[terraform-provider-octopusdeploy] octopusdeploy_tag create panics (nil pointer) when tag set update rejected

## Observed symptom `octopusdeploy_tag` create panics (nil pointer) when the tag set update is rejected, hiding the server's error **Describe the bug** When the server rejects the tag set update during `octopusdeploy_tag` create, the provider crashes instead of reporting the server's error. For example, a target tag whose name already exists in another Target-scoped tag set returns HTTP 400: "The following tag names already exist in other Target tag sets". **Cause (from reading the v1.20.0 source)** In `tagCreate` (`octopusdeploy_framework/resource_tag.go`), the error from `tagsets.Update` is added to `diag`, but execution continues to `findByIdOrNameAndSetTag(ctx, data, tag, updatedTagSet)` with `updatedTagSet == nil`. That function then ranges over `tagSet.Tags`, which panics. Separately, `Create` calls `tagCreate( ## Literal error text ``` octopusdeploy_tag create panics nil pointer ``` ## Environment GitHub OctopusDeploy/terraform-provider-octopusdeploy #305 ## Trigger / context **Describe the bug** When the server rejects the tag set update during `octopusdeploy_tag` create, the provider crashes instead of reporting the server's error. For example, a target tag whose name already exists in another Target-scoped tag set returns HTTP 400: "The following tag names already exist in other Target tag sets". **Cause (from reading the v1.20.0 source)** In `tagCreate` (`octopusdeploy_framework/resource_tag.go`), the error from `tagsets.Update` is added to `diag`, but execution continues to `findByIdOrNameAndSetTag(ctx, data, tag, updatedTagSet)` with `updatedTagSet == nil`. That function then ranges over `tagSet.Tags`, which panics. Separately, `Create` calls `tagCreate(ctx, data, resp.Diagnostics, r.Client)` and discards the return value. `diag.Diagnostics` is a slice passed by value, so errors that `tagCreate` adds never reach `resp.Diagnostics`. That means **no** tag create error is ever reported, crash or not. The duplicate-name check just above has the same sh ## Source evidence - https://github.com/OctopusDeploy/terraform-provider-octopusdeploy/issues/305 (2026-09-30T19:06:23Z) — #305 ## Freshness - classification: FRESH_7D - retrieved_at: 2026-10-02T09:49:02.645589Z - scout_id: C4674f755ca ## Scout notes This Problem was published by the KFA Fresh Friction Scout from public sources. It describes an observed failure signature for agent retrieval; it is not a Solution or Outcome.