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docs/snippets/elixir/plugins/min_length_validator.md

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+<!-- snippet:skip reason="Elixir Rustler NIFs cannot host async Send + Sync + 'static Rust trait objects via callbacks; the BEAM actor-model boundary requires plugin work to live in the Rust core. The alef-generated Elixir trait_call macro additionally has a backslash/encoding bug (separate alef-codegen ticket). Custom plugins must be implemented in Rust." -->
+Custom validator implementation is not available in the Elixir binding. Validators must be implemented in Rust using the `Validator` trait.
+
+To implement a minimum length validator in Rust:
+
+```rust
+use kreuzberg::plugins::{Plugin, Validator};
+use kreuzberg::{Result, ExtractionResult, ExtractionConfig, KreuzbergError};
+use async_trait::async_trait;
+
+struct MinLengthValidator {
+    min_length: usize,
+}
+
+impl Plugin for MinLengthValidator {
+    fn name(&self) -> &str { "min-length-validator" }
+    fn version(&self) -> String { "1.0.0".to_string() }
+    fn initialize(&self) -> Result<()> { Ok(()) }
+    fn shutdown(&self) -> Result<()> { Ok(()) }
+}
+
+#[async_trait]
+impl Validator for MinLengthValidator {
+    async fn validate(
+        &self,
+        result: &ExtractionResult,
+        _config: &ExtractionConfig,
+    ) -> Result<()> {
+        if result.content.len() < self.min_length {
+            return Err(KreuzbergError::validation(format!(
+                "Content too short: {} < {} characters",
+                result.content.len(),
+                self.min_length
+            )));
+        }
+        Ok(())
+    }
+
+    fn priority(&self) -> i32 {
+        100
+    }
+}
+```
+
+Register this in your Rust initialization and Elixir will be able to use it.