feat(resource): add virtual core resource types

Add 6 built-in virtual resource types (file, directory, commit, branch, tag,
tree) with equivalence metadata for content-hash and git-object identity
matching.

- YAML configs under examples/resource-types/
- Bootstrap registration with virtual types hidden from resource add scaffolding
- Equivalence criteria per spec (content_hash, merkle_hash, git SHA identity)
- Behave tests (83 scenarios), Robot tests, ASV benchmarks
- Documentation in docs/reference/resource_types_builtin.md

ISSUES CLOSED: #329

examples/resource-types/branch.yaml

@@ -0,0 +1,22 @@
+# Spec reference: docs/specification.md ~lines 10133-10143, 24548-24632
+schema_version: "1.0"
+name: branch
+description: "Cross-repo branch identity linking branches with the same name and HEAD"
+resource_kind: virtual
+sandbox_strategy: none
+user_addable: false
+built_in: true
+cli_args: []
+parent_types: []
+child_types: ["git-branch"]
+capabilities:
+  read: false
+  write: false
+  sandbox: false
+  checkpoint: false
+equivalence:
+  criteria:
+    - name
+    - head_commit_hash
+  description: "Two physical branches are equivalent when they share the same branch name and HEAD commit hash"
+handler: null

examples/resource-types/commit.yaml

@@ -0,0 +1,21 @@
+# Spec reference: docs/specification.md ~lines 10133-10143, 24548-24632
+schema_version: "1.0"
+name: commit
+description: "Cross-repo commit identity linking commits with the same hash"
+resource_kind: virtual
+sandbox_strategy: none
+user_addable: false
+built_in: true
+cli_args: []
+parent_types: []
+child_types: ["git-commit"]
+capabilities:
+  read: false
+  write: false
+  sandbox: false
+  checkpoint: false
+equivalence:
+  criteria:
+    - commit_hash
+  description: "Two physical commits are equivalent when they share the same commit hash"
+handler: null

examples/resource-types/directory.yaml

@@ -0,0 +1,23 @@
+# Spec reference: docs/specification.md ~lines 10133-10143, 24548-24632
+schema_version: "1.0"
+name: directory
+description: "Cross-layer directory identity linking equivalent physical directories"
+resource_kind: virtual
+sandbox_strategy: none
+user_addable: false
+built_in: true
+cli_args: []
+parent_types: []
+child_types: ["fs-directory", "git-tree"]
+capabilities:
+  read: false
+  write: false
+  sandbox: false
+  checkpoint: false
+equivalence:
+  criteria:
+    - merkle_hash
+    - name
+    - permissions
+  description: "Two physical resources are equivalent when they share the same Merkle hash, name, and permissions"
+handler: null

examples/resource-types/file.yaml

@@ -0,0 +1,23 @@
+# Spec reference: docs/specification.md ~lines 10133-10143, 24548-24632
+schema_version: "1.0"
+name: file
+description: "Cross-layer file identity linking equivalent physical files"
+resource_kind: virtual
+sandbox_strategy: none
+user_addable: false
+built_in: true
+cli_args: []
+parent_types: []
+child_types: ["fs-file", "git-tree-entry"]
+capabilities:
+  read: false
+  write: false
+  sandbox: false
+  checkpoint: false
+equivalence:
+  criteria:
+    - content_hash
+    - filename
+    - permissions
+  description: "Two physical resources are equivalent when they share the same content bytes (SHA-256), filename, and permissions"
+handler: null

examples/resource-types/tag.yaml

@@ -0,0 +1,22 @@
+# Spec reference: docs/specification.md ~lines 10133-10143, 24548-24632
+schema_version: "1.0"
+name: tag
+description: "Cross-repo tag identity linking tags with the same name and target"
+resource_kind: virtual
+sandbox_strategy: none
+user_addable: false
+built_in: true
+cli_args: []
+parent_types: []
+child_types: ["git-tag"]
+capabilities:
+  read: false
+  write: false
+  sandbox: false
+  checkpoint: false
+equivalence:
+  criteria:
+    - name
+    - target_sha
+  description: "Two physical tags are equivalent when they share the same tag name and target object"
+handler: null

examples/resource-types/tree.yaml

@@ -0,0 +1,21 @@
+# Spec reference: docs/specification.md ~lines 10133-10143, 24548-24632
+schema_version: "1.0"
+name: tree
+description: "Cross-repo/cross-commit tree identity linking trees with the same hash"
+resource_kind: virtual
+sandbox_strategy: none
+user_addable: false
+built_in: true
+cli_args: []
+parent_types: []
+child_types: ["git-tree"]
+capabilities:
+  read: false
+  write: false
+  sandbox: false
+  checkpoint: false
+equivalence:
+  criteria:
+    - tree_hash
+  description: "Two physical tree objects are equivalent when they share the same tree hash"
+handler: null