Context propagation with graceful cancellation (bd-rtp, bd-yb8, bd-2o2)

Complete implementation of signal-aware context propagation for graceful
cancellation across all commands and storage operations.

Key changes:

1. Signal-aware contexts (bd-rtp):
   - Added rootCtx/rootCancel in main.go using signal.NotifyContext()
   - Set up in PersistentPreRun, cancelled in PersistentPostRun
   - Daemon uses same pattern in runDaemonLoop()
   - Handles SIGINT/SIGTERM for graceful shutdown

2. Context propagation (bd-yb8):
   - All commands now use rootCtx instead of context.Background()
   - sqlite.New() receives context for cancellable operations
   - Database operations respect context cancellation
   - Storage layer propagates context through all queries

3. Cancellation tests (bd-2o2):
   - Added import_cancellation_test.go with comprehensive tests
   - Added export cancellation test in export_test.go
   - Tests verify database integrity after cancellation
   - All cancellation tests passing

Fixes applied during review:
   - Fixed rootCtx lifecycle (removed premature defer from PersistentPreRun)
   - Fixed test context contamination (reset rootCtx in test cleanup)
   - Fixed export tests missing context setup

Impact:
   - Pressing Ctrl+C during import/export now cancels gracefully
   - No database corruption or hanging transactions
   - Clean shutdown of all operations

Tested:
   - go build ./cmd/bd ✓
   - go test ./cmd/bd -run TestImportCancellation ✓
   - go test ./cmd/bd -run TestExportCommand ✓
   - Manual Ctrl+C testing verified

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

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

cmd/bd/ready.go

@@ -1,6 +1,5 @@
 package main
 import (
-	"context"
 	"encoding/json"
 	"fmt"
 	"os"
@@ -97,7 +96,7 @@ var readyCmd = &cobra.Command{
 			return
 		}
 		// Direct mode
-		ctx := context.Background()
+		ctx := rootCtx
 
 		// Check database freshness before reading (bd-2q6d, bd-c4rq)
 		// Skip check when using daemon (daemon auto-imports on staleness)
@@ -158,16 +157,16 @@ var blockedCmd = &cobra.Command{
 	Run: func(cmd *cobra.Command, args []string) {
 		// Use global jsonOutput set by PersistentPreRun (respects config.yaml + env vars)
 		// If daemon is running but doesn't support this command, use direct storage
+		ctx := rootCtx
 		if daemonClient != nil && store == nil {
 			var err error
-			store, err = sqlite.New(dbPath)
+			store, err = sqlite.New(ctx, dbPath)
 			if err != nil {
 			fmt.Fprintf(os.Stderr, "Error: failed to open database: %v\n", err)
 			os.Exit(1)
 			}
 			defer func() { _ = store.Close() }()
 			}
-			ctx := context.Background()
 		blocked, err := store.GetBlockedIssues(ctx)
 		if err != nil {
 			fmt.Fprintf(os.Stderr, "Error: %v\n", err)
@@ -238,7 +237,7 @@ var statsCmd = &cobra.Command{
 			return
 		}
 		// Direct mode
-		ctx := context.Background()
+		ctx := rootCtx
 		stats, err := store.GetStatistics(ctx)
 		if err != nil {
 		fmt.Fprintf(os.Stderr, "Error: %v\n", err)