feat: complete bd-kwro messaging & knowledge graph epic

- Add bd cleanup --ephemeral flag for transient message cleanup (bd-kwro.9)
- Add Ephemeral filter to IssueFilter type
- Add ephemeral filtering to SQLite storage queries

Tests (bd-kwro.10):
- Add internal/hooks/hooks_test.go for hook system
- Add cmd/bd/mail_test.go for mail commands
- Add internal/storage/sqlite/graph_links_test.go for graph links

Documentation (bd-kwro.11):
- Add docs/messaging.md for full messaging reference
- Add docs/graph-links.md for graph link types
- Update AGENTS.md with inter-agent messaging section
- Update CHANGELOG.md with all bd-kwro features

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cmd/bd/cleanup.go

@@ -42,6 +42,9 @@ Delete all closed issues and prune tombstones:
 Delete issues closed more than 30 days ago:
   bd cleanup --older-than 30 --force
 
+Delete only closed ephemeral issues (transient messages):
+  bd cleanup --ephemeral --force
+
 Preview what would be deleted/pruned:
   bd cleanup --dry-run
   bd cleanup --older-than 90 --dry-run
@@ -64,6 +67,7 @@ SEE ALSO:
 		cascade, _ := cmd.Flags().GetBool("cascade")
 		olderThanDays, _ := cmd.Flags().GetInt("older-than")
 		hardDelete, _ := cmd.Flags().GetBool("hard")
+		ephemeralOnly, _ := cmd.Flags().GetBool("ephemeral")
 
 		// Calculate custom TTL for --hard mode
 		// When --hard is set, use --older-than days as the tombstone TTL cutoff
@@ -108,6 +112,12 @@ SEE ALSO:
 			filter.ClosedBefore = &cutoffTime
 		}
 
+		// Add ephemeral filter if specified (bd-kwro.9)
+		if ephemeralOnly {
+			ephemeralTrue := true
+			filter.Ephemeral = &ephemeralTrue
+		}
+
 		// Get all closed issues matching filter
 		closedIssues, err := store.SearchIssues(ctx, "", filter)
 		if err != nil {
@@ -124,11 +134,18 @@ SEE ALSO:
 				if olderThanDays > 0 {
 					result["filter"] = fmt.Sprintf("older than %d days", olderThanDays)
 				}
+				if ephemeralOnly {
+					result["ephemeral"] = true
+				}
 				output, _ := json.MarshalIndent(result, "", "  ")
 				fmt.Println(string(output))
 			} else {
 				msg := "No closed issues to delete"
-				if olderThanDays > 0 {
+				if ephemeralOnly && olderThanDays > 0 {
+					msg = fmt.Sprintf("No closed ephemeral issues older than %d days to delete", olderThanDays)
+				} else if ephemeralOnly {
+					msg = "No closed ephemeral issues to delete"
+				} else if olderThanDays > 0 {
 					msg = fmt.Sprintf("No closed issues older than %d days to delete", olderThanDays)
 				}
 				fmt.Println(msg)
@@ -144,15 +161,23 @@ SEE ALSO:
 
 		// Show preview
 		if !force && !dryRun {
-			fmt.Fprintf(os.Stderr, "Would delete %d closed issue(s). Use --force to confirm or --dry-run to preview.\n", len(issueIDs))
+			issueType := "closed"
+			if ephemeralOnly {
+				issueType = "closed ephemeral"
+			}
+			fmt.Fprintf(os.Stderr, "Would delete %d %s issue(s). Use --force to confirm or --dry-run to preview.\n", len(issueIDs), issueType)
 			os.Exit(1)
 		}
 
 		if !jsonOutput {
+			issueType := "closed"
+			if ephemeralOnly {
+				issueType = "closed ephemeral"
+			}
 			if olderThanDays > 0 {
-				fmt.Printf("Found %d closed issue(s) older than %d days\n", len(closedIssues), olderThanDays)
+				fmt.Printf("Found %d %s issue(s) older than %d days\n", len(closedIssues), issueType, olderThanDays)
 			} else {
-				fmt.Printf("Found %d closed issue(s)\n", len(closedIssues))
+				fmt.Printf("Found %d %s issue(s)\n", len(closedIssues), issueType)
 			}
 			if dryRun {
 				fmt.Println(color.YellowString("DRY RUN - no changes will be made"))
@@ -211,5 +236,6 @@ func init() {
 	cleanupCmd.Flags().Bool("cascade", false, "Recursively delete all dependent issues")
 	cleanupCmd.Flags().Int("older-than", 0, "Only delete issues closed more than N days ago (0 = all closed issues)")
 	cleanupCmd.Flags().Bool("hard", false, "Bypass tombstone TTL safety; use --older-than days as cutoff")
+	cleanupCmd.Flags().Bool("ephemeral", false, "Only delete closed ephemeral issues (transient messages)")
 	rootCmd.AddCommand(cleanupCmd)
 }