diff --git a/rust/crates/runtime/src/session.rs b/rust/crates/runtime/src/session.rs
index 6d6ff8fb..79a3d684 100644
--- a/rust/crates/runtime/src/session.rs
+++ b/rust/crates/runtime/src/session.rs
@@ -13,6 +13,9 @@ use serde::{Deserialize, Serialize};
 const SESSION_VERSION: u32 = 1;
 const ROTATE_AFTER_BYTES: u64 = 256 * 1024;
 const MAX_ROTATED_FILES: usize = 3;
+const MAX_JSONL_FIELD_CHARS: usize = 16 * 1024;
+const JSONL_TRUNCATION_MARKER: &str = "… [truncated for session JSONL]";
+const JSONL_REDACTION_MARKER: &str = "[redacted]";
 static SESSION_ID_COUNTER: AtomicU64 = AtomicU64::new(0);
 static LAST_TIMESTAMP_MS: AtomicU64 = AtomicU64::new(0);
 
@@ -920,7 +923,7 @@ impl SessionCompaction {
         );
         object.insert(
             "summary".to_string(),
-            JsonValue::String(self.summary.clone()),
+            JsonValue::String(sanitize_jsonl_field(&self.summary)),
         );
         Ok(JsonValue::Object(object))
     }
@@ -980,7 +983,10 @@ impl SessionPromptEntry {
             "timestamp_ms".to_string(),
             JsonValue::Number(i64::try_from(self.timestamp_ms).unwrap_or(i64::MAX)),
         );
-        object.insert("text".to_string(), JsonValue::String(self.text.clone()));
+        object.insert(
+            "text".to_string(),
+            JsonValue::String(sanitize_jsonl_field(&self.text)),
+        );
         JsonValue::Object(object)
     }
 
@@ -998,10 +1004,156 @@ impl SessionPromptEntry {
 fn message_record(message: &ConversationMessage) -> JsonValue {
     let mut object = BTreeMap::new();
     object.insert("type".to_string(), JsonValue::String("message".to_string()));
-    object.insert("message".to_string(), message.to_json());
+    object.insert("message".to_string(), persisted_message_json(message));
     JsonValue::Object(object)
 }
 
+fn persisted_message_json(message: &ConversationMessage) -> JsonValue {
+    let mut object = BTreeMap::new();
+    object.insert(
+        "role".to_string(),
+        JsonValue::String(
+            match message.role {
+                MessageRole::System => "system",
+                MessageRole::User => "user",
+                MessageRole::Assistant => "assistant",
+                MessageRole::Tool => "tool",
+            }
+            .to_string(),
+        ),
+    );
+    object.insert(
+        "blocks".to_string(),
+        JsonValue::Array(message.blocks.iter().map(persisted_block_json).collect()),
+    );
+    if let Some(usage) = message.usage {
+        object.insert("usage".to_string(), usage_to_json(usage));
+    }
+    JsonValue::Object(object)
+}
+
+fn persisted_block_json(block: &ContentBlock) -> JsonValue {
+    let mut object = BTreeMap::new();
+    match block {
+        ContentBlock::Text { text } => {
+            object.insert("type".to_string(), JsonValue::String("text".to_string()));
+            object.insert("text".to_string(), JsonValue::String(sanitize_jsonl_field(text)));
+        }
+        ContentBlock::Thinking {
+            thinking,
+            signature,
+        } => {
+            object.insert(
+                "type".to_string(),
+                JsonValue::String("thinking".to_string()),
+            );
+            object.insert(
+                "thinking".to_string(),
+                JsonValue::String(sanitize_jsonl_field(thinking)),
+            );
+            if let Some(signature) = signature {
+                object.insert(
+                    "signature".to_string(),
+                    JsonValue::String(sanitize_jsonl_field(signature)),
+                );
+            }
+        }
+        ContentBlock::ToolUse { id, name, input } => {
+            object.insert(
+                "type".to_string(),
+                JsonValue::String("tool_use".to_string()),
+            );
+            object.insert("id".to_string(), JsonValue::String(sanitize_jsonl_field(id)));
+            object.insert("name".to_string(), JsonValue::String(name.clone()));
+            object.insert(
+                "input".to_string(),
+                JsonValue::String(sanitize_jsonl_field(input)),
+            );
+        }
+        ContentBlock::ToolResult {
+            tool_use_id,
+            tool_name,
+            output,
+            is_error,
+        } => {
+            object.insert(
+                "type".to_string(),
+                JsonValue::String("tool_result".to_string()),
+            );
+            object.insert(
+                "tool_use_id".to_string(),
+                JsonValue::String(sanitize_jsonl_field(tool_use_id)),
+            );
+            object.insert("tool_name".to_string(), JsonValue::String(tool_name.clone()));
+            object.insert(
+                "output".to_string(),
+                JsonValue::String(sanitize_jsonl_field(output)),
+            );
+            object.insert("is_error".to_string(), JsonValue::Bool(*is_error));
+        }
+    }
+    JsonValue::Object(object)
+}
+
+fn sanitize_jsonl_field(value: &str) -> String {
+    truncate_jsonl_field(&redact_jsonl_secrets(value))
+}
+
+fn truncate_jsonl_field(value: &str) -> String {
+    let char_count = value.chars().count();
+    if char_count <= MAX_JSONL_FIELD_CHARS {
+        return value.to_string();
+    }
+
+    let keep = MAX_JSONL_FIELD_CHARS.saturating_sub(JSONL_TRUNCATION_MARKER.chars().count());
+    let mut truncated = value.chars().take(keep).collect::<String>();
+    truncated.push_str(JSONL_TRUNCATION_MARKER);
+    truncated
+}
+
+fn redact_jsonl_secrets(value: &str) -> String {
+    let mut redacted = value.to_string();
+    for marker in [
+        "ANTHROPIC_API_KEY=",
+        "ANTHROPIC_AUTH_TOKEN=",
+        "OPENAI_API_KEY=",
+        "DASHSCOPE_API_KEY=",
+        "XAI_API_KEY=",
+        "Authorization: Bearer ",
+        "authorization: Bearer ",
+        "Bearer sk-",
+        "sk-ant-",
+    ] {
+        redacted = redact_after_marker(&redacted, marker);
+    }
+    redacted
+}
+
+fn redact_after_marker(value: &str, marker: &str) -> String {
+    let mut output = String::with_capacity(value.len());
+    let mut rest = value;
+
+    while let Some(index) = rest.find(marker) {
+        let (before, after_before) = rest.split_at(index);
+        output.push_str(before);
+        output.push_str(marker);
+        output.push_str(JSONL_REDACTION_MARKER);
+
+        let secret_start = marker.len();
+        let after_marker = &after_before[secret_start..];
+        let secret_end = after_marker
+            .char_indices()
+            .find_map(|(idx, ch)| {
+                (ch.is_whitespace() || matches!(ch, '\'' | '"' | ',' | '}' | ']')).then_some(idx)
+            })
+            .unwrap_or(after_marker.len());
+        rest = &after_marker[secret_end..];
+    }
+
+    output.push_str(rest);
+    output
+}
+
 fn usage_to_json(usage: TokenUsage) -> JsonValue {
     let mut object = BTreeMap::new();
     object.insert(