docs(kanvas): relationship evaluation engine selection & diagnostics

content/en/kanvas/designer/relationship-evaluation/index.md

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+---
+title: Policy Engine
+description: >
+  Choose how Kanvas evaluates relationships in your designs, understand the
+  relationship indicator states, and diagnose failing or unexpected relationship
+  results.
+weight: 11
+categories: [Designer]
+tags: [designs, relationships, components, troubleshooting]
+---
+
+As you build a design, Kanvas continuously evaluates the
+[relationships](/kanvas/concepts/relationships/) between your components — to
+identify connections, validate them, and keep related configuration in sync.
+This page explains how you can choose which engine performs that evaluation, how
+to read the relationship indicator, and how to diagnose results that look wrong.
+
+## How Relationships Are Evaluated
+
+Kanvas can run relationship evaluation using one of two interchangeable engines:
+
+- **Server-side** — the policy engine running inside your Meshery server. It
+  is always available and is the default.
+- **Client-side** — the same policy engine, compiled to WebAssembly and
+  run inside a background worker in your browser. Because it runs locally, there
+  are no round-trips to the server, so evaluation is typically faster. It is
+  available only when your Meshery server provides the WebAssembly artifact.
+
+Both engines produce the same relationship results. The choice affects
+performance, and where toil (evaluation) is done, not correctness.
+
+{{< alert type="info" title="Editing is never blocked" >}} Relationship
+evaluation runs alongside your work — it never blocks editing or saving a
+design. If evaluation fails for any reason, you can keep designing and saving
+normally; only the relationship results are affected. {{< /alert >}}
+
+## Changing the Evaluation Engine Preference
+
+The engine is controlled by the **Relationship Evaluation Engine** preference.
+
+1. In Kanvas Designer, open **Settings**.
+2. Find the **Relationship Evaluation Engine** preference.
+3. Choose one of the following values:
+
+| Value                       | What it does                                                                                                                                                                                 |
+| --------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| **Automatic** (recommended) | Runs a one-time health check at the start of the session. If the client-side (WASM) engine passes a self-test, it is used for the rest of the session; otherwise the Meshery server is used. |
+| **Meshery server**          | Always uses the Meshery server's policy engine.                                                                                                                                              |
+| **Client-side (WASM)**      | Uses the in-browser WebAssembly engine.                                                                                                                                                      |
+
+The engine is selected **once per session**. Changing the preference takes full
+effect on the next session (for example, after reloading Kanvas).
+
+{{< alert type="info" title="When to prefer the server engine" >}} Leave the
+preference on **Automatic** unless you have a specific reason to change it. If
+client-side results ever look wrong, switching to **Meshery server** is the most
+reliable way to rule out the engine as the cause — see
+[Diagnosing failing or unexpected results](#diagnosing-failing-or-unexpected-relationship-results).
+{{< /alert >}}
+
+## Reading the Relationship Indicator
+
+The relationship indicator tells you the state of the most recent evaluation:
+
+- **Evaluating** — evaluation is in progress. This is normal after you add,
+  remove, or reconfigure components.
+- **Evaluated** — evaluation completed successfully and the relationships shown
+  on the canvas are up to date.
+- **Error** — the most recent evaluation failed. This is a distinct state from
+  "no relationships evaluated yet". When evaluation fails:
+  - The last successful relationship results stay on screen so your design
+    remains readable.
+  - A one-time, non-blocking notification appears to let you know.
+  - You can continue editing and saving the design without interruption.
+
+If the client-side (WASM) engine was active and faults during the session, it
+automatically self-heals: Kanvas falls back to the Meshery server engine for the
+remainder of the session, without requiring any action from you.
+
+### What the one-time notifications mean
+
+When evaluation first fails, or when Kanvas falls back from the client-side
+engine to the server engine, a single non-blocking notification is shown. It is
+informational — it does not require a response, and it will not repeat for every
+subsequent evaluation in that session. Its purpose is to let you know that
+relationship results may be stale or that the active engine changed.
+
+## Diagnosing Failing or Unexpected Relationship Results
+
+If relationships are missing, look wrong, or the indicator shows an error, use
+the **Relationship Evaluation Diagnostics** view to investigate.
+
+### Step 1 — Enable the debugger preference
+
+The Diagnostics view is exposed under the Designer **debugger** preference.
+
+1. In Kanvas Designer, open **Settings**.
+2. Enable the **debugger** preference.
+3. Open the **Relationship Evaluation Diagnostics** view.
+
+### Step 2 — Read the Diagnostics view
+
+The Diagnostics view reports the current state of relationship evaluation:
+
+- **Active engine and why** — which engine is in use (Meshery server or
+  client-side WASM) and the reason it was selected (for example, the result of
+  the Automatic health check, an explicit preference, or a runtime fallback).
+- **Contract / version** — the evaluation contract and engine version, used to
+  confirm the client and server are compatible.
+- **Last error** — the most recent evaluation error, if any.
+- **Fallback count** — how many times Kanvas has fallen back from the
+  client-side engine to the server engine this session.
+- **Latency** — how long recent evaluations took.
+
+### Step 3 — Force the server engine if client results look wrong
+
+If you suspect the client-side engine is producing incorrect results:
+
+1. Open **Settings**.
+2. Set **Relationship Evaluation Engine** to **Meshery server**.
+3. Reload Kanvas so the new engine is used for the session.
+4. Re-check the design's relationships.
+
+If the relationships are correct with the server engine but wrong with the
+client-side engine, that points to a client engine issue worth reporting (see
+below).
+
+### Step 4 — Re-trigger evaluation
+
+Evaluation re-runs automatically whenever you change the design — for example,
+by adding, removing, or reconfiguring a component, or by toggling a relationship
+kind on or off from the **Relationships** section of the Designer. Making any such
+change re-triggers evaluation with the active engine. If the indicator was in
+the error state, a successful re-evaluation clears it.
+
+### Step 5 — When and how to file a bug
+
+If relationship results are still wrong or evaluation keeps failing after the
+steps above — especially if the **Meshery server** engine also produces
+incorrect or failing results — file a bug. Include the following from the
+Relationship Evaluation Diagnostics view so the issue can be reproduced:
+
+- The **active engine** and the reason it was selected.
+- The **contract / version** shown in the Diagnostics view.
+- The **last error** text.
+- The **fallback count**, if relevant.
+- A description of the expected relationships versus what Kanvas showed, and the
+  design (or a minimal reproduction) if you can share it.
+
+{{< alert type="info" title="Related reading" >}} For an overview of what
+relationships are and the kinds Kanvas supports, see
+[Understanding Relationships](/kanvas/concepts/relationships/). For creating and
+managing relationships in a design, see
+[Creating Relationships](/kanvas/getting-started/creating-relationships/).
+{{< /alert >}}