Fix(ui): reduce dialog initialization complexity

[inseokk]

P1B: Starter Task: Refactoring PR

Use this pull request template to briefly answer the questions below in one to two sentences each.
Feel free to delete this text at the top after filling out the template.

1. Issue

Link to the associated GitHub issue: https://github.com/CMU-313/opencode/issues/170

Full path to the refactored file: https://github.com/inseokk/opencode/blob/fix-complexity/packages/ui/src/context/dialog.tsx

What do you think this file does?
It centralizes dialog-related functions so individual components do not need to manage those details themselves.

What is the scope of your refactoring within that file?
init function

Which Qlty‑reported issue did you address?
Function with high complexity (count = 27): init

2. Refactoring

How did the specific issue you chose impact the codebase’s maintainability?
The init function in dialog.tsx had high cognitive complexity because it managed dialog state, keyboard events, mounting, closing, timers, cleanup, and stacking in one function. This made the lifecycle harder to understand, test, and modify safely.

What changes did you make to resolve the issue?
I extracted the dialog lifecycle responsibilities into focused helpers, including timer cleanup, active-dialog lookup, closing behavior, Escape-key handling, and dialog-node creation. The init function now primarily wires these pieces together. I also added tests covering dialog mounting, Escape-key closing, overlay closing, callbacks, and cleanup.

How do your changes improve maintainability? Did you consider alternatives?
The smaller helpers reduce the complexity of init, make each behavior easier to reason about independently, and make future changes less likely to introduce regressions. I considered leaving the logic inline or suppressing the Qlty warning, but extraction was preferable because it addressed the underlying complexity while preserving the existing public API and behavior.

3. Validation

How did you validate that the change is correct?:
I ensured that the same bun lint and bun test pass correctly. Because there were no existing tests covering this dialog.tsx file, I created a new test file and ensured that it was integrated into the CI workflow. Specifically, I added dialog.test.ts, which covers the refactored dialog lifecycle through DialogProvider and useDialog. The tests verify dialog mounting, Escape-key closing, overlay closing, onClose callbacks, timer-based cleanup, and stack removal. These tests execute the changed code paths directly and passed with 29 total UI tests, providing evidence that the refactor preserved existing dialog behavior.

Screenshot of the test coverage showing the lines were executed by the tests:

Screenshot of the tests that cover the change passing during CI:

Screenshot of bun test and bun lint passing locally:

Screenshot of qlty smells --no-snippets packages/ui/src/context/dialog.tsx after changes: