fix(resource): preserve pre-enqueue semantic update mode

[myysy]

Description

Fix resource semantic update mode detection so new add-resource imports are not misclassified as incremental updates after internal lifecycle lock setup creates the target directory.

Related Issue

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test update

Changes Made

• Preserve the target's pre-enqueue existence state before lifecycle lock acquisition and pass it through semantic queue messages.
• Restrict resource incremental semantic updates to targets that already existed before enqueue time, avoiding false incremental mode for newly added resources.
• Silence expected "directory not found" cases during incremental target-side directory comparison in the semantic DAG.
• Add unit coverage for viking://resources root splitting and explicit pre-enqueue existence overrides.

Testing

• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have tested this on the following platforms:
  • Linux
  • macOS
  • Windows
    Notes:
• Verified from runtime logs that a new ov add-resource tt_a --wait import now enqueues SemanticMsg(... target_exists_before_enqueue=False ...) and no longer logs Target URI exists, using incremental update: viking://resources/tt_a.
• Verified that the previous semantic_dag.py "Failed to list directory ... Directory not found" warnings no longer appear for this flow.
• Full local pytest execution is currently blocked by missing environment dependencies (_sqlite3, pathspec).

Checklist

• My code follows the project's coding style
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Screenshots (if applicable)

N/A

Additional Notes

This PR intentionally keeps the existing semantic processor structure and applies the smallest safe fix:

• decide whether the target originally existed before enqueue-side state is mutated by lifecycle locking
• carry that fact through SemanticMsg
• keep parent refresh behavior unchanged (viking://resources still performs direct incremental refresh when child content changes)

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