diff --git a/TODO b/TODO
index 6fb9efd..1039c22 100644
--- a/TODO
+++ b/TODO
@@ -248,7 +248,7 @@ Content-Type: application/issue
 ID: 19
 Type: feature
 Title: config framework with CLI integration
-Status: in-progress
+Status: done
 Priority: medium
 Created: 2026-06-06
 Relationships: 
diff --git a/src/byteb4rb1e/utils/argparse/__init__.py b/src/byteb4rb1e/utils/argparse/__init__.py
index 84ae3ed..5bf1156 100644
--- a/src/byteb4rb1e/utils/argparse/__init__.py
+++ b/src/byteb4rb1e/utils/argparse/__init__.py
@@ -1,6 +1,7 @@
 """Utilities for building composable CLIs from command dataclasses."""
 
+from byteb4rb1e.utils.argparse.actions import KeyValueAction
 from byteb4rb1e.utils.argparse.command import CLICommand
 from byteb4rb1e.utils.argparse.dispatcher import CLI
 
-__all__ = ["CLI", "CLICommand"]
+__all__ = ["CLI", "CLICommand", "KeyValueAction"]
diff --git a/src/byteb4rb1e/utils/argparse/actions.py b/src/byteb4rb1e/utils/argparse/actions.py
new file mode 100644
index 0000000..79a5e8f
--- /dev/null
+++ b/src/byteb4rb1e/utils/argparse/actions.py
@@ -0,0 +1,33 @@
+"""Custom argparse actions."""
+
+from __future__ import annotations
+
+import argparse
+from typing import Any
+
+
+class KeyValueAction(argparse.Action):
+    """Argparse action that accumulates ``KEY=VALUE`` pairs into a dict.
+
+    Usage::
+
+        parser.add_argument("--config", action=KeyValueAction,
+                            default={}, metavar="KEY=VALUE",
+                            help="Set a config option (can be repeated)")
+
+    Then ``args.config`` is a ``dict[str, str]``.
+    """
+
+    def __call__(
+        self,
+        parser: argparse.ArgumentParser,
+        namespace: argparse.Namespace,
+        values: Any,
+        option_string: str | None = None,
+    ) -> None:
+        d = getattr(namespace, self.dest, None) or {}
+        if "=" not in values:
+            parser.error(f"Invalid format: {values!r} (expected KEY=VALUE)")
+        key, _, value = values.partition("=")
+        d[key.strip()] = value.strip()
+        setattr(namespace, self.dest, d)
diff --git a/src/byteb4rb1e/utils/config.py b/src/byteb4rb1e/utils/config.py
new file mode 100644
index 0000000..8bece72
--- /dev/null
+++ b/src/byteb4rb1e/utils/config.py
@@ -0,0 +1,369 @@
+"""Config framework — INI-backed dataclasses with CLI integration.
+
+A config dataclass is the single source of truth for settings.  Values
+come from three layers (later wins):
+
+    1. Dataclass field defaults
+    2. INI file sections
+    3. CLI overrides (via argparse flags or ``--config KEY=VALUE``)
+
+Two CLI integration styles:
+
+- ``add_config_arguments`` — generates one ``--flag`` per field.
+- ``apply_overrides`` — accepts a ``dict[str, str]`` of dotted-path
+  overrides from a unified ``--config KEY=VALUE`` flag.
+"""
+
+import configparser
+from argparse import ArgumentParser, Namespace
+from dataclasses import MISSING, fields
+from pathlib import Path
+from typing import Any, Type, TypeVar, get_type_hints
+
+T = TypeVar("T")
+
+
+# ---------------------------------------------------------------------------
+# Internal helpers
+# ---------------------------------------------------------------------------
+
+def _parse_bool(value: str) -> bool:
+    """Parse a boolean from INI/CLI string."""
+    return value.lower() in ("true", "yes", "1", "on")
+
+
+_TYPE_MAP = {
+    int: int,
+    float: float,
+    str: str,
+    bool: _parse_bool,
+}
+
+
+def resolve_hints(cls: Type) -> dict[str, type]:
+    """Resolve type hints for a dataclass, handling both evaluated
+    and string annotations.
+
+    :param cls: a dataclass class.
+    :returns: dict mapping field names to resolved types.
+    """
+    try:
+        return get_type_hints(cls)
+    except Exception:
+        return {
+            f.name: f.type if isinstance(f.type, type)
+            else str
+            for f in fields(cls)
+        }
+
+
+def _section_name(cls: Type, section: str | None = None) -> str:
+    """Derive INI section name from class name if not provided."""
+    if section is not None:
+        return section
+    name = cls.__name__
+    if name.endswith("Config"):
+        name = name[: -len("Config")]
+    return name.lower()
+
+
+# ---------------------------------------------------------------------------
+# INI loading
+# ---------------------------------------------------------------------------
+
+def load_ini(
+    cls: Type[T],
+    path: Path,
+    section: str | None = None,
+) -> T:
+    """Load a config dataclass from an INI file.
+
+    If *section* is not given, the dataclass name (lowercased,
+    without trailing "Config") is used.
+
+    Unknown keys in the INI file raise ValueError.  Missing keys
+    use the dataclass default.
+    """
+    section = _section_name(cls, section)
+
+    parser = configparser.ConfigParser(
+        comment_prefixes=("#", ";"),
+        inline_comment_prefixes=("#", ";"),
+    )
+    parser.read(path)
+
+    if not parser.has_section(section):
+        return cls()  # type: ignore[call-arg]
+
+    hints = resolve_hints(cls)
+    field_names = {f.name for f in fields(cls) if f.init}
+    kwargs: dict[str, Any] = {}
+
+    for key, raw_value in parser.items(section):
+        if key not in field_names:
+            raise ValueError(
+                f"Unknown config key '{key}' in"
+                f" [{section}]. Valid keys:"
+                f" {sorted(field_names)}"
+            )
+
+        field_type = hints.get(key, str)
+        coerce = _TYPE_MAP.get(field_type, field_type)
+        kwargs[key] = coerce(raw_value)
+
+    return cls(**kwargs)  # type: ignore[call-arg]
+
+
+# ---------------------------------------------------------------------------
+# INI writing
+# ---------------------------------------------------------------------------
+
+def format_section(cls: Type, section: str | None = None) -> str:
+    """Format a config dataclass as an INI section string.
+
+    Returns the section header and all fields with their defaults
+    as commented key-value pairs.
+
+    :param cls: a dataclass class.
+    :param section: section name (derived from class name if None).
+    :returns: INI section string.
+    """
+    section = _section_name(cls, section)
+    hints = resolve_hints(cls)
+    lines = [f"[{section}]"]
+
+    for f in fields(cls):
+        if not f.init:
+            continue
+        field_type = hints.get(f.name, str)
+        type_name = getattr(field_type, "__name__", str(field_type))
+
+        if f.default is not MISSING:
+            default = f.default
+        elif f.default_factory is not MISSING:  # type: ignore[arg-type]
+            default = f.default_factory()  # type: ignore[misc]
+        else:
+            continue
+
+        lines.append(f"# {f.name} ({type_name})")
+        lines.append(f"{f.name} = {default}")
+        lines.append("")
+
+    return "\n".join(lines)
+
+
+def ensure_ini(
+    cls: Type[T],
+    path: Path,
+    section: str | None = None,
+) -> T:
+    """Load config from INI, creating the file with defaults if
+    it does not exist.
+
+    On first run, writes a commented INI file with all fields and
+    their default values.  On subsequent runs, reads the existing
+    file.  Never writes back CLI overrides.
+    """
+    section = _section_name(cls, section)
+
+    if not path.exists():
+        _write_default_ini(cls, path, section)
+
+    return load_ini(cls, path, section)
+
+
+def ensure_ini_multi(
+    configs: list[tuple[Type, str | None]],
+    path: Path,
+) -> None:
+    """Create an INI file with multiple sections if it does not exist.
+
+    Each entry is a (dataclass_cls, section_name) tuple.  If
+    section_name is None, it is derived from the class name.
+
+    Does not overwrite an existing file.
+
+    :param configs: list of (cls, section) tuples.
+    :param path: path to the INI file.
+    """
+    if path.exists():
+        return
+
+    sections = [format_section(cls, section) for cls, section in configs]
+    path.parent.mkdir(parents=True, exist_ok=True)
+    path.write_text("\n".join(sections) + "\n")
+
+
+def _write_default_ini(
+    cls: Type,
+    path: Path,
+    section: str,
+) -> None:
+    """Write an INI file with all fields as commented defaults."""
+    path.parent.mkdir(parents=True, exist_ok=True)
+    path.write_text(format_section(cls, section) + "\n")
+
+
+# ---------------------------------------------------------------------------
+# CLI: per-flag style (add_config_arguments / apply_cli_overrides)
+# ---------------------------------------------------------------------------
+
+def add_config_arguments(
+    cls: Type[T],
+    parser: ArgumentParser,
+    prefix: str = "",
+) -> None:
+    """Add CLI arguments for each field in a config dataclass.
+
+    Field names are converted to CLI flags: ``heart_rate_resolution``
+    becomes ``--heart-rate-resolution`` (or ``--<prefix>-heart-rate-resolution``
+    if a prefix is given).
+    """
+    hints = resolve_hints(cls)
+
+    for f in fields(cls):
+        if not f.init:
+            continue
+        flag_name = f.name.replace("_", "-")
+        if prefix:
+            flag_name = f"{prefix}-{flag_name}"
+
+        field_type = hints.get(f.name, str)
+
+        kwargs: dict[str, Any] = {
+            "dest": f.name,
+        }
+
+        if field_type is bool:
+            kwargs["action"] = (
+                "store_false"
+                if f.default is True
+                else "store_true"
+            )
+            kwargs["default"] = None
+        else:
+            kwargs["type"] = _TYPE_MAP.get(
+                field_type, field_type
+            )
+            kwargs["default"] = None
+            kwargs["metavar"] = field_type.__name__.upper()
+
+        parser.add_argument(f"--{flag_name}", **kwargs)
+
+
+def apply_cli_overrides(
+    config: T,
+    args: Namespace,
+) -> T:
+    """Apply CLI argument values to a config instance.
+
+    Only overrides fields that were explicitly set on the command
+    line (not None).  Returns a new instance.
+    """
+    overrides = {}
+    for f in fields(config):  # type: ignore[arg-type]
+        if not f.init:
+            continue
+        cli_value = getattr(args, f.name, None)
+        if cli_value is not None:
+            overrides[f.name] = cli_value
+
+    if not overrides:
+        return config
+
+    from dataclasses import asdict
+    merged = asdict(config)  # type: ignore[arg-type]
+    merged.update(overrides)
+    return type(config)(**merged)  # type: ignore[return-value]
+
+
+# ---------------------------------------------------------------------------
+# CLI: dotted-path style (apply_overrides)
+# ---------------------------------------------------------------------------
+
+def apply_overrides(
+    config: T,
+    overrides: dict[str, str],
+    prefix: str = "",
+) -> T:
+    """Apply dotted-path string overrides to a config dataclass.
+
+    Used with a unified ``--config KEY=VALUE`` CLI flag.  Each key
+    is a dotted path relative to the prefix.
+
+    Example::
+
+        overrides = {
+            "provider.base_url": "http://localhost:4000",
+            "provider.model": "qwen2.5:7b",
+        }
+        config = apply_overrides(config, overrides, prefix="provider")
+        # config.base_url == "http://localhost:4000"
+        # config.model == "qwen2.5:7b"
+
+    :param config: a dataclass instance.
+    :param overrides: dict of dotted keys to string values.
+    :param prefix: only apply keys starting with this prefix.
+    :returns: new config instance with overrides applied.
+    """
+    hints = resolve_hints(type(config))
+    kwargs: dict[str, Any] = {}
+    changed = False
+
+    for f in fields(config):
+        if not f.init:
+            continue
+        full_key = f"{prefix}.{f.name}" if prefix else f.name
+        if full_key in overrides:
+            raw = overrides[full_key]
+            field_type = hints.get(f.name, str)
+            coerce = _TYPE_MAP.get(field_type, field_type)
+            kwargs[f.name] = coerce(raw)
+            changed = True
+        else:
+            kwargs[f.name] = getattr(config, f.name)
+
+    if not changed:
+        return config
+
+    return type(config)(**kwargs)  # type: ignore[return-value]
+
+
+def format_help(cls: Type, prefix: str = "") -> list[str]:
+    """Generate help lines for a config dataclass.
+
+    Each line shows the dotted key path, type, and default value.
+    Suitable for CLI epilog text.
+
+    :param cls: a dataclass class.
+    :param prefix: prepended to each key path.
+    :returns: list of formatted help strings.
+    """
+    hints = resolve_hints(cls)
+    lines = []
+
+    for f in fields(cls):
+        if not f.init:
+            continue
+        field_type = hints.get(f.name, str)
+        type_name = getattr(field_type, "__name__", str(field_type))
+        key = f"{prefix}.{f.name}" if prefix else f.name
+
+        if f.default is not MISSING:
+            default = f.default
+        elif f.default_factory is not MISSING:  # type: ignore[arg-type]
+            default = repr(f.default_factory())  # type: ignore[misc]
+        else:
+            default = "(required)"
+
+        lines.append(f"  {key} ({type_name}, default: {default})")
+
+    return lines
+
+
+# ---------------------------------------------------------------------------
+# Backwards compat
+# ---------------------------------------------------------------------------
+
+# keep the old private name working for existing callers
+_resolve_hints = resolve_hints
diff --git a/tests/unit/byteb4rb1e/utils/argparse/test_actions.py b/tests/unit/byteb4rb1e/utils/argparse/test_actions.py
new file mode 100644
index 0000000..3d0c150
--- /dev/null
+++ b/tests/unit/byteb4rb1e/utils/argparse/test_actions.py
@@ -0,0 +1,52 @@
+"""Tests for custom argparse actions."""
+
+from argparse import ArgumentParser
+
+import pytest
+
+from byteb4rb1e.utils.argparse.actions import KeyValueAction
+
+
+def _parse(*args):
+    parser = ArgumentParser()
+    parser.add_argument("--config", action=KeyValueAction, default={}, metavar="KEY=VALUE")
+    return parser.parse_args(list(args))
+
+
+class TestKeyValueAction:
+
+    def test_single_pair(self):
+        args = _parse("--config", "key=value")
+        assert args.config == {"key": "value"}
+
+    def test_multiple_pairs(self):
+        args = _parse("--config", "a=1", "--config", "b=2")
+        assert args.config == {"a": "1", "b": "2"}
+
+    def test_dotted_key(self):
+        args = _parse("--config", "provider.base_url=http://localhost")
+        assert args.config == {"provider.base_url": "http://localhost"}
+
+    def test_value_with_equals(self):
+        args = _parse("--config", "url=http://host?a=1&b=2")
+        assert args.config == {"url": "http://host?a=1&b=2"}
+
+    def test_empty_value(self):
+        args = _parse("--config", "key=")
+        assert args.config == {"key": ""}
+
+    def test_strips_whitespace(self):
+        args = _parse("--config", " key = value ")
+        assert args.config == {"key": "value"}
+
+    def test_overwrites_duplicate_key(self):
+        args = _parse("--config", "key=first", "--config", "key=second")
+        assert args.config == {"key": "second"}
+
+    def test_default_empty_dict(self):
+        args = _parse()
+        assert args.config == {}
+
+    def test_no_equals_raises(self):
+        with pytest.raises(SystemExit):
+            _parse("--config", "no_equals_here")
diff --git a/tests/unit/byteb4rb1e/utils/config/test_config.py b/tests/unit/byteb4rb1e/utils/config/test_config.py
new file mode 100644
index 0000000..6b25306
--- /dev/null
+++ b/tests/unit/byteb4rb1e/utils/config/test_config.py
@@ -0,0 +1,347 @@
+"""Unit tests for the config framework."""
+
+from argparse import ArgumentParser, Namespace
+from dataclasses import dataclass
+from pathlib import Path
+
+import pytest
+
+from byteb4rb1e.utils.config import (
+    add_config_arguments,
+    apply_cli_overrides,
+    apply_overrides,
+    ensure_ini,
+    ensure_ini_multi,
+    format_help,
+    format_section,
+    load_ini,
+    resolve_hints,
+)
+
+
+@dataclass
+class SampleConfig:
+    name: str = "default"
+    count: int = 10
+    ratio: float = 0.5
+    enabled: bool = True
+
+
+class TestLoadIni:
+    def test_loads_values(self, tmp_path):
+        ini = tmp_path / "test.ini"
+        ini.write_text(
+            "[sample]\n"
+            "name = custom\n"
+            "count = 42\n"
+            "ratio = 0.75\n"
+        )
+        config = load_ini(SampleConfig, ini)
+        assert config.name == "custom"
+        assert config.count == 42
+        assert config.ratio == 0.75
+        assert config.enabled is True  # default
+
+    def test_missing_section_uses_defaults(self, tmp_path):
+        ini = tmp_path / "test.ini"
+        ini.write_text("[other]\nfoo = bar\n")
+        config = load_ini(SampleConfig, ini)
+        assert config.name == "default"
+        assert config.count == 10
+
+    def test_missing_file_uses_defaults(self, tmp_path):
+        config = load_ini(
+            SampleConfig, tmp_path / "missing.ini"
+        )
+        assert config.name == "default"
+
+    def test_unknown_key_raises(self, tmp_path):
+        ini = tmp_path / "test.ini"
+        ini.write_text("[sample]\nunknown_key = bad\n")
+        with pytest.raises(ValueError, match="unknown_key"):
+            load_ini(SampleConfig, ini)
+
+    def test_custom_section_name(self, tmp_path):
+        ini = tmp_path / "test.ini"
+        ini.write_text("[mysection]\nname = custom\n")
+        config = load_ini(
+            SampleConfig, ini, section="mysection"
+        )
+        assert config.name == "custom"
+
+    def test_comments_ignored(self, tmp_path):
+        ini = tmp_path / "test.ini"
+        ini.write_text(
+            "[sample]\n"
+            "# this is a comment\n"
+            "name = works  # inline comment\n"
+        )
+        config = load_ini(SampleConfig, ini)
+        assert config.name == "works"
+
+
+class TestAddConfigArguments:
+    def test_generates_flags(self):
+        parser = ArgumentParser()
+        add_config_arguments(SampleConfig, parser)
+        args = parser.parse_args(
+            ["--name", "cli", "--count", "99"]
+        )
+        assert args.name == "cli"
+        assert args.count == 99
+
+    def test_defaults_are_none(self):
+        parser = ArgumentParser()
+        add_config_arguments(SampleConfig, parser)
+        args = parser.parse_args([])
+        assert args.name is None
+        assert args.count is None
+
+    def test_underscores_become_dashes(self):
+        @dataclass
+        class DashConfig:
+            my_long_name: str = "x"
+
+        parser = ArgumentParser()
+        add_config_arguments(DashConfig, parser)
+        args = parser.parse_args(
+            ["--my-long-name", "val"]
+        )
+        assert args.my_long_name == "val"
+
+
+class TestApplyCliOverrides:
+    def test_overrides_set_values(self):
+        config = SampleConfig()
+        args = Namespace(name="override", count=None,
+                         ratio=None, enabled=None)
+        result = apply_cli_overrides(config, args)
+        assert result.name == "override"
+        assert result.count == 10  # unchanged
+
+    def test_no_overrides_returns_same(self):
+        config = SampleConfig()
+        args = Namespace(name=None, count=None,
+                         ratio=None, enabled=None)
+        result = apply_cli_overrides(config, args)
+        assert result.name == "default"
+        assert result is config
+
+
+class TestEnsureIni:
+    def test_creates_file_if_missing(self, tmp_path):
+        ini = tmp_path / "new.ini"
+        assert not ini.exists()
+        config = ensure_ini(SampleConfig, ini)
+        assert ini.exists()
+        assert config.name == "default"
+        assert config.count == 10
+
+    def test_created_file_has_all_fields(self, tmp_path):
+        ini = tmp_path / "new.ini"
+        ensure_ini(SampleConfig, ini)
+        content = ini.read_text()
+        assert "name" in content
+        assert "count" in content
+        assert "ratio" in content
+        assert "enabled" in content
+
+    def test_created_file_has_comments(self, tmp_path):
+        ini = tmp_path / "new.ini"
+        ensure_ini(SampleConfig, ini)
+        content = ini.read_text()
+        assert "# name (str)" in content
+        assert "# count (int)" in content
+
+    def test_reads_existing_file(self, tmp_path):
+        ini = tmp_path / "existing.ini"
+        ini.write_text("[sample]\ncount = 42\n")
+        config = ensure_ini(SampleConfig, ini)
+        assert config.count == 42
+
+    def test_does_not_overwrite_existing(self, tmp_path):
+        ini = tmp_path / "existing.ini"
+        ini.write_text("[sample]\ncount = 42\n")
+        ensure_ini(SampleConfig, ini)
+        content = ini.read_text()
+        assert content == "[sample]\ncount = 42\n"
+
+    def test_created_file_is_loadable(self, tmp_path):
+        ini = tmp_path / "new.ini"
+        ensure_ini(SampleConfig, ini)
+        config = load_ini(SampleConfig, ini)
+        assert config.name == "default"
+        assert config.count == 10
+        assert config.ratio == 0.5
+
+
+class TestIntegration:
+    def test_ini_then_cli_override(self, tmp_path):
+        ini = tmp_path / "test.ini"
+        ini.write_text("[sample]\ncount = 42\n")
+        config = load_ini(SampleConfig, ini)
+        assert config.count == 42
+
+        args = Namespace(name=None, count=99,
+                         ratio=None, enabled=None)
+        config = apply_cli_overrides(config, args)
+        assert config.count == 99
+        assert config.name == "default"
+
+    def test_ensure_then_cli_override(self, tmp_path):
+        ini = tmp_path / "new.ini"
+        config = ensure_ini(SampleConfig, ini)
+        assert config.count == 10
+
+        args = Namespace(name=None, count=99,
+                         ratio=None, enabled=None)
+        config = apply_cli_overrides(config, args)
+        assert config.count == 99
+        assert config.name == "default"
+
+        # Config file unchanged
+        reloaded = load_ini(SampleConfig, ini)
+        assert reloaded.count == 10
+
+
+class TestResolveHints:
+    def test_returns_type_dict(self):
+        hints = resolve_hints(SampleConfig)
+        assert hints["name"] is str
+        assert hints["count"] is int
+        assert hints["ratio"] is float
+        assert hints["enabled"] is bool
+
+
+class TestFormatSection:
+    def test_includes_section_header(self):
+        text = format_section(SampleConfig)
+        assert "[sample]" in text
+
+    def test_custom_section_name(self):
+        text = format_section(SampleConfig, "custom")
+        assert "[custom]" in text
+
+    def test_includes_all_fields(self):
+        text = format_section(SampleConfig)
+        assert "name = default" in text
+        assert "count = 10" in text
+        assert "ratio = 0.5" in text
+        assert "enabled = True" in text
+
+    def test_includes_type_comments(self):
+        text = format_section(SampleConfig)
+        assert "# name (str)" in text
+        assert "# count (int)" in text
+
+    def test_is_loadable(self, tmp_path):
+        ini = tmp_path / "test.ini"
+        ini.write_text(format_section(SampleConfig) + "\n")
+        config = load_ini(SampleConfig, ini)
+        assert config.name == "default"
+        assert config.count == 10
+
+
+class TestEnsureIniMulti:
+    def test_creates_file_with_multiple_sections(self, tmp_path):
+        @dataclass
+        class OtherConfig:
+            host: str = "localhost"
+            port: int = 8080
+
+        ini = tmp_path / "multi.ini"
+        ensure_ini_multi([
+            (SampleConfig, None),
+            (OtherConfig, "server"),
+        ], ini)
+
+        content = ini.read_text()
+        assert "[sample]" in content
+        assert "[server]" in content
+        assert "name = default" in content
+        assert "host = localhost" in content
+
+    def test_does_not_overwrite_existing(self, tmp_path):
+        ini = tmp_path / "multi.ini"
+        ini.write_text("[existing]\nfoo = bar\n")
+        ensure_ini_multi([(SampleConfig, None)], ini)
+        content = ini.read_text()
+        assert content == "[existing]\nfoo = bar\n"
+
+    def test_sections_are_loadable(self, tmp_path):
+        @dataclass
+        class DbConfig:
+            url: str = "sqlite:///test.db"
+
+        ini = tmp_path / "multi.ini"
+        ensure_ini_multi([
+            (SampleConfig, None),
+            (DbConfig, "database"),
+        ], ini)
+
+        sample = load_ini(SampleConfig, ini)
+        db = load_ini(DbConfig, ini, section="database")
+        assert sample.name == "default"
+        assert db.url == "sqlite:///test.db"
+
+
+class TestApplyOverrides:
+    def test_applies_dotted_path(self):
+        config = SampleConfig()
+        result = apply_overrides(config, {
+            "provider.name": "custom",
+            "provider.count": "99",
+        }, prefix="provider")
+        assert result.name == "custom"
+        assert result.count == 99
+
+    def test_without_prefix(self):
+        config = SampleConfig()
+        result = apply_overrides(config, {
+            "name": "direct",
+            "count": "42",
+        })
+        assert result.name == "direct"
+        assert result.count == 42
+
+    def test_no_matching_keys_returns_same(self):
+        config = SampleConfig()
+        result = apply_overrides(config, {"other.key": "val"}, prefix="provider")
+        assert result is config
+
+    def test_bool_coercion(self):
+        config = SampleConfig()
+        result = apply_overrides(config, {"enabled": "false"})
+        assert result.enabled is False
+
+    def test_preserves_unset_fields(self):
+        config = SampleConfig()
+        result = apply_overrides(config, {"name": "changed"})
+        assert result.name == "changed"
+        assert result.count == 10  # unchanged
+        assert result.ratio == 0.5  # unchanged
+
+
+class TestFormatHelp:
+    def test_lists_all_fields(self):
+        lines = format_help(SampleConfig)
+        assert len(lines) == 4
+        assert any("name" in l for l in lines)
+        assert any("count" in l for l in lines)
+
+    def test_includes_types(self):
+        lines = format_help(SampleConfig)
+        text = "\n".join(lines)
+        assert "str" in text
+        assert "int" in text
+
+    def test_includes_defaults(self):
+        lines = format_help(SampleConfig)
+        text = "\n".join(lines)
+        assert "default" in text
+        assert "10" in text
+
+    def test_with_prefix(self):
+        lines = format_help(SampleConfig, prefix="provider")
+        assert any("provider.name" in l for l in lines)
+        assert any("provider.count" in l for l in lines)