fix(terminal): unset NODE_CHANNEL_FD for PTY shells on every POSIX host

The PTY runtime exported an empty NODE_CHANNEL_FD to override the daemon's
IPC descriptor, because bun-pty merges the native environ back into the
child and a JS-only delete does not stick. Node CLIs launched from the
shell (opencode, claude) then printed "warn: Failed to parse IPC channel
number ''" on exit.

The Linux-only env -u ARGV0 wrapper now applies on macOS and Linux and
also unsets NODE_CHANNEL_FD, so the variable is gone instead of empty.

Testing: runtime and inherited-env tests updated for the POSIX wrapper;
verified in the running app that exiting opencode no longer prints the
warning.

packages/web/server/lib/terminal/DOCUMENTATION.md

@@ -28,8 +28,8 @@ HTTP remains the authenticated command plane for create, resize, appearance upda
 - Concurrent creates for one ID are single-flight only when working directory, shell preference, login mode, launch mode, and session purpose match. Command-mode creates must also match the command text, unless the purpose is a project action that is already running for the same resolved `(cwd, actionId)` pair. In that case the runtime returns the existing session and its existing execution identity, even when another client requested a different session ID. Existing IDs cannot be reused for another working directory or another purpose.
 - Dimensions are bounded to 1-1000 columns and 1-500 rows; input is capped at 64 KiB.
 - A client may create before its renderer has mounted. It derives an initial size from the container and font metrics (falling back to 80x24 when unavailable), then sends a resize once Ghostty reports its final dimensions. This allows shell startup and renderer initialization to overlap.
-- PTY children explicitly clear `NODE_CHANNEL_FD`; daemon IPC descriptors are host-private and invalid after PTY descriptor cleanup.
-- PTY children also strip AppImage `ARGV0` (and other host-private shell vars such as `ELECTRON_RUN_AS_NODE`, `BASH_ENV`, `ENV`, `BASH_XTRACEFD`). An exported `ARGV0` makes zsh rewrite argv[0] for every external command, which breaks Python venv detection and other argv[0]/$0 consumers while leaving `/proc/self/exe` correct. On Linux, PTY spawn is wrapped with `env -u ARGV0` because `bun-pty` merges the native OS environ and would otherwise reintroduce `ARGV0` after a JS-only delete.
+- PTY children never inherit `NODE_CHANNEL_FD`; daemon IPC descriptors are host-private and invalid after PTY descriptor cleanup, and an inherited value (even empty) makes Node CLIs such as opencode print `Failed to parse IPC channel number` on exit.
+- PTY children also strip AppImage `ARGV0` (and other host-private shell vars such as `ELECTRON_RUN_AS_NODE`, `BASH_ENV`, `ENV`, `BASH_XTRACEFD`). An exported `ARGV0` makes zsh rewrite argv[0] for every external command, which breaks Python venv detection and other argv[0]/$0 consumers while leaving `/proc/self/exe` correct. On POSIX, PTY spawn is wrapped with `env -u ARGV0 -u NODE_CHANNEL_FD` (`resolvePosixPtyLaunch`) because `bun-pty` merges the native OS environ and would otherwise reintroduce both after a JS-only delete.
 - `GET /api/terminal/shells` reports shell IDs available on the active server using the same augmented PATH provided to spawned PTYs, plus whether each executable has a supported login-mode argument. `auto` preserves environment/platform fallback order; an explicit unavailable shell fails creation instead of silently running a different shell. Login mode is opt-in and uses only built-in arguments for known shells. Interactive shells still launch as before. Command-mode launches reuse the same environment and login support, but switch argv by shell family: POSIX and Fish use interactive `-c`, Nushell uses `-c`, PowerShell uses `-Command`, and cmd uses `/d /s /c`. Preference changes affect new sessions and explicit restarts, not running PTYs.
 - PTY data and exit callbacks enter one FIFO queue. The runtime wires those listeners in the same synchronous turn that receives the PTY object. `node-pty` and `bun-pty` both expose the PTY before dispatching registered callbacks. If a backend emitted exit before listener registration, this layer could not recover it, so the wiring stays adjacent to PTY creation.
 - Scrollback is retained on the server and capped at 512 KiB with UTF-8-safe trimming. Device-status, device-attribute, cursor-position reply, and color-query exchanges are removed from replay history with incomplete control sequences carried across PTY chunks; live output remains byte-for-byte unchanged.