fix: raise on offline tracker configuration errors

[davidberenstein1957]

Closes #1311

What changed

Removed @suppress(Exception) from OfflineEmissionsTracker.__init__ (codecarbon/emissions_tracker.py).

Why

The decorator swallowed configuration errors raised during construction, most visibly the OSError from _set_from_conf when output_dir does not exist. The constructor then returned an object that had never reached _initialize_runtime_state() / _initialize_scheduler_state(), so it had no _start_time, _hardware, _scheduler or _output_handlers. The subsequent start() and stop() calls are themselves suppressed, so they degraded into AttributeError warnings and the run finished with no emissions file and no exception. Under the CLI default log_level="error" nothing was printed at all.

The online EmissionsTracker already raises for the same input, so this also removes an asymmetry between the two constructors.

Suppression on start, flush and stop is deliberately left in place: runtime measurement errors must never crash a user job. Only construction, where the object invariants were never established, now fails loudly.

Verification

Added test_offline_tracker_raises_on_invalid_output_dir in tests/test_offline_emissions_tracker.py, asserting both the offline and the online tracker raise OSError for a non-existent output_dir. It fails on master and passes with this change.

uv run pytest tests/test_offline_emissions_tracker.py tests/test_emissions_tracker.py -q
35 passed

Note for reviewers

This is a behaviour change at a public boundary: code that today constructs a misconfigured offline tracker and carries on will now raise. That is the intended correction but it deserves a changelog entry, and ideally a minor release.

🤖 Generated with Claude Code

Changelog / release note (added)

CHANGELOG.md is not on master yet (it lands with docs/traction-batch), so the entry lives in the docs: docs/reference/api.md now carries a "Constructor errors (changed in v3.4.0)" warning. When the changelog lands, copy:

Changed — OfflineEmissionsTracker no longer swallows exceptions raised while constructing the tracker. Configuration errors (for example a non-existent output_dir) now propagate to the caller, matching EmissionsTracker. Suppression on start/flush/stop is unchanged.

This must ride a minor release (3.4.0), not a patch.

A second constructor-raise case is now covered: test_offline_tracker_raises_on_invalid_region exercises the offline-only region check, which runs before super().__init__ and so was suppressed by a different code path than the output_dir OSError. Both new tests fail when @suppress(Exception) is put back on the constructor.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.47%. Comparing base (065d0e6) to head (85eedc8).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1334      +/-   ##
==========================================
+ Coverage   91.39%   91.47%   +0.07%     
==========================================
  Files          49       49              
  Lines        5056     5055       -1     
==========================================
+ Hits         4621     4624       +3     
+ Misses        435      431       -4     

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