Please address the comments from this code review:

## Individual Comments

### Comment 1
<location> `central/metrics/custom/tracker/tracker_base.go:311-312` </location>
<code_context>
 		if !gr.trySetRunning() {
 			return nil
 		}
+		// Recreate aggregator if config has changed since last run.
+		if gr.config != cfg {
+			gr.aggregator = makeAggregator(cfg.metrics, cfg.filters, tracker.getters)
+			gr.config = cfg
</code_context>

<issue_to_address>
**suggestion (bug_risk):** Pointer-based config comparison may miss changes if the configuration is mutated in place

This relies on pointer inequality (`gr.config != cfg`) rather than config content or a version, so it only works if callers always replace the `*Configuration` instead of mutating or reusing it. If a `Configuration` is updated in place, the pointers remain equal, the aggregator won’t be rebuilt, and metrics can become stale. Either enforce/clarify immutability of `Configuration` or introduce a version/epoch or other change indicator instead of comparing pointers.

Suggested implementation:

```golang
		// Recreate aggregator if config has changed since last run.
		// Use a configuration version/epoch instead of pointer identity so that
		// in-place configuration mutations are also detected.
		if gr.configVersion != cfg.Version {
			gr.aggregator = makeAggregator(cfg.metrics, cfg.filters, tracker.getters)
			gr.configVersion = cfg.Version
			gr.config = cfg
		}

```

To fully implement this correctly, you will also need to:

1. **Add a version/epoch field to the configuration type** (whatever `cfg` is):
   - For example:
     ```go
     type Configuration struct {
         Version uint64
         // existing fields: metrics, filters, ...
     }
     ```
   - Ensure that any code that mutates the configuration either:
     - Treats it as immutable and creates a new `Configuration` with an incremented `Version`, or
     - Explicitly increments `Version` whenever the configuration is changed in place.

2. **Extend the `gatherer` struct to store the last-seen config version**:
   - In the `gatherer[F]` type definition, add:
     ```go
     configVersion uint64
     config        *Configuration // or the actual config type, if not already present
     ```
     (If `config` is already present in the struct, just add `configVersion`.)

3. **Initialize `configVersion` when a new gatherer is created**:
   - Wherever a new `gatherer` is constructed (likely in the same file), set:
     ```go
     gr.configVersion = cfg.Version
     gr.config = cfg
     ```
   - This ensures the first run starts with the correct baseline version.

4. **Update all existing references to config comparison**:
   - If there are other places that compare `gr.config` and `cfg` by pointer (`gr.config != cfg` or `==`), update them to compare `configVersion` vs `cfg.Version` instead, or remove redundant checks if they become unnecessary.

These additional changes ensure the aggregator is safely rebuilt whenever the configuration changes, regardless of whether the change is via replacement or in-place mutation.
</issue_to_address>

### Comment 2
<location> `central/metrics/custom/tracker/tracker_base_test.go:360-369` </location>
<code_context>
+func TestTrackerBase_Gather_afterReconfiguration(t *testing.T) {
</code_context>

<issue_to_address>
**suggestion (testing):** Also assert that old metrics are no longer gathered after reconfiguration

To fully validate the unregister path and aggregator re-creation, please also assert that metrics from the initial configuration (e.g., keys from `md1`) are absent from `newMetrics`. This will confirm we’re not emitting stale metrics after a config change and that old aggregations are correctly cleaned up.
</issue_to_address>