feat(monitoring): robust macOS memory usage with TASK_VM_INFO fallback

[yogeshnimangre007]

feat(monitoring): robust macOS memory usage with TASK_VM_INFO fallback

Summary

Adds reliable process memory tracking on macOS (Intel & Apple Silicon). Previously the monitor endpoint sometimes returned:

"memory": { "available": false, ... }

due to a rigid struct definition or task_info flavor failure.

Changes

• Correct mach_task_basic_info struct layout.
• Compute flavor count using natural_t (u32) sizing.
• Add fallback to TASK_VM_INFO when basic flavor fails.
• Return first non‑zero resident size.
• Add debug logs for each failure path.

Expected JSON

"memory": {
  "available": true,
  "current_bytes": <u64>,
  "peak_bytes": <u64>,
  "current_mb": <f64>,
  "peak_mb": <f64>
}

Verification (macOS)

RUST_LOG=debug cargo run -- --directory . --port 0
# note printed port
curl -s http://localhost:<PORT>/_irondrop/monitor?json=1 | jq '.memory'

Should show available: true. If not, debug logs will contain:

• mach_task_basic_info failed
• and possibly TASK_VM_INFO failed

Edge Cases

Case	Result
Both flavors fail	available:false (previous behavior)
Resident size 0 once	Next poll (5s cache) retries
Sandbox restrictions	Likely both fail, safe fallback

Performance

Negligible impact. Memory probe still cached for 5s.

Risks

• Future macOS struct layout changes (unlikely for fields used).
• If API changes, both flavors may fail (debug logs guide remediation).

Future Improvements (Optional)

• Add proc_pid_rusage third fallback.
• Percent of physical memory field.
• Config flag to disable memory probing.
• Clamp unrealistic ( > physical ) values.

Testing

• Built on macOS (debug build).
• Manual curl of monitor endpoint.
• Verified no regression on Linux (code gated by #[cfg(target_os = "macos")]).

Notes

No external dependencies added; pure FFI approach. Safe failure path maintained.

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Closes intermittent “memory tracking unavailable” observations on macOS.