Nine fixes from a review of the docker-shm-devices diff:
* GNS3_STOP_TIMEOUT >300 s aborted at the manager's default HTTP timeout
before Docker finished the stop — the stop query now gets a timeout
with a margin over the grace period.
* Overlapping bind targets (GNS3_MASK_UDEV + GNS3_MASK_SYSTEMD on the
same unit, a unit named twice, an extra_configs target equal to a
masked unit) made Docker reject the create with 'Duplicate mount
point' — Mounts are deduplicated by target.
* ExtraConfig.target now carries a pydantic validator (absolute file
path, no '..'), so bad targets 422 at template-save time instead of
failing at node-create time after a multi-GB image pull; directory
forms ('/', '/etc/') are also rejected by the runtime guard instead
of raising IsADirectoryError (raw 500).
* _check_host_readiness skipped every remaining check when one
/proc/sys key was unreadable (mid-loop return) — now continues.
* The base-class GNS3_* env parser strips trailing commas like the
vendor parser, so 'GNS3_MASK_UDEV=1,' composed from a list still
activates.
* Vendor env knobs are re-parsed on every create(), so a PUT to the
node's environment takes effect on the next (re)create.
* The graceful SIGTERM stop is now limited to the explicit user stop
route; delete/update/close/crash-cleanup keep the immediate kill
(those paths force-delete or recreate the container right after).
* An extra_configs target beneath a persisted volume is shadowed by the
volume bind — warn at create time.
Add an `extra_configs` field (list of {target, content}) to the docker
node/template/appliance schemas. For each entry GNS3 writes `content` to a
file in the node working directory and bind-mounts it read-only at `target`
inside the container.
This lets a NOS appliance seed its startup config without rebuilding the
image: XRd points XR_FIRST_BOOT_CONFIG at an injected /firstboot.cfg, FRR at
/etc/frr/frr.conf, etc. The bind is a single-file mount applied at create
time, so it works for both the generic init.sh path and vendor nodes that
skip init.sh (console_type=docker_exec). Entries are only injected when
present, so ordinary nodes are unaffected.
The content can't go through `environment` (it is line-delimited, one var per
line), hence a dedicated field -- the same plumbing shape as extra_volumes.
