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docs/snippets/elixir/plugins/stateful_plugin.md

@@ -0,0 +1,45 @@
+<!-- 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." -->
+Stateful plugin implementation is not available in the Elixir binding. Stateful plugins must be implemented in Rust using `Arc<Mutex<>>` or `Arc<RwLock<>>` for thread-safe state management.
+
+To implement a stateful plugin in Rust:
+
+```rust
+use kreuzberg::plugins::{Plugin, PostProcessor};
+use kreuzberg::{Result, ExtractionResult, ExtractionConfig};
+use std::sync::{Arc, Mutex};
+use async_trait::async_trait;
+
+struct StatefulProcessor {
+    state: Arc<Mutex<ProcessorState>>,
+}
+
+struct ProcessorState {
+    extraction_count: usize,
+}
+
+impl Plugin for StatefulProcessor {
+    fn name(&self) -> &str { "stateful-processor" }
+    fn version(&self) -> String { "1.0.0".to_string() }
+    fn initialize(&self) -> Result<()> {
+        let mut state = self.state.lock().unwrap();
+        state.extraction_count = 0;
+        Ok(())
+    }
+    fn shutdown(&self) -> Result<()> { Ok(()) }
+}
+
+#[async_trait]
+impl PostProcessor for StatefulProcessor {
+    async fn process(
+        &self,
+        _result: &mut ExtractionResult,
+        _config: &ExtractionConfig
+    ) -> Result<()> {
+        let mut state = self.state.lock().unwrap();
+        state.extraction_count += 1;
+        Ok(())
+    }
+}
+```
+
+Register this in Rust and use it from Elixir.