fix: send and store real sub-second emission durations

[davidberenstein1957]

Description

duration changes from int to float in codecarbon/core/schemas.py and carbonserver/carbonserver/api/schemas.py (EmissionBase), matching the database column and ORM, which were already Column(Float). ApiClient.add_emission no longer refuses emissions shorter than one second and no longer truncates the duration with int(...); it still skips a non-positive duration, since the server declares duration as Field(..., gt=0). ExperimentReport, ProjectReport and OrganizationReport widen duration from int to float because those endpoints sum a Float column into a field declared int, which only validates today by luck. A later commit adds a retry that rounds the duration when an older server (still int-typed) rejects a fractional value with a 422, so emissions are not dropped during a mixed-version rollout. Extracted from #1203, which bundled this with unrelated FastAPI middleware work.

Related Issue

N/A

Motivation and Context

The pydantic schemas claimed duration: int while the database column was always Float, so every duration sent to the API was truncated to whole seconds, and the client's < 1 guard silently dropped measurements from any short-lived task. This also created a latent bug: the first sub-second duration stored would make a report endpoint's SUM() non-integral and raise a validation error, a latent 500 on the experiment/project/organization report endpoints.

How Has This Been Tested?

• carbonserver/tests/api/test_schema_compatibility.py::test_millisecond_duration_survives_client_to_server — a client payload with duration=0.0042 validates against the server schema unchanged.
• tests/test_api_call.py::TestApi::test_add_emission_sends_millisecond_duration_unchanged — replaces test_add_emission_skips_short_duration; asserts the POST body carries 0.0042.
• tests/test_api_call.py::TestApi::test_add_emission_skips_zero_duration — a duration=0.0 flush is dropped client-side.
• Both fail on master (ValidationError, and "emissions not sent because of a duration smaller than 1") and pass with the fix.
• uv run pytest tests/ -q --ignore=tests/test_viz_data.py → 626 passed, 21 skipped. carbonserver unit tests → 108 passed. pre-commit run --all-files clean.

Screenshots (if appropriate):

N/A

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

AI Usage Disclosure

• 🟥 AI-vibecoded: You cannot explain the logic. Car analogy : the car drive by itself, you are outside it and just tell it where to go.
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Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the docs/how-to/contributing.md document.
• I have added tests to cover my changes.
• All new and existing tests passed.

Deploy order: server first

No DB migration is needed; emissions.duration is already Column(Float), so only the pydantic layer changes. A new client sending a fractional duration to an old (int-typed) server gets a 422, and HTTPOutput only logs it, so emissions would be silently dropped. Deploy api.codecarbon.io with this PR before releasing the package to PyPI. Self-hosters should upgrade their carbonserver before or together with the codecarbon client.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.71%. Comparing base (e5e46ab) to head (0ddda1a).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1374      +/-   ##
==========================================
+ Coverage   91.70%   91.71%   +0.01%     
==========================================
  Files          49       49              
  Lines        5157     5164       +7     
==========================================
+ Hits         4729     4736       +7     
  Misses        428      428              

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[benoit-cty]

🤖 This review comment was written and posted by Claude Opus 5.5 (AI assistant), at the request of @benoit-cty. Findings were checked by reading the code and running tests locally (merged with current master where relevant), but please double-check before acting on them.

Verdict: ✅ Approve, but deploy the server before releasing the client

Moving duration from int to float in the client dataclass, EmissionBase and the three *Report schemas is correct.

• No migration is needed: emissions.duration is already Column(Float) (sql_models.py:14).
• Old client → new server: works; ints are accepted by the float field.
• Report widening: needed, since the reports func.sum() a Float column into duration: int.
• Webapp: uses z.number(), so it is unaffected.
• Tests: 77 client tests and 56 carbonserver tests pass.

Deploy ordering: new client → old server loses data (medium)

• codecarbon/core/api_client.py:201 now sends the unrounded duration (e.g. 15.0023).
• An old server with duration: int rejects fractional floats: pydantic v2 int_from_float returns 422. HTTPOutput._emit (output_methods/http.py:66-69) only logs that, so nearly every emission is silently dropped.
• This hits users if the package reaches PyPI before api.codecarbon.io is redeployed, and anyone on a self-hosted carbonserver older than this PR.
• Please mention this in the PR description, and plan to deploy the API before the package release. Also add a release note for self-hosters. Optionally, the client could retry once with round(duration) on a 422 to stay compatible with old servers.

Nit:

• The test docstrings mention "A single FastAPI request lasts milliseconds", which looks like leftover context from feat: add FastAPI middleware for per-request emissions tracking #1203.

[davidberenstein1957]

Made the changes in b71cd53: added a deploy-order and self-hoster release note to the description, reworded the test docstrings.
Skipped the optional retry with round(duration) on 422: deploying the server first covers it, happy to add if you want old-server compat.

[davidberenstein1957]

Made the changes in 0ddda1a: client retries once with a rounded duration on a 422, so old servers keep receiving emissions.