diff --git a/rust/Cargo.toml b/rust/Cargo.toml
index effbbba7..387e690c 100644
--- a/rust/Cargo.toml
+++ b/rust/Cargo.toml
@@ -20,6 +20,14 @@ members = [
     "crates/openjarvis-scheduler",
 ]
 
+# Minimum supported Rust version. The workspace uses let-chains (via rig-core)
+# and `is_multiple_of` (openjarvis-skills), both stabilized in Rust 1.88 —
+# building on 1.86/1.87 fails with cryptic E0658 errors deep in dependencies
+# (see #252). Declared here and pinned in rust-toolchain.toml so users get a
+# clear "requires rustc 1.88" signal instead.
+[workspace.package]
+rust-version = "1.88"
+
 [workspace.dependencies]
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
diff --git a/rust/crates/openjarvis-agents/src/loop_guard.rs b/rust/crates/openjarvis-agents/src/loop_guard.rs
index f41e4b5c..082b35e7 100644
--- a/rust/crates/openjarvis-agents/src/loop_guard.rs
+++ b/rust/crates/openjarvis-agents/src/loop_guard.rs
@@ -32,8 +32,7 @@ impl LoopGuard {
         // Check identical calls
         if self.seen_hashes.contains(&hash) {
             return Some(format!(
-                "Loop detected: identical call to '{}' with same arguments",
-                tool_name
+                "Loop detected: identical call to '{tool_name}' with same arguments"
             ));
         }
         self.seen_hashes.insert(hash);
diff --git a/rust/crates/openjarvis-agents/src/monitor_operative.rs b/rust/crates/openjarvis-agents/src/monitor_operative.rs
index 3ac60aee..7b201c4a 100644
--- a/rust/crates/openjarvis-agents/src/monitor_operative.rs
+++ b/rust/crates/openjarvis-agents/src/monitor_operative.rs
@@ -355,7 +355,7 @@ impl<M: CompletionModel + 'static> OjAgent for MonitorOperativeAgent<M> {
                 // Loop guard check
                 if let Some(loop_msg) = guard.check(&action, &action_input) {
                     return Ok(AgentResult {
-                        content: format!("Agent stopped: {}", loop_msg),
+                        content: format!("Agent stopped: {loop_msg}"),
                         tool_results: all_tool_results,
                         turns: turn,
                         metadata: self.strategy_metadata(),
@@ -379,7 +379,7 @@ impl<M: CompletionModel + 'static> OjAgent for MonitorOperativeAgent<M> {
                 let compressed = self.compress_observation(&tool_result.content);
 
                 history.push(RigMessage::assistant(&text));
-                current_input = format!("Observation: {}", compressed);
+                current_input = format!("Observation: {compressed}");
 
                 all_tool_results.push(tool_result);
             } else {
diff --git a/rust/crates/openjarvis-agents/src/native_openhands.rs b/rust/crates/openjarvis-agents/src/native_openhands.rs
index b9bb8501..f35be65c 100644
--- a/rust/crates/openjarvis-agents/src/native_openhands.rs
+++ b/rust/crates/openjarvis-agents/src/native_openhands.rs
@@ -202,7 +202,7 @@ impl<M: CompletionModel + 'static> OjAgent for NativeOpenHandsAgent<M> {
 
                 if let Some(loop_msg) = guard.check(tool_name, &args_str) {
                     return Ok(AgentResult {
-                        content: format!("Agent stopped: {}", loop_msg),
+                        content: format!("Agent stopped: {loop_msg}"),
                         tool_results: all_tool_results,
                         turns: turn,
                         metadata: HashMap::new(),
@@ -221,7 +221,7 @@ impl<M: CompletionModel + 'static> OjAgent for NativeOpenHandsAgent<M> {
 
                 let obs = Self::truncate_observation(&tool_result.content, 4000);
                 history.push(RigMessage::assistant(&text));
-                current_input = format!("Output:\n{}", obs);
+                current_input = format!("Output:\n{obs}");
 
                 all_tool_results.push(tool_result);
                 continue;
@@ -231,7 +231,7 @@ impl<M: CompletionModel + 'static> OjAgent for NativeOpenHandsAgent<M> {
             if let Some((action, action_input)) = Self::parse_action(&text) {
                 if let Some(loop_msg) = guard.check(&action, &action_input) {
                     return Ok(AgentResult {
-                        content: format!("Agent stopped: {}", loop_msg),
+                        content: format!("Agent stopped: {loop_msg}"),
                         tool_results: all_tool_results,
                         turns: turn,
                         metadata: HashMap::new(),
@@ -253,7 +253,7 @@ impl<M: CompletionModel + 'static> OjAgent for NativeOpenHandsAgent<M> {
 
                 let obs = Self::truncate_observation(&tool_result.content, 4000);
                 history.push(RigMessage::assistant(&text));
-                current_input = format!("Result: {}", obs);
+                current_input = format!("Result: {obs}");
 
                 all_tool_results.push(tool_result);
                 continue;
diff --git a/rust/crates/openjarvis-agents/src/native_react.rs b/rust/crates/openjarvis-agents/src/native_react.rs
index 0f01678d..88c4fc04 100644
--- a/rust/crates/openjarvis-agents/src/native_react.rs
+++ b/rust/crates/openjarvis-agents/src/native_react.rs
@@ -143,7 +143,7 @@ impl<M: CompletionModel + 'static> OjAgent for NativeReActAgent<M> {
             if let Some((action, action_input)) = Self::parse_action(&text) {
                 if let Some(loop_msg) = guard.check(&action, &action_input) {
                     return Ok(AgentResult {
-                        content: format!("Agent stopped: {}", loop_msg),
+                        content: format!("Agent stopped: {loop_msg}"),
                         tool_results: all_tool_results,
                         turns: turn,
                         metadata: HashMap::new(),
diff --git a/rust/crates/openjarvis-engine/src/discovery.rs b/rust/crates/openjarvis-engine/src/discovery.rs
index d777a3d9..9c9b55fe 100644
--- a/rust/crates/openjarvis-engine/src/discovery.rs
+++ b/rust/crates/openjarvis-engine/src/discovery.rs
@@ -104,8 +104,7 @@ pub fn get_engine_static(
         ))),
         other => Err(OpenJarvisError::Engine(
             openjarvis_core::error::EngineError::ModelNotFound(format!(
-                "Unknown engine: {}",
-                other
+                "Unknown engine: {other}"
             )),
         )),
     }
diff --git a/rust/crates/openjarvis-engine/src/llamacpp.rs b/rust/crates/openjarvis-engine/src/llamacpp.rs
index f38322e0..65820c80 100644
--- a/rust/crates/openjarvis-engine/src/llamacpp.rs
+++ b/rust/crates/openjarvis-engine/src/llamacpp.rs
@@ -28,7 +28,7 @@ impl LlamaCppEngine {
         let host = if host.starts_with("http") {
             host
         } else {
-            format!("http://{}", host)
+            format!("http://{host}")
         };
         let host = host.trim_end_matches('/').to_string();
         let timeout = std::time::Duration::from_secs_f64(timeout_secs);
@@ -120,8 +120,7 @@ impl InferenceEngine for LlamaCppEngine {
             let status = resp.status();
             let body = resp.text().unwrap_or_default();
             return Err(OpenJarvisError::Engine(EngineError::Http(format!(
-                "llama.cpp returned {}: {}",
-                status, body
+                "llama.cpp returned {status}: {body}"
             ))));
         }
 
diff --git a/rust/crates/openjarvis-engine/src/ollama.rs b/rust/crates/openjarvis-engine/src/ollama.rs
index 7056646c..832ea780 100644
--- a/rust/crates/openjarvis-engine/src/ollama.rs
+++ b/rust/crates/openjarvis-engine/src/ollama.rs
@@ -119,7 +119,7 @@ impl InferenceEngine for OllamaEngine {
                         ToolCall {
                             id: tc["id"]
                                 .as_str()
-                                .unwrap_or(&format!("call_{}", i))
+                                .unwrap_or(&format!("call_{i}"))
                                 .to_string(),
                             name: func["name"].as_str().unwrap_or("").to_string(),
                             arguments: args,
diff --git a/rust/crates/openjarvis-engine/src/openai_compat.rs b/rust/crates/openjarvis-engine/src/openai_compat.rs
index bac79b33..3fd3e874 100644
--- a/rust/crates/openjarvis-engine/src/openai_compat.rs
+++ b/rust/crates/openjarvis-engine/src/openai_compat.rs
@@ -84,7 +84,7 @@ impl OpenAICompatEngine {
         if let Some(ref key) = self.api_key {
             headers.insert(
                 reqwest::header::AUTHORIZATION,
-                format!("Bearer {}", key).parse().unwrap(),
+                format!("Bearer {key}").parse().unwrap(),
             );
         }
         headers
@@ -239,7 +239,7 @@ impl InferenceEngine for OpenAICompatEngine {
         if let Some(ref key) = self.api_key {
             headers.insert(
                 reqwest::header::AUTHORIZATION,
-                format!("Bearer {}", key).parse().unwrap(),
+                format!("Bearer {key}").parse().unwrap(),
             );
         }
 
diff --git a/rust/crates/openjarvis-engine/src/rig_adapter.rs b/rust/crates/openjarvis-engine/src/rig_adapter.rs
index 873086a8..b96e3f5b 100644
--- a/rust/crates/openjarvis-engine/src/rig_adapter.rs
+++ b/rust/crates/openjarvis-engine/src/rig_adapter.rs
@@ -107,8 +107,7 @@ fn rig_request_to_oj_messages(request: &CompletionRequest) -> Vec<Message> {
             .collect::<Vec<_>>()
             .join("\n\n");
         messages.push(Message::system(format!(
-            "Relevant context:\n{}",
-            doc_context
+            "Relevant context:\n{doc_context}"
         )));
     }
 
diff --git a/rust/crates/openjarvis-engine/src/sglang.rs b/rust/crates/openjarvis-engine/src/sglang.rs
index 3c7aadd5..311ff8fa 100644
--- a/rust/crates/openjarvis-engine/src/sglang.rs
+++ b/rust/crates/openjarvis-engine/src/sglang.rs
@@ -24,7 +24,7 @@ impl SGLangEngine {
         let host = if host.starts_with("http") {
             host
         } else {
-            format!("http://{}", host)
+            format!("http://{host}")
         };
         let host = host.trim_end_matches('/').to_string();
         let timeout = std::time::Duration::from_secs_f64(timeout_secs);
@@ -115,8 +115,7 @@ impl InferenceEngine for SGLangEngine {
             let status = resp.status();
             let body = resp.text().unwrap_or_default();
             return Err(OpenJarvisError::Engine(EngineError::Http(format!(
-                "SGLang returned {}: {}",
-                status, body
+                "SGLang returned {status}: {body}"
             ))));
         }
 
diff --git a/rust/crates/openjarvis-engine/src/vllm.rs b/rust/crates/openjarvis-engine/src/vllm.rs
index 01ef4932..7cbba17a 100644
--- a/rust/crates/openjarvis-engine/src/vllm.rs
+++ b/rust/crates/openjarvis-engine/src/vllm.rs
@@ -26,7 +26,7 @@ impl VLLMEngine {
         let host = if host.starts_with("http") {
             host
         } else {
-            format!("http://{}", host)
+            format!("http://{host}")
         };
         let host = host.trim_end_matches('/').to_string();
         let timeout = std::time::Duration::from_secs_f64(timeout_secs);
@@ -70,7 +70,7 @@ impl VLLMEngine {
         if let Some(ref key) = self.api_key {
             headers.insert(
                 reqwest::header::AUTHORIZATION,
-                format!("Bearer {}", key).parse().unwrap(),
+                format!("Bearer {key}").parse().unwrap(),
             );
         }
         headers
@@ -135,8 +135,7 @@ impl InferenceEngine for VLLMEngine {
             let status = resp.status();
             let body = resp.text().unwrap_or_default();
             return Err(OpenJarvisError::Engine(EngineError::Http(format!(
-                "vLLM returned {}: {}",
-                status, body
+                "vLLM returned {status}: {body}"
             ))));
         }
 
@@ -231,7 +230,7 @@ impl InferenceEngine for VLLMEngine {
         if let Some(ref key) = self.api_key {
             headers.insert(
                 reqwest::header::AUTHORIZATION,
-                format!("Bearer {}", key).parse().unwrap(),
+                format!("Bearer {key}").parse().unwrap(),
             );
         }
 
diff --git a/rust/crates/openjarvis-learning/src/agent_advisor.rs b/rust/crates/openjarvis-learning/src/agent_advisor.rs
index 186cd3a1..0fe21852 100644
--- a/rust/crates/openjarvis-learning/src/agent_advisor.rs
+++ b/rust/crates/openjarvis-learning/src/agent_advisor.rs
@@ -78,8 +78,7 @@ impl AgentAdvisorPolicy {
                 recs.push(Recommendation {
                     rec_type: "routing".to_string(),
                     suggestion: format!(
-                        "Query class '{}' has {} failures — consider different model or agent",
-                        qclass, count,
+                        "Query class '{qclass}' has {count} failures — consider different model or agent",
                     ),
                     severity: "high".to_string(),
                 });
@@ -160,7 +159,7 @@ mod tests {
         let traces: Vec<TraceInfo> = (0..5)
             .map(|i| TraceInfo {
                 outcome: "failure".into(),
-                query: format!("query {}", i),
+                query: format!("query {i}"),
                 tool_call_count: 8,
                 total_latency_seconds: 2.0,
             })
@@ -178,7 +177,7 @@ mod tests {
         let traces: Vec<TraceInfo> = (0..5)
             .map(|i| TraceInfo {
                 outcome: "failure".into(),
-                query: format!("def func_{}():", i),
+                query: format!("def func_{i}():"),
                 tool_call_count: 2,
                 total_latency_seconds: 1.0,
             })
diff --git a/rust/crates/openjarvis-learning/src/icl_updater.rs b/rust/crates/openjarvis-learning/src/icl_updater.rs
index cf2fb544..65c57c9b 100644
--- a/rust/crates/openjarvis-learning/src/icl_updater.rs
+++ b/rust/crates/openjarvis-learning/src/icl_updater.rs
@@ -209,7 +209,7 @@ mod tests {
     fn test_max_examples_trim() {
         let mut policy = ICLUpdaterPolicy::new(0.0, 3, 3);
         for i in 0..5 {
-            policy.add_example(format!("q{}", i), format!("r{}", i), 0.5, HashMap::new());
+            policy.add_example(format!("q{i}"), format!("r{i}"), 0.5, HashMap::new());
         }
         assert_eq!(policy.example_db().len(), 3);
         assert_eq!(policy.example_db()[0].query, "q2");
diff --git a/rust/crates/openjarvis-mcp/src/server.rs b/rust/crates/openjarvis-mcp/src/server.rs
index 6ce3e6f0..d5ec33e7 100644
--- a/rust/crates/openjarvis-mcp/src/server.rs
+++ b/rust/crates/openjarvis-mcp/src/server.rs
@@ -97,7 +97,7 @@ impl McpServer {
                 let resp = McpResponse::error(
                     Value::Null,
                     -32700,
-                    &format!("Parse error: {}", e),
+                    &format!("Parse error: {e}"),
                 );
                 serde_json::to_string(&resp).unwrap_or_default()
             }
diff --git a/rust/crates/openjarvis-python/src/engine.rs b/rust/crates/openjarvis-python/src/engine.rs
index 166e12d6..00952a40 100644
--- a/rust/crates/openjarvis-python/src/engine.rs
+++ b/rust/crates/openjarvis-python/src/engine.rs
@@ -93,7 +93,7 @@ impl PyEngine {
             ),
             other => {
                 return Err(PyErr::new::<pyo3::exceptions::PyValueError, _>(
-                    format!("Unknown engine: {}", other),
+                    format!("Unknown engine: {other}"),
                 ));
             }
         };
diff --git a/rust/crates/openjarvis-python/src/scheduler.rs b/rust/crates/openjarvis-python/src/scheduler.rs
index 8f6e40dd..1f7a33d5 100644
--- a/rust/crates/openjarvis-python/src/scheduler.rs
+++ b/rust/crates/openjarvis-python/src/scheduler.rs
@@ -20,8 +20,7 @@ impl PySchedulerStore {
     fn create_task(&self, name: &str, schedule_type: &str, schedule_value: &str) -> PyResult<String> {
         let st = openjarvis_scheduler::ScheduleType::parse(schedule_type).ok_or_else(|| {
             PyErr::new::<pyo3::exceptions::PyValueError, _>(format!(
-                "invalid schedule_type '{}', expected cron/interval/once",
-                schedule_type
+                "invalid schedule_type '{schedule_type}', expected cron/interval/once"
             ))
         })?;
         let task = self.inner.create_task(name, st, schedule_value);
@@ -41,8 +40,7 @@ impl PySchedulerStore {
     fn update_status(&self, id: &str, status: &str) -> PyResult<bool> {
         let s = openjarvis_scheduler::TaskStatus::parse(status).ok_or_else(|| {
             PyErr::new::<pyo3::exceptions::PyValueError, _>(format!(
-                "invalid status '{}', expected active/paused/cancelled/completed",
-                status
+                "invalid status '{status}', expected active/paused/cancelled/completed"
             ))
         })?;
         Ok(self.inner.update_status(id, s))
diff --git a/rust/crates/openjarvis-python/src/storage.rs b/rust/crates/openjarvis-python/src/storage.rs
index 5a5b7502..332aff2a 100644
--- a/rust/crates/openjarvis-python/src/storage.rs
+++ b/rust/crates/openjarvis-python/src/storage.rs
@@ -266,8 +266,7 @@ impl PyHybridMemory {
                 }
                 other => {
                     return Err(PyErr::new::<pyo3::exceptions::PyValueError, _>(format!(
-                        "Unknown backend key: {}. Supported: sqlite, bm25, faiss, colbert",
-                        other
+                        "Unknown backend key: {other}. Supported: sqlite, bm25, faiss, colbert"
                     )));
                 }
             };
diff --git a/rust/crates/openjarvis-security/src/audit.rs b/rust/crates/openjarvis-security/src/audit.rs
index 7df2a8d0..99f3d231 100644
--- a/rust/crates/openjarvis-security/src/audit.rs
+++ b/rust/crates/openjarvis-security/src/audit.rs
@@ -303,7 +303,7 @@ mod tests {
                 event_type: SecurityEventType::SecretDetected,
                 timestamp: 1000.0 + i as f64,
                 findings: vec![],
-                content_preview: format!("event {}", i),
+                content_preview: format!("event {i}"),
                 action_taken: "warn".into(),
             };
             logger.log(&event).unwrap();
diff --git a/rust/crates/openjarvis-security/src/ssrf.rs b/rust/crates/openjarvis-security/src/ssrf.rs
index 20ec58ac..4ca5fee4 100644
--- a/rust/crates/openjarvis-security/src/ssrf.rs
+++ b/rust/crates/openjarvis-security/src/ssrf.rs
@@ -135,14 +135,13 @@ pub fn check_ssrf(url_str: &str) -> Option<String> {
 
     if BLOCKED_HOSTS.contains(canonical_host.as_str()) {
         return Some(format!(
-            "Blocked host: {} (cloud metadata endpoint)",
-            canonical_host
+            "Blocked host: {canonical_host} (cloud metadata endpoint)"
         ));
     }
 
     if let Some(ip) = literal_ip {
         if is_private_ip(&ip) {
-            return Some(format!("URL resolves to private IP: {}", ip));
+            return Some(format!("URL resolves to private IP: {ip}"));
         }
         return None;
     }
@@ -153,7 +152,7 @@ pub fn check_ssrf(url_str: &str) -> Option<String> {
         _ => 80,
     });
 
-    let addr_str = format!("{}:{}", canonical_host, port);
+    let addr_str = format!("{canonical_host}:{port}");
     if let Ok(addrs) = addr_str.to_socket_addrs() {
         for addr in addrs {
             if is_private_ip(&addr.ip()) {
@@ -207,7 +206,7 @@ mod tests {
     fn test_ipv4_mapped_ipv6_rfc1918_is_private() {
         for s in ["::ffff:10.0.0.1", "::ffff:172.16.0.1", "::ffff:192.168.1.1"] {
             let v6: Ipv6Addr = s.parse().unwrap();
-            assert!(is_private_ip(&IpAddr::V6(v6)), "{} should be private", s);
+            assert!(is_private_ip(&IpAddr::V6(v6)), "{s} should be private");
         }
     }
 
@@ -244,7 +243,7 @@ mod tests {
             "http://[::ffff:172.16.0.1]/",
         ] {
             let result = check_ssrf(url);
-            assert!(result.is_some(), "{} must be blocked", url);
+            assert!(result.is_some(), "{url} must be blocked");
         }
     }
 
diff --git a/rust/crates/openjarvis-sessions/src/lib.rs b/rust/crates/openjarvis-sessions/src/lib.rs
index f40c7339..aa894acf 100644
--- a/rust/crates/openjarvis-sessions/src/lib.rs
+++ b/rust/crates/openjarvis-sessions/src/lib.rs
@@ -230,7 +230,7 @@ impl SessionStore {
             params![session_id, remove_up_to as i64],
         );
 
-        let summary = format!("[consolidated {} earlier messages]", remove_up_to);
+        let summary = format!("[consolidated {remove_up_to} earlier messages]");
         let now = now_secs();
         let _ = self.conn.execute(
             "INSERT INTO session_messages (session_id, role, content, channel, timestamp)
@@ -292,15 +292,13 @@ impl SessionStore {
             let cutoff = now_secs() - self.max_age_hours * 3600.0;
             format!(
                 "SELECT session_id FROM sessions
-                 WHERE last_activity >= {}
-                 ORDER BY last_activity DESC LIMIT {}",
-                cutoff, limit
+                 WHERE last_activity >= {cutoff}
+                 ORDER BY last_activity DESC LIMIT {limit}"
             )
         } else {
             format!(
                 "SELECT session_id FROM sessions
-                 ORDER BY last_activity DESC LIMIT {}",
-                limit
+                 ORDER BY last_activity DESC LIMIT {limit}"
             )
         };
 
@@ -356,7 +354,7 @@ impl SessionStore {
                 params![checkpoint_id, session_id],
                 |row| Ok((row.get(0)?, row.get(1)?)),
             )
-            .map_err(|e| format!("Checkpoint not found: {}", e))?;
+            .map_err(|e| format!("Checkpoint not found: {e}"))?;
 
         let deleted: usize = self
             .conn
@@ -573,7 +571,7 @@ mod tests {
 
         for i in 0..10 {
             store
-                .save_message(&s.session_id, "user", &format!("msg {}", i), "irc")
+                .save_message(&s.session_id, "user", &format!("msg {i}"), "irc")
                 .unwrap();
         }
 
diff --git a/rust/crates/openjarvis-tools/src/builtin/calculator.rs b/rust/crates/openjarvis-tools/src/builtin/calculator.rs
index f31ac28a..5c2618c3 100644
--- a/rust/crates/openjarvis-tools/src/builtin/calculator.rs
+++ b/rust/crates/openjarvis-tools/src/builtin/calculator.rs
@@ -48,7 +48,7 @@ impl BaseTool for CalculatorTool {
             Ok(result) => Ok(ToolResult::success("calculator", result.to_string())),
             Err(e) => Ok(ToolResult::failure(
                 "calculator",
-                format!("Error evaluating '{}': {}", expression, e),
+                format!("Error evaluating '{expression}': {e}"),
             )),
         }
     }
diff --git a/rust/crates/openjarvis-tools/src/builtin/file_tools.rs b/rust/crates/openjarvis-tools/src/builtin/file_tools.rs
index eca0cfc8..60bcfe8e 100644
--- a/rust/crates/openjarvis-tools/src/builtin/file_tools.rs
+++ b/rust/crates/openjarvis-tools/src/builtin/file_tools.rs
@@ -63,7 +63,7 @@ impl BaseTool for FileReadTool {
         if is_sensitive_file(path) {
             return Ok(ToolResult::failure(
                 "file_read",
-                format!("Access denied: '{}' is a sensitive file", path_str),
+                format!("Access denied: '{path_str}' is a sensitive file"),
             ));
         }
 
@@ -71,7 +71,7 @@ impl BaseTool for FileReadTool {
             Ok(content) => Ok(ToolResult::success("file_read", content)),
             Err(e) => Ok(ToolResult::failure(
                 "file_read",
-                format!("Error reading '{}': {}", path_str, e),
+                format!("Error reading '{path_str}': {e}"),
             )),
         }
     }
@@ -94,7 +94,7 @@ impl BaseTool for FileWriteTool {
         if is_sensitive_file(path) {
             return Ok(ToolResult::failure(
                 "file_write",
-                format!("Access denied: '{}' is a sensitive file", path_str),
+                format!("Access denied: '{path_str}' is a sensitive file"),
             ));
         }
 
@@ -103,7 +103,7 @@ impl BaseTool for FileWriteTool {
                 if let Err(e) = std::fs::create_dir_all(parent) {
                     return Ok(ToolResult::failure(
                         "file_write",
-                        format!("Error creating directory: {}", e),
+                        format!("Error creating directory: {e}"),
                     ));
                 }
             }
@@ -116,7 +116,7 @@ impl BaseTool for FileWriteTool {
             )),
             Err(e) => Ok(ToolResult::failure(
                 "file_write",
-                format!("Error writing '{}': {}", path_str, e),
+                format!("Error writing '{path_str}': {e}"),
             )),
         }
     }
diff --git a/rust/crates/openjarvis-tools/src/builtin/git_tools.rs b/rust/crates/openjarvis-tools/src/builtin/git_tools.rs
index 192c157f..da7dab8d 100644
--- a/rust/crates/openjarvis-tools/src/builtin/git_tools.rs
+++ b/rust/crates/openjarvis-tools/src/builtin/git_tools.rs
@@ -21,7 +21,7 @@ fn run_git(args: &[&str], cwd: Option<&str>) -> Result<String, String> {
                 Err(String::from_utf8_lossy(&output.stderr).to_string())
             }
         }
-        Err(e) => Err(format!("Failed to run git: {}", e)),
+        Err(e) => Err(format!("Failed to run git: {e}")),
     }
 }
 
@@ -84,7 +84,7 @@ impl BaseTool for GitLogTool {
     fn execute(&self, params: &Value) -> Result<ToolResult, OpenJarvisError> {
         let cwd = params["cwd"].as_str();
         let n = params["n"].as_i64().unwrap_or(10);
-        match run_git(&["log", "--oneline", &format!("-{}", n)], cwd) {
+        match run_git(&["log", "--oneline", &format!("-{n}")], cwd) {
             Ok(output) => Ok(ToolResult::success("git_log", output)),
             Err(e) => Ok(ToolResult::failure("git_log", e)),
         }
diff --git a/rust/crates/openjarvis-tools/src/builtin/http_tools.rs b/rust/crates/openjarvis-tools/src/builtin/http_tools.rs
index 8b27a88f..31ce5f7d 100644
--- a/rust/crates/openjarvis-tools/src/builtin/http_tools.rs
+++ b/rust/crates/openjarvis-tools/src/builtin/http_tools.rs
@@ -83,7 +83,7 @@ impl BaseTool for HttpRequestTool {
                 } else {
                     body
                 };
-                let content = format!("Status: {}\n{}", status, truncated);
+                let content = format!("Status: {status}\n{truncated}");
                 if status < 400 {
                     Ok(ToolResult::success("http_request", content))
                 } else {
@@ -92,7 +92,7 @@ impl BaseTool for HttpRequestTool {
             }
             Err(e) => Ok(ToolResult::failure(
                 "http_request",
-                format!("Request failed: {}", e),
+                format!("Request failed: {e}"),
             )),
         }
     }
diff --git a/rust/crates/openjarvis-tools/src/builtin/shell.rs b/rust/crates/openjarvis-tools/src/builtin/shell.rs
index f5aa795b..a7bb6330 100644
--- a/rust/crates/openjarvis-tools/src/builtin/shell.rs
+++ b/rust/crates/openjarvis-tools/src/builtin/shell.rs
@@ -61,8 +61,7 @@ impl BaseTool for ShellExecTool {
                 let exit_code = output.status.code().unwrap_or(-1);
 
                 let content = format!(
-                    "Exit code: {}\n--- stdout ---\n{}\n--- stderr ---\n{}",
-                    exit_code, stdout, stderr
+                    "Exit code: {exit_code}\n--- stdout ---\n{stdout}\n--- stderr ---\n{stderr}"
                 );
 
                 if output.status.success() {
@@ -73,7 +72,7 @@ impl BaseTool for ShellExecTool {
             }
             Err(e) => Ok(ToolResult::failure(
                 "shell_exec",
-                format!("Failed to execute: {}", e),
+                format!("Failed to execute: {e}"),
             )),
         }
     }
diff --git a/rust/crates/openjarvis-tools/src/executor.rs b/rust/crates/openjarvis-tools/src/executor.rs
index 37a87c61..fedebd32 100644
--- a/rust/crates/openjarvis-tools/src/executor.rs
+++ b/rust/crates/openjarvis-tools/src/executor.rs
@@ -66,7 +66,7 @@ impl ToolExecutor {
                 if !policy.check(aid, cap, "") {
                     return Err(OpenJarvisError::Tool(ToolError::CapabilityDenied(
                         aid.to_string(),
-                        format!("{} (tool: {})", cap, tool_name),
+                        format!("{cap} (tool: {tool_name})"),
                     )));
                 }
             }
diff --git a/rust/crates/openjarvis-tools/src/storage/knowledge_graph.rs b/rust/crates/openjarvis-tools/src/storage/knowledge_graph.rs
index 1919a6fa..eabd3f4a 100644
--- a/rust/crates/openjarvis-tools/src/storage/knowledge_graph.rs
+++ b/rust/crates/openjarvis-tools/src/storage/knowledge_graph.rs
@@ -170,7 +170,7 @@ impl MemoryBackend for KnowledgeGraphMemory {
         top_k: usize,
     ) -> Result<Vec<RetrievalResult>, OpenJarvisError> {
         let conn = self.conn.lock();
-        let pattern = format!("%{}%", query);
+        let pattern = format!("%{query}%");
         let mut stmt = conn
             .prepare(
                 "SELECT name, entity_type, properties
diff --git a/rust/crates/openjarvis-traces/src/store.rs b/rust/crates/openjarvis-traces/src/store.rs
index 60506f84..fe7faaf1 100644
--- a/rust/crates/openjarvis-traces/src/store.rs
+++ b/rust/crates/openjarvis-traces/src/store.rs
@@ -233,8 +233,8 @@ mod tests {
         let store = TraceStore::in_memory().unwrap();
         for i in 0..5 {
             let trace = Trace {
-                trace_id: format!("t{}", i),
-                query: format!("query {}", i),
+                trace_id: format!("t{i}"),
+                query: format!("query {i}"),
                 ..Default::default()
             };
             store.save(&trace).unwrap();
diff --git a/rust/rust-toolchain.toml b/rust/rust-toolchain.toml
new file mode 100644
index 00000000..b6a8a616
--- /dev/null
+++ b/rust/rust-toolchain.toml
@@ -0,0 +1,10 @@
+# Pin the Rust toolchain for the openjarvis_rust workspace.
+#
+# The workspace requires Rust >= 1.88: rig-core uses let-chains and
+# openjarvis-skills uses `is_multiple_of`, both stabilized in 1.88. On older
+# stable toolchains the build fails with cryptic E0658 errors deep inside a
+# transitive dependency (see #252). Pinning here makes rustup install/select a
+# compatible toolchain automatically and gives a clear requirement up front.
+[toolchain]
+channel = "1.88"
+components = ["rustfmt", "clippy"]