[FEATURE] Focus View should apply to the whole transcript, not only messages after the toggle

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

Turning on Focus View (/focus) condenses tool calls and agent actions only for messages rendered after the toggle. Everything above it in the transcript keeps its full tool-call output.

That rules out the case where Focus View helps most: coming back to a long-running session and reading what happened. I keep Focus View off while I'm watching, because seeing the tool calls is how I check the agent is heading the right way. When I return later, turning it on changes nothing I scroll back through, so the conversation is still buried under every tool call.

Proposed Solution

Make Focus View a view mode over the whole transcript, not a setting captured when each message renders:

• Turning /focus on re-renders the existing transcript with tool calls, tool results and agent actions collapsed, keeping user messages and assistant prose.
• Turning it off restores the full detail, including for messages rendered while it was on.
• The toggle can be flipped any number of times mid-session and behaves the same for old and new messages.

Alternative Solutions

• Leaving Focus View on all the time. This loses the live view of tool calls, which I need while supervising the agent.
• /export and reading the transcript in another tool. This leaves the session, loses my place, and still includes the tool output unless I strip it by hand.
• Scrolling past the tool calls. This is what I do today. On a long agentic session the prose is a small fraction of the scrollback.

Priority

High - Significant impact on productivity

Feature Category

Interactive mode (TUI)

Use Case Example

1. Start a long agentic task with Focus View off, and watch the tool calls to confirm the approach is right.
2. Switch to another session while it works.
3. Come back, run /focus, and scroll up.
4. Expected: the whole conversation reads as messages only (my prompts and the assistant's replies), so I can catch up quickly.
5. Actual: only messages after the /focus command are condensed; everything above still shows every tool call.
6. Run /focus again to get full detail back when I want to inspect a specific step.

Additional Context

• Claude Code 2.1.284, Linux, xterm-256color inside tmux.
• Also submitted through /feedback, feedback ID 8693c48f-7078-4603-82d6-28bf63344d16.
• Technical note: /focus already requires the fullscreen renderer; otherwise it refuses with "Focus view needs the fullscreen renderer…", as quoted in #97166. In fullscreen the app draws the whole transcript itself on the alternate screen instead of handing lines to the terminal's scrollback, so earlier messages can be redrawn. From outside, the forward-only behaviour looks like an implementation choice rather than a terminal limit. The one design detail: keep the message being read anchored in view while the blocks above it collapse or expand.
• Related but distinct requests:
• #83746 asks for human-related messages to stay visible inside Focus View.
• #97166 asks for Focus View in the default renderer.
• #67470 reports assistant text between tool calls not being displayed.
• #97597 asks for Focus View in the Desktop Code tab.