Persist CLI conversation history across sessions

The Rust CLI now stores managed sessions under ~/.claude/sessions,
records additive session metadata in the canonical JSON transcript,
and exposes a /sessions listing alias alongside ID-or-path resume.
Inactive oversized sessions are compacted automatically so old
transcripts remain resumable without growing unchecked.

Constraint: Session JSON must stay backward-compatible with legacy files that lack metadata
Constraint: Managed sessions must use a single canonical JSON file per session without new dependencies
Rejected: Sidecar metadata/index files | duplicated state and diverged from the requested single-file persistence model
Confidence: high
Scope-risk: moderate
Reversibility: clean
Directive: Keep CLI policy in the CLI; only add transcript-adjacent metadata to runtime::Session unless another consumer truly needs more
Tested: cargo fmt; cargo clippy --workspace --all-targets -- -D warnings; cargo test --workspace
Not-tested: Manual interactive REPL smoke test against the live Anthropic API

rust/crates/runtime/src/compact.rs

@@ -105,6 +105,7 @@ pub fn compact_session(session: &Session, config: CompactionConfig) -> Compactio
         compacted_session: Session {
             version: session.version,
             messages: compacted_messages,
+            metadata: session.metadata.clone(),
         },
         removed_message_count: removed.len(),
     }
@@ -393,6 +394,7 @@ mod tests {
         let session = Session {
             version: 1,
             messages: vec![ConversationMessage::user_text("hello")],
+            metadata: None,
         };
 
         let result = compact_session(&session, CompactionConfig::default());
@@ -420,6 +422,7 @@ mod tests {
                     usage: None,
                 },
             ],
+            metadata: None,
         };
 
         let result = compact_session(