ADR on dataset overall base path (#3725)

* Create 2026-02-10-dataset-base-path.md

* Create 2026-02-10-dataset-base-path.md

* new ADR sketch

* Update 20260210-dataset-base-path.md

adrs/2026-02-10-dataset-base-path.md

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adrs/20260210-dataset-base-path.md

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+# Adopt a base path for datasets
+
+**authors:** [Julio](https://github.com/juliocc) [Ludo](https://github.com/ludoo)
+**date:** Feb 10, 2026
+
+## Status
+
+Draft
+
+## Context
+
+This ADR provides a potential solution to two concurrent issues.
+
+FAST stages still use the old per-factory path approach, which makes it harder to switch datasets.
+
+```hcl
+variable "factories_config" {
+  description = "Configuration for the resource factories or external data."
+  type = object({
+    billing_accounts  = optional(string, "datasets/classic/billing-accounts")
+    cicd_workflows    = optional(string)
+    defaults          = optional(string, "datasets/classic/defaults.yaml")
+    folders           = optional(string, "datasets/classic/folders")
+    observability     = optional(string, "datasets/classic/observability")
+    organization      = optional(string, "datasets/classic/organization")
+    project_templates = optional(string, "datasets/classic/templates")
+    projects          = optional(string, "datasets/classic/projects")
+  })
+  nullable = false
+  default  = {}
+}
+```
+
+Project-level factories in the project factory module use relative paths based on the root module in scope, forcing users to embed paths in the YAML files.
+
+```yaml
+factories_config:
+  observability: datasets/classic/observability/iac-0
+```
+
+## Proposed Approach
+
+The proposed approach changes the `factories_config` variable in FAST stages so that a new `dataset` attribute is added, and existing lower-level paths are moved to a `paths` attribute.
+
+```hcl
+variable "factories_config" {
+  description = "Configuration for the resource factories or external data."
+  type = object({
+    dataset = optional(string, "datasets/classic")
+    paths   = optional(object({
+      billing_accounts  = optional(string, "billing-accounts")
+      cicd_workflows    = optional(string)
+      defaults          = optional(string, "defaults.yaml")
+      folders           = optional(string, "folders")
+      observability     = optional(string, "observability")
+      organization      = optional(string, "organization")
+      project_templates = optional(string, "templates")
+      projects          = optional(string, "projects")
+    }), {})
+  })
+  nullable = false
+  default  = {}
+}
+```
+
+This allows one-line configuration of the dataset, while still providing a way to cancel out individual factories by omitting the path, or pointing to a non-existing folder. The base path will not be prepended for paths starting with `/` or `.`, to allow for different absolute or relative paths, and to also allow our testing framweork to inject fixtures.
+
+On the project factory side, the `factories_config` variable will also change by adopting a "base path" and grouping existing attributes under a `paths` variable.
+
+```hcl
+variable "factories_config" {
+  description = "Path to folder with YAML resource description data files."
+  type = object({
+    base_path = "data"
+    paths = optional(object({
+      folders           = optional(string)
+      project_templates = optional(string)
+      projects          = optional(string)
+      budgets = optional(object({
+        billing_account_id = string
+        data               = string
+      }))
+    }), {})
+  })
+  nullable = false
+}
+```
+
+The lower level modules will not change interface, but the base path will be prepended by the project factory to in-project `factories_config` paths, to allow decoupling from the dataset and creating portable files.
+
+```yaml
+factories_config:
+  observability: observability/iac-0
+```