Regression of: Variable substitution not working for JSON array with index zero

[SeanStanway-Octopus]

Severity

one customer reported, can recreate on latest cloud instance

Version

2026.1.11242, 2026.2.999

Latest Version

None

What happened?

Unable to use a JSON array, or JSON object array, when trying to select the zero index. The value is not found/is written as blank. This happens both in script bodies, as well as utilisation in the selection of scripts themselves.

This was previously fixed in #9888

Reproduction

See #9888 reproduction. Same failure occurs.

Error and Stacktrace

From customer:
16:09:06   Error    |         Error: Invalid input: RPC ListVolumes Field managedcatalog.volume.ListVolumes.schema_name: name "#{workspace.groups.users[0].name}" is not a valid name. Valid names must contain only alphanumeric characters and underscores, and cannot contain spaces, periods, forward slashes, or control characters.

More Information

Variable:

Usage:
Write-Host "Checking:" $OctopusParameters["Workspace.Catalog.Schemas[0]"]

Result:

Workaround

No response

[wlthomson]

Although this understandably was classified as a regression, it looks like it was actually a miss in the original fix.

Octopus Server and Calamari both manage their own version of Octostache, meaning that customers on a given version of Octopus Deploy are potentially relying on two different versions of Octostache. In this case, only one Octostache dependency was bumped to the patched version, leaving Calamari still reliant on a version containing the buggy "zero-index" behaviour.

A patch for versions 2026.1 onwards will be out shortly.

Thanks for your patience!