feat(docs): update architecture and state machines documentation

- Refactor architecture documentation to consolidate controller state machine information.
- Add detailed state machines documentation for CRDs, including transitions and conditions.
- Include state machines in the navigation of the operator manual.
- Update requirements.txt for dependency management.
- Modify mkdocs configuration to support Mermaid diagrams.

Author: nlevee

.github/workflows/docs.yaml

@@ -33,7 +33,7 @@ jobs:
             mkdocs-material-
 
       - name: Install dependencies
-        run: pip install mkdocs-material mike
+        run: pip install -r requirements.txt
 
       - name: Lint Markdown files
         uses: DavidAnson/markdownlint-cli2-action@ce4853d43830c74c1753b39f3cf40f71c2031eb9 # v23

docs/operator-manual/architecture.md

@@ -57,45 +57,12 @@ The CLI used to start the different components is implemented using [`cobra`](ht
 
 For more details on how the repository controller works with Git bundles and revisions, see the [Repository Controller documentation](./repository-controller.md).
 
-### The TerraformLayer Controller
+### Controller state machines
 
-The status of a `TerraformLayer` is defined using the [conditions standards defined by the community](https://github.com/kubernetes/community/blob/master/contributors/devel/sig-architecture/api-conventions.md#typical-status-properties).
-
-3 conditions are defined for a layer:
-
-- `IsPlanArtifactUpToDate`. This condition is used for drift detection. The evaluation is made by compraing the timestamp of the last `terraform plan` which ran and the current date. The timestamp of the last plan is "stored" using an annotation.
-- `IsApplyUpToDate`. This condition is used to check if an `apply` needs to run after the last `plan`. Comparison is made by comparing a checksum of the last planned binary and a checksum last applied binary stored in the annotations.
-- `IsLastRelevantCommitPlanned`. This condition is used to check if a new commit has been made to the layer and need to be applied. It is evaluated by comparing the commit used for the last `plan`, the last commit which intoduced changes to the layer and the last commit made to the same branch of the repository. Those commits are "stored" as annotations.
-
-With those 3 conditions, we defined 3 states:
-
-- `Idle`. This is the state of a layer if no runner needs be started
-- `PlanNeeded`. This is the state of a layer if burrito needs to start a `plan` runner
-- `ApplyNeeded`. This is the state of a layer if burrito needs to start an `apply` runner
-
-!!! info
-    If you use [`dry` remediation strategy](../user-guide/remediation-strategy.md) and an apply is needed, the layer will stay in the `ApplyNeeded` as long as it does not need to enter the `PlanNeeded`.
-
-### The TerraformRun Controller
-
-The status of a `TerraformRun` is also defined using the same [conditions standards defined by the community](https://github.com/kubernetes/community/blob/master/contributors/devel/sig-architecture/api-conventions.md#typical-status-properties).
-
-5 conditions are defined for a run:
-
-- `HasStatus`. This condition is used to check if a `TerraformRun` has already been reconciled by the controller.
-- `HasReachedRetryLimit`. Used to check if a `TerraformRun` has reached the maximum number of retries.
-- `HasSucceeded`. Used to check if a `TerraformRun` has already succeeded (runner pod exited successfully).
-- `IsRunning`. Used to check if a `TerraformRun` is currently running by checking the current phase of its associated pod.
-- `IsInfailureGracePeriod`. This condition is used to check if a Terraform workflow has already failed. If so, we use an exponential backoff strategy before restarting a runner on the given layer.
-
-With those 5 conditions, we defined 6 states:
-
-- `Initial`. This is the state of a run when it has just been created and has launched its first runner pod.
-- `Running`. This is the state of a run if a runner pod is currently running.
-- `FailureGracePeriod`. This is the state of a layer if a `plan` or `apply` runner has failed
-- `Retrying`. This is an intermediate state of a run if a runner pod has failed and is being restarted (not in failure grace period anymore).
-- `Succeeded`. This is one of the two final states a run can have. It means that the runner pod has exited successfully.
-- `Failed`. This is the other final state a run can have. It means that the run has failed multiple times and has reached the maximum number of retries.
+Each controller drives its resource through a state machine whose status is
+expressed using the [conditions standards defined by the community](https://github.com/kubernetes/community/blob/master/contributors/devel/sig-architecture/api-conventions.md#typical-status-properties).
+For the full state machines of each CRD, the conditions that drive them, and how
+the resources interact, see [CRD State Machines](./state-machines.md).
 
 The `TerraformRun` controller also creates and deletes the [Kubernetes leases](https://kubernetes.io/docs/concepts/architecture/leases/) to avoid concurrent use of Terraform on the same layer.
 

docs/operator-manual/state-machines.md

@@ -0,0 +1,123 @@
+# CRD State Machines
+
+Each Burrito custom resource is driven by a state machine implemented in its
+reconciler (`internal/controllers/<crd>/states.go`). Burrito controllers are
+**level-based**: on every reconcile the controller *recomputes* the current state
+from a set of boolean conditions through an ordered `switch`. There are no stored
+transitions — a state's handler performs a side-effect (creating a `TerraformRun`,
+a runner pod, an annotation…), and the *next* reconcile observes the changed
+conditions and yields the next state.
+
+A practical consequence: some states are **transient triggers**. For example a
+`TerraformLayer` in `PlanNeeded` creates a run and, on the following reconcile,
+is seen as running and reported as `Idle` again.
+
+## TerraformRepository
+
+The repository controller keeps Git bundles in the datastore in sync with the
+remote. It has two states, decided by whether the last sync is too old or failed.
+
+- `Synced` — bundles are up to date; requeue at the repository sync interval.
+- `SyncNeeded` — fetch latest revisions per branch, store bundles, and annotate
+  the affected layers.
+
+```mermaid
+stateDiagram-v2
+    [*] --> Synced
+    Synced --> SyncNeeded: last sync too old / last sync failed
+    SyncNeeded --> Synced: all branches synced successfully
+    SyncNeeded --> SyncNeeded: sync error (requeue)
+```
+
+## TerraformLayer
+
+The layer controller watches declared layers and creates `TerraformRun` resources
+to plan (drift detection) and, when auto-apply is enabled, to apply. The state is
+computed from conditions such as *is a run in flight*, *is a sync scheduled*, *is
+the last plan too old*, *is the last relevant commit planned*, *is the apply up to
+date*, and *has the last run reached its retry limit*.
+
+Because the first `switch` case is "a run is in flight → `Idle`", a layer with a
+running plan/apply is reported as `Idle`. `PlanNeeded` and `ApplyNeeded` are
+transient: their handler creates the run and the next reconcile returns to `Idle`.
+
+- `Idle` — nothing to do; requeue at the drift-detection interval.
+- `PlanNeeded` — create a plan `TerraformRun`.
+- `ApplyNeeded` — create an apply `TerraformRun` (only if auto-apply is enabled).
+- `MaxRetriesReached` — the last run exhausted its retries; manual intervention
+  needed.
+
+```mermaid
+stateDiagram-v2
+    [*] --> Idle
+    Idle --> PlanNeeded: plan outdated / new relevant commit / sync scheduled
+    Idle --> ApplyNeeded: plan up to date but apply needed (autoApply on)
+    PlanNeeded --> Idle: TerraformRun (plan) created — run in flight
+    ApplyNeeded --> Idle: TerraformRun (apply) created — run in flight
+    Idle --> MaxRetriesReached: last run exhausted its retries
+    MaxRetriesReached --> Idle: new relevant commit / retry window reset
+```
+
+## TerraformRun
+
+The run controller executes a plan or apply by creating runner pods, and handles
+retries with an exponential backoff grace period. `Succeeded` and `Failed` are
+terminal.
+
+- `Initial` — freshly created; sets the lease and launches the first runner pod.
+- `Running` — a runner pod is currently running.
+- `FailureGracePeriod` — the runner failed; wait (exponential backoff) before retry.
+- `Retrying` — grace period elapsed and retry limit not reached; launch a new pod.
+- `Succeeded` — the runner pod exited successfully (lease released).
+- `Failed` — retries exhausted (lease released).
+
+```mermaid
+stateDiagram-v2
+    [*] --> Initial
+    Initial --> Running: runner pod created
+    Running --> Succeeded: pod exited successfully
+    Running --> FailureGracePeriod: pod failed, retry limit not reached
+    FailureGracePeriod --> Retrying: grace period elapsed
+    FailureGracePeriod --> Failed: retry limit reached
+    Retrying --> Running: retry pod created
+    Succeeded --> [*]
+    Failed --> [*]
+```
+
+## TerraformPullRequest
+
+The pull-request controller discovers layers affected by a PR/MR, waits for their
+plans, and posts a comment. Note that "comment up to date" is checked before
+"layers still planning", so a PR with an up-to-date comment is reported as `Idle`.
+
+- `DiscoveryNeeded` — a new commit was detected; (re)create the temporary layers
+  affected by the PR.
+- `Planning` — the temporary layers are still planning.
+- `CommentNeeded` — plans finished; post/update the PR comment.
+- `Idle` — comment is up to date; nothing to do.
+
+```mermaid
+stateDiagram-v2
+    [*] --> DiscoveryNeeded
+    DiscoveryNeeded --> Planning: temp layers created, commit discovered
+    Planning --> CommentNeeded: all layers finished planning
+    CommentNeeded --> Idle: comment posted on PR/MR
+    Idle --> DiscoveryNeeded: new commit on the PR branch
+```
+
+## How the CRDs interact
+
+The resources form a chain: the repository annotates layers with the latest
+relevant commit, layers create runs, runs create runner pods, and pods write plan
+and apply results back onto the layer's annotations. A pull request creates
+temporary layers and reports their plan results as a comment.
+
+```mermaid
+flowchart LR
+    Repo[TerraformRepository] -->|annotates last relevant commit| Layer[TerraformLayer]
+    Layer -->|creates on plan/apply needed| Run[TerraformRun]
+    Run -->|creates runner| Pod[Runner Pod]
+    Pod -->|updates plan/apply annotations| Layer
+    PR[TerraformPullRequest] -->|creates temp layers| Layer
+    PR -->|reads plan results, comments| Git[Git provider]
+```

internal/controllers/AGENTS.md

@@ -15,3 +15,4 @@ custom resource: `terraformlayer/`, `terraformrun/`, `terraformrepository/`,
 - Use structured logging via the `logr.Logger` carried in `ctx` (`log.FromContext(ctx)`).
 - Propagate `ctx` and set timeouts on every external call (GitHub, GitLab, Terraform).
 - CRD shapes live in `api/v1alpha1`; never edit generated deepcopy code. After API changes run `make manifests && make generate`.
+- **State machines are documented.** When you change a reconciler's states or transitions (its `states.go` — the `GetState` switch, state structs, or the conditions in `conditions.go` that drive them), update the matching Mermaid diagram in [`docs/operator-manual/state-machines.md`](../../docs/operator-manual/state-machines.md) so it stays in sync.

mkdocs.yml

@@ -12,7 +12,12 @@ extra:
 markdown_extensions:
   - codehilite
   - admonition
-  - pymdownx.superfences
+  - pymdownx.superfences:
+    # make exceptions to highlighting of code:
+      custom_fences:
+        - name: mermaid
+          class: mermaid
+          format: !!python/name:mermaid2.fence_mermaid_custom
   - toc:
       permalink: true
 nav:
@@ -30,6 +35,7 @@ nav:
   - Operator Manual:
       - operator-manual/index.md
       - operator-manual/architecture.md
+      - operator-manual/state-machines.md
       - operator-manual/user-authentication.md
       - operator-manual/repository-controller.md
       - Git Authentication:

requirements.txt

@@ -0,0 +1,39 @@
+babel==2.18.0
+backrefs==7.0
+beautifulsoup4==4.15.0
+certifi==2026.6.17
+charset-normalizer==3.4.9
+click==8.4.2
+colorama==0.4.6
+editorconfig==0.17.1
+ghp-import==2.1.0
+idna==3.18
+jinja2==3.1.6
+jsbeautifier==2.0.3
+markdown==3.10.2
+markupsafe==3.0.3
+mergedeep==1.3.4
+mike==2.2.0
+mkdocs==1.6.1
+mkdocs-get-deps==0.2.2
+mkdocs-material==9.7.6
+mkdocs-material-extensions==1.3.1
+mkdocs-mermaid2-plugin==1.2.3
+packaging==26.2
+paginate==0.5.7
+pathspec==1.1.1
+platformdirs==4.10.0
+pygments==2.20.0
+pymdown-extensions==11.0.1
+pyparsing==3.3.2
+python-dateutil==2.9.0.post0
+pyyaml==6.0.3
+pyyaml-env-tag==1.1
+requests==2.34.2
+setuptools==83.0.0
+six==1.17.0
+soupsieve==2.8.4
+typing-extensions==4.16.0
+urllib3==2.7.0
+verspec==0.1.0
+watchdog==6.0.0