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/usage.rs

@@ -300,6 +300,7 @@ mod tests {
                     cache_read_input_tokens: 0,
                 }),
             }],
+            metadata: None,
         };
 
         let tracker = UsageTracker::from_session(&session);