Inject filesystem I/O into discover_tracked_lockfiles and surface failures via exceptions

[coderabbitai]

Background

Raised during review of PR #75 (refresh stale Cargo lockfiles before publish preflight).

Problem

discover_tracked_lockfiles in lading/commands/lockfile.py mixes direct filesystem I/O (workspace_root.rglob, Path.exists) with injected runner calls. Failures are hidden via LOGGER.warning and silent empty-tuple returns rather than being surfaced through explicit APIs. Tests compensate by mocking filesystem layout rather than testing integrations.

Resolution

• Route filesystem operations (lockfile enumeration, manifest existence checks) through the injected runner or a dedicated filesystem port so the function has no direct Path I/O.
• Make discovery failures explicit in the public API (raise a typed exception or return a Result-style type) rather than logging warnings and returning empty tuples silently.
• Replace mock-based unit tests with real integration tests that exercise discovery and refresh against temporary directory fixtures without stubbing the internals.

References

• PR: Refresh stale Cargo lockfiles before publish preflight (#61) #75
• Requested by: @leynos

[coderabbitai]

🔗 Related PRs

leynos/axinite#175 - Flatten build tool override resolution (#39) [merged]
leynos/theoremc#44 - Run Rust tests with cargo-nextest [merged]
leynos/dear-diary#27 - Adopt Cranelift codegen and mold linking [merged]
leynos/repovec-appliance#37 - Serialize qdrant key provisioning (#29) [merged]

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