Extract TitleBuilder for PR title composition

[kbukum1]

What are you trying to accomplish?

Extract a lightweight TitleBuilder class from MessageBuilder so that PR title composition (prefix + capitalization + base title) can be reused by dependabot-api for multi-ecosystem combined PRs.

The current MessageBuilder inlines prefix/capitalize logic in pr_name, which cannot be called from dependabot-api without instantiating the entire builder. The API currently hardcodes combined PR titles, completely bypassing commit-message prefix configuration.

What changed?

1 new file — common/lib/dependabot/pull_request_creator/message_builder/title_builder.rb:

• TitleBuilder#build — composes prefix + capitalization + base title
• Works with a full PrNamePrefixer (updater path) or lightweight commit_message_options hash (API path, no network calls)
• TitleBuilder.multi_ecosystem_base_title — class method for generating multi-ecosystem group titles

MessageBuilder#pr_name now delegates to TitleBuilder instead of inlining the prefix/capitalize logic. No feature flag — the change is a pure extraction with identical behavior.

Anything you want to highlight for special attention from reviewers?

The change to MessageBuilder is minimal (5 lines changed). TitleBuilder follows the same pattern as existing helpers (IssueLinker, MetadataPresenter, LinkAndMentionSanitizer).

How will you know you have accomplished your goal?

• New TitleBuilder spec passes (10 examples covering prefix, capitalization, scope, dev dependencies, multi-ecosystem)
• Existing MessageBuilder specs continue to pass (behavior unchanged)
• dependabot-api companion PR can use TitleBuilder to apply commit-message prefix to combined PRs

Checklist

• I have run the complete test suite to ensure all tests and linters pass.
• I have thoroughly tested my code changes to ensure they work as expected, including adding additional tests for new functionality.
• I have written clear and descriptive commit messages.
• I have provided a detailed description of the changes in the pull request, including the problem it addresses, how it fixes the problem, and any relevant details about the implementation.
• I have ensured that the code is well-documented and easy to understand.

[Copilot]

Pull request overview

This PR extracts PR title composition logic out of MessageBuilder into a new TitleBuilder helper so title prefixing/capitalization can be reused (notably by dependabot-api for multi-ecosystem combined PRs) while keeping MessageBuilder#pr_name behavior consistent.

Changes:

• Add TitleBuilder to compose a final PR title from a base title plus either a PrNamePrefixer (updater path) or explicit commit_message_options (API path).
• Update MessageBuilder#pr_name to delegate title composition to TitleBuilder.
• Add specs covering prefix, scope, dev prefix behavior, and multi-ecosystem base title generation.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
common/lib/dependabot/pull_request_creator/message_builder/title_builder.rb	Introduces extracted title composition logic intended for reuse outside MessageBuilder.
common/lib/dependabot/pull_request_creator/message_builder.rb	Delegates pr_name formatting to TitleBuilder and requires the new helper.
common/spec/dependabot/pull_request_creator/message_builder/title_builder_spec.rb	Adds unit tests for the new TitleBuilder behavior.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

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[AbhishekBhaskar]

LGTM