Fix terminal restoration and TUI redraws

[parsakhaz]

Summary

• model every live PTY with headless xterm so alternate-screen state and RunPane screen reads remain authoritative when the renderer unmounts
• restore the active terminal buffer instead of replaying normal shell history over a live TUI
• force a timed one-column PTY resize transition on activation and manual refresh so foreground TUIs emit a canonical redraw
• document Pane's renderer lifecycle and cover terminal modes, restoration selection, RunPane screen output, and forced redraw behavior

Fixes #324.

Why

Pane disposes renderer-side xterm/WebGL resources when a top-level session unmounts while keeping its PTY alive. Reconstructing only from normal scrollback restored the wrong buffer for full-screen and cursor-addressed applications. Even after restoring the correct cells, Claude's TUI could retain a frame computed for the previous renderer geometry until a real window resize delivered a resize notification.

The main process now owns an xterm-compatible screen model. Renderer activation restores that authoritative state, then performs a real PTY size transition and return so the foreground application redraws at the settled dimensions. runpane panels screen reads the same model and no longer sees the launch command in place of the agent screen.

Testing

• pnpm lint (passes; existing warning baseline only)
• pnpm typecheck
• pnpm --filter main test -- --run (41 files, 339 tests)
• pnpm --filter frontend test (8 files, 93 tests)
• pnpm build:frontend
• pnpm build:main
• pnpm --filter runpane build
• manually reproduced with Claude default and fullscreen TUI modes in an isolated PANE_DIR; switching panes and tabs now restores and redraws correctly without a physical window resize

Dependency Notes

• adds @xterm/headless and @xterm/addon-serialize to the main process
• regenerates NOTICES

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Bound terminal-state idle waits

When a live panel is running high-volume or continuous output, this unbounded waitForIdle() can stay pending because each PTY chunk increments the emulator's pending-write count and the promise only resolves after it reaches zero. This path backs terminal:getState during renderer remount/activation and is also used by runpane panels screen/wait, so commands like yes, a long build, or a log tail can leave the terminal refresh/loading path and local-control commands hanging until output stops. Consider taking the best current snapshot after a short timeout instead of waiting indefinitely.

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