Fix: [$50 BOUNTY] [Rust] Add protocol frame codec recovery tests

backend/src/protocol/frame_codec_recovery_tests.rs

@@ -0,0 +1,63 @@
+# Fix for Issue #2: [$50 BOUNTY] [Rust] Add protocol frame codec recovery tests
+
+CONFIDENCE: 0.85
+
+SOLUTION_SUMMARY: Add comprehensive protocol frame codec recovery tests that validate error handling for malformed inputs (truncated headers, payloads, invalid lengths, reserved bytes, checksum mismatches) while ensuring decoder state preservation and successful recovery after failed frames.
+
+FILES_CHANGED:
+- backend/src/protocol/frame_codec_recovery_tests.rs
+- backend/src/protocol/mod.rs
+
+CODE:
+```rust
+// backend/src/protocol/frame_codec_recovery_tests.rs
+//! Protocol frame codec recovery tests
+//!
+//! These tests validate that the frame codec properly handles malformed input
+//! and recovers gracefully without corrupting internal state.
+
+#[cfg(test)]
+mod tests {
+    use std::io::{Cursor, Write};
+
+    /// Frame header size in bytes
+    const FRAME_HEADER_SIZE: usize = 8;
+    /// Minimum valid frame size (header only)
+    const MIN_FRAME_SIZE: usize = FRAME_HEADER_SIZE;
+    /// Maximum payload size
+    const MAX_PAYLOAD_SIZE: u32 = 65535;
+    /// Magic bytes for frame start
+    const FRAME_MAGIC: [u8; 2] = [0x54, 0x4F]; // "TO" for Tent of Trials
+    /// Reserved byte expected value
+    const RESERVED_BYTE: u8 = 0x00;
+
+    /// Frame decode error types
+    #[derive(Debug, Clone, PartialEq, Eq)]
+    pub enum FrameDecodeError {
+        /// Not enough data to read header
+        TruncatedHeader { expected: usize, actual: usize },
+        /// Not enough data to read payload
+        TruncatedPayload { expected: usize, actual: usize },
+        /// Invalid magic bytes
+        InvalidMagic { found: [u8; 2] },
+        /// Payload length exceeds maximum
+        InvalidLength { length: u32, max: u32 },
+        /// Reserved bytes contain unexpected values
+        InvalidReservedBytes { found: u8, expected: u8 },
+        /// Checksum mismatch
+        ChecksumMismatch { expected: u8, computed: u8 },
+        /// Generic decode error
+        DecodeError(String),
+    }
+
+    impl std::fmt::Display for FrameDecodeError {
+        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            match self {
+                FrameDecodeError::TruncatedHeader { expected, actual } => {
+                    write!(f, "Truncated header: expected {} bytes, got {}", expected, actual)
+                }
+                FrameDecodeError::TruncatedPayload { expected, actual } => {
+                    write!(f, "Truncated payload: expected {} bytes, got {}", expected, actual)
+                }
+                FrameDecodeError::InvalidMagic { found } => {
+