[BUG] Memory leak detected in Tiny Shell process management

[sumin-world]

Bug Description

When running Tiny Shell under moderate load (spawning/exiting many child processes), memory usage grows over time and is not reclaimed. After ~1000 short-lived commands, the process RSS steadily increases until OOM occurs on constrained containers.

To Reproduce

Steps to reproduce the behavior:

1. Build and run Tiny Shell:

git checkout <commit-hash>
cargo build --release

2. Run a loop to spawn multiple short-lived processes:

for i in $(seq 1 2000); do ./target/release/tinysh -c "true"; done

3. Monitor memory usage:

# In a separate terminal
watch -n 1 'ps aux | grep tinysh | head -n 1'

Expected Behavior

Memory footprint should remain stable with resources being properly freed after each child process exits.

Actual Behavior

• Resident memory (RSS) steadily increases and is not freed
• Observed ~10–20MB leak per 100–200 commands (platform dependent)
• Eventually leads to OOM in memory-constrained containers

Environment

• OS: Ubuntu 22.04 / macOS 12
• Rust Version: stable (1.70.0 – please specify exact version)
• Build Command: cargo build --release
• Commit:
• Module: tiny-shell

Additional Context / Investigation Clues

• No panic or crash observed during execution
• valgrind / jemalloc profiling suggests missing cleanup in process table or wait handling
• Suspected issue in child reaping path (wait() / waitpid() calls)
• Memory appears to accumulate with each process spawn/exit cycle