fix(cli): make lint-translations exit non-zero when translations differ

[Zuhef]

Problem

chainlit lint-translations reports differences and then exits 0, so it cannot gate anything. Issue #2993 identified this as the reason locale keys drift unnoticed, and it is true even for the app translations the command is actually pointed at.

The chain is silent end to end:

• lint_translation_json prints the differences and returns None
• lint_translations returns None
• chainlit_lint_translations calls it and ignores the result, so Click exits 0

Change

• lint_translation_json returns the differences it printed. Additive - existing callers that ignore the return value are unaffected, and the printed output is unchanged.
• lint_translations returns the total count across all linted files.
• The CLI command prints a summary and raises SystemExit(1) when the count is non-zero.

Two incidental cleanups in the same function: the per-file loop was nested inside the ground-truth with open(...) block, holding that handle open for the entire run, so it is dedented; and os.listdir is now sorted so the report order is deterministic. Happy to drop either if you would rather keep the diff to the exit code alone.

Verification

Ran on Windows against a directory containing all 23 packaged locales, comparing a clean main worktree with the patched tree:

	files linted	differences reported	exit code
main	23	6	0
patched	23	6	1

Same six differences either way - only the exit code changes. A directory whose translations match the ground truth still exits 0.

The six it finds are the real gaps from #2993, which is a useful independent cross-check: this is the CLI path rather than the test suite, and it reports exactly chat.favorites.remove (ar-SA, da-DK), components.DatePickerInput (de-DE, it, ko) and chat.fileUpload.browse (ja).

pytest backend/tests/test_translations.py - 39 passed. New tests cover the returned error list, the aggregate count for both clean and broken input, and that non-JSON files in the directory are ignored.

ruff format --check clean on all four files. ruff check reports two RUF036 findings at config.py:391-392, which are pre-existing and outside this change.

Note

While verifying this I hit a separate pre-existing problem: on a stock Windows console the command dies with a UnicodeEncodeError printing the ✅/❌ markers, since the console code page cannot encode them. It only runs with PYTHONIOENCODING=utf-8 set. That is independent of this change and I have not touched it here - happy to open a separate issue or PR for it if useful.

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Summary by cubic

Fix the CLI so chainlit lint-translations exits non-zero when any translation differs. This enables CI to fail on missing or extra keys and prevents locale drift.

• Bug Fixes

  • lint_translation_json now returns the list of differences (printing unchanged).
  • lint_translations returns the total difference count across files.
  • The CLI prints a summary and exits 1 when the count is non-zero.
  • Tests cover return values, aggregate counts, and ignoring non-JSON files.

• Refactors

  • Moved the per-file loop out of the ground-truth with open(...) block to avoid holding the file open.
  • Sorted os.listdir for deterministic reporting order.

^{Written for commit f89b44b. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 4 files

_{Re-trigger cubic}