feat: add ContractKey::from_id_and_code constructor

This allows reconstructing a ContractKey from stored index data
when the node has the instance ID and code hash but not the
original contract code.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: sanity

rust/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "freenet-stdlib"
-version = "0.1.25"
+version = "0.1.26"
 edition = "2021"
 rust-version = "1.71.1"
 publish = true

rust/src/contract_interface/key.rs

@@ -183,6 +183,18 @@ impl ContractKey {
     pub fn id(&self) -> &ContractInstanceId {
         &self.instance
     }
+
+    /// Constructs a ContractKey from a pre-computed instance ID and code hash.
+    ///
+    /// This is useful when the node needs to reconstruct a key from stored index data.
+    /// Callers must ensure the instance_id was correctly derived from the code_hash
+    /// and parameters, as this constructor does not verify consistency.
+    pub fn from_id_and_code(instance_id: ContractInstanceId, code_hash: CodeHash) -> Self {
+        Self {
+            instance: instance_id,
+            code: code_hash,
+        }
+    }
 }
 
 impl PartialEq for ContractKey {