fix: allow submitting comments on completely deleted files

[menil]

Description

Fixes a bug in code review comment submission where comments on completely deleted files would fail validation or relocation and could not be submitted.

Root causes

1. Missing Base Content: When applying a diff to a deleted file, the code editor's base content (set_base) was never initialized. This caused line relocation to fail and mark comments as outdated = true.
2. Missing File Path Metadata: Deleted files have no backing on-disk file model and are initialized with no file path metadata. LocalCodeEditorEvent::CommentSaved was querying the editor's path metadata, which returned None and aborted comment saving.
3. Empty Target Range Bounds: When commenting on a deleted line in an empty/deleted file, the line range was hardcoded to line_number..line_number + 1 (evaluating to 0..1). Because the file has 0 lines, this range was out of bounds, failing backend validation.

Fixes

1. Reinitialize Base Content: Call set_base with the old base content for deleted files during diff application.
2. Direct Path Propagation: Used the file_location parameter already supplied to the event handler closure directly instead of attempting to query the empty editor metadata.
3. Dynamic Range Calculation: Compute target ranges as line_number..line_number + span. We ensure pure deletions in normal files receive a minimum 1-line range span, while completely deleted files receive the correct 0..0 range.

Linked Issue

Fixes #14182

Testing

Added unit tests:

• test_relocate_comments_on_deleted_file: Verifies comment relocation on deleted files.

• test_save_comment_on_deleted_file: Verifies that CommentSaved events attach comments successfully to deleted file editors.

• test_api_review_comment_line_range_deleted_file, test_api_review_comment_line_range_normal_file, test_api_review_comment_line_range_multiline, and test_api_review_comment_line_range_pure_deletion: Verifies range boundaries.

• I have manually tested my changes locally with ./script/run

Screenshots / Videos

Before

Screen.Recording.2026-07-22.at.21.33.56.mov

After

Screen.Recording.2026-07-22.at.22.48.41.mov

Agent Mode

• Warp Agent Mode - This PR was created via Warp's AI Agent Mode

CHANGELOG-BUG-FIX: Fixed bug where code review comments could not be submitted on completely deleted files

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@menil

Every PR must be linked to a same-repo issue before Oz can review it.

This PR is linked to #14182, but no linked issue is marked ready-to-implement yet. Only repository maintainers apply that label, so please wait for a maintainer to mark the issue. Once it is marked, push a new commit or comment /oz-review to re-trigger review.

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