docs: update architecture diagram and AGENTS.md for composition refactoring

Replace the old SubProject inheritance model (ArchiveSubProject/GitSubproject/
SvnSubproject each implementing abstract SubProject) with the new composition
design: SubProject composes with a Fetcher; Fetcher and VcsFetcher as protocols;
AbstractVcsFetcher as shared ABC; GitFetcher and SvnFetcher implementing
VcsFetcher; ArchiveFetcher implementing Fetcher only.

Update AGENTS.md to describe the concrete SubProject aggregate and direct
developers to implement Fetcher/VcsFetcher protocols when adding new backends.

https://claude.ai/code/session_01BMSF8XFAxV6hABQgL7RZ3z

Author: claude

AGENTS.md

@@ -71,7 +71,7 @@ dfetch.log          ← logging (lowest layer)
 - **`dfetch/__main__.py`** — CLI entry point; builds argparse subcommands and dispatches
 - **`dfetch/commands/`** — One file per CLI command (e.g., `update.py`, `check.py`); all inherit from `command.py`'s abstract `Command` base
 - **`dfetch/manifest/`** — YAML manifest loading/writing with `strictyaml` schema validation; `manifest.py` is the main handler
-- **`dfetch/project/`** — Abstract `Subproject`/`Superproject` classes with concrete Git, SVN, and Archive implementations; factory functions `create_sub_project()` and `create_super_project()` are the main entry points
+- **`dfetch/project/`** — Concrete `SubProject` domain aggregate that composes with a `Fetcher`; `GitFetcher`, `SvnFetcher`, and `ArchiveFetcher` implement the `Fetcher`/`VcsFetcher` protocols defined in `fetcher.py`; factory functions `create_sub_project()` and `create_super_project()` are the main entry points
 - **`dfetch/vcs/`** — Low-level VCS operations: `git.py`, `svn.py`, `archive.py` (with hash verification in `integrity_hash.py`), and `patch.py`
 - **`dfetch/reporting/`** — Output formatters; check results can be emitted as stdout, Jenkins JSON, SARIF, or Code Climate format; SBOM output uses CycloneDX format
 - **`dfetch/terminal/`** — Terminal UI components (interactive prompts, tree browser, ANSI colors)
@@ -84,7 +84,7 @@ dfetch.log          ← logging (lowest layer)
 
 ### Adding a new VCS backend
 
-Implement the abstract interfaces in `dfetch/project/subproject.py` and `dfetch/vcs/` and register via the factory in `dfetch/project/`.
+Implement the `Fetcher` protocol (or `VcsFetcher` if you need branch/tag/revision semantics) defined in `dfetch/project/fetcher.py`, add a concrete class in `dfetch/project/`, add low-level VCS operations in `dfetch/vcs/` if needed, and register via the factory in `dfetch/project/__init__.py`.
 
 ## Testing conventions
 

doc/static/uml/c3_dfetch_components_project.puml

@@ -12,22 +12,29 @@ System_Boundary(DFetch, "Dfetch") {
     Boundary(DfetchProject, "Project", "python", "Main project that has a manifest.") {
 
         Component(compAbstractCheckReporter, "AbstractCheckReporter", "python", "Abstract interface for generating a check report.")
-        Component(compArchiveSub, "ArchiveSubProject", "python", "A subproject based on an archive.")
-        Component(compGitSub, "GitSubproject", "python", "A subproject based on git.")
+        Component(compSubProject, "SubProject", "python", "Concrete domain aggregate; composes with a Fetcher.")
+        Component(compFetcher, "Fetcher", "python", "Protocol: minimal contract for all fetcher types.")
+        Component(compVcsFetcher, "VcsFetcher", "python", "Protocol: Fetcher extended with VCS semantics (branches, tags, revisions).")
+        Component(compAbstractVcsFetcher, "AbstractVcsFetcher", "python", "Shared VCS implementation (latest_available_version, freeze).")
+        Component(compGitFetcher, "GitFetcher", "python", "Fetcher implementation for Git repositories.")
+        Component(compSvnFetcher, "SvnFetcher", "python", "Fetcher implementation for SVN repositories.")
+        Component(compArchiveFetcher, "ArchiveFetcher", "python", "Fetcher implementation for archive URLs (no VCS semantics).")
         Component(compMetadata, "Metadata", "python", "A file containing metadata about a project.")
-        Component(compSvnSub, "SvnSubproject", "python", "A subproject based on svn.")
-        Component(compSubProject, "SubProject", "python", "An abstract subproject.")
         Component(compSuperProject, "SuperProject", "python", "An abstract superproject.")
         Component(compGitSuper, "GitSuperProject", "python", "A superproject based on git.")
         Component(compSvnSuper, "SvnSuperProject", "python", "A superproject based on svn.")
         Component(compNoVcsSuper, "NoVcsSuperProject", "python", "A superproject without VCS.")
 
-        Rel_U(compArchiveSub, compSubProject, "Implements")
-        Rel_U(compGitSub, compSubProject, "Implements")
-        Rel_U(compSvnSub, compSubProject, "Implements")
+        Rel(compSubProject, compFetcher, "Composes")
         Rel(compSubProject, compAbstractCheckReporter, "Uses")
         Rel_L(compSubProject, compMetadata, "Uses")
 
+        Rel_U(compVcsFetcher, compFetcher, "Extends")
+        Rel_U(compAbstractVcsFetcher, compVcsFetcher, "Implements")
+        Rel_U(compGitFetcher, compAbstractVcsFetcher, "Extends")
+        Rel_U(compSvnFetcher, compAbstractVcsFetcher, "Extends")
+        Rel_U(compArchiveFetcher, compFetcher, "Implements")
+
         Rel_U(compGitSuper, compSuperProject, "Implements")
         Rel_U(compSvnSuper, compSuperProject, "Implements")
         Rel_U(compNoVcsSuper, compSuperProject, "Implements")
@@ -43,9 +50,9 @@ System_Boundary(DFetch, "Dfetch") {
     Rel_U(compMetadata, contManifest, "Has")
     Rel(compSuperProject, contManifest, "Has")
     Rel_U(contReporting, contManifest, "Uses")
-    Rel(compArchiveSub, contVcs, "Uses")
-    Rel(compGitSub, contVcs, "Uses")
-    Rel(compSvnSub, contVcs, "Uses")
+    Rel(compGitFetcher, contVcs, "Uses")
+    Rel(compSvnFetcher, contVcs, "Uses")
+    Rel(compArchiveFetcher, contVcs, "Uses")
     Rel(compGitSuper, contVcs, "Uses")
     Rel(compSvnSuper, contVcs, "Uses")
 }