[FEATURE] Collapsible/disclosure sections for output verbosity control

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Claude Code outputs a lot of information — tool calls, file contents, diffs, reasoning — and while all of it is useful sometimes, most of it isn't useful _most_ of the time.

Currently, the options are all-or-nothing: either you see everything (default) or you reduce verbosity globally (compact mode), losing detail you might occasionally want.

Proposed Solution

Support collapsible/disclosure sections in terminal output, similar to HTML <details>/<summary>.

Claude would wrap routine details (file reads, edit diffs, search results, intermediate reasoning) in collapsed sections that show a one-line summary by default, with the ability to expand inline if you want to inspect them.

Example behavior:

▶ Read src/store/selectors.js (147 lines) ← collapsed, one line
▶ Edit src/store/selectors.js (+3 -1) ← collapsed, one line

The selector was missing memoization. Fixed by wrapping ← Claude's actual response the derivation in createSelector.

▶ Ran: yarn tap test/selectors.tap.js (passed) ← collapsed, one line

Clicking or pressing a key on a ▶ line would expand it to show the full content.

Alternative Solutions

• Logging levels (debug/info/warn) — but these are static and require restarting or mode-switching
• Scrollback search — works but forces you to hunt through noise
• Compact mode — loses detail entirely rather than making it available on demand

Priority

Medium - Would be very helpful

Feature Category

Interactive mode (TUI)

Use Case Example

I'm working on a feature and Claude reads 5 files, edits 2, and runs tests. I care about Claude's decision summary and whether tests passed.

The file contents and diffs are noise unless something is wrong — then I want to expand and inspect without re-running anything.

Additional Context

Related issues that address parts of this but not the interactive disclosure concept: #21246, #11173, #20542