New docs

docs/dependencies-and-build/versioning-and-lock-file.md

@@ -1,2 +1,32 @@
 # Versioning & lock file
 
+DCR generates `dcr.lock` when dependency resolution succeeds and at least one dependency exists.
+
+## What is stored
+
+- Project entry (`name`, `version`, dependency names).
+- One entry per resolved dependency:
+  - `name`
+  - `version` (from dependency `dcr.toml`, fallback `0.0.0`)
+  - `source` (`path+...`)
+  - `checksum` (SHA-256 over dependency files, excluding nested `target/`).
+
+## Example shape
+
+```toml
+[[package]]
+name = "my-app"
+version = "0.1.0"
+dependencies = ["fmt"]
+
+[[package]]
+name = "fmt"
+version = "1.2.3"
+source = "path+./third_party/fmt"
+checksum = "..."
+```
+
+## Notes
+
+- `dcr.lock` is rewritten on successful dependency resolution.
+- If `[dependencies]` is empty, lock generation is skipped.