feat: govern attachment exceptions and ownership transfers

docs/ACCESS_EXPLANATION_COVERAGE.md

@@ -0,0 +1,40 @@
+# Campaign Access Explanation Coverage
+
+Campaign access explanations are resource-specific evidence. They inherit the
+parent Campaign decision only where the child has no independent grant model,
+and they must identify that inheritance explicitly.
+
+## Implemented
+
+- Campaign
+- Campaign version
+- Campaign delivery job / built message
+- Computed Campaign report, identified by Campaign, version, and report kind
+
+## Planned Slices
+
+1. Recipient rows and imported recipient-source snapshots
+2. Attachment bindings and frozen attachment resolutions
+3. Validation issues, review decisions, and attachment-policy overrides
+4. Delivery attempts, IMAP append attempts, Postbox attempts, and
+   reconciliation decisions
+5. Campaign shares and ownership-transfer records
+6. Import mapping profiles and import executions
+7. Reusable Campaign templates and template revisions when the template
+   library becomes persistent
+8. Export packages and protocol/report artifacts
+
+Each child explanation must include:
+
+- the child resource identity and current state;
+- the parent Campaign and version where applicable;
+- whether access is inherited, independently granted, or further restricted;
+- effective owner/share/policy provenance;
+- missing-module or unavailable-evidence reasons without leaking the hidden
+  object;
+- a stable resource identifier suitable for audit and support links.
+
+Delivery attempts, review decisions, reports, and exports can contain more
+sensitive evidence than the Campaign summary. Their read and diagnostic/export
+permissions therefore remain independently enforceable even when the parent
+Campaign is readable.