feat(agent): side-question mode (Slice 5)

crates/domain/src/application/services/mod.rs

@@ -20,6 +20,7 @@ pub mod memory_mutation;
 pub mod memory_sharing;
 pub mod pipeline_service;
 pub mod retention;
+pub mod side_question;
 pub mod tool_filtering;
 pub mod post_turn_orchestrator;
 pub mod task_intent;

crates/domain/src/application/services/side_question.rs

@@ -0,0 +1,123 @@
+//! Side question policy — ephemeral tangent handling.
+//!
+//! Detects when a user message is a side question (tangent) and
+//! provides a lighter processing policy: no todo/standing-order mutation,
+//! minimal memory writeback, does not derail main task state.
+
+/// Whether a message is a side question.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum SideQuestionStatus {
+    /// Regular message — full processing.
+    MainFlow,
+    /// Side question — lighter processing.
+    SideQuestion,
+}
+
+/// Detect if a user message is a side question.
+///
+/// Heuristic-based: checks for explicit markers and common tangent patterns.
+pub fn detect_side_question(message: &str) -> SideQuestionStatus {
+    let lower = message.to_lowercase();
+    let trimmed = lower.trim();
+
+    // Explicit markers
+    let explicit_markers = [
+        "btw ",
+        "btw,",
+        "by the way",
+        "quick question",
+        "unrelated:",
+        "unrelated,",
+        "/aside",
+        "off topic",
+        "off-topic",
+        "side note",
+        "random question",
+        "not related but",
+        "кстати",
+        "кстати,",
+        "между прочим",
+    ];
+
+    for marker in &explicit_markers {
+        if trimmed.starts_with(marker) || trimmed.contains(marker) {
+            return SideQuestionStatus::SideQuestion;
+        }
+    }
+
+    SideQuestionStatus::MainFlow
+}
+
+/// Policy: what to suppress for side questions.
+pub struct SideQuestionPolicy {
+    /// Skip todo list mutations.
+    pub skip_todo_updates: bool,
+    /// Skip standing order creation.
+    pub skip_standing_orders: bool,
+    /// Reduce memory writeback (no consolidation, only if explicit signal).
+    pub reduce_memory_writeback: bool,
+    /// Don't update dialogue state focus entities.
+    pub preserve_focus: bool,
+}
+
+impl SideQuestionPolicy {
+    pub fn for_side_question() -> Self {
+        Self {
+            skip_todo_updates: true,
+            skip_standing_orders: true,
+            reduce_memory_writeback: true,
+            preserve_focus: true,
+        }
+    }
+
+    pub fn for_main_flow() -> Self {
+        Self {
+            skip_todo_updates: false,
+            skip_standing_orders: false,
+            reduce_memory_writeback: false,
+            preserve_focus: false,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn explicit_btw_detected() {
+        assert_eq!(detect_side_question("btw what time is it?"), SideQuestionStatus::SideQuestion);
+        assert_eq!(detect_side_question("BTW, unrelated"), SideQuestionStatus::SideQuestion);
+    }
+
+    #[test]
+    fn by_the_way_detected() {
+        assert_eq!(
+            detect_side_question("by the way, what's your version?"),
+            SideQuestionStatus::SideQuestion
+        );
+    }
+
+    #[test]
+    fn aside_command_detected() {
+        assert_eq!(detect_side_question("/aside quick thought"), SideQuestionStatus::SideQuestion);
+    }
+
+    #[test]
+    fn russian_detected() {
+        assert_eq!(detect_side_question("кстати, а который час?"), SideQuestionStatus::SideQuestion);
+    }
+
+    #[test]
+    fn regular_message_is_main_flow() {
+        assert_eq!(detect_side_question("deploy the service"), SideQuestionStatus::MainFlow);
+        assert_eq!(detect_side_question("what's the weather?"), SideQuestionStatus::MainFlow);
+    }
+
+    #[test]
+    fn policy_for_side_question() {
+        let p = SideQuestionPolicy::for_side_question();
+        assert!(p.skip_todo_updates);
+        assert!(p.preserve_focus);
+    }
+}