fix: temperature filter panics when bounds not configured (#175)

## Problem

The `filter_temperature` function in the temperature WASM operator
panics when `temperature_lower_bound` and `temperature_upper_bound` are
not provided via `moduleConfigurations`. The complex graph YAML
(`graph-complex.yaml`) does not include these parameters, so deploying
the complex graph example causes the temperature filter to crash on
every message with:

```
Lower bound not initialized
```

This means the complex graph never produces temperature statistics in
its output (humidity and object detection work fine).

## Fix

Two changes (belt and suspenders):

1. **Code fix** (`temperature/src/lib.rs`): Use sensible defaults
(`-40°C` lower, `3422°C` upper / melting point of tungsten) instead of
panicking. Logs which defaults are in use.
2. **Graph fix** (`graph-complex.yaml`): Add `temperature_lower_bound`
and `temperature_upper_bound` to `moduleConfigurations` so the
parameters are discoverable and configurable.

## Testing

- Built and verified with `cargo build --target wasm32-wasip2 --release`
(Rust 1.87)
- Also verified with `wasm32-wasip1` target
- Discovered during end-to-end documentation validation of the WASM data
flow graph docs on a live AIO k3s cluster

Author: jlian

samples/wasm/graph-complex.yaml

@@ -20,6 +20,14 @@ moduleConfigurations:
       snapshot_topic:
         name: snapshot_topic
         description: Transform app snapshot_topic in snapshot branch's init routine
+  - name: module-temperature/filter
+    parameters:
+      temperature_lower_bound:
+        name: temperature_lower_bound
+        description: "Minimum valid temperature in Celsius (default: -40)"
+      temperature_upper_bound:
+        name: temperature_upper_bound
+        description: "Maximum valid temperature in Celsius (default: 3422)"
 operations:
   - operationType: "source"
     name: "source"

samples/wasm/operators/temperature/src/lib.rs

@@ -291,15 +291,15 @@ mod filter_temperature {
     use wasm_graph_sdk::macros::filter_operator;
     use wasm_graph_sdk::metrics::{self, CounterValue, Label};
 
+    const DEFAULT_LOWER_BOUND: f64 = -40.0; // reasonable minimum for sensor data
+    const DEFAULT_UPPER_BOUND: f64 = 3422.0; // melting point of tungsten
+
     static LOWER_BOUND: OnceLock<f64> = OnceLock::new();
     static UPPER_BOUND: OnceLock<f64> = OnceLock::new();
 
-    // Note!: The initialization parameters LOWER_BOUND and UPPER_BOUND must be set via
-    // configuration properties. If these values are not configured, the function
-    // filter_temperature will panic when attempting to access them.
-    //
-    // Users can define these parameters either by using default values or by specifying
-    // them during application setup.
+    // The initialization parameters LOWER_BOUND and UPPER_BOUND can be set via
+    // configuration properties. If not configured, sensible defaults are used
+    // (-40°C lower bound, 3422°C upper bound / melting point of tungsten).
     #[allow(clippy::needless_pass_by_value)]
     fn filter_temperature_init(configuration: ModuleConfiguration) -> bool {
         logger::log(
@@ -311,7 +311,7 @@ mod filter_temperature {
         if let Some(value_string) = configuration
             .properties
             .iter()
-            .find(|(key, _value)| key == "temperature_lower_bound") // or whatever it is
+            .find(|(key, _value)| key == "temperature_lower_bound")
             .map(|(_key, value)| value.clone())
         {
             match value_string.parse::<f64>() {
@@ -331,12 +331,18 @@ mod filter_temperature {
                     );
                 }
             }
+        } else {
+            logger::log(
+                Level::Info,
+                "module-temperature/filter",
+                &format!("temperature_lower_bound not configured, using default: {DEFAULT_LOWER_BOUND}"),
+            );
         }
 
         if let Some(value_string) = configuration
             .properties
             .iter()
-            .find(|(key, _value)| key == "temperature_upper_bound") // or whatever it is
+            .find(|(key, _value)| key == "temperature_upper_bound")
             .map(|(_key, value)| value.clone())
         {
             match value_string.parse::<f64>() {
@@ -356,6 +362,12 @@ mod filter_temperature {
                     );
                 }
             }
+        } else {
+            logger::log(
+                Level::Info,
+                "module-temperature/filter",
+                &format!("temperature_upper_bound not configured, using default: {DEFAULT_UPPER_BOUND}"),
+            );
         }
 
         true
@@ -386,8 +398,8 @@ mod filter_temperature {
             &format!("incoming measurement {measurement:?}"),
         );
 
-        let lower_bound = LOWER_BOUND.get().expect("Lower bound not initialized");
-        let upper_bound = UPPER_BOUND.get().expect("Upper bound not initialized");
+        let lower_bound = LOWER_BOUND.get().copied().unwrap_or(DEFAULT_LOWER_BOUND);
+        let upper_bound = UPPER_BOUND.get().copied().unwrap_or(DEFAULT_UPPER_BOUND);
 
         // Malfunctioning probe sometimes reports higher temperature than melting point of tungsten.
         // Ignore these values.
@@ -402,7 +414,7 @@ mod filter_temperature {
                 last: _,
                 unit: MeasurementTemperatureUnit::Celsius,
                 overtemp: _,
-            }) if value.unwrap() < *upper_bound && value.unwrap() > *lower_bound,
+            }) if value.unwrap() < upper_bound && value.unwrap() > lower_bound,
         ))
     }
 }