fix(types): correct nullability of config fields in command TypedDicts

[bearomorphism]

Description

Several command TypedDicts declared fields as non-nullable (int, str, dict, list) while argparse produces None when CLI flags are omitted. Runtime code already handles None correctly (via or fallbacks, .get(), explicit None checks), but the type annotations were misleading to both developers and mypy.

Changes

• CommitArgs: message_length_limit: int → int | None
• CheckArgs: message_length_limit: int → int | None, allowed_prefixes: list[str] → list[str] | None
• BumpArgs: file_name: str → str | None
• ChangelogArgs: file_name, start_rev, tag_format, version_scheme, export_template, template → add | None; extras → dict[str, Any] | None

Scope

Type annotations only — no behavioral changes.

Audit findings

A full audit of all Settings fields and command TypedDicts found these inconsistency patterns:

1. CLI args produce None but TypedDict says non-nullable (fixed in this PR)

Field	TypedDict	CLI default
message_length_limit	int in CommitArgs, CheckArgs	None (no argparse default)
allowed_prefixes	list[str] in CheckArgs	None (nargs="*", no default)
file_name	str in BumpArgs, ChangelogArgs	None (no default)
start_rev, tag_format, version_scheme, export_template, template	str in ChangelogArgs	None
extras	dict[str, Any] in ChangelogArgs	None (ParseKwargs action, no default)

2. <= 0 guard consistency for message_length_limit

Both code paths correctly treat 0 and negatives as "no limit":

• commit.py:92-93: if message_length_limit is None or message_length_limit <= 0
• check.py → base.py:133: if max_msg_length is not None and max_msg_length > 0

The None check in commit.py:93 was dead code to mypy (type said int). This PR makes it type-correct.

The behavioral bug where arguments.get("key", fallback) returns None instead of falling through to config is tracked separately in #1899 / #1900.

3. Out of scope (no changes needed or separate concerns)

• Settings TypedDict itself: already total=False, so missing defaults aren't a type error
• Fields missing from DEFAULT_SETTINGS (annotated_tag, gpg_sign, change_type_map, style, customize, version_type): all accessed via .get() or guarded — no runtime risk
• BumpArgs(Settings) inheritance design: structural refactor tracked in Use ChainMap to rewrite the cmd options <- configuration file <- default configuration chain #1672 / fix: try to use ChainMap to chain settings, fix message_length_limit inconsistency #1812
• Config validation/coercion layer: base_config.py:49 does raw update() with no type checking — larger effort

Related

• Fix: message_length_limit config is ignored when CLI flag is unset (commit/check) #1899 — the message_length_limit config-ignored bug (this PR makes the types accurate; the behavioral fix is in Fix and improve test: message_length_limit #1900)
• Fix and improve test: message_length_limit #1900 — behavioral fix for message_length_limit precedence (complementary, no conflict)
• fix: try to use ChainMap to chain settings, fix message_length_limit inconsistency #1812 — ChainMap-based settings refactor (complementary, no conflict)
• Use ChainMap to rewrite the cmd options <- configuration file <- default configuration chain #1672 — tracking issue for the settings chain redesign

Checklist

• I have read the contributing guidelines

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• Yes (please specify the tool below)

Generated-with: GitHub Copilot CLI following the guidelines

Code Changes

• Add test cases to all the changes you introduce
• Run uv run poe all locally to ensure this change passes linter check and tests
• Manually test the changes
• Update the documentation for the changes

No test or doc changes needed — this is a pure type annotation fix with no behavioral impact.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.23%. Comparing base (4b93a50) to head (bef33f7).
⚠️ Report is 1 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1952   +/-   ##
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  Coverage   98.23%   98.23%           
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  Files          61       61           
  Lines        2779     2779           
=======================================
  Hits         2730     2730           
  Misses         49       49           

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