Goal

Rewrite the session right-side detail panel in smaller steps that can be measured and reverted independently.

Scope

In scope (remaining):

• File chip expanded view / Files tab body rewrite (beyond inactive-tab unmount).
• Terminal panel lifecycle boundaries (mount/measure/scroll on toggle).
• Session review surface lifecycle boundaries.
• Area B audit / checklist closeout: mark which slices are done, which are dropped.

Dropped from scope:

• Tool output detail view. Never implemented in the right panel; tool calls expand inline in the message flow and the right panel intentionally does not duplicate them. Recorded here so future readers don't reopen it.

Out of scope:

• Message flow from [Feature] UI rewrite v2 Area A: message flow modular rollout #601.
• Home from [Task] UI rewrite v2 Area C: home surface modular rollout #603.
• Settings from [Feature] UI rewrite v2 Area D: settings modular rollout #604.
• Visual shell / final shell from [Feature] UI rewrite v2 Area E1: visual shell modular rollout #605 and [Task] UI rewrite v2 Area E2: final shell modular rollout #606.

Delivered so far

• perf(app): unmount closed right panel body #619 — PR0: closed right panel no longer keeps tab body mounted; stale review scroll refs cleared.
• perf(app): gate right-panel context and files tabs when inactive #854 — Inactive Context and Files tab bodies unmount when not selected.
• refactor(app): replace right-panel status todo dots with widget marker #861 — Right-panel Status todo dots replaced with widget marker.
• refactor(app): right-panel visual reshape & portal tabs into titlebar #878 — Right-panel visual reshape; tabs portaled into titlebar.
• fix(app): right-panel titlebar seam — alignment, stable toggle, drag-resize sync #887 / fix(ui): align picker list-header surface and disable stuck gradient in dark mode #888 / refactor(app): extract RightPanelTabStrip and RightPanelReviewBody from SessionSidePanel #890 — Titlebar seam alignment, stable toggle, drag-resize sync, and SessionSidePanel extracted into RightPanelTabStrip + RightPanelReviewBody.

Relevant files or context

Parent: #599
Audit: docs/research/2026-05-23-area-b-right-panel-audit.md (landed).

File set under active review:

• packages/ui/src/components/file.tsx
• packages/app/src/components/terminal.tsx
• packages/ui/src/components/session-review.tsx
• packages/app/src/pages/session/session-side-panel.tsx
• packages/app/src/pages/session/file-tabs.tsx
• packages/app/src/pages/session/terminal-panel.tsx
• packages/app/src/components/file-tree.tsx
• packages/app/src/components/session/session-context-tab.tsx
• packages/app/src/pages/session/use-session-review-state.ts

Constraints:

• Same PR0 gate and soft file-size rule as other areas.
• No regression of already-delivered surfaces.

Verification

• Every Area B PR passes [Task] UI rewrite v2 PR0: perf-gated regression CI #600.
• The 5-minute visual pass in docs/design/session-view-w1-manual-checklist.md passes for right-panel flows.

Execution mode

Agent should investigate and propose a plan first.