Make SevenTTY usable with Claude Code and other modern TUIs

[ctar]

Summary

Three small fixes that together make SevenTTY work with Claude Code (the Anthropic CLI, an Ink-based TUI) and similar modern terminal apps that rely heavily on Unicode box-drawing and dingbats. Also fixes building SevenTTY on macOS (case-insensitive APFS).

Commits

1. Strip DECSET 2026 synchronized-output markers in SSH/telnet — Claude Code wraps every typed character draw in ESC[?2026l...ESC[?2026h. libvterm doesn't implement synchronized output, so these become unknown DEC private modes. Stripped defensively in ansi_sys_fixup (net.c + telnet.c) to keep the byte stream clean. ansi_fixup_state state machine extended with states 3–7 to match the 8-byte sequence across SSH read boundaries.

2. Fall back to ASCII for Unicode box-drawing, blocks, and TUI dingbats — The symbol-font rendering path produces blank glyphs for codepoints in U+2500–U+259F and common dingbats like ❯ (U+276F), so anything drawn through it was invisible. This made Claude Code's input box borders, welcome banner borders, and prompt character completely invisible. Intercept these codepoints in both draw_screen_color and draw_screen_fast BEFORE symbol_font_lookup and remap them to ASCII equivalents (─→-, │→|, corners/joints→+, diagonals→/ \ X, blocks→# ., half-blocks→" _, ❯→>, arrows→<>^v, bullets→*, checks→v x). Renders via Monaco and preserves column alignment. This is a workaround rather than a root-cause fix for the symbol-font issue itself — not sure why the custom NFNT produces blank glyphs on my build — but it reliably unblocks Claude Code, htop's dim bars, and other modern TUIs.

3. Rename icons.r to app_icons.r (case-insensitive FS collision) — On macOS's case-insensitive APFS, SevenTTY's icons.r resolves to the same path as Apple's Icons.r from the MPW RIncludes, so #include "Icons.r" inside SevenTTY's own icons.r recurses into itself and hits Rez's "include files nested too deep" limit. Rename to app_icons.r and update resources.r. Doesn't affect Linux builds but is required for cross-compilation on macOS.

Test plan

• Build PPC target on macOS 14.8 (Apple Silicon) with Retro68 + MPW 3.5 Universal Interfaces
• Tested on a real PowerPC G3 All-in-One running OS 9
• claude (Claude Code CLI) over SSH: typed input visible, welcome banner borders visible, input box borders visible, ❯ prompt visible
• htop over SSH: dim USER/CPU% columns now visible as ASCII fallbacks
• Smoke test: normal SSH sessions, local shell, theme loading, scrollback all still work

🤖 Generated with Claude Code