feat(audit): add append-only agent audit trail (.beads/interactions.jsonl)

Implements audit logging for agent interactions to support auditing and
dataset generation (fixes #649).

New features:
- .beads/interactions.jsonl (append-only audit log)
- bd audit record: log LLM calls, tool calls, or pipe JSON via stdin
- bd audit label <id>: append labels (good/bad) for dataset curation
- bd compact --audit: optionally log LLM prompt/response during compaction
- bd init: creates empty interactions.jsonl
- bd sync: includes interactions.jsonl in staging

Audit entries are append-only - labeling creates new entries that
reference parent entries by ID.

Closes #649

Co-authored-by: Dmitry Chichkov <dchichkov@nvidia.com>

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

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

internal/compact/compactor.go

@@ -15,9 +15,11 @@ const (
 
 // Config holds configuration for the compaction process.
 type Config struct {
-	APIKey      string
-	Concurrency int
-	DryRun      bool
+	APIKey       string
+	Concurrency  int
+	DryRun       bool
+	AuditEnabled bool
+	Actor        string
 }
 
 // Compactor handles issue compaction using AI summarization.
@@ -53,6 +55,10 @@ func New(store *sqlite.SQLiteStorage, apiKey string, config *Config) (*Compactor
 			}
 		}
 	}
+	if haikuClient != nil {
+		haikuClient.auditEnabled = config.AuditEnabled
+		haikuClient.auditActor = config.Actor
+	}
 
 	return &Compactor{
 		store:  store,

internal/compact/haiku.go

@@ -13,6 +13,7 @@ import (
 
 	"github.com/anthropics/anthropic-sdk-go"
 	"github.com/anthropics/anthropic-sdk-go/option"
+	"github.com/steveyegge/beads/internal/audit"
 	"github.com/steveyegge/beads/internal/types"
 )
 
@@ -32,6 +33,8 @@ type HaikuClient struct {
 	tier1Template  *template.Template
 	maxRetries     int
 	initialBackoff time.Duration
+	auditEnabled   bool
+	auditActor     string
 }
 
 // NewHaikuClient creates a new Haiku API client. Env var ANTHROPIC_API_KEY takes precedence over explicit apiKey.
@@ -67,7 +70,23 @@ func (h *HaikuClient) SummarizeTier1(ctx context.Context, issue *types.Issue) (s
 		return "", fmt.Errorf("failed to render prompt: %w", err)
 	}
 
-	return h.callWithRetry(ctx, prompt)
+	resp, callErr := h.callWithRetry(ctx, prompt)
+	if h.auditEnabled {
+		// Best-effort: never fail compaction because audit logging failed.
+		e := &audit.Entry{
+			Kind:     "llm_call",
+			Actor:    h.auditActor,
+			IssueID:  issue.ID,
+			Model:    string(h.model),
+			Prompt:   prompt,
+			Response: resp,
+		}
+		if callErr != nil {
+			e.Error = callErr.Error()
+		}
+		_, _ = audit.Append(e)
+	}
+	return resp, callErr
 }
 
 func (h *HaikuClient) callWithRetry(ctx context.Context, prompt string) (string, error) {