[BUG] Clearing Command (optional) on Edit container does not persist after Update #1489

Description

In Edit container → Update container, clearing the optional Command field (non-empty → empty) appears to succeed, but the container still runs the previous command. Re-opening Edit shows the old value; it never becomes empty / image default.

This is the same “empty means absent, not cleared” merge as #1119 / #747 / #892, but Command was not included in the #1119 null-vs-omit fix.

In EditContainerModal.svelte, the update payload comment already documents the contract:

send null when the user cleared them so the server can distinguish "cleared" from "absent" (#1119). … explicit null = clear; undefined would be dropped by JSON.stringify and the merge would preserve the old value.

env, memory, user, etc. follow that (?? null / || null). Command does not:

const cmd = command.trim() ? parseShellCommand(command.trim()) : undefined;
// …
const payload = {
  // …
  cmd,  // omitted from JSON when empty → server keeps old Cmd
};

Expected: empty Command → send cmd: null → recreate without a user override so Docker uses the image CMD.

Not a duplicate of #1371 (that was auto-update keeping the old image Cmd when the new image Cmd changed).

Steps to reproduce

1. Create or edit a container and set Command (optional) to a non-empty override (e.g. sleep 9999). Update container.
2. Confirm inspect / Edit still shows that command.
3. Edit container again. Clear Command (optional) so the field is empty.
4. Click Update container.
5. Re-open Edit (or docker inspect Config.Cmd).

Expected

Command is empty / image default CMD.

Actual

Command remains the previous override. Update reports success.

Logs

N/A — UI-only; no Dockhand error. The POST /api/containers/{id}/update body omits `cmd` when the field is cleared (JSON.stringify drops `undefined`). When Command is filled, `cmd` is an array in the same body.

Browser logs

N/A — compare the update POST: cleared Command has no `cmd` key; non-empty Command has `"cmd": [ … ]`.

Dockhand version

Current main (EditContainerModal.svelte still uses cmd = … : undefined). Please fill Settings → About if you need a specific build.

Hawser version (if used)

No response

Connection mode

socket (likely irrelevant; payload is built in the UI)

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• I have already searched for relevant existing issues and discussions before opening this report.
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