fix: join root task sections with newlines

[sean-kim05]

Closes #682

What

build_root_task() in strix/core/inputs.py joined the parts list with a single space. Because section headers (e.g. "\n\nURLs:") and per-item bullets (e.g. "- https://a") are separate list elements, every bullet after a header was concatenated with spaces instead of newlines.

Why

A scan with more than one target (or diff-scope constraints) rendered a run-on line in the root task prompt:

Before

URLs: - https://a.example.com - https://b.example.com

After

URLs:
- https://a.example.com
- https://b.example.com

The section headers already embed \n\n, and the sibling builder child_initial_input() in the same file joins its parts with newlines — confirming newline is the intended separator.

Change

One line: " ".join(parts) → "\n".join(parts).

Tests

Added test_build_root_task_multiple_targets_are_newline_separated, which fails on the old space-join (both URLs collapse onto one line) and passes with the fix. Full suite green:

• uv run pytest → 84 passed
• uv run ruff check / ruff format --check → clean
• uv run mypy strix/core/inputs.py → no issues

[greptile-apps]

Greptile Summary

This PR fixes root task prompt formatting for multi-item sections.

• build_root_task() now joins prompt parts with newlines.
• Multiple target URLs now render as separate bullet lines.
• A regression test covers the collapsed URL formatting case.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.

Important Files Changed

Filename	Overview
strix/core/inputs.py	Updates root task string assembly so section headers and bullets stay on separate lines.
tests/test_inputs.py	Adds coverage for newline-separated multiple web application targets.

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