The container's collector has never shipped a line. `journalctl --follow`
— which the journald receiver passes unconditionally — scopes itself to
the current boot unless `--merge` is given too, and `--link-journal=host`
makes /var/log/journal the HOST's journal tree, where this container's
current boot has no entry. journalctl exited 1 with "No journal boot
entry found for the specified boot (+0)" and the receiver respawned it
every ~2s, so nothing was ever read and nothing was ever exported.
`merge = true` is the receiver's key for `--merge` (buildArgs() in
pkg/stanza/operator/input/journald/config_linux.go at tag
receiver/journaldreceiver/v0.151.0, the deployed collector's version),
and --merge is what clears the implicit boot scope in journalctl.c
(systemd v260.4, the version on the host).
The module-eval arm pins both halves: the boot filter is gone AND the
directory is still the host-linked one — either alone is satisfiable by
the broken config.
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