Phase 1: Edge schema consolidation infrastructure (Decision 004)

Add metadata and thread_id columns to dependencies table to support:
- Edge metadata: JSON blob for type-specific data (similarity scores, etc.)
- Thread queries: O(1) conversation threading via thread_id

Changes:
- New migration 020_edge_consolidation.go
- Updated Dependency struct with Metadata and ThreadID fields
- Added new entity types: authored-by, assigned-to, approved-by
- Relaxed DependencyType validation (any non-empty string ≤50 chars)
- Added IsWellKnown() and AffectsReadyWork() methods
- Updated SQL queries to include new columns
- Updated tests for new behavior

This enables HOP knowledge graph requirements and Reddit-style threading.

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

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

internal/storage/sqlite/migrations/020_edge_consolidation.go

@@ -0,0 +1,60 @@
+package migrations
+
+import (
+	"database/sql"
+	"fmt"
+)
+
+// MigrateEdgeConsolidation adds metadata and thread_id columns to the dependencies table.
+// This is Phase 1 of the Edge Schema Consolidation (Decision 004):
+// - metadata: JSON blob for type-specific edge data (similarity scores, reasons, etc.)
+// - thread_id: For efficient conversation threading queries
+//
+// These columns enable:
+// - Edge metadata without schema changes (extensibility)
+// - O(1) thread queries for Reddit-style conversations
+// - HOP knowledge graph foundation
+func MigrateEdgeConsolidation(db *sql.DB) error {
+	columns := []struct {
+		name       string
+		definition string
+	}{
+		{"metadata", "TEXT DEFAULT '{}'"},
+		{"thread_id", "TEXT DEFAULT ''"},
+	}
+
+	for _, col := range columns {
+		var columnExists bool
+		err := db.QueryRow(`
+			SELECT COUNT(*) > 0
+			FROM pragma_table_info('dependencies')
+			WHERE name = ?
+		`, col.name).Scan(&columnExists)
+		if err != nil {
+			return fmt.Errorf("failed to check %s column: %w", col.name, err)
+		}
+
+		if columnExists {
+			continue
+		}
+
+		_, err = db.Exec(fmt.Sprintf(`ALTER TABLE dependencies ADD COLUMN %s %s`, col.name, col.definition))
+		if err != nil {
+			return fmt.Errorf("failed to add %s column: %w", col.name, err)
+		}
+	}
+
+	// Add index for thread queries - only index non-empty thread_ids
+	_, err := db.Exec(`CREATE INDEX IF NOT EXISTS idx_dependencies_thread ON dependencies(thread_id) WHERE thread_id != ''`)
+	if err != nil {
+		return fmt.Errorf("failed to create thread_id index: %w", err)
+	}
+
+	// Add composite index for finding all edges in a thread by type
+	_, err = db.Exec(`CREATE INDEX IF NOT EXISTS idx_dependencies_thread_type ON dependencies(thread_id, type) WHERE thread_id != ''`)
+	if err != nil {
+		return fmt.Errorf("failed to create thread_type index: %w", err)
+	}
+
+	return nil
+}