Extended thinking needed to travel end-to-end through the API,
runtime, and CLI so the client can request a thinking budget,
preserve streamed reasoning blocks, and present them in a
collapsed text-first form. The implementation keeps thinking
strictly opt-in, adds a session-local toggle, and reuses the
existing flag/slash-command/reporting surfaces instead of
introducing a new UI layer.
Constraint: Existing non-thinking text/tool flows had to remain backward compatible by default
Constraint: Terminal UX needed a lightweight collapsed representation rather than an interactive TUI widget
Rejected: Heuristic CLI-only parsing of reasoning text | brittle against structured stream payloads
Rejected: Expanded raw thinking output by default | too noisy for normal assistant responses
Confidence: medium
Scope-risk: moderate
Reversibility: clean
Directive: Keep thinking blocks structurally separate from answer text unless the upstream API contract changes
Tested: cargo fmt --all; cargo clippy --workspace --all-targets -- -D warnings; cargo test -q
Not-tested: Live upstream thinking payloads against the production API contract
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
