analysis: lock DTO fields passed as X.class to databind calls

Gson/Jackson/fastjson2/Moshi bind fields by reflection from a Class
literal, with no field-name string for the string-based detection:
renaming such a field silently breaks deserialization. Absorb_databind
finds the nearest Const::Class before fromJson/readValue/parseObject/
adapter calls (10-insn window, control-flow boundaries stop the search)
and keeps every field of that class; the class itself still renames.

Tests: noxis-analysis/tests/dto.rs (red first), keep unit tests moved
to tests/keep.rs (file budget). Code comments migrated to English.

crates/noxis-analysis/tests/dto.rs

@@ -0,0 +1,70 @@
+//! Databinding keep: `X.class` passed to Gson/Jackson locks the fields of `X`.
+//!
+//! JSON libraries bind fields by reflection from a `Class` literal, with no
+//! field-name string in the bytecode for the existing string-based detection
+//! to catch. Renaming such a field silently breaks deserialization, so every
+//! field of the literal's class stays.
+
+#![allow(clippy::expect_used, clippy::unwrap_used)]
+
+use noxis_analysis::Analysis;
+use noxis_classfile::{ClassBuilder, Code, Const, Field, Insn, InvokeKind, Program, Version};
+use noxis_core::Config;
+
+/// `gson.fromJson(reader, State.class)`: `State` has a private field.
+fn sample() -> Program {
+    let caller = Code {
+        max_stack: 3,
+        max_locals: 2,
+        insns: vec![
+            Insn::Load {
+                slot: 1,
+                kind: noxis_classfile::SlotKind::Ref,
+            },
+            Insn::Const(Const::Class("demo/State".to_string())),
+            Insn::Invoke {
+                kind: InvokeKind::Virtual,
+                owner: "com/google/gson/Gson".to_string(),
+                name: "fromJson".to_string(),
+                descriptor: "(Ljava/io/Reader;Ljava/lang/Class;)Ljava/lang/Object;".to_string(),
+                itf: false,
+            },
+            Insn::Pop,
+            Insn::Return(None),
+        ],
+        exception_table: Vec::new(),
+        frames: Vec::new(),
+        attributes: Vec::new(),
+    };
+    let mut state = ClassBuilder::new("demo/State", Some("java/lang/Object"))
+        .version(Version::JAVA_21)
+        .build();
+    state.fields.push(Field {
+        access_flags: 0x0002,
+        name: "nickname".to_string(),
+        descriptor: "Ljava/lang/String;".to_string(),
+        attributes: Vec::new(),
+    });
+    let app = ClassBuilder::new("demo/App", Some("java/lang/Object"))
+        .version(Version::JAVA_21)
+        .method_with_code(0x0009, "load", "()V", caller)
+        .build();
+    Program {
+        classes: vec![state, app],
+        resources: Vec::new(),
+    }
+}
+
+#[test]
+fn databind_class_literal_locks_fields() {
+    let program = sample();
+    let analysis = Analysis::run(&program, &Config::default()).expect("analysis");
+    assert!(
+        analysis.keep.keeps_member("nickname"),
+        "DTO field must survive renaming"
+    );
+    assert!(
+        !analysis.keep.keeps_member("load"),
+        "unrelated members must still rename"
+    );
+}