refactor(gt-i18n): registration interface

[ErnestM1234]

for string registration, move arguments from a dictionary to kwargs and convert sugar syntax to underscores

Greptile Summary

This PR refactors the gt-i18n string registration interface by renaming all $-prefixed GT reserved keys to underscore-prefixed equivalents ($context → _context, $id → _id, $max_chars → _max_chars, $_source → __source, $_hash → __hash, $_fallback → __fallback), making kwargs valid Python identifiers. It also addresses previous review feedback by replacing the brittle prefix-based variable filtering with an explicit _GT_RESERVED_KEYS blocklist, and by extracting duplicated test helper code into a shared helpers.py module.

Key changes:

• _extract_variables.py: New _GT_RESERVED_KEYS frozenset replaces startswith("$") filter — user variables with _ prefixes are no longer silently dropped
• _msg.py, _t.py, _interpolate.py, _is_encoded.py: All internal key lookups updated to new naming convention
• tests/helpers.py + tests/conftest.py: Shared test utilities extracted (resolving the duplicated-helper concern from the prior review)
• Minor docstring inconsistency in _interpolate.py: step 1 still describes the old prefix-filtering behavior rather than the new explicit blocklist

Confidence Score: 5/5

• This PR is safe to merge — it is a clean, consistent rename across the library with no logic changes and good test coverage.
• All $-prefixed keys are replaced uniformly across production code and tests. The blocklist-based filtering in extract_variables is correct and complete (_context, _id, _max_chars, __hash, __source, __fallback all included). A new test explicitly verifies user _-prefixed vars are preserved. The only finding is a minor stale docstring on a single line in _interpolate.py.
• No files require special attention beyond the minor docstring fix in _interpolate.py.

Important Files Changed

Filename	Overview
packages/gt-i18n/src/gt_i18n/translation_functions/_extract_variables.py	Replaced prefix-based filtering with an explicit _GT_RESERVED_KEYS blocklist, correctly addressing the previous review concern about user variables starting with _ being silently dropped.
packages/gt-i18n/src/gt_i18n/translation_functions/_interpolate.py	Key references updated from $_fallback/$max_chars to __fallback/_max_chars. Minor docstring inconsistency on line 28 still says "filter out _-prefixed keys" but the actual logic now uses an explicit blocklist.
packages/gt-i18n/src/gt_i18n/translation_functions/_msg.py	All $-prefixed keys ($_hash, $context, $id, $max_chars) correctly renamed to their _/__ equivalents. Encoding path and hash logic remain intact.
packages/gt-i18n/tests/helpers.py	New shared test utility module with JS_TO_PY_KEY_MAP, convert_keys, and convert_encoded_string, directly resolving the duplicated-helper concern from the previous review.
packages/gt-i18n/tests/test_extract_variables.py	Tests updated to reflect the new key naming and a new test (test_user_underscore_prefixed_keys_preserved) correctly validates that user variables with a _ prefix are no longer silently dropped.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["t(message, **kwargs)\n_context, _id, _max_chars"] --> B["hash_message()\nuses _context, _id, _max_chars"]
    A --> C{"translation found?"}
    C -->|yes| D["interpolate_message(translated,\n{**kwargs, __fallback: message})"]
    C -->|no| E["interpolate_message(message, kwargs)"]
    D --> F["extract_variables(options)\nblocks _GT_RESERVED_KEYS"]
    E --> F
    F --> G["user vars only\n(e.g. name, count, _custom_var ✓)"]
    F --> H["GT reserved keys removed\n_context, _id, _max_chars\n__hash, __source, __fallback"]
    D --> I{"format error?"}
    I -->|"__fallback present"| J["retry with source msg\n(__fallback=None)"]
    I -->|no fallback| K["return raw + _max_chars cutoff"]
    J --> L["interpolated result"]
    G --> L

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_{Last reviewed commit: 1da7587}

Greptile also left 1 inline comment on this PR.

[pie575]

@greptileai review

[pie575]

@greptileai review

[ErnestM1234]

@greptileai review

idk if greptile is real bro

[ErnestM1234]

@greptileai plz review

[pie575]