Switch CLI rendering to alternate screen buffer#151
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Replaces main-buffer rendering with the alternate screen buffer. The alternate buffer gives the CLI full screen ownership: no scrollback to corrupt, absolute positioning works without caveats, and resize is clear and redraw. This replaces the position tracking, resize heuristics, and scrollback corruption workarounds from prior fixes. Changes: - Screen: add enterAltBuffer/exitAltBuffer to interface and StdoutScreen - MockScreen: dual-buffer model with save/restore on switch, remove readonly from cells, add assertInAltBuffer/assertInMainBuffer/getMainRow - Renderer: remove lastVisibleCursorRow, lastFrame, pendingResize, zoneHeight, notifyResize, writeHistoryLine, writeHistory. Simplified stateless render() always starts with cursorAt(1,1) - Terminal: remove notifyResize, add enterAltBuffer/exitAltBuffer, historyBuffer and inAltBuffer fields. writeHistory accumulates in historyBuffer when in alt buffer, writes directly to screen otherwise - ClaudeCli: enter alt buffer after startup messages, before first redraw. Exit alt buffer as first operation in cleanup. Add SIGTERM and uncaughtException handlers that exit alt buffer before process exit. Remove notifyResize call from resize handler. - Tests: replace main-buffer Renderer tests with alt-buffer equivalents, add MockScreen buffer-switch tests, update terminal-integration tests
Completed responses accumulate in historyBuffer during alt buffer rendering. flushHistory() exits the alt buffer, writes accumulated lines to main buffer scrollback, then re-enters alt buffer and redraws. Called in sendQuery() after showSkills() so every completed response is permanently visible in scrollback.
bananabot9000
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Mar 29, 2026
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Clean implementation. The Phase 0 design in the session log is thorough and the code follows it precisely.
What I like:
- Renderer is now stateless. No
lastVisibleCursorRow, nopendingResize, nozoneHeight, nolastFrame.render()is a pure function of its input pluscursorAt(1,1). That's a massive simplification Screeninterface extended cleanly --enterAltBuffer()/exitAltBuffer()keeps escape sequences centralised. MockScreen's dual-buffer model with save/restore is the right testing abstractionflushHistory()usesscreen.exitAltBuffer/enterAltBufferdirectly (bypassingTerminal.inAltBuffer) so the logical state stays consistent. Subtle but correct- Cleanup handler ordering:
exitAltBuffer()FIRST incleanup(), before kitty keyboard protocol restore. If the process dies mid-cleanup, the user at least sees their main buffer writeHistory()routing based oninAltBuffer-- main buffer writes go direct, alt buffer writes accumulate. Clean dual-path- Tests replaced, not just removed. The new
MockScreen dual-bufferandHistory flushdescribe blocks cover the new contracts.assertInAltBuffer()/assertInMainBuffer()assertions are a nice touch
Observations (not blocking):
flushHistory()callsthis.screen.exitAltBuffer()/enterAltBuffer()but doesn't touchthis.inAltBuffer. The flag staystruethroughout the flush, which is the correct choice (the flush is transparent to the rest of Terminal). Worth a comment if it's not already documented- The SIGTERM handler exits with code 0. If the process was asked to terminate, 0 is fine. Some prefer 128+SIGNUM (143) for signal exits but it doesn't matter in practice
cursorUpandcursorToconsts removed entirely. The only positioning primitive iscursorAt. Clean
191 tests pass per the session log. Ship it.
This was referenced Mar 29, 2026
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Summary
Related Issues
Closes #149
Co-Authored-By: Claude noreply@anthropic.com