refactor(ui): isolate extension pane controller

[benvinegar]

Summary

• move extension pane state, availability, responsive reveal, resizing, and fallback behavior into useExtensionPaneController
• make pane geometry planning pure and probe extension availability only after commit
• preserve current-line retention, files replacement recovery, capability leases, and responsive resize behavior

Testing

• focused pane controller and geometry tests
• AppHost sidebar, responsive, visibility, resize, and extension tests
• PTY extension, layout, and current-line integration tests
• TTY smoke tests
• bun run typecheck
• bun run deps:check
• bun run lint
• targeted formatting and diff checks

Stack

• Builds on refactor(ui): centralize extension review events #879
• Followed by refactor(ui): extract extension runtime lifecycle #882

This PR description was generated by Pi using GPT-5.6 Sol

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
hunk-web	Ignored	Preview	Aug 27, 2026 12:13pm

[greptile-apps]

Greptile Summary

This PR extracts extension-pane state, availability handling, fallback recovery, responsive visibility, and resizing from App into a dedicated controller hook.

• Moves pane availability probing outside React render and isolates extension failures by registration identity.
• Preserves the built-in files-pane fallback when an extension replacement fails.
• Adds focused controller, pane-planning, and AppHost regression coverage.

Confidence Score: 5/5

The PR appears safe to merge; no concrete changed-code defect remains after reviewing pane availability, fallback, reload, and resize behavior.

The extracted controller preserves logical pane choices, probes extension availability after commit, restores the built-in files pane after replacement failures, retires stale controls, and guards resizing by exact registration identity, with focused regression coverage for these transitions.

Important Files Changed

Filename	Overview
src/ui/hooks/useExtensionPaneController.ts	Centralizes pane state, availability probing, fallback recovery, responsive visibility, current-line retention, capability controls, and resizing with focused identity guards.
src/ui/App.tsx	Replaces inline pane orchestration with the controller while retaining rendering and application-level menu integration.
src/ui/lib/extensionPanes.ts	Separates extension availability probing from pure pane geometry planning.
src/ui/hooks/useExtensionPaneController.test.tsx	Covers availability, quarantine, fallback toggling, reload identity, capability retirement, current-line retention, and resize cancellation.
src/ui/AppHost.extension-sidebar.test.tsx	Adds an end-to-end regression test proving the files toggle can close and reopen an injected fallback.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart LR
  App[App terminal and review inputs] --> Controller[useExtensionPaneController]
  Controller --> Availability[Commit-phase availability probe]
  Availability -->|accepted| Planner[Pane layout planner]
  Availability -->|failure| Quarantine[Quarantine registration]
  Quarantine --> Fallback[Built-in files-pane fallback]
  Controller --> Controls[Extension pane controls]
  Controller --> Resize[Pane resize state]
  Planner --> Render[App pane rendering]
  Render -->|render failure| Quarantine

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