Fail fast with an actionable error when a local registry, dependency, template, or policy path does not exist

[ANcpLua]

Problem

A relative registry_path in a registry manifest dependency resolves against the process working directory. Running weaver from any other directory fails late in resolution with a bare

× The following error occurred during the processing of semantic convention
│ file: IO error for operation on ./dep-model: No such file or directory (os error 2)

— no mention of which base directory the path was resolved against, or that the CWD is what matters. Hit in practice consuming semantic-conventions-genai (multi-registry manifest with registry_path: ./.build/sc-upstream-filtered) from an external codegen pipeline: the main registry resolves fine via -r, then the dependency dies with the message above.

Change

VirtualDirectory now rejects a nonexistent LocalFolder eagerly. The error names the path as written, the absolute path it resolved to against the current working directory, and explains the resolution semantics:

× Virtual directory `./dep-model` is invalid: local path does not exist
│ (resolved to `/home/user/somewhere/dep-model` against the current working
│ directory). Relative paths — including `registry_path` entries in a
│ registry manifest — resolve against the current working directory, not the
│ location of the file that declares them; run weaver from the directory the
│ path is relative to, or use an absolute path

Absolute paths get a plain "local path does not exist". No behavior change for existing paths. Because the check lives in the shared VirtualDirectory layer, it also covers the main -r registry path, template and policy paths, and the case where a mistyped URL parses as a LocalFolder.

Non-goal

This does not change resolution semantics. Whether a dependency registry_path should (also) resolve relative to the manifest location is a separate design discussion — happy to open an issue laying out the options (resolution fallback order, opt-in field, breaking switch) if there is interest.

Testing

• New unit test covering both branches (relative path with CWD hint, absolute path without).
• Full workspace test suite passes.
• Manually verified end-to-end: a minimal registry with a ./dep-model dependency fails with the new message from the wrong CWD and resolves unchanged from the correct one.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.2%. Comparing base (2ff9817) to head (1eb4ba1).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #1598   +/-   ##
=====================================
  Coverage   81.2%   81.2%           
=====================================
  Files        130     130           
  Lines      11463   11476   +13     
=====================================
+ Hits        9308    9319   +11     
- Misses      2155    2157    +2     

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