fix(qbittorrent): the comment warning about doubled dollars contained one

The new flux-postbuild-substitution guard failed the merge on
apps/wave-0/qbittorrent.yaml:155 — a run of two dollars in a substituted
path that nothing justifies. It was inside the postStart hook's own comment
EXPLAINING the hazard: prose about what envsubst does to a doubled dollar,
written with a literal doubled dollar.

Functionally harmless — it is a bash comment, and collapsing it changes no
behaviour — but the guard cannot distinguish a comment from content that
reaches the workload, and it is right not to try: that is precisely how the
nextcloud-db break slipped through. Reworded in words instead.

Worth recording that this is the second time today the same trap caught an
explanation of itself: my own fix for the nextcloud-db incident (16b7fcd)
also shipped dollars inside the comment describing the danger, and I only
caught it because I re-read the file. This time the guard caught it, on work
merged minutes earlier — which is the guard earning its place.

Re-rendered so the golden matches the catalog.

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

apps/wave-0/qbittorrent.yaml

@@ -152,7 +152,7 @@ spec:
               command:
               - /bin/bash
               - -c
-              - "# Assert the durable WebUI credential in the config PVC's qBittorrent.conf, then PROVE the\n# running WebUI accepts it. Idempotent: the steady-state path writes nothing at all.\n#\n# THIS SCRIPT CONTAINS NO BRACED DOLLAR EXPANSION AT ALL, AND THAT IS DELIBERATE.\n# apps-wave-0 declares postBuild.substituteFrom cluster-vars, so Flux runs envsubst over\n# this whole manifest at RECONCILE time. The repo's escape contract (double the dollar;\n# enforced by render.py's assert_substitution_safe) makes such a form correct ON THE\n# CLUSTER \u2014 but only there:\n# envsubst collapses the doubled dollar, so the SAME text run any other way (a `kubectl\n# apply` of the golden, which runs no envsubst; a hand `kubectl exec` of the script during\n# development) keeps `$$`, which bash expands to its own PID. That is not a hypothetical;\n# see the PORT comment below for the bug it actually caused here. Bare `$VAR` and `$(cmd)`\n# are untouched by envsubst, so they are used throughout and the script behaves IDENTICALLY\n# however it is run.\nset -u\nCONF=/config/qBittorrent/qBittorrent.conf\nSVC=/run/service/svc-qbittorrent\n# The WebUI's listening port, as a LITERAL. It matches ingressRoutes[0].port in this\n# ServiceDefinition \u2014 which is the single place the renderer takes the containerPort, the\n# Service port and the HTTPRoute backend port from \u2014 and the image exposes no WEBUI_PORT\n# env var for a lookup to read anyway.\n# It USED to be a doubled-dollar default-operator expansion of a WEBUI_PORT env var, and\n# that cost real time: run without envsubst, bash read the doubled dollar as its own PID,\n# so PORT became \"<pid>{WEBUI_PORT:-8080}\" \u2014 the brace never expanded, the digits never\n# matched. Every curl below then got an unparseable URL, returned nothing, and the hook\n# logged \"the WebUI rejected the durable\n# credential\" \u2014 having never actually asked it. That MISDIAGNOSIS is preserved in this\n# service's own marker log at 2026-09-13T05:35Z (three \"rejected\" lines, then GAVE UP,\n# against a WebUI that accepted the credential perfectly well). A literal cannot be mangled.\nPORT=8080\n# A postStart hook's stdout/stderr goes to the KUBELET, not to `kubectl logs` \u2014 so a hook\n# that only echoes is effectively silent (gitea's hits the same wall and writes a marker\n# file for it). Every outcome therefore also lands, timestamped, on the persistent config\n# volume: /config/qbittorrent-webui-cred.log is where an operator looks to see whether the\n# credential from git was asserted and accepted on this start.\nlog() {\n  echo \"[qbt-webui-cred] $*\"\n  printf '%s [qbt-webui-cred] %s\\n' \"$(date -u +%Y-%m-%dT%H:%M:%SZ)\" \"$*\" \\\n    >> /config/qbittorrent-webui-cred.log 2>/dev/null || true\n}\n\n# (1) The image's init-qbittorrent-config copies /defaults/qBittorrent.conf onto the PVC\n#     before it starts the service. Wait (bounded, ~30s) so we EDIT that file instead of\n#     racing to create one it would then not overwrite.\nn=0\nwhile [ ! -s \"$CONF\" ] && [ \"$n\" -lt 120 ]; do n=$((n + 1)); sleep 0.25; done\n\nwaited=0\nattempt=0\nwhile [ \"$attempt\" -lt 3 ]; do\n  attempt=$((attempt + 1))\n\n  # (2) Converge the conf. 0 = already correct (steady state: NO write, NO re-salt),\n  #     10 = rewritten, anything else = could not write.\n  python3 - \"$CONF\" <<'PY'\nimport base64, hashlib, hmac, os, stat, sys\n\nconf = sys.argv[1]\nuser = os.environ.get(\"QBT_WEBUI_USERNAME\", \"\")\npw = os.environ.get(\"QBT_WEBUI_PASSWORD\", \"\")\nif not user or not pw:\n    sys.stderr.write(\"[qbt-webui-cred] credential env is empty - refusing to touch the conf\\n\")\n    raise SystemExit(1)\n\n# qBittorrent's OWN parameters (base/utils/password.cpp): PBKDF2-HMAC-SHA512, 100000\n# iterations, 16-byte random salt, 64-byte digest, stored as\n#   WebUI\\Password_PBKDF2=\"@ByteArray(<base64 salt>:<base64 digest>)\"\n# Get any one of them wrong and the app simply rejects every login.\nITERATIONS, DIGEST_LEN, SALT_LEN = 100000, 64, 16\nUKEY, PKEY, SECTION = \"WebUI\\\\Username\", \"WebUI\\\\Password_PBKDF2\"\
+              - "# Assert the durable WebUI credential in the config PVC's qBittorrent.conf, then PROVE the\n# running WebUI accepts it. Idempotent: the steady-state path writes nothing at all.\n#\n# THIS SCRIPT CONTAINS NO BRACED DOLLAR EXPANSION AT ALL, AND THAT IS DELIBERATE.\n# apps-wave-0 declares postBuild.substituteFrom cluster-vars, so Flux runs envsubst over\n# this whole manifest at RECONCILE time. The repo's escape contract (double the dollar;\n# enforced by render.py's assert_substitution_safe) makes such a form correct ON THE\n# CLUSTER \u2014 but only there:\n# envsubst collapses the doubled dollar, so the SAME text run any other way (a `kubectl\n# apply` of the golden, which runs no envsubst; a hand `kubectl exec` of the script during\n# development) keeps the doubled dollar, which bash reads as its own PID. Not hypothetical;\n# see the PORT comment below for the bug it actually caused here. Bare `$VAR` and `$(cmd)`\n# are untouched by envsubst, so they are used throughout and the script behaves IDENTICALLY\n# however it is run.\nset -u\nCONF=/config/qBittorrent/qBittorrent.conf\nSVC=/run/service/svc-qbittorrent\n# The WebUI's listening port, as a LITERAL. It matches ingressRoutes[0].port in this\n# ServiceDefinition \u2014 which is the single place the renderer takes the containerPort, the\n# Service port and the HTTPRoute backend port from \u2014 and the image exposes no WEBUI_PORT\n# env var for a lookup to read anyway.\n# It USED to be a doubled-dollar default-operator expansion of a WEBUI_PORT env var, and\n# that cost real time: run without envsubst, bash read the doubled dollar as its own PID,\n# so PORT became \"<pid>{WEBUI_PORT:-8080}\" \u2014 the brace never expanded, the digits never\n# matched. Every curl below then got an unparseable URL, returned nothing, and the hook\n# logged \"the WebUI rejected the durable\n# credential\" \u2014 having never actually asked it. That MISDIAGNOSIS is preserved in this\n# service's own marker log at 2026-09-13T05:35Z (three \"rejected\" lines, then GAVE UP,\n# against a WebUI that accepted the credential perfectly well). A literal cannot be mangled.\nPORT=8080\n# A postStart hook's stdout/stderr goes to the KUBELET, not to `kubectl logs` \u2014 so a hook\n# that only echoes is effectively silent (gitea's hits the same wall and writes a marker\n# file for it). Every outcome therefore also lands, timestamped, on the persistent config\n# volume: /config/qbittorrent-webui-cred.log is where an operator looks to see whether the\n# credential from git was asserted and accepted on this start.\nlog() {\n  echo \"[qbt-webui-cred] $*\"\n  printf '%s [qbt-webui-cred] %s\\n' \"$(date -u +%Y-%m-%dT%H:%M:%SZ)\" \"$*\" \\\n    >> /config/qbittorrent-webui-cred.log 2>/dev/null || true\n}\n\n# (1) The image's init-qbittorrent-config copies /defaults/qBittorrent.conf onto the PVC\n#     before it starts the service. Wait (bounded, ~30s) so we EDIT that file instead of\n#     racing to create one it would then not overwrite.\nn=0\nwhile [ ! -s \"$CONF\" ] && [ \"$n\" -lt 120 ]; do n=$((n + 1)); sleep 0.25; done\n\nwaited=0\nattempt=0\nwhile [ \"$attempt\" -lt 3 ]; do\n  attempt=$((attempt + 1))\n\n  # (2) Converge the conf. 0 = already correct (steady state: NO write, NO re-salt),\n  #     10 = rewritten, anything else = could not write.\n  python3 - \"$CONF\" <<'PY'\nimport base64, hashlib, hmac, os, stat, sys\n\nconf = sys.argv[1]\nuser = os.environ.get(\"QBT_WEBUI_USERNAME\", \"\")\npw = os.environ.get(\"QBT_WEBUI_PASSWORD\", \"\")\nif not user or not pw:\n    sys.stderr.write(\"[qbt-webui-cred] credential env is empty - refusing to touch the conf\\n\")\n    raise SystemExit(1)\n\n# qBittorrent's OWN parameters (base/utils/password.cpp): PBKDF2-HMAC-SHA512, 100000\n# iterations, 16-byte random salt, 64-byte digest, stored as\n#   WebUI\\Password_PBKDF2=\"@ByteArray(<base64 salt>:<base64 digest>)\"\n# Get any one of them wrong and the app simply rejects every login.\nITERATIONS, DIGEST_LEN, SALT_LEN = 100000, 64, 16\nUKEY, PKEY, SECTION = \"WebUI\\\\Username\", \"WebUI\\\\Password_PBKDF2\"\
                 , \"[Preferences]\"\n\ndef matches(raw):\n    \"\"\"True iff the stored digest is one OUR password produces (salt is read from it).\"\"\"\n    v = raw.strip().strip('\"')\n    if v.startswith(\"@ByteArray(\") and v.endswith(\")\"):\n        v = v[len(\"@ByteArray(\"):-1]\n    try:\n        salt_b64, digest_b64 = v.split(\":\", 1)\n        salt = base64.b64decode(salt_b64, validate=True)\n        digest = base64.b64decode(digest_b64, validate=True)\n    except Exception:\n        return False\n    if not salt or not digest:\n        return False\n    return hmac.compare_digest(\n        hashlib.pbkdf2_hmac(\"sha512\", pw.encode(), salt, ITERATIONS, len(digest)), digest)\n\ntry:\n    lines = open(conf, encoding=\"utf-8\", errors=\"replace\").read().splitlines()\nexcept FileNotFoundError:\n    lines = []\n\ndef value_of(key):\n    for i, line in enumerate(lines):\n        if line.startswith(key + \"=\"):\n            return i, line.split(\"=\", 1)[1]\n    return -1, None\n\nui, uval = value_of(UKEY)\npi, pval = value_of(PKEY)\nif uval == user and pval is not None and matches(pval):\n    raise SystemExit(0)          # converged - leave the file (and its salt) alone\n\nsalt = os.urandom(SALT_LEN)\ndigest = hashlib.pbkdf2_hmac(\"sha512\", pw.encode(), salt, ITERATIONS, DIGEST_LEN)\nstored = base64.b64encode(salt).decode() + \":\" + base64.b64encode(digest).decode()\ndesired = [UKEY + \"=\" + user, PKEY + '=\"@ByteArray(' + stored + ')\"']\n\nout = [line for i, line in enumerate(lines) if i not in (ui, pi)]\nif SECTION in out:\n    at = out.index(SECTION) + 1\nelse:\n    if out and out[-1].strip():\n        out.append(\"\")\n    out.append(SECTION)\n    at = len(out)\nout[at:at] = desired\n\ntry:\n    os.makedirs(os.path.dirname(conf) or \".\", exist_ok=True)\n    tmp = conf + \".webui-cred.new\"\n    with open(tmp, \"w\", encoding=\"utf-8\") as fh:\n        fh.write(\"\\n\".join(out) + \"\\n\")\n        fh.flush()\n        os.fsync(fh.fileno())\n    # This hook runs as ROOT; the service runs as PUID:PGID. A root-owned 0600 conf would\n    # cost the app the ability to save its own settings, so carry the ownership over.\n    try:\n        st = os.stat(conf)\n        os.chown(tmp, st.st_uid, st.st_gid)\n        os.chmod(tmp, stat.S_IMODE(st.st_mode))\n    except FileNotFoundError:\n        os.chown(tmp, int(os.environ.get(\"PUID\", \"1000\")),\n                 int(os.environ.get(\"PGID\", \"1000\")))\n        os.chmod(tmp, 0o664)\n    os.replace(tmp, conf)        # atomic: the app never reads a half-written conf\nexcept OSError as exc:\n    sys.stderr.write(\"[qbt-webui-cred] cannot write %s: %s\\n\" % (conf, exc))\n    raise SystemExit(1)\nraise SystemExit(10)\nPY\n  rc=$?\n\n  if [ \"$rc\" = 0 ]; then\n    log \"conf already holds the durable credential for '$QBT_WEBUI_USERNAME' (no write)\"\n  elif [ \"$rc\" = 10 ]; then\n    log \"asserted WebUI Username + Password_PBKDF2 into $CONF\"\n    # postStart runs CONCURRENTLY with the s6 init chain, so qbittorrent-nox may ALREADY\n    # have read the old, credential-less conf and be serving a random temporary password.\n    # Restart the SUPERVISED SERVICE (not the pod) so it re-reads what was just written.\n    # Nothing to do when the service has not started yet - it will read the new file.\n    # Its own counter, NOT the shared `waited` API budget: sharing one counter is how the\n    # 2026-09-13 failure spent the entire verification budget before the first login and\n    # then fired attempts 2 and 3 with no wait left at all.\n    sv=0\n    while [ \"$sv\" -lt 60 ] && [ \"$(s6-svstat -u \"$SVC\" 2>/dev/null)\" != \"true\" ]; do\n      sv=$((sv + 1)); sleep 1\n    done\n    if [ \"$(s6-svstat -u \"$SVC\" 2>/dev/null)\" = \"true\" ]; then\n      log \"qbittorrent-nox was already running - restarting it to load the credential\"\n      s6-svc -r \"$SVC\" || log \"s6-svc -r failed (continuing to verify anyway)\"\n      sleep 3\n    fi\n  else\n    log \"FAILED to write the credential into $CONF (helper exit $rc). The WebUI will keep\" >&2\n    log \"minting a random password\
                 \ every start and BOTH arrs will break. Fix and restart.\" >&2\n    exit 0\n  fi\n\n  # (3) GROUND TRUTH: the WebUI itself must accept it. Wait for the API to answer at ALL\n  #     (shared ~120s budget across attempts), then spend exactly ONE login per attempt -\n  #     at most 3 rejected logins, which stays under qBittorrent's default ban threshold.\n  #\n  # \"THE API NEVER ANSWERED\" IS A DIFFERENT FAULT FROM \"THE PASSWORD WAS REJECTED\", and\n  # conflating them is what made this hook lie once already (see the PORT comment). An\n  # unreachable WebUI is reported as unreachable, and the hook stops rather than spending\n  # its remaining login attempts to produce two more identical wrong diagnoses.\n  api_ok=0\n  while [ \"$waited\" -lt 120 ]; do\n    code=$(curl -s -o /dev/null -m 3 -w '%{http_code}' \"http://127.0.0.1:$PORT/\" 2>/dev/null)\n    if [ -n \"$code\" ] && [ \"$code\" != \"000\" ]; then api_ok=1; break; fi\n    waited=$((waited + 1)); sleep 1\n  done\n  if [ \"$api_ok\" != 1 ]; then\n    log \"the WebUI never answered on 127.0.0.1:$PORT within the wait budget, so the\" >&2\n    log \"credential in $CONF is UNVERIFIED. This is NOT a rejected password - it was\" >&2\n    log \"never submitted. Do not rotate the credential on the strength of this line.\" >&2\n    exit 0\n  fi\n  body=$(curl -sS -m 10 \\\n           --data-urlencode \"username=$QBT_WEBUI_USERNAME\" \\\n           --data-urlencode \"password=$QBT_WEBUI_PASSWORD\" \\\n           \"http://127.0.0.1:$PORT/api/v2/auth/login\" 2>/dev/null)\n  if [ \"$body\" = \"Ok.\" ]; then\n    log \"VERIFIED: the WebUI accepts the durable credential for '$QBT_WEBUI_USERNAME'\"\n    exit 0\n  fi\n  log \"WebUI rejected the durable credential (login said '$body')\" >&2\n  # A rejection when the conf was ALREADY converged (rc=0, nothing written) can only mean\n  # the running qbittorrent-nox is serving something it read from an EARLIER conf, so\n  # rewriting the same bytes on the next attempt would change nothing. The remedy is to\n  # make the process RE-READ the file, so restart the supervised service and let the next\n  # attempt re-verify. Without this the retry loop could never change its own outcome.\n  if [ \"$(s6-svstat -u \"$SVC\" 2>/dev/null)\" = \"true\" ]; then\n    log \"restarting qbittorrent-nox so it re-reads $CONF, then re-verifying\" >&2\n    s6-svc -r \"$SVC\" || log \"s6-svc -r failed (continuing to verify anyway)\" >&2\n    sleep 3\n  fi\ndone\n\nlog \"GAVE UP after $attempt attempts: the WebUI does not accept the credential from git.\" >&2\n# A postStart hook MUST exit 0 - a non-zero exit makes the kubelet KILL the container\n# (FailedPostStartHook -> CrashLoopBackOff), turning a credential fault into an outage.\n# Both failure paths above therefore log LOUDLY and exit 0; the `up` SLI still watches the\n# app, and the arrs' own download-client health check surfaces a broken credential.\nexit 0\n"
       - name: oauth2-proxy

catalog/qbittorrent.yaml

@@ -127,7 +127,7 @@ lifecycle:
           # CLUSTER — but only there:
           # envsubst collapses the doubled dollar, so the SAME text run any other way (a `kubectl
           # apply` of the golden, which runs no envsubst; a hand `kubectl exec` of the script during
-          # development) keeps `$$`, which bash expands to its own PID. That is not a hypothetical;
+          # development) keeps the doubled dollar, which bash reads as its own PID. Not hypothetical;
           # see the PORT comment below for the bug it actually caused here. Bare `$VAR` and `$(cmd)`
           # are untouched by envsubst, so they are used throughout and the script behaves IDENTICALLY
           # however it is run.