fix(docker): address code-review findings in supercronic integration

Five findings from a post-merge review, all verified:

C1 — graceful restart (/restart) re-execs the bare odek binary, bypassing
cron-entrypoint.sh; supercronic was never restarted.
Fix: cron-entrypoint.sh exports ODEK_ENTRYPOINT=$0 and ODEK_SUPERCRONIC_PID.
spawnChild() uses ODEK_ENTRYPOINT when set so the wrapper is re-entered on
restart. The wrapper kills the old supercronic PID before starting a new one,
preventing duplicate scheduler instances.

C2+C3 — no init process: supercronic zombies on exit; SIGTERM from docker stop
not forwarded to supercronic (in-flight jobs killed abruptly at SIGKILL).
Fix: init: true on both telegram compose services. Docker's built-in init
becomes PID 1, reaping orphaned children and forwarding SIGTERM to the process
group.

C4 — arch="${TARGETARCH:-amd64}" silently installed the wrong-arch supercronic
binary on arm64 hosts building without BuildKit; the SHA check still passed.
Fix: change to ${TARGETARCH:?...} — a hard build failure with an actionable
error message rather than a silent wrong-arch download.

C5 — Docker creates a root-owned directory at ./crontab on the host when the
source path is missing from a bind mount; [ -f ] returned false silently.
Fix: add [ -d ] branch with an explicit warning explaining the cause and fix.

C6 — supercronic backgrounded with &; set -e does not apply to background
processes, so an immediate startup failure was silently swallowed.
Fix: sleep 1 + kill -0 liveness check after launch; emits a clear WARNING if
supercronic exits immediately, rather than proceeding as if cron is running.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: jkyberneees

cmd/odek/telegram.go

@@ -899,6 +899,14 @@ func spawnChild() error {
 	if err != nil {
 		return fmt.Errorf("executable: %w", err)
 	}
+	// When running inside the Docker container the entrypoint script exports
+	// ODEK_ENTRYPOINT=$0. Re-exec through the wrapper so supercronic is
+	// restarted alongside the new odek process. The wrapper reads
+	// ODEK_SUPERCRONIC_PID (also in childEnv via os.Environ()) and kills the
+	// previous supercronic before starting a new one — no duplicate instances.
+	if ep := os.Getenv("ODEK_ENTRYPOINT"); ep != "" {
+		exe = ep
+	}
 	// Copy args (same as current process).
 	argv := make([]string, len(os.Args))
 	copy(argv, os.Args)

docker/Dockerfile

@@ -76,7 +76,7 @@ RUN apk add --no-cache ca-certificates git github-cli bash coreutils curl jq
 ARG SUPERCRONIC_VERSION=v0.2.46
 ARG TARGETARCH
 RUN set -eu; \
-    arch="${TARGETARCH:-amd64}"; \
+    arch="${TARGETARCH:?TARGETARCH is empty — build with BuildKit (docker buildx build) or pass --build-arg TARGETARCH=amd64|arm64}"; \
     case "$arch" in \
       amd64) sha=5adff01c5a797663948e656d2b61d10932369ee437eb5cb54fa872b2960f222b ;; \
       arm64) sha=c0576a8eb092e3f79108ed0a2155a25c7766af78456e5a6070e54757ef513bfe ;; \

docker/cron-entrypoint.sh

@@ -16,15 +16,48 @@ set -eu
 # Path to the crontab. Overridable so an operator can relocate the mount.
 CRONTAB="${ODEK_CRONTAB:-/home/odek/.crontabs/crontab}"
 
-if [ -f "$CRONTAB" ]; then
-	echo "cron-entrypoint: starting supercronic for $CRONTAB" >&2
-	# -passthrough-logs keeps each job's own stdout/stderr intact in the
-	# container log alongside supercronic's scheduling lines.
-	supercronic -passthrough-logs "$CRONTAB" &
+# Graceful-restart support: odek's /restart command re-execs via this script
+# (see ODEK_ENTRYPOINT below). Kill any supercronic from the previous run so we
+# never end up with two instances scheduling the same crontab concurrently.
+if [ -n "${ODEK_SUPERCRONIC_PID:-}" ]; then
+    kill "$ODEK_SUPERCRONIC_PID" 2>/dev/null || true
+    unset ODEK_SUPERCRONIC_PID
+fi
+
+if [ -d "$CRONTAB" ]; then
+    # Docker creates a directory when the bind-mount source doesn't exist on the
+    # host. This is almost always a misconfiguration — warn loudly rather than
+    # silently skipping so the operator knows why reminders aren't firing.
+    echo "cron-entrypoint: WARNING: $CRONTAB is a directory, not a file" >&2
+    echo "cron-entrypoint: Docker created it because the host path was missing." >&2
+    echo "cron-entrypoint: Fix: remove the directory on the host and create the file." >&2
+    echo "cron-entrypoint: Skipping supercronic — cron jobs will NOT run." >&2
+elif [ -f "$CRONTAB" ]; then
+    echo "cron-entrypoint: starting supercronic for $CRONTAB" >&2
+    # -passthrough-logs keeps each job's own stdout/stderr intact in the
+    # container log alongside supercronic's scheduling lines.
+    supercronic -passthrough-logs "$CRONTAB" &
+    ODEK_SUPERCRONIC_PID=$!
+    export ODEK_SUPERCRONIC_PID
+    # Brief liveness check: supercronic parses the crontab at startup and exits
+    # immediately on a syntax error or missing binary. Neither is recoverable at
+    # runtime, so catching it here produces a clear warning rather than silent
+    # non-delivery. set -e does not cover backgrounded processes, so we check
+    # explicitly after a short window.
+    sleep 1
+    if ! kill -0 "$ODEK_SUPERCRONIC_PID" 2>/dev/null; then
+        echo "cron-entrypoint: WARNING: supercronic exited immediately — cron jobs will NOT run" >&2
+        unset ODEK_SUPERCRONIC_PID
+    fi
 else
-	echo "cron-entrypoint: no crontab at $CRONTAB — skipping supercronic" >&2
+    echo "cron-entrypoint: no crontab at $CRONTAB — skipping supercronic" >&2
 fi
 
+# Advertise this script's own path so spawnChild (odek's /restart handler) can
+# re-exec through the wrapper instead of the bare binary. Without this, a
+# graceful restart would skip supercronic entirely.
+export ODEK_ENTRYPOINT="$0"
+
 # Default to printing usage if no command was provided (matches the previous
 # `ENTRYPOINT ["odek"]` behaviour for a bare `docker run`).
 exec odek "$@"

docker/docker-compose.yml

@@ -62,6 +62,13 @@ services:
     image: odek:local
     env_file: .env
     command: ["telegram"]
+    # init: true adds Docker's built-in init (tini) as PID 1. This gives us:
+    # - Zombie reaping: supercronic child processes are reaped when they exit.
+    # - Signal forwarding: SIGTERM from `docker stop` reaches all children,
+    #   giving in-flight cron jobs a clean shutdown window.
+    # - Graceful restart safety: when odek exits during /restart, the spawned
+    #   child is reparented to the init rather than dying with odek.
+    init: true
     volumes:
       - ./workspace:/workspace
       - ./.odek:/home/odek/.odek
@@ -82,6 +89,7 @@ services:
     image: odek:local
     env_file: .env
     command: ["telegram"]
+    init: true   # zombie reaping + SIGTERM forwarding (see telegram-restricted)
     volumes:
       - ./workspace:/workspace
       - ./.odek:/home/odek/.odek