diff --git a/Cargo.lock b/Cargo.lock
index 4fb0f9106..041a86617 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -11029,6 +11029,7 @@ dependencies = [
  "proptest",
  "rand 0.10.1",
  "rand_distr 0.6.0",
+ "reqwest 0.12.28",
  "reqwest 0.13.3",
  "ripemd",
  "rubato",
diff --git a/crates/zeph-agent-context/src/helpers.rs b/crates/zeph-agent-context/src/helpers.rs
index ad62717b4..560986d05 100644
--- a/crates/zeph-agent-context/src/helpers.rs
+++ b/crates/zeph-agent-context/src/helpers.rs
@@ -969,9 +969,9 @@ pub async fn fetch_semantic_recall(
 
 fn format_plain_recall_entry(item: &zeph_memory::RecalledMessage) -> String {
     let role_label = match item.message.role {
-        Role::User => "user",
         Role::Assistant => "assistant",
         Role::System => "system",
+        Role::User | _ => "user",
     };
     format!("- [{}] {}\n", role_label, item.message.content)
 }
@@ -979,9 +979,9 @@ fn format_plain_recall_entry(item: &zeph_memory::RecalledMessage) -> String {
 #[allow(clippy::map_unwrap_or)]
 fn format_structured_recall_entry(item: &zeph_memory::RecalledMessage) -> String {
     let source = match item.message.role {
-        Role::User => "user",
         Role::Assistant => "assistant",
         Role::System => "system",
+        Role::User | _ => "user",
     };
     // Use compacted_at as a proxy for message age when available; otherwise "unknown".
     // A full timestamp lookup from SQLite would require an async DB call in the assembler
diff --git a/crates/zeph-agent-context/src/memory_backend.rs b/crates/zeph-agent-context/src/memory_backend.rs
index 0fbd36c85..9946c430f 100644
--- a/crates/zeph-agent-context/src/memory_backend.rs
+++ b/crates/zeph-agent-context/src/memory_backend.rs
@@ -69,9 +69,9 @@ fn map_correction(c: zeph_memory::UserCorrectionRow) -> MemCorrection {
 fn map_recalled_message(r: zeph_memory::RecalledMessage) -> MemRecalledMessage {
     use zeph_llm::provider::Role;
     let role = match r.message.role {
-        Role::User => "user",
         Role::Assistant => "assistant",
         Role::System => "system",
+        Role::User | _ => "user",
     }
     .to_owned();
     MemRecalledMessage {
diff --git a/crates/zeph-agent-context/src/summarization/scheduling.rs b/crates/zeph-agent-context/src/summarization/scheduling.rs
index 839ee3454..4577d9291 100644
--- a/crates/zeph-agent-context/src/summarization/scheduling.rs
+++ b/crates/zeph-agent-context/src/summarization/scheduling.rs
@@ -383,9 +383,9 @@ fn spawn_task_goal_extraction(
         let mut context_text = String::new();
         for (role, content) in &recent {
             let role_str = match role {
-                Role::User => "user",
                 Role::Assistant => "assistant",
                 Role::System => "system",
+                Role::User | _ => "user",
             };
             let preview = if content.len() > 300 {
                 let end = content.floor_char_boundary(300);
@@ -460,9 +460,9 @@ fn spawn_subgoal_extraction(
         let mut context_text = String::new();
         for (role, content) in &recent {
             let role_str = match role {
-                Role::User => "user",
                 Role::Assistant => "assistant",
                 Role::System => "system",
+                Role::User | _ => "user",
             };
             let preview = if content.len() > 300 {
                 let end = content.floor_char_boundary(300);
diff --git a/crates/zeph-context/src/fidelity.rs b/crates/zeph-context/src/fidelity.rs
index 4023b00a3..d0abf334c 100644
--- a/crates/zeph-context/src/fidelity.rs
+++ b/crates/zeph-context/src/fidelity.rs
@@ -525,7 +525,7 @@ fn role_weight(role: Role) -> f32 {
     match role {
         Role::System => 1.0,
         Role::User => 0.8,
-        Role::Assistant => 0.6,
+        Role::Assistant | _ => 0.6,
     }
 }
 
@@ -785,8 +785,8 @@ fn truncate_to_tokens(content: &mut String, max_tokens: usize, tc: &dyn TokenCou
 fn render_placeholder(msg: &mut Message, score: f32, original_tokens: u32) {
     let role_str = match msg.role {
         Role::System => "system",
-        Role::User => "user",
         Role::Assistant => "assistant",
+        Role::User | _ => "user",
     };
     msg.content = format!(
         "[placeholder: role={role_str}, original_tokens={original_tokens}, importance={score:.2}]"
@@ -836,8 +836,8 @@ fn merge_consecutive_placeholders(messages: &mut Vec<Message>) -> usize {
         };
         let role_str = match role {
             Role::System => "system",
-            Role::User => "user",
             Role::Assistant => "assistant",
+            Role::User | _ => "user",
         };
         let merged_content = format!(
             "[placeholder: {count} messages, role={role_str}, total_tokens={total_tokens}, avg_importance={avg_importance:.2}]"
diff --git a/crates/zeph-context/src/summarization.rs b/crates/zeph-context/src/summarization.rs
index 82214821c..44be33150 100644
--- a/crates/zeph-context/src/summarization.rs
+++ b/crates/zeph-context/src/summarization.rs
@@ -456,6 +456,7 @@ pub fn build_metadata_summary(messages: &[Message], truncate: fn(&str, usize) ->
                 }
             }
             Role::System => system_count += 1,
+            _ => {}
         }
     }
 
@@ -649,9 +650,9 @@ fn format_history(messages: &[Message]) -> String {
             history_text.push_str("\n\n");
         }
         let role = match m.role {
-            Role::User => "user",
             Role::Assistant => "assistant",
             Role::System => "system",
+            Role::User | _ => "user",
         };
         let _ = write!(history_text, "[{role}]: {}", m.content);
     }
diff --git a/crates/zeph-core/src/agent/magic_docs.rs b/crates/zeph-core/src/agent/magic_docs.rs
index c8afe7da5..e58cf6d10 100644
--- a/crates/zeph-core/src/agent/magic_docs.rs
+++ b/crates/zeph-core/src/agent/magic_docs.rs
@@ -439,7 +439,7 @@ mod tests {
                         }
                     }
                 }
-                Role::System => {}
+                _ => {}
             }
         }
 
diff --git a/crates/zeph-core/src/agent/mod.rs b/crates/zeph-core/src/agent/mod.rs
index 1c4aef753..8cfe34fbd 100644
--- a/crates/zeph-core/src/agent/mod.rs
+++ b/crates/zeph-core/src/agent/mod.rs
@@ -610,9 +610,9 @@ impl<C: Channel> Agent<C> {
             .iter()
             .map(|m| {
                 let role = match m.role {
-                    Role::User => "user".to_owned(),
                     Role::Assistant => "assistant".to_owned(),
                     Role::System => "system".to_owned(),
+                    Role::User | _ => "user".to_owned(),
                 };
                 (zeph_memory::MessageId(0), role, m.content.clone())
             })
diff --git a/crates/zeph-core/src/agent/session_digest.rs b/crates/zeph-core/src/agent/session_digest.rs
index 8ddb15065..9ebd52cd0 100644
--- a/crates/zeph-core/src/agent/session_digest.rs
+++ b/crates/zeph-core/src/agent/session_digest.rs
@@ -94,9 +94,9 @@ fn format_and_sanitize_conversation(
     let mut result = String::new();
     for msg in messages {
         let role = match msg.role {
-            Role::User => "User",
             Role::Assistant => "Assistant",
             Role::System => "System",
+            Role::User | _ => "User",
         };
         // Redact credentials first, then sanitize for injection patterns.
         let redacted: Cow<'_, str> = scrub_content(&msg.content);
diff --git a/crates/zeph-core/src/agent/speculative/stream_drainer.rs b/crates/zeph-core/src/agent/speculative/stream_drainer.rs
index e703daff5..68e2b4cb6 100644
--- a/crates/zeph-core/src/agent/speculative/stream_drainer.rs
+++ b/crates/zeph-core/src/agent/speculative/stream_drainer.rs
@@ -125,9 +125,6 @@ impl SpeculativeStreamDrainer {
                 ToolSseEvent::ThinkingBlockDone(block) => {
                     thinking_blocks.push(block);
                 }
-                ToolSseEvent::ThinkingChunk(_) => {
-                    // Pass-through; full block assembled via ThinkingBlockDone.
-                }
                 ToolSseEvent::ContentChunk(text) => {
                     text_buf.push_str(&text);
                 }
@@ -140,6 +137,8 @@ impl SpeculativeStreamDrainer {
                 ToolSseEvent::Error(e) => {
                     return Err(e);
                 }
+                // ThinkingChunk pass-through; full block assembled via ThinkingBlockDone.
+                ToolSseEvent::ThinkingChunk(_) | _ => {}
             }
         }
 
diff --git a/crates/zeph-core/src/agent/tool_execution/focus.rs b/crates/zeph-core/src/agent/tool_execution/focus.rs
index ffa70c29b..1e120907e 100644
--- a/crates/zeph-core/src/agent/tool_execution/focus.rs
+++ b/crates/zeph-core/src/agent/tool_execution/focus.rs
@@ -421,9 +421,9 @@ fn build_compression_prompt(
     to_compress: &[zeph_llm::provider::Message],
 ) -> Vec<zeph_llm::provider::Message> {
     let role_label = |role: &zeph_llm::provider::Role| match role {
-        zeph_llm::provider::Role::User => "user",
         zeph_llm::provider::Role::Assistant => "assistant",
         zeph_llm::provider::Role::System => "system",
+        zeph_llm::provider::Role::User | _ => "user",
     };
     let bullet_list: String = to_compress
         .iter()
diff --git a/crates/zeph-core/src/debug_dump/mod.rs b/crates/zeph-core/src/debug_dump/mod.rs
index b308bf303..a0f323e89 100644
--- a/crates/zeph-core/src/debug_dump/mod.rs
+++ b/crates/zeph-core/src/debug_dump/mod.rs
@@ -480,7 +480,7 @@ fn messages_to_api_value(messages: &[Message]) -> serde_json::Value {
             let role = match m.role {
                 Role::User => "user",
                 Role::Assistant => "assistant",
-                Role::System => return None,
+                Role::System | _ => return None,
             };
             let is_assistant = m.role == Role::Assistant;
             let has_structured = m.parts.iter().any(|p| {
diff --git a/crates/zeph-core/src/memory_tools.rs b/crates/zeph-core/src/memory_tools.rs
index 67b47bfaf..3880c4b15 100644
--- a/crates/zeph-core/src/memory_tools.rs
+++ b/crates/zeph-core/src/memory_tools.rs
@@ -147,9 +147,9 @@ impl ToolExecutor for MemoryToolExecutor {
                 let _ = writeln!(output, "## Recalled Messages ({} results)", recalled.len());
                 for r in &recalled {
                     let role = match r.message.role {
-                        zeph_llm::provider::Role::User => "user",
                         zeph_llm::provider::Role::Assistant => "assistant",
                         zeph_llm::provider::Role::System => "system",
+                        zeph_llm::provider::Role::User | _ => "user",
                     };
                     let content = r.message.content.trim();
                     let _ = writeln!(output, "[score: {:.2}] {role}: {content}", r.score);
diff --git a/crates/zeph-llm/Cargo.toml b/crates/zeph-llm/Cargo.toml
index 18ec262fc..597beb6e3 100644
--- a/crates/zeph-llm/Cargo.toml
+++ b/crates/zeph-llm/Cargo.toml
@@ -42,6 +42,7 @@ parking_lot.workspace = true
 rand.workspace = true
 rand_distr.workspace = true
 reqwest = { workspace = true, features = ["json", "multipart", "rustls", "stream"] }
+reqwest012 = { package = "reqwest", version = "0.12", default-features = false, features = ["rustls-tls"] }
 ripemd = { workspace = true, optional = true }
 rubato = { workspace = true, optional = true }
 schemars = { workspace = true }
diff --git a/crates/zeph-llm/src/any.rs b/crates/zeph-llm/src/any.rs
index 05a9eae9a..541050a79 100644
--- a/crates/zeph-llm/src/any.rs
+++ b/crates/zeph-llm/src/any.rs
@@ -76,6 +76,7 @@ macro_rules! delegate_provider {
 /// [`Arc<dyn LlmProviderDyn>`](crate::provider_dyn::LlmProviderDyn).
 ///
 /// The `Candle` variant is only available when the `candle` feature is enabled.
+#[non_exhaustive]
 #[derive(Debug, Clone)]
 pub enum AnyProvider {
     Ollama(OllamaProvider),
diff --git a/crates/zeph-llm/src/candle_provider/loader.rs b/crates/zeph-llm/src/candle_provider/loader.rs
index 3bbf7444f..0ed3f4d89 100644
--- a/crates/zeph-llm/src/candle_provider/loader.rs
+++ b/crates/zeph-llm/src/candle_provider/loader.rs
@@ -10,6 +10,7 @@ use candle_core::quantized::gguf_file;
 use candle_transformers::models::quantized_llama::ModelWeights;
 use tokenizers::Tokenizer;
 
+#[non_exhaustive]
 #[derive(Debug, Clone)]
 pub enum ModelSource {
     Local {
diff --git a/crates/zeph-llm/src/candle_provider/template.rs b/crates/zeph-llm/src/candle_provider/template.rs
index cc68fd7cb..cf6f25340 100644
--- a/crates/zeph-llm/src/candle_provider/template.rs
+++ b/crates/zeph-llm/src/candle_provider/template.rs
@@ -3,6 +3,7 @@
 
 use crate::provider::{Message, Role};
 
+#[non_exhaustive]
 #[derive(Debug, Clone, Copy)]
 pub enum ChatTemplate {
     Llama3,
diff --git a/crates/zeph-llm/src/ollama.rs b/crates/zeph-llm/src/ollama.rs
index 9ec1eb470..98d8554c6 100644
--- a/crates/zeph-llm/src/ollama.rs
+++ b/crates/zeph-llm/src/ollama.rs
@@ -55,6 +55,17 @@ use crate::provider::{
 };
 use crate::usage::UsageTracker;
 
+/// Build a reqwest 0.12 HTTP client (the version used by ollama-rs) with a 600-second hard
+/// backstop timeout and a 30-second connect timeout.
+fn ollama_reqwest_client() -> reqwest012::Client {
+    reqwest012::Client::builder()
+        .connect_timeout(std::time::Duration::from_secs(30))
+        .timeout(std::time::Duration::from_mins(10))
+        .user_agent(concat!("zeph/", env!("CARGO_PKG_VERSION")))
+        .build()
+        .expect("Ollama HTTP client construction must not fail")
+}
+
 /// Metadata returned by `/api/show` for the configured chat model.
 #[derive(Debug)]
 pub struct ModelInfo {
@@ -114,7 +125,7 @@ impl OllamaProvider {
     pub fn new(base_url: &str, model: String, embedding_model: String) -> Self {
         let (host, port) = parse_host_port(base_url);
         Self {
-            client: Ollama::new(host, port),
+            client: Ollama::new_with_client(host, port, ollama_reqwest_client()),
             model,
             embedding_model,
             context_window_size: None,
@@ -647,6 +658,14 @@ mod tests {
         std::env::var("OLLAMA_EMBED_MODEL").unwrap_or_else(|_| "qwen3-embedding".into())
     }
 
+    // --- #4729: Ollama HTTP client smoke test ---
+
+    #[test]
+    fn ollama_reqwest_client_builds_without_panicking() {
+        // Verify that constructing the timeout-configured reqwest client does not panic.
+        let _client = ollama_reqwest_client();
+    }
+
     #[test]
     fn context_length_error_keywords_are_detected() {
         // Verify the helper used at each chat/stream/tools call site works for Ollama error strings.
diff --git a/crates/zeph-llm/src/provider.rs b/crates/zeph-llm/src/provider.rs
index d299ae41b..36030339b 100644
--- a/crates/zeph-llm/src/provider.rs
+++ b/crates/zeph-llm/src/provider.rs
@@ -246,6 +246,7 @@ pub struct GenerationOverrides {
 /// - `System` — global instructions prepended before the conversation
 /// - `User` — human turn input
 /// - `Assistant` — previous model output (used for multi-turn context)
+#[non_exhaustive]
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize)]
 #[serde(rename_all = "lowercase")]
 pub enum Role {
diff --git a/crates/zeph-llm/src/sse.rs b/crates/zeph-llm/src/sse.rs
index 188164bd3..ad19e134c 100644
--- a/crates/zeph-llm/src/sse.rs
+++ b/crates/zeph-llm/src/sse.rs
@@ -13,6 +13,7 @@ use crate::provider::{ChatStream, StreamChunk, ThinkingBlock, ToolUseRequest};
 /// Never exposed as a `StreamChunk` downstream — the drainer consumes these and
 /// surfaces only `StreamChunk` variants, keeping `StreamChunk` exhaustiveness stable
 /// (critic M3). `pub` so `zeph-core` can use the drainer without feature-gating.
+#[non_exhaustive]
 #[derive(Debug)]
 pub enum ToolSseEvent {
     /// Tool block opened: id and name are now known, before any `InputJsonDelta` for this index.
@@ -320,7 +321,12 @@ fn parse_tool_delta_event(state: &mut ClaudeSseState, data: &str) -> Vec<ToolSse
         }
         "input_json_delta" if !delta.partial_json.is_empty() => {
             if let Some((_, _, _, ref mut json)) = state.tool_block {
-                json.push_str(&delta.partial_json);
+                const MAX_TOOL_JSON_BUF: usize = 4 * 1024 * 1024;
+                if json.len() >= MAX_TOOL_JSON_BUF {
+                    tracing::warn!("tool JSON buffer exceeded 4 MiB cap; discarding excess");
+                } else {
+                    json.push_str(&delta.partial_json);
+                }
             }
             let index = state.current_block_index;
             vec![ToolSseEvent::InputJsonDelta {
@@ -330,7 +336,12 @@ fn parse_tool_delta_event(state: &mut ClaudeSseState, data: &str) -> Vec<ToolSse
         }
         "thinking_delta" if !delta.thinking.is_empty() => {
             if let Some((ref mut t, _)) = state.thinking_block {
-                t.push_str(&delta.thinking);
+                const MAX_THINKING_BUF: usize = 1024 * 1024;
+                if t.len() >= MAX_THINKING_BUF {
+                    tracing::warn!("thinking buffer exceeded 1 MiB cap; discarding excess");
+                } else {
+                    t.push_str(&delta.thinking);
+                }
             }
             vec![ToolSseEvent::ThinkingChunk(delta.thinking)]
         }
@@ -995,4 +1006,70 @@ mod tests {
         let chunk = result.unwrap().unwrap();
         assert!(matches!(chunk, StreamChunk::Content(s) if s == "Hello world"));
     }
+
+    // --- #4727: SSE buffer cap tests ---
+
+    #[test]
+    fn tool_json_buf_capped_at_4mib() {
+        let mut state = ClaudeSseState {
+            tool_block: Some((
+                0,
+                "toolu_01".into(),
+                "bash".into(),
+                "x".repeat(4 * 1024 * 1024),
+            )),
+            current_block_index: 0,
+            ..Default::default()
+        };
+        let data = r#"{"type":"content_block_delta","index":0,"delta":{"type":"input_json_delta","partial_json":"OVERFLOW"}}"#;
+        parse_tool_delta_event(&mut state, data);
+        let buf_len = state.tool_block.as_ref().unwrap().3.len();
+        assert_eq!(
+            buf_len,
+            4 * 1024 * 1024,
+            "tool JSON buffer must not grow beyond 4 MiB"
+        );
+    }
+
+    #[test]
+    fn tool_json_buf_accepts_data_below_cap() {
+        let mut state = ClaudeSseState {
+            tool_block: Some((0, "toolu_01".into(), "bash".into(), String::new())),
+            current_block_index: 0,
+            ..Default::default()
+        };
+        let data = r#"{"type":"content_block_delta","index":0,"delta":{"type":"input_json_delta","partial_json":"{\"k\":1}"}}"#;
+        parse_tool_delta_event(&mut state, data);
+        let buf = &state.tool_block.as_ref().unwrap().3;
+        assert_eq!(buf, r#"{"k":1}"#);
+    }
+
+    #[test]
+    fn thinking_buf_capped_at_1mib() {
+        let mut state = ClaudeSseState {
+            thinking_block: Some(("t".repeat(1024 * 1024), String::new())),
+            in_thinking_block: true,
+            ..Default::default()
+        };
+        let data = r#"{"type":"content_block_delta","index":0,"delta":{"type":"thinking_delta","thinking":"OVERFLOW"}}"#;
+        parse_tool_delta_event(&mut state, data);
+        let thinking_len = state.thinking_block.as_ref().unwrap().0.len();
+        assert_eq!(
+            thinking_len,
+            1024 * 1024,
+            "thinking buffer must not grow beyond 1 MiB"
+        );
+    }
+
+    #[test]
+    fn thinking_buf_accepts_data_below_cap() {
+        let mut state = ClaudeSseState {
+            thinking_block: Some((String::new(), String::new())),
+            in_thinking_block: true,
+            ..Default::default()
+        };
+        let data = r#"{"type":"content_block_delta","index":0,"delta":{"type":"thinking_delta","thinking":"step one"}}"#;
+        parse_tool_delta_event(&mut state, data);
+        assert_eq!(state.thinking_block.as_ref().unwrap().0, "step one");
+    }
 }
diff --git a/crates/zeph-memory/src/compaction_probe.rs b/crates/zeph-memory/src/compaction_probe.rs
index b1d9d177a..4f67de4d5 100644
--- a/crates/zeph-memory/src/compaction_probe.rs
+++ b/crates/zeph-memory/src/compaction_probe.rs
@@ -335,9 +335,9 @@ pub async fn generate_probe_questions(
     let mut history = String::new();
     for msg in &truncated {
         let role = match msg.role {
-            Role::User => "user",
             Role::Assistant => "assistant",
             Role::System => "system",
+            Role::User | _ => "user",
         };
         history.push_str(role);
         history.push_str(": ");
diff --git a/crates/zeph-memory/src/store/messages/mod.rs b/crates/zeph-memory/src/store/messages/mod.rs
index 511db8575..930f536a1 100644
--- a/crates/zeph-memory/src/store/messages/mod.rs
+++ b/crates/zeph-memory/src/store/messages/mod.rs
@@ -27,8 +27,8 @@ fn parse_role(s: &str) -> Role {
 pub fn role_str(role: Role) -> &'static str {
     match role {
         Role::System => "system",
-        Role::User => "user",
         Role::Assistant => "assistant",
+        Role::User | _ => "user",
     }
 }