+## 2026-11-07 — LithosAnanke v4.0.0-alpha.3: the first published alpha
+
+`v4.0.0-alpha.2` (`2d43db25`) used the image's HOL-Library as intended, but its release run (200) ran
+the proofs with Isabelle's defaults -- Java's heap up to 4 GiB, a thread per CPU -- and they were
+killed in the StarForth session. Nothing was published; the tag stays where it is. The proofs now run
+capped (`scripts/nightly.sh proofs`: one thread, Java 512 MiB, Poly/ML 900 MiB; 47 s, ~1.8 GiB), and
+`v4.0.0-alpha.3` is the first alpha published. `docs/fabric/FABRIC-3.md` XLVII.6.
+
+## 2026-11-07 — LithosAnanke v4.0.0-alpha.2: not published
 
 `v4.0.0-alpha.1` (`233025da`) was accepted and tagged, but its release run (196) built HOL-Library
 from scratch in the proofs step and was killed: `release.yml`'s full `make init` replaced the

demo/DEPLOY.md

@@ -0,0 +1,96 @@
+# Deploying "Try it" on the server
+
+The public demo: each visitor gets a StarshipOS machine of their own in the browser, resumed at
+Zuse's prompt, gone when they leave. Two at a time on today's server (384 MiB each); a third visitor
+is told every machine is busy and to try back in a few minutes. Issues #115, #116, #117.
+
+Run as root on the server, **after PR #148 is merged** (it carries the 384 MiB guests and the busy
+message), **while CI is idle** (each step that boots QEMU boots one, in the foreground).
+
+## 1. The checkout and what the build needs (~15 min)
+
+```bash
+apt-get install -y ttyd qemu-system-x86 ovmf python3 git
+git clone https://gitea.starshipos-f18.org/rajames/LithosAnanke.git /opt/starshipos-demo
+cd /opt/starshipos-demo
+git checkout master                  # after #148: alpha.3's kernel, and the demo's limits
+make ARCH=amd64 init INIT_DOCS=0 INIT_PROOFS=0     # amd64 only: no docs, no Isabelle
+```
+
+Master after #148 is the `v4.0.0-alpha.3` kernel unchanged, plus #148's scripts.
+
+## 2. The demo's own Zuse (~3 min, two QEMU boots)
+
+```bash
+demo/mint-zuse.sh /var/lib/starshipos-demo-zuse
+ls -la /var/lib/starshipos-demo-zuse/zusestick.img     # the stick every session attaches
+```
+
+Never anyone's real Zuse: minted for the demo (#111), its writes discarded in every session.
+
+## 3. The image and the saved machine (~2 min, one QEMU boot)
+
+```bash
+demo/build-iso.sh /tmp/StarshipOS.iso
+DEMO_PROMPT='[zuse@Hera]' demo/make-snapshot.sh /tmp/StarshipOS.iso /var/lib/starshipos-demo \
+    /var/lib/starshipos-demo-zuse/zusestick.img
+ls -la /var/lib/starshipos-demo/            # StarshipOS.iso identity.img vars.fd state
+```
+
+The saved machine belongs to this image, this QEMU and 384 MiB: re-run step 3 after any of them
+changes. Sessions already running keep theirs.
+
+## 4. The service (~5 min)
+
+Ubuntu's `ttyd` package starts its own `ttyd.service`, which runs **`login` on port 7681** -- our
+port. Left running, it takes the port, and Apache hands visitors the server's own login prompt
+(found 2026-11-08, after step 5). Disable it first:
+
+```bash
+systemctl disable --now ttyd                 # the package's service: a login prompt on 7681
+useradd --system --home /var/lib/starshipos-demo --shell /usr/sbin/nologin starshipos-demo
+chown -R starshipos-demo: /var/lib/starshipos-demo
+cp demo/starshipos-demo.service /etc/systemd/system/
+systemctl daemon-reload && systemctl enable --now starshipos-demo
+systemctl status starshipos-demo --no-pager | head -5
+curl -s -o /dev/null -w '%{http_code}\n' http://127.0.0.1:7681/     # 200: ttyd answers
+ss -ltnp | grep 7681                          # the ttyd of starshipos-demo, nothing else
+```
+
+The service expects the checkout's `demo/` at `/opt/starshipos-demo/demo` (step 1 put it there).
+
+## 5. TLS and Apache for try.starshipos-f18.com (~10 min)
+
+DNS: `try.starshipos-f18.com` must point at this server (an A record) before certbot.
+
+```bash
+a2enmod proxy proxy_http proxy_wstunnel headers ssl rewrite
+certbot certonly --apache -d try.starshipos-f18.com
+cp demo/apache-demo.conf /etc/apache2/sites-available/starshipos-demo.conf
+a2ensite starshipos-demo && apachectl configtest && systemctl reload apache2
+curl -sI https://try.starshipos-f18.com/ | head -3                   # 200, its own certificate
+```
+
+`apache-demo.conf` lets only the .com frame the terminal (`frame-ancestors`).
+
+## 6. The check (done 2026-11-08)
+
+From outside: a session ready 1.5 s after the page opens; `3 4 + .` answers `7  ok`, `: SQUARE DUP *
+;  7 SQUARE .` answers `49  ok`; a third visitor at once is told every machine is busy. The
+certificate is try.starshipos-f18.com's own (Let's Encrypt), and only the .com may frame it.
+
+## 7. Tell Claude
+
+Then I check from outside: a session reaches `[zuse@Hera] ok>`, `3 4 + .` answers `7 ok`, a third
+visitor gets the busy message, and the .com's Try it page shows the console. Then the "Try it" link
+goes into the .com's navigation (#117).
+
+## If something goes wrong
+
+- `journalctl -u starshipos-demo -n 50` -- ttyd and the sessions
+- A session that ends at once: the saved machine does not match (re-run step 3)
+- Memory: `free -h` -- a session's QEMU holds ~150 MB of its 384 MiB guest; two at most
+  (`DEMO_MAX_GUESTS` in the service)
+- CPU: an idle guest keeps a host core busy (the kernel's idle loop polls -- its own issue), so the
+  service caps all sessions together at one core (`CPUQuota=100%`, `Nice=19`). After changing the
+  service file: `systemctl daemon-reload && systemctl restart starshipos-demo`

demo/README.md

@@ -20,7 +20,8 @@ XWiki "Try it" page (iframe) -> Apache: TLS, websocket -> ttyd -> start-session.
 | `start-session.sh` | One visitor's session: resumes the saved machine, ends it on hang-up, close or time-out (#112) |
 | `console.py` | Joins the visitor's terminal to the machine only once it runs, discarding keys typed while it loads |
 | `qemu-args.sh` | The machine, shared by the two above: a resumed machine must match the saved one exactly |
-| `starshipos-demo.service` | ttyd as a systemd service, on localhost, at most 3 sessions (#114) |
+| `starshipos-demo.service` | ttyd as a systemd service, on localhost; two guests at once, a busy message for the rest (#114, #116) |
+| `DEPLOY.md` | Putting it on the server, step by step |
 | `apache-demo.conf` | Example vhost: TLS, the websocket, framing allowed for the `.com` only (#115) |
 | `xwiki-try-it.xwiki` | The "Try it" page, its own page on the `.com` XWiki (`TryIt`), in the landing page's style |
 

demo/qemu-args.sh

@@ -3,8 +3,10 @@
 # A session resumes a machine saved by make-snapshot.sh, and QEMU can resume a saved machine only
 # into the same machine: the same board, CPU, memory, firmware and devices. Both scripts build the
 # command line here, so they cannot drift apart. It is the machine `make -f kernel/Makefile
-# ARCH=amd64 qemu` boots (q35, TCG, 1 GiB, OVMF, the ISO as a CD), less what a visitor must not
-# have: no network device, no Artemis disk, no display, and QEMU's seccomp sandbox on.
+# ARCH=amd64 qemu` boots (q35, TCG, OVMF, the ISO as a CD) -- in 384 MiB, not its 1 GiB: v4 boots
+# to Zuse's prompt from 256 MiB, refuses at 128 ("no memory for the block chain"), measured
+# 2026-11-07 (#116) -- less what a visitor must not have: no network device, no Artemis disk, no
+# display, and QEMU's seccomp sandbox on.
 #
 #   demo_qemu_args <state-dir> <vars.fd>   -> fills the array QEMU_ARGS
 #
@@ -18,7 +20,7 @@ demo_qemu_args() {
     QEMU_ARGS=(
         -machine q35,accel=tcg
         -cpu qemu64,+rdrand
-        -m 1024
+        -m 384                                   # v4 boots from 256 MiB; 384 leaves room (#116)
         -smp 1
         -drive "if=pflash,format=raw,readonly=on,file=$OVMF_CODE"
         -drive "if=pflash,format=raw,file=$vars"

demo/starshipos-demo.service

@@ -13,8 +13,13 @@ User=starshipos-demo
 Group=starshipos-demo
 Environment=DEMO_STATE=/var/lib/starshipos-demo
 Environment=DEMO_SESSION_LIMIT=1800
-# -m: sessions at once -- each a QEMU of about 1 GiB and most of a core (issue #116 measures it)
-ExecStart=/usr/bin/ttyd --port 7681 --interface lo --writable --max-clients 3 \
+Environment=DEMO_MAX_GUESTS=2
+# the guests' slot locks (start-session.sh): /run/starshipos-demo, made for this user, gone at stop
+RuntimeDirectory=starshipos-demo
+# --max-clients: the guests and a few more, so a visitor over the limit reaches the busy message
+# instead of a refused connection; still a cap on open connections
+# each guest a QEMU of 384 MiB and most of a core (demo/qemu-args.sh; #116)
+ExecStart=/usr/bin/ttyd --port 7681 --interface lo --writable --max-clients 6 \
     --client-option titleFixed=StarshipOS --client-option disableLeaveAlert=true \
     /opt/starshipos-demo/demo/start-session.sh
 Restart=on-failure
@@ -25,8 +30,15 @@ ProtectHome=yes
 PrivateTmp=yes
 PrivateDevices=yes
 ReadOnlyPaths=/var/lib/starshipos-demo
-MemoryMax=4G
-CPUQuota=300%
+# Sized for this server (3.8 GiB, two cores; both wikis, Gitea, Nexus, CI). Since #151 an idle guest
+# halts (1% of a core at the prompt, was 100%), so a session costs CPU only while its visitor runs
+# something. All sessions together get 1.5 cores at the lowest priority (Captain Bob, 2026-11-08):
+# one busy visitor a full core, two busy at once three-quarters each, and half a core always left
+# to the wikis and Gitea. 1 GiB holds two sessions (~150 MB resident each) with room. Raise both
+# with the server (8 GB: MemoryMax=2G, CPUQuota=200% or more).
+MemoryMax=1G
+CPUQuota=150%
+Nice=19
 TasksMax=200
 
 [Install]

demo/start-session.sh

@@ -12,8 +12,29 @@ here=$(cd "$(dirname "$0")" && pwd)
 . "$here/qemu-args.sh"
 dir=${1:-${DEMO_STATE:-/var/lib/starshipos-demo}}
 limit=${DEMO_SESSION_LIMIT:-1800}               # seconds a session may last
+guests=${DEMO_MAX_GUESTS:-2}                     # machines at once: 384 MiB each (qemu-args.sh, #116)
+slots=${DEMO_SLOTS:-/run/starshipos-demo}        # a lock file per machine
 
 [ -f "$dir/state" ] || { echo "The demo is not set up yet: no saved machine in $dir." >&2; exit 1; }
+
+# One of $guests slots, or a busy message (Captain Bob, 2026-11-07: "Limit guests and have a Busy,
+# try back in a few minutes"). A slot is a lock this script holds for the session's life (flock -n:
+# two visitors cannot both take the last one); it goes when the script does, however it ends. The
+# machine's processes are started without the lock's descriptor ({slot}>&-), so it is this
+# script's alone.
+mkdir -p "$slots"
+slot=
+for i in $(seq 1 "$guests"); do
+    exec {fd}>"$slots/slot-$i.lock"
+    if flock -n "$fd"; then slot=$fd; break; fi
+    exec {fd}>&-
+done
+if [ -z "$slot" ]; then
+    printf '\r\nEvery StarshipOS machine is busy right now (%d at once on this small server).\r\n' "$guests"
+    printf 'Try back in a few minutes.\r\n'
+    sleep 20
+    exit 0
+fi
 tmp=$(mktemp -d "${TMPDIR:-/tmp}/starshipos-session.XXXXXX")
 trap 'rm -rf "$tmp"' EXIT
 cp "$dir/vars.fd" "$tmp/vars.fd"
@@ -28,13 +49,13 @@ printf 'Try:  3 4 + .      : SQUARE DUP * ;  7 SQUARE .\r\n\r\n'
 qemu-system-x86_64 "${QEMU_ARGS[@]}" \
     -chardev "socket,id=con,path=$tmp/con.sock,server=on,wait=off" -serial chardev:con \
     -qmp "unix:$tmp/qmp.sock,server=on,wait=off" -monitor none \
-    -incoming "file:$dir/state" </dev/null &
+    -incoming "file:$dir/state" </dev/null {slot}>&- &
 qemu=$!
-( sleep "$limit"; kill "$qemu" 2>/dev/null ) &
+( sleep "$limit"; kill "$qemu" 2>/dev/null ) {slot}>&- &
 timer=$!
 # The bridge is a tracked child too: bash runs a trap only once its foreground command returns,
 # so a hang-up would otherwise wait on the bridge. `wait` returns to the trap at once.
-python3 -I "$here/console.py" "$tmp/qmp.sock" "$tmp/con.sock" 0<&0 &
+python3 -I "$here/console.py" "$tmp/qmp.sock" "$tmp/con.sock" 0<&0 {slot}>&- &
 bridge=$!
 trap 'kill "$bridge" "$qemu" "$timer" 2>/dev/null; rm -rf "$tmp"' EXIT
 trap 'exit 0' HUP TERM INT

docs/fabric/FABRIC-3.md

@@ -6178,3 +6178,113 @@ packages, which also fetched Isabelle into the workspace and pointed `/usr/local
 2026-11-07): the tag stays where it is; `release.yml` runs `init INIT_PROOFS=0` (as
 `nightly-docs.yml` does), `LITHOS_VERSION` becomes `4.0.0-alpha.2`, and `v4.0.0-alpha.2` is the
 first published alpha.
+
+### 6. v4.0.0-alpha.2 not published either; v4.0.0-alpha.3
+
+PR #130 merged (`2d43db25`, acceptance run 199; run 197 before it failed one riscv64 check, #131);
+`v4.0.0-alpha.2` tagged there. Its release run (200) passed acceptance and used the image's
+Isabelle and HOL-Library, as XLVII.5 meant -- then the StarForth session was killed (exit 137) in
+the proofs: Isabelle ran with its defaults, Java's heap up to 4 GiB and a thread per CPU, more than
+the server (3.8 GiB, ~2.3 GiB free with the wikis stopped; perhaps a per-job cap besides). Capped
+-- one thread, Java 512 MiB, Poly/ML 900 MiB, in a settings file of a home made for the run, its
+heaps linked to the user's -- the session passes in 47 s at ~1.8 GiB, through
+`scripts/nightly.sh proofs` itself (`logs/20261107-195341`). Nothing was published. Ruled (Captain
+Bob, 2026-11-07): the tag stays; `LITHOS_VERSION` `4.0.0-alpha.3`, the first published alpha; the
+review list begun meanwhile goes to the milestone v4.0.0-alpha.4.
+
+## XLVIII. After the first published alpha: the review, the protocol, the SDK, the demo's limits (2026-11-07)
+
+### 1. Ruled
+
+- **A ranked list for the next release** (Captain Bob: "a list of problems, deficiencies, smells and
+  so on placed in issues by rank priority"): milestone **v4.0.0-alpha.4**, its index #147. Must:
+  Gitea's plain-HTTP logins (#133), rotating what was exposed (#134), the riscv64 flake (#131), the
+  developer protocol (#135), CI's litter (#129). Should: a failed check prints its serial log
+  (#136), capsule trust against the root and unsigned capsules (#139, a ruling), the queue's
+  cancelling of waiting runs (#140, a ruling), CLAUDE.md's drift (#137), the Book of Fabric (#138),
+  downloads (#126). Nice: the empty DoE CSVs (#141 -- no DoE has run since 2026-09-16: noise, not
+  breakage), DoE columns always 0 (#142), mkcapsule's warnings (#143), a stale header (#144),
+  tracked files a build rewrites (#145), the sites' small things (#146).
+- **The developer protocol** (#135): "We can simply run nightly as developers to further make sure
+  nothing sneaks in. Just no Nexus push ... a protocol for programmers. Then the protocol evidence
+  can be submitted in the PR." -- `scripts/nightly.sh protocol`, a `PROTOCOL.md` per run, checked
+  by CI against the PR's head.
+- **The Book of Fabric** (#138): the FABRIC record as one book, published with every release --
+  and this record kept at the pace of the work, so the book is (Captain Bob: "the book of fabric
+  needs to keep pace").
+- **v4.0.0-alpha.5: the SDK**, for FORTH and capsule developers; a systems SDK later, FPGA when we
+  get there (milestone 11). In it:
+  - **A capsule repository in blocks**, like `~/.m2/repository` (#149): on Artemis, indexed by
+    coordinates and capsule hash, a TTL by default as the rest of the system has, pinning one-way,
+    verified in and on use, composed in FORTH; filled by hand now, from Nexus once there is
+    networking. To rule: its block range and size, the default TTL, what is pinned.
+  - **K under network latency** (#150): "Networking latency will be a super good K test." -- the
+    repository pulling from Nexus with delay, jitter, loss and bandwidth dialled in (`tc netem`),
+    K and the DoE's measures per architecture. After networking, #141 and #142.
+- **The demo's limits** (#116): "Limit guests and have a Busy, try back in a few minutes."
+
+### 2. Built
+
+- **#136:** `scripts/qemu_session.py`'s `check()` prints, on a FAIL, the serial lines after an anchor
+  the check names (the boot-disk checks: `Boot successful!`), else the log's last lines, control
+  characters as escapes -- so #131's next occurrence explains itself in the job's output.
+- **The demo:** guests of **384 MiB** (`demo/qemu-args.sh`); `start-session.sh` takes one of
+  `DEMO_MAX_GUESTS` slots (2), a lock held for the session's life, and with every slot taken tells
+  the visitor every machine is busy and to try back in a few minutes; the service makes the locks'
+  directory and lets ttyd take 6 connections so the extra visitors reach the message.
+
+### 3. Verified
+
+- The demo machine, booted here with only `-m` changed: POST 538/538 and Zuse's prompt at 1024, 512,
+  384 and 256 MiB (82-84 s); at 128 MiB POST passes, then "StarForth v4: no memory for the block
+  chain". The slots: every slot held -- the busy message; slot 1 held -- slot 2 taken.
+- `excerpt()` against a real riscv64 serial log, with an anchor and without; a riscv64 acceptance
+  with the new script, passing as before.
+- With both wikis up again (Shenandoah, the .com's heap at 512 MiB, the .org's given 256 more): the
+  server at 2.6 of 3.8 GiB used, 1.2 GiB available, 2 GiB of swap used; Build 204 (three images, the
+  v4 tests) passed alongside them.
+
+### 4. Try it, deployed (2026-11-08)
+
+Captain Bob ran `demo/DEPLOY.md` on the server (#115): try.starshipos-f18.com with its own Let's
+Encrypt certificate, ttyd behind Apache, framing allowed to the .com alone. Checked from outside: a
+session ready 1.5 s after the page opens, `3 4 + .` -> `7  ok`, `: SQUARE DUP * ;  7 SQUARE .` ->
+`49  ok`, a third visitor at once told every machine is busy.
+
+Found on the way:
+- Ubuntu's `ttyd` package starts its own `ttyd.service` -- `login` on port 7681, ours -- and
+  until it was disabled the page served the server's login prompt to anyone. `DEPLOY.md` step 4
+  now disables it first and checks what listens on 7681.
+- **An idle StarshipOS keeps a host core 100% busy** (#151): the demo machine at its prompt, idle
+  20 s, QEMU at 100% of a core, 148 MiB resident -- the kernel's idle loop polls, never halts. Two
+  visitors' sessions with Gitea's diff statistics on a burst of pushes (#152, 1.75 GiB) filled the
+  server's swap and stalled both wikis. The service now caps all sessions together at one core at
+  the lowest priority (`CPUQuota=100%`, `Nice=19`, `MemoryMax=1G`), until #151 is fixed.
+- **Try it in the .com's navigation** (#117): "Try it" added to the canvas's Home and Inquiries
+  artboards, the .com rebuilt from them (`site/com`) and installed. Checked as a visitor: the home
+  page, the "Try it" link, the Try it page in 1.1 s, its framed console Ready.
+
+### 5. #151: the idle loop halts (2026-11-08)
+
+Ruled (Captain Bob): "Fix the kernel problem." The v4 system waited for a key -- `sk_v4_readline()`
+with nothing typed, and `sk_v4_identity_wait()` headless until Zuse -- in `arch_relax()`, a spin.
+Both now wait in `arch_halt()` (`hlt` on amd64, `wfi` on aarch64 and riscv64) until the next
+interrupt: the heartbeat's timer, which is ISR-driven on all three (`heartbeat_tick()`), wakes them
+at 100 Hz, so a key is seen within a tick, as the cursor's blink and the identity beat already
+were. v3's REPL (`repl.c`) still spins; v3 is not in acceptance.
+
+Verified: idle at Zuse's prompt for 20 s, QEMU's CPU **100% -> 1%** of a core on amd64 (the demo
+machine), and **1%** on aarch64 and riscv64 (`logs/20261108-011614`, `-011931`); the acceptance
+protocol passes -- amd64 `logs/20261108-005539`, aarch64 `-005753`, riscv64 `-010136`, POST
+538/538, `dict_hash 0xfec8c47cfc6f437f` on all three, `7 ok` typed and answered; the stick loaded
+high; `test-32` (39 programs, 0 failures). The demo's CPU cap (`CPUQuota=100%`) can be relaxed
+once this reaches the server.
+
+### 6. #131 closed: QEMU's capture, not our kernel (2026-11-08)
+
+Run 197's riscv64 serial log, read from Gitea's artifact store on the server (`acceptance-logs-185`),
+had the line with one character doubled -- "Boot diisk: not a StarshipOS stick" -- and a doubled
+byte in OpenSBI's banner too, printed before our kernel runs. So the byte was doubled in QEMU's
+serial capture under the server's load, not by the kernel (Captain Bob closed #131). The check that
+failed was right to: it refuses a line that is not what was printed. The capture itself (the log is
+`logfile=` on the socket chardev the acceptance types through) is what is left to harden.

kernel/Makefile

@@ -98,6 +98,10 @@ endif
 #   v4.0.0-alpha.2 — the first published alpha: v4.0.0-alpha.1 (233025da) was accepted and tagged,
 #             but its release run's proofs step built HOL-Library from scratch and was killed, so
 #             nothing was published; the tag stays where it is (Captain Bob, 2026-11-07).
+#   v4.0.0-alpha.3 — the first published alpha: v4.0.0-alpha.2 (2d43db25) kept the image's
+#             HOL-Library, but its proofs ran with Isabelle's defaults (Java 4 GiB, a thread per CPU)
+#             and were killed in the StarForth session; nothing was published, the tag stays. The
+#             proofs now run capped (scripts/nightly.sh: 1 thread, Java 512 MiB, ML 900 MiB).
 # LITHOS_VERSION (kernel) and VERSION (embedded StarForth engine) are independent
 # and do not auto-sync (§XXX.4) — do not infer a relationship if they ever coincide.
 # Engine VERSION bumps at tag time by what actually changed (§XXX.6): major = any
@@ -106,7 +110,7 @@ endif
 # the messaging layer was replaced by kernel-Hermes, PLOT/FB-* relocated to Hestia —
 # all dictionary-visible, no FORTH-79 word semantics changed.
 VERSION       ?= 3.2.0
-LITHOS_VERSION ?= 4.0.0-alpha.2
+LITHOS_VERSION ?= 4.0.0-alpha.3
 
 # ==============================================================================
 # BUILD PATHS

kernel/src/v4/sk_v4.c

@@ -113,7 +113,11 @@ static int sk_v4_readline(void)
             } else {
                 heartbeat_service();
             }
-            arch_relax();
+            /* Nothing typed: wait for the next interrupt, not in a spin (#151 -- the spin kept a
+             * CPU core 100% busy at the prompt, and the demo's host with it). The heartbeat's
+             * timer wakes it at 100 Hz, so a key is seen within a tick, as the blink and the
+             * identity beat are. */
+            arch_halt();
             continue;
         }
         if (c == '\r' || c == '\n') {

kernel/src/v4/sk_v4_identity.c

@@ -331,7 +331,7 @@ void sk_v4_identity_wait(void)
     while (!g_zuse_session) {
         sk_v4_discard_input();
         sk_v4_identity_beat();
-        arch_relax();
+        arch_halt();                 /* headless, until Zuse: wait for the next tick, not a spin (#151) */
     }
     sk_v4_discard_input();
 }