Feature/vt (#6)

VT emulation instead of clipping sync blocks.

README.md

@@ -7,7 +7,7 @@
 ![Windows](https://img.shields.io/badge/Windows-unsupported-red)
 ![Rust](https://img.shields.io/badge/rust-2024-orange)
 
-A PTY proxy that tames Claude Code's massive terminal updates.
+A PTY proxy that tames Claude Code's massive terminal updates using VT-based rendering.
 
 ## The Problem
 
@@ -15,25 +15,13 @@ Claude Code uses synchronized output to update the terminal atomically. It wraps
 
 The problem: Claude Code sends *entire* screen redraws in these sync blocks - often thousands of lines. Your terminal receives a 5000-line atomic update when only 20 lines are visible. This causes lag, flicker, and makes scrollback useless since each update clears history.
 
-Analysis of terminal recordings confirms Claude Code wraps 100% of its output in sync blocks - every byte of visible output goes through synchronized updates.
-
-Sync blocks start with one of three patterns (from a 3.5GB recording sample):
-
-| Pattern | Count | Frequency | Avg Size |
-|---------|-------|-----------|----------|
-| Line clearing (`2K` + `1A` repeated) | 3,544 | 55% | 2.7 KB |
-| Full screen clear (`2J` + `3J` + `H`) | 2,891 | 45% | 94.5 KB |
-| CRLF + color codes | 1 | <1% | 2.0 KB |
-
-The full screen clears are 35x larger than incremental line clears - these are the real problem.
-
 ## The Solution
 
 claude-chill sits between your terminal and Claude Code:
 
 1. **Intercepts sync blocks** - Catches those massive atomic updates
-2. **Truncates full screen clears** - Only the 45% that are full redraws (94.5 KB avg) get truncated to the last N lines (default: 100). The 55% incremental updates (2.7 KB avg) pass through unchanged.
-3. **Preserves history** - Accumulates content in a buffer. Clears on full screen clear, accumulates otherwise.
+2. **VT-based rendering** - Uses a VT100 emulator to track screen state and renders only the differences
+3. **Preserves history** - Accumulates content in a buffer for lookback
 4. **Enables lookback** - Press a key to pause Claude and view the full history buffer
 
 ## Installation
@@ -47,7 +35,6 @@ cargo install --path crates/claude-chill
 ```bash
 claude-chill claude
 claude-chill -- claude --verbose   # Use -- for command flags
-claude-chill -l 50 -- claude       # Set max lines to 50
 ```
 
 ## Lookback Mode
@@ -66,11 +53,12 @@ When you exit lookback mode, any cached output is processed and the current stat
 Create `~/.config/claude-chill.toml`:
 
 ```toml
-max_lines = 100        # Lines shown per sync block
-history_lines = 100000 # Lines stored for lookback
+history_lines = 100000 # Max lines stored for lookback
 lookback_key = "[ctrl][6]"
 ```
 
+Note: History is cleared on full screen redraws, so lookback shows output since Claude's last full render.
+
 ### Key Format
 
 `[modifier][key]` - Examples: `[f12]`, `[ctrl][g]`, `[ctrl][shift][j]`
@@ -97,9 +85,9 @@ claude-chill creates a pseudo-terminal (PTY) and spawns Claude Code as a child p
 
 1. **Input handling**: Keystrokes pass through to Claude, except for the lookback key which toggles lookback mode
 2. **Output processing**: Scans output for sync block markers. Non-sync output passes through directly
-3. **Sync block buffering**: Accumulates sync block content until the end marker arrives
-4. **Truncation decision**: If the sync block contains a full screen clear (`ESC[2J` + `ESC[H`), truncates to the last N lines. Otherwise passes through unchanged
-5. **History tracking**: Maintains a rolling buffer of output for lookback mode
+3. **VT emulation**: Feeds output through a VT100 emulator to track the virtual screen state
+4. **Differential rendering**: Compares current screen to previous and emits only the changes
+5. **History tracking**: Maintains a buffer of output for lookback mode since the last full redraw
 6. **Signal forwarding**: Window resize (SIGWINCH), interrupt (SIGINT), and terminate (SIGTERM) signals are forwarded to Claude
 
 ## Disclaimer