Isolate unparseable prompts instead of poisoning workspace commands

[omridevk]

Context

During the parallel ::: test migrations, one temporarily unparseable prompt caused every workspace-level napl command to fail before it could present any module view. This made an ordinary mid-edit state look like total workspace corruption and stalled unrelated module work.

Issue #36 covers the analogous LSP failure mode. This issue covers CLI discovery, compilation, query, and status behavior.

Problem

Workspace discovery currently couples prompt parsing too early and too globally. A syntax error in one module poisons commands whose useful result could still be produced for every other module, including commands needed to diagnose and repair the broken module.

Required behavior

• Discovery identifies prompt files and module candidates without requiring every prompt to parse successfully.
• Parse failures are retained as module-scoped diagnostics with the offending prompt path and exact location.
• Workspace commands continue to expose valid modules and include the invalid module as an error-bearing entry where the command shape permits it.
• A command that explicitly requires the invalid module fails for that module with its parse diagnostic.
• Global invariants that cannot be decided safely under partial parsing fail honestly and explain which invalid modules block the decision.
• No command silently omits an invalid prompt or fabricates committed state for it.

Acceptance criteria

• With one valid prompt and one unparseable prompt, napl status and napl q still expose the valid module and a scoped diagnostic for the invalid prompt.
• Module-targeted operations on the valid module remain usable when their invariants do not depend on the invalid module.
• Module-targeted operations on the invalid module fail with the pinned parse diagnostic.
• Fixing the prompt restores the full workspace view without repair of unrelated state.
• Conformance covers mid-edit invalid syntax, duplicate names under partial parsing, dependency uncertainty, and recovery.

References

• LSP must survive discovery errors; discovery needs ignore config #36
• docs/specs/2026-07-28-test-directives-v1.md
• docs/specs/2026-07-28-generation-workflow.md