Feature proposal: `codecarbon doctor` to report measurement quality

[davidberenstein1957]

Feature proposal.

The problem

CodeCarbon always produces a number, but it never tells the user how that number was obtained. On a Linux box where /sys/class/powercap/intel-rapl is root-only, the CPU silently falls back to a TDP-times-load model. On an unrecognised CPU model the TDP itself is a generic constant. On macOS without sudo for powermetrics it falls back again. RAM is always modelled, never measured. In every one of those cases the tracker keeps going and writes a confident float to emissions.csv.

The information exists — ResourceTracker picks a backend and logs it, CPU._mode records the mode, CPU._is_generic_tdp records whether the TDP was a real match — but it is only visible at INFO/DEBUG log level, mixed into startup noise, and codecarbon detect (which is where users look) prints a correct hardware list and says nothing about quality. Users find out their measurement was mostly an estimate later, usually from a reviewer.

This is a disclosure problem, not a measurement problem: the fallbacks are reasonable, they are just invisible.

Proposed design

A new CLI command:

codecarbon doctor [--json] [--strict]

It runs the existing hardware detection (EmissionsTracker(save_to_file=False).get_detected_hardware() path) and, for each power component, prints a status, the method, why a better method was not used, and the concrete fix:

CPU     12th Gen Intel(R) Core(TM) i7-1260P
        ESTIMATED - CPU load model over a 28 W TDP
        Why: /sys/class/powercap/intel-rapl exists but its energy counters are
             not readable by this user (permission denied)
        Fix: sudo chmod -R a+r /sys/class/powercap/intel-rapl
             https://docs.codecarbon.io/how-to/enable-rapl/

--json gives a machine-readable version for CI gates and bug reports, --strict exits non-zero when any component is estimated.

The public shape is one dataclass and one function in codecarbon/diagnostics.py:

@dataclass
class ComponentDiagnostic:
    component: str   # "CPU" | "RAM" | "GPU"
    detail: str
    status: str      # "measured" | "estimated" | "unavailable"
    method: str
    reason: str | None
    fix: str | None

def diagnose(hardware) -> list[ComponentDiagnostic]: ...

Why it fits existing extension points

No new measurement code and no new dependency. ResourceTracker already centralises the "which backend won" decision, CPU._mode and CPU._is_generic_tdp already encode the answer, and cpu.is_rapl_available() / powermetrics.is_powermetrics_available() / windows_emi.is_emi_available() already run the checks whose failure reason we want to surface. diagnose() reads the hardware objects the tracker builds; it does not duplicate detection. typer and rich are already required.

Scope boundary

First PR: diagnostics.py, the doctor command, docs. Deliberately out of scope, because they change behaviour for every existing user and deserve their own review:

• a start-of-run warning from EmissionsTracker.__init__ when a component is estimated;
• a measurement_quality provenance field on EmissionsData / the CSV;
• per-backend why_unavailable() methods on each of rapl.py, powermetrics.py, windows_emi.py, gpu_*.py — the first version derives the reason from the existing availability checks instead, which covers the common Linux/macOS cases without touching six modules.

Also explicitly not in scope: doctor running privileged fix commands itself. It prints them.