[config] Add --no-defaults flag to config command

[jesserockz]

What does this implement/fix?

Adds a --no-defaults flag to esphome config that emits only the user-supplied configuration, without the values voluptuous fills in from schema defaults.

Today the config command dumps the fully-validated config, which buries the few keys the user actually wrote under hundreds of injected defaults (every framework knob, every wifi/api timeout, etc.). The new flag is useful for diffing against another machine's config, sharing a minimal reproduction in an issue, or just sanity-checking what you actually typed after substitutions and packages are resolved.

Mechanically: validate_config now deep-copies the config dict into result.user_config right after substitutions/packages/extend-remove are resolved but before preload_core_config (the first step that injects defaults). Substitutions are re-added at the top of the snapshot so the output is a faithful "user YAML" view. When --no-defaults is set, command_config dumps that snapshot instead of the validated config.

Types of changes

• Bugfix (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 not work as expected) — policy
• Developer breaking change (an API change that could break external components) — policy
• Undocumented C++ API change (removal or change of undocumented public methods that lambda users may depend on) — policy
• Code quality improvements to existing code or addition of tests
• Other

Related issue or feature (if applicable):

• fixes

Pull request in esphome.io with documentation (if applicable):

• [cli] Document --no-defaults and --show-secrets for esphome config esphome.io#6716

Test Environment

• ESP32
• ESP32 IDF
• ESP8266
• RP2040/RP2350
• BK72xx
• RTL87xx
• LN882x
• nRF52840

Example entry for config.yaml:

# Example config.yaml

Usage:

```
esphome config my-device.yaml --no-defaults
```

Checklist:

• The code change is tested and works locally.
• Tests have been added to verify that the new code works (under `tests/` folder).

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in esphome.io.

[esphome]

👋 Hi there! This PR modifies 2 file(s) with codeowners.

@esphome/core - As codeowner(s) of the affected files, your review would be appreciated! 🙏

Note: Automatic review request may have failed, but you're still welcome to review.

[Copilot]

Pull request overview

Adds an esphome config --no-defaults flag that emits only the user-supplied configuration, omitting the many schema defaults that voluptuous would otherwise inject. validate_config() now deep-copies the config into result.user_config after substitutions/packages/extend-remove are resolved but before preload_core_config() and full schema validation, and command_config() dumps that snapshot when the new flag is set.

Changes:

• Add a user_config snapshot field on Config populated in validate_config() with substitutions re-added at the front.
• Add --no-defaults CLI flag and corresponding branch in command_config() with a warning-and-fallback path when the snapshot is unavailable.
• Add unit tests for snapshot capture/independence and for the new command_config branch (including the warning fallback and skipping strip_default_ids).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
esphome/config.py	Imports copy, declares Config.user_config, and snapshots the resolved user config before defaults are injected.
esphome/main.py	Adds the --no-defaults argparse option and a branch in command_config() that dumps config.user_config (or warns and falls back).
tests/unit_tests/test_substitutions.py	Adds tests verifying the snapshot's contents, substitutions ordering, and that it is an independent deep copy.
tests/unit_tests/test_main.py	Adds tests for --no-defaults dumping the snapshot, warning-and-fallback when missing, and skipping strip_default_ids.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 92.30769% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 75.90%. Comparing base (4b8e06b) to head (63f2143).
⚠️ Report is 4 commits behind head on dev.

Files with missing lines	Patch %	Lines
esphome/__main__.py	85.71%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev   #16718      +/-   ##
==========================================
+ Coverage   75.88%   75.90%   +0.01%     
==========================================
  Files          69       69              
  Lines       14599    14611      +12     
  Branches     2107     2110       +3     
==========================================
+ Hits        11078    11090      +12     
  Misses       3067     3067              
  Partials      454      454              

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[swoboda1337]

@esphbot review

[esphbot]

Code Review

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Automated review by Kōan63f2143