fix: route boo ui stderr to BOO_LOG or /dev/null to stop viewport log noise

[kylecarbs]

Problem

boo ui renders an in-process libghostty VT stream. std.log writes to stderr, which is the user's terminal, so log lines paint over the rendered viewport until a manual redraw (C-a l).

#65 only silenced the stream scope at info level. libghostty logs under many other scopes (osc, terminal_dcs, kitty_gfx, ...) and levels, so lines like info(osc): failed to parse OSC ... or info(terminal_dcs): unknown DCS hook: ... still corrupt the UI on v0.5.22+.

Fix

Drop the narrow std_options.logFn filter and instead redirect the UI process's stderr for the lifetime of boo ui:

• Point fd 2 at $BOO_LOG (appended) when set, otherwise /dev/null.
• Restore the original stderr after the UI exits, so the [boo ui closed] notice still shows.

This suppresses every scope and level from the viewport while keeping an opt-in debug log. The daemon already did this for its own stderr; that logic is factored into openLogSink() and shared.

Behavior notes

• BOO_LOG now also captures boo ui logs (help text updated).
• Daemon stderr handling is unchanged except that a BOO_LOG path which fails to open now falls back to /dev/null instead of the inherited stderr. It is a detached daemon, so this is strictly safer.
• Removing the global logFn is safe: only boo ui (and BOO_FOREGROUND=1, a debug mode) runs an in-process VT stream on a terminal; the attach client passes bytes through without parsing.

Testing

• zig build clean; zig fmt --check clean.
• zig build test test-integration -> 206/206 tests pass (130 unit + 76 PTY integration, including all ui: tests).
• Manual: created a detached session with BOO_LOG set, confirmed the daemon logged to the file (info(daemon): renamed to ...) and that ls/rename/kill work.

Implementation notes / decision log

• Why redirect instead of a broader scope filter? A scope/level allowlist would have to track every libghostty scope indefinitely. Redirecting fd 2 is comprehensive and mirrors what the daemon already does.
• Why save/restore rather than redirect the whole process? Normal CLI commands (ls, errors via std.debug.print/std.log.err) should still reach the terminal. Only boo ui owns the screen, so the redirect is scoped to it and restored before the closing notice.
• IO safety: the UI reads input from fd 0 and writes its rendering to fd 1 (protocol.writeAll(1, ...)); only fd 2 is moved, so drawing is unaffected.
• redirectStderr() returns -1 (no-op restore) if the sink cannot be opened or dup fails, leaving stderr untouched.

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🤖 Generated by Coder Agents on behalf of @kylecarbs.