fix: TTY detection for hook subprocesses

[wasikarn]

Problem

Hook subprocesses spawned by Claude Code lack a controlling terminal, causing OSC 777 notifications to fail silently.

Root Cause

When Claude Code spawns hook scripts (e.g., on Stop events), the subprocess does not have a controlling terminal. Writing to /dev/tty fails with "Device not configured", preventing Warp notifications from being sent.

Evidence:

# Original approach
$ printf '\033]777;notify;Test;Body\007' > /dev/tty
bash: /dev/tty: Device not configured

Impact

• Warp notifications fail intermittently or not at all
• Users don't receive "Task completed" notifications when Claude finishes work
• Breaks the core value proposition of the Warp + Claude Code integration

Solution

Walk the parent process chain to find the actual TTY device that Claude Code is running on.

Changes

1. TTY Detection: Traverse PPID chain until valid TTY is found
2. Termination Check: Stop at PID 0/1 to prevent infinite loops
3. Robust Trimming: Use [[:space:]] to handle spaces and tabs
4. Safe Fallback: Skip notification if TTY not found (don't write to broken /dev/tty)

Key Implementation Details

# Read TTY and PPID in one ps call
read -r tty_val ppid_val < <(ps -o tty=,ppid= -p  2>/dev/null)

# Trim all whitespace
tty_val=

# Skip if not found
if [ -n  ] && [ -w  ]; then
    printf '...' > 
fi

Testing

Verified Working

• Warp Version: v0.2026.04.08.08.36.stable_05
• OS: macOS (also tested on Linux via CI)
• All Tests Pass: 43 passed, 0 failed

Test Coverage

• TTY detection for current shell
• Parent chain walking (PPID → TTY)
• Invalid PID handling
• Platform-agnostic assertions (works with /dev/ttysXXX on macOS and /dev/pts/N on Linux)

Manual Verification

# Before fix: fails silently
# After fix: Warp notification appears in notification center

Checklist

• Fix tested locally with Warp stable
• All existing tests pass (43/43)
• New tests added for TTY detection logic
• Tests match production code exactly
• Platform-agnostic (macOS/Linux)
• Backward compatible (graceful degradation)
• Code follows bash best practices
• No breaking changes

Platform Notes

Unix-like systems (macOS, Linux): ✅ Fully supported
Windows: Not supported by this fix (requires different TTY detection logic)

---

cc: @harryalbert (previous contributor)

[wasikarn]

Hi @harryalbert and team,

This PR is ready for review. It fixes the TTY detection issue where hook subprocesses fail to send OSC 777 notifications because /dev/tty is unavailable.

Key changes:

• Walks parent process chain to find actual TTY device
• Adds PID 0/1 termination check
• Uses [[:space:]] for robust whitespace handling
• Skip notification if TTY not found (no broken fallback)
• Includes tests that match production code

All 43 tests pass. Tested on Warp v0.2026.04.08.08.36.stable_05.

Please review when you have time. Thanks!