Bug: scheduler process cleanup leaks resources

[pbalduino]

Summary

The scheduler reap path does not appear to use the full process resource cleanup path. scheduler_cleanup_process frees some process-owned data, but can skip file descriptor cleanup and user VM region release.

That can leak file references, VM regions, and physical pages after terminated tasks are reaped.

Current Notes

Tracked locally in scheduler_issues.md as "Process Teardown Leaks Resources".

Relevant code:

• src/kernel/proc/proc.c: scheduler_cleanup_process
• src/kernel/proc/proc.c: proc_free_resources
• src/kernel/proc/proc.c: proc_file_table_cleanup
• src/kernel/proc/proc.c: proc_release_user_memory

Expected Behavior

A terminated process should release all owned resources exactly once when reaped, including stacks, file descriptors, VM regions, address-space mappings, and any process table entries.

Proposed Fix

Reuse proc_free_resources from scheduler_cleanup_process, or refactor teardown into a single helper with explicit ownership stages so scheduler reap, exec failure, and process exit paths cannot drift apart.

The fix should preserve zombie/wait semantics: resources that must remain visible to the parent should stay until wait, while heavyweight runtime resources should be released promptly and consistently.

Dependencies

• Issue Implement fork/exec process creation system #93: Fork/exec process creation (CLOSED)
• Issue Implement file descriptor management and pipes #96: File descriptor management (CLOSED)
• Issue Build lightweight virtual memory manager (vm_map/vm_unmap/vm_clone) #57: Virtual memory manager (CLOSED)
• Issue Bug: process PID table is not populated #426: Process PID table is not populated

Blocks

• Issue Design formal per-process virtual memory layout system #55: Design formal per-process virtual memory layout system
• Issue Implement thread-aware system calls and kernel integration #113: Thread-aware system calls and kernel integration

Related Issues

• Issue Bug: ready queue updates are not atomic #425: Ready queue updates are not atomic
• Issue Implement /proc filesystem (procfs) #244: Implement /proc filesystem (CLOSED)
• Issue Improved ps command to match Linux behavior #283: Improved ps command to match Linux behavior

Validation

• Add or update tests for process exit/reap resource cleanup where practical.
• Stress repeated fork/exec/exit/wait cycles and inspect memory/file reference behavior.
• Boot smoke test after userland process churn.
• Confirm make test still passes.