[ctawiah]

Context

Link needs a write-free preparation step before command prompts and targeted sync use it.

What changes

• Add explicit source link inputs.
• Validate the descriptor target, source path, adapter, mapping, and projection.
• Render the descriptor without writing it.
• Publish only through an explicit Write call.
• Add a no-write-before-confirmation unit test.

Prepare -> review -> Write

Design notes

• The new API is additive.
• Existing Phase 1 link behavior remains unchanged until final cleanup.

Review focus

• Can preparation write any file?
• Does preparation validate the exact compiled resource?

Verification

• make build
• go test ./...
• Repository lint
• Relevant race tests

Related changes

1. ctawiah/sync-projection-core-3bbf: projection and problem core
2. ctawiah/sync-reference-core-3bbf: reference registry and Markdown
3. ctawiah/sync-structured-adapters-3bbf: structured adapters
4. ctawiah/sync-provider-profiles-3bbf: provider profiles
5. ctawiah/sync-python-adapter-3bbf: Python adapter
6. ctawiah/sync-typescript-adapters-3bbf: TypeScript and JavaScript adapters
7. ctawiah/sync-descriptor-storage-3bbf: descriptor storage
8. ctawiah/sync-source-publication-3bbf: source compilation and publication
9. ctawiah/sync-source-planner-3bbf: planner integration
10. ctawiah/sync-descriptor-detach-3bbf: descriptor detach
11. This PR: link preparation
12. ctawiah/sync-link-command-3bbf: link commands
13. ctawiah/sync-reference-cleanup-3bbf: Phase 1 cleanup