feat: merge 2nd round from all rcc/* sessions

- api: tool_use parsing, message_delta, request_id tracking, retry logic
- tools: extended tool suite (WebSearch, WebFetch, Agent, etc.)
- cli: live streamed conversations, session restore, compact commands
- runtime: config loading, system prompt builder, token usage, compaction

rust/crates/commands/src/lib.rs

@@ -1,3 +1,5 @@
+use runtime::{compact_session, CompactionConfig, Session};
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct CommandManifestEntry {
     pub name: String,
@@ -27,3 +29,82 @@ impl CommandRegistry {
         &self.entries
     }
 }
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct SlashCommandResult {
+    pub message: String,
+    pub session: Session,
+}
+
+#[must_use]
+pub fn handle_slash_command(
+    input: &str,
+    session: &Session,
+    compaction: CompactionConfig,
+) -> Option<SlashCommandResult> {
+    let trimmed = input.trim();
+    if !trimmed.starts_with('/') {
+        return None;
+    }
+
+    match trimmed.split_whitespace().next() {
+        Some("/compact") => {
+            let result = compact_session(session, compaction);
+            let message = if result.removed_message_count == 0 {
+                "Compaction skipped: session is below the compaction threshold.".to_string()
+            } else {
+                format!(
+                    "Compacted {} messages into a resumable system summary.",
+                    result.removed_message_count
+                )
+            };
+            Some(SlashCommandResult {
+                message,
+                session: result.compacted_session,
+            })
+        }
+        _ => None,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::handle_slash_command;
+    use runtime::{CompactionConfig, ContentBlock, ConversationMessage, MessageRole, Session};
+
+    #[test]
+    fn compacts_sessions_via_slash_command() {
+        let session = Session {
+            version: 1,
+            messages: vec![
+                ConversationMessage::user_text("a ".repeat(200)),
+                ConversationMessage::assistant(vec![ContentBlock::Text {
+                    text: "b ".repeat(200),
+                }]),
+                ConversationMessage::tool_result("1", "bash", "ok ".repeat(200), false),
+                ConversationMessage::assistant(vec![ContentBlock::Text {
+                    text: "recent".to_string(),
+                }]),
+            ],
+        };
+
+        let result = handle_slash_command(
+            "/compact",
+            &session,
+            CompactionConfig {
+                preserve_recent_messages: 2,
+                max_estimated_tokens: 1,
+            },
+        )
+        .expect("slash command should be handled");
+
+        assert!(result.message.contains("Compacted 2 messages"));
+        assert_eq!(result.session.messages[0].role, MessageRole::System);
+    }
+
+    #[test]
+    fn ignores_unknown_slash_commands() {
+        let session = Session::new();
+        assert!(handle_slash_command("/unknown", &session, CompactionConfig::default()).is_none());
+    }
+}