fix(message-builder): replace as-cast with explicit type annotation for defaultRules

[kitsuyui]

Summary

Replace the as type assertion on defaultRules with an explicit type annotation so TypeScript enforces exhaustiveness at compile time.

Problem

defaultRules was declared as:

const defaultRules = {
  pr_reaches_contain_only_one_nonzero_digit: true,
  // ...
} as { [key in RulesKey]: boolean }

The as assertion tells TypeScript to trust the object unconditionally. If a new key is added to Rules (and thus to RulesKey), omitting it from defaultRules produces no compile error. The missing key resolves to undefined at runtime, which is falsy, silently disabling the new rule in the default configuration without any warning.

Change

const defaultRules: { [key in RulesKey]: boolean } = {
  pr_reaches_contain_only_one_nonzero_digit: true,
  // ...
}

With the explicit annotation, TypeScript checks at compile time that every key in RulesKey has a corresponding entry in defaultRules. Adding a new rule to Rules without updating defaultRules now produces a type error.

No runtime behavior changes — the object contents are identical.

Trade-offs

• The exhaustiveness check is now enforced by the type system rather than by convention, removing a silent failure mode.
• Any future contributor who adds a rule to Rules must consciously decide whether it should be enabled by default, rather than having it silently default to disabled.

[github-actions]

🎉 Happy commit!

• dogfooding: PR fix(message-builder): replace as-cast with explicit type annotation for defaultRules #837 always celebrates.
• dogfooding: 24a90dfdfecf3d985a37f5b62e28d458e493fd87 always celebrates.
• dogfooding: fd6ce4e61695d87261d7847b5cc1b87dad68135a always celebrates.

[github-actions]

gh-counter

PR gate

	Removed	Added	+/-
TODO/FIXME	0	0	0

Repo dashboard

	main (98984a1)	#837 (42d508f)	+/-
TODO/FIXME	0	0	0

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Reported by gh-counter

[github-actions]

Code Metrics Report

	main (fd2ef70)	#837 (42d508f)	+/-
Coverage	99.1%	99.2%	+0.0%
Code to Test Ratio	1:0.5	1:0.5	-0.1
Test Execution Time	1s	2s	+1s

Details

  |                     | main (fd2ef70) | #837 (42d508f) |  +/-  |
  |---------------------|----------------|----------------|-------|
+ | Coverage            |          99.1% |          99.2% | +0.0% |
  |   Files             |              5 |              5 |     0 |
  |   Lines             |            122 |            131 |    +9 |
+ |   Covered           |            121 |            130 |    +9 |
- | Code to Test Ratio  |          1:0.5 |          1:0.5 |  -0.1 |
  |   Code              |           1598 |           1616 |   +18 |
+ |   Test              |            898 |            899 |    +1 |
- | Test Execution Time |             1s |             2s |   +1s |

Code coverage of files in pull request scope (96.0% → 96.0%)

Files	Coverage	+/-	Status
src/message_builder.ts	96.0%	0.0%	modified

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Reported by octocov

[github-actions]

gh-build-size

Target	main	#837	+/-
Total action artifacts	23,300,320 B	23,300,319 B	-1 B
Source maps	17,130,662 B	17,130,661 B	-1 B

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Reported by gh-build-size