fix: address PR #14 review feedback (exposure layer)

[shaypal5]

Summary

• Rename redaction.py → metadata.py — module writes metadata, not redactions; name now matches behavior
• Clean stale metadata/ on path reuse — apply_exposure() removes any pre-existing metadata/ dir when mode is student_public, preventing accidental hidden-truth leakage
• Widen get_filter() signature — now accepts str | ExposureMode with automatic coercion via ExposureMode(mode)
• Add tests — path-reuse leakage regression test + string-mode acceptance test (22 exposure tests pass, 547 total)

Addresses all 4 Copilot review comments from #14.

Test plan

• All 22 exposure tests pass
• Full suite: 547 passed
• Ruff lint + format clean

🤖 Generated with Claude Code

[github-actions]

pr-agent-context report:

No unresolved review comments, failing checks, or actionable patch coverage gaps were found on PR
#15. Treat this PR as all clear unless new signals appear.

Run metadata:

Tool ref: v4
Tool version: 4.0.20
Trigger: pull request opened
Workflow run: 25092980048 attempt 1
Comment timestamp: 2026-04-29T05:45:51.708753+00:00
PR head commit: 8087a7063a831dc5ef6db8012bcfd1fdb39476f2

[Copilot]

Pull request overview

This PR refines the exposure layer to better match naming/behavior, prevent hidden-truth leakage when reusing output directories, and broaden get_filter() to accept string exposure modes with appropriate errors.

Changes:

• Renames the exposure metadata writer module to metadata.py and updates imports.
• Ensances apply_exposure() to delete any pre-existing metadata/ directory when writing student_public bundles.
• Updates get_filter() to accept str | ExposureMode and adds regression/behavior tests for string modes and path reuse.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
tests/exposure/test_exposure.py	Adds tests for string-mode support and for removing stale metadata/ on output path reuse.
leadforge/exposure/modes.py	Updates metadata writer import and removes existing metadata/ for student_public mode.
leadforge/exposure/metadata.py	Houses metadata writing logic (module renamed from redaction.py); minor comment cleanup.
leadforge/exposure/filters.py	Widens get_filter() to accept string modes via ExposureMode(mode) coercion and updates docs/errors.

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[Copilot]

shutil.rmtree(meta_dir) will raise if bundle_root/metadata exists but is not a directory (e.g., a file). Since this cleanup runs in student_public mode to prevent leakage on path reuse, consider handling both cases (remove dir tree when it’s a dir; unlink when it’s a file/symlink) so save() can’t fail due to an unexpected existing path.

Suggested change

	elif meta_dir.exists():
	shutil.rmtree(meta_dir)
	elif meta_dir.exists() or meta_dir.is_symlink():
	if meta_dir.is_symlink() or not meta_dir.is_dir():
	meta_dir.unlink()
	else:
	shutil.rmtree(meta_dir)