fix(installer): preserve existing core config (#2435)

[sanmaxdev]

What

Preserve existing core configuration when an update supplies core command-line overrides. Add regression coverage for the update path.

Why

The existing configuration loader stores prior values separately, but the override merge read the new collection instead. As a result, values such as project_name were dropped.

Fixes #2435

How

• Merge supplied overrides on top of the loaded core configuration
• Cover preserved values and explicit replacements through the installer UI path

Testing

• npm ci
• npm run test:install
• npm run quality

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

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Review profile: CHILL

Plan: Pro

Run ID: 41ad53da-b727-4635-88f7-7ad151a812b0

📥 Commits

Reviewing files that changed from the base of the PR and between 8ea1b76 and 4ed9a3a.

📒 Files selected for processing (2)

• test/test-installation-components.js
• tools/installer/ui.js

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📝 Walkthrough

Walkthrough

The installer now reads existing core settings from the configuration collector’s loaded state before applying CLI overrides. A new installation-component test verifies that unspecified values such as project_name remain intact while supplied values are replaced or added.

Changes

Core configuration preservation

Layer / File(s)	Summary
Merge existing core configuration tools/installer/ui.js, test/test-installation-components.js	collectModuleConfigs() uses the loaded existing core configuration when applying CLI overrides, and the new test verifies selective preservation, replacement, and temporary-install cleanup.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• bmad-code-org/BMAD-METHOD#2129: Introduced or rewired installer core configuration handling used by this fix.
• bmad-code-org/BMAD-METHOD#2354: Added CLI core override handling in the same installer flow.
• bmad-code-org/BMAD-METHOD#2411: Changed existing core configuration loading to populate _existingConfig.core.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main fix: preserving existing core config during installer updates.
Description check	✅ Passed	The description is directly related to the changes and explains the bug fix, rationale, and testing.
Linked Issues check	✅ Passed	The code change and regression test address #2435 by preserving preexisting core values while applying CLI overrides.
Out of Scope Changes check	✅ Passed	The PR only includes the targeted installer fix and a regression test, with no unrelated changes evident.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[bmadcode]

Just saw this, thank you @sanmaxdev will review and merge after I get a chance to test it.