diff --git a/docs/current-status-card.md b/docs/current-status-card.md
index bff07d6..19f209f 100644
--- a/docs/current-status-card.md
+++ b/docs/current-status-card.md
@@ -240,8 +240,8 @@ Continuous execution plan R6f-R14 is approved and execution has started:
 - Plan file: `docs/superpowers/plans/2026-07-10-r6f-r14-continuous-execution-plan.md`.
 - Scope: 15 ordered rounds covering send-message connector/gate hardening, send-file preview/idempotency/package, receive-file download preview, receive-message reconciliation, end-to-end business smoke, and release-candidate report.
 - Execution rule after approval: one round at a time, status-card update, verification, commit, push, then continue automatically until an evidence-only blocker requires user action.
-- Last completed round: R7 send-file preview tool.
-- Next active round: R8 send-file idempotency and audit hardening.
+- Last completed round: R8 send-file idempotency and audit hardening.
+- Next active round: R9 send-file upload evidence package.
 
 R6g send audit and idempotency replay diagnostics is complete:
 
@@ -305,3 +305,13 @@ R7 send-file preview tool is complete:
 - `execution_mode="production"` returns structured blocked metadata; no upload, click, type, hook, network capture, or client mutation is introduced.
 - Verification passed: focused send-file tests, 10-tool MCP registration test, `go test ./...`, `go build ./cmd/isphere-mcp`, `scripts\verify-go-mcp.ps1`, and `go run ./cmd/isphere-capability-smoke`.
 - Next node: R8 send-file idempotency and audit hardening.
+
+R8 send-file idempotency and audit hardening is complete:
+
+- Added `ISPHERE_SEND_FILE_AUDIT_PATH` and `ISPHERE_SEND_FILE_IDEMPOTENCY_PATH` support.
+- Duplicate same target/file/idempotency key returns `duplicate_detected=true` and remains no-send.
+- Reusing the same idempotency key for a different target or file hash returns structured blocked metadata with `conflict_detected=true`.
+- Send-file audit/idempotency JSONL stores hashes, target refs, size, result, and side-effect flags; it does not store raw file content, raw local file path, or raw idempotency key.
+- Production file upload remains blocked with `production_send_enabled=false` and `real_send_attempted=false`.
+- Verification passed: focused send-file tests, `go test ./...`, `go build ./cmd/isphere-mcp`, `scripts\verify-go-mcp.ps1`, and `go run ./cmd/isphere-capability-smoke`.
+- Next node: R9 send-file upload evidence package.
diff --git a/docs/go-mcp-runbook.md b/docs/go-mcp-runbook.md
index 57029fa..3efdd55 100644
--- a/docs/go-mcp-runbook.md
+++ b/docs/go-mcp-runbook.md
@@ -284,7 +284,14 @@ Send-file preview requires an explicit allowed directory. Put only the files you
 $env:ISPHERE_SEND_FILE_ALLOWED_DIR = "E:\coding\codex\isphere-ai-bridge\runs\send-file-preview"
 ```
 
-`isphere_send_file` rejects `file_path` values outside that directory. It computes file SHA256 and size, but does not upload, click, type, or return file content.
+Optional send-file audit/idempotency paths:
+
+```powershell
+$env:ISPHERE_SEND_FILE_AUDIT_PATH = "E:\coding\codex\isphere-ai-bridge\runs\send-audit\send-file-preview.jsonl"
+$env:ISPHERE_SEND_FILE_IDEMPOTENCY_PATH = "E:\coding\codex\isphere-ai-bridge\runs\send-audit\send-file-idempotency.jsonl"
+```
+
+`isphere_send_file` rejects `file_path` values outside that directory. It computes file SHA256 and size, but does not upload, click, type, or return file content. If `ISPHERE_SEND_FILE_IDEMPOTENCY_PATH` is set, duplicate same-key/same-target/same-file preview calls set `duplicate_detected=true`; reusing the same key for a different target or file hash returns blocked metadata with `conflict_detected=true`. The audit/idempotency JSONL stores file hash, size, target ref, and hashed idempotency key; it does not store raw file content, raw local file path, or raw idempotency key.
 
 R6g adds a local diagnostic for replaying the redacted audit/idempotency files without opening iSphere:
 
diff --git a/docs/superpowers/plans/2026-07-10-r6f-r14-continuous-execution-plan.md b/docs/superpowers/plans/2026-07-10-r6f-r14-continuous-execution-plan.md
index 10944d8..af387e3 100644
--- a/docs/superpowers/plans/2026-07-10-r6f-r14-continuous-execution-plan.md
+++ b/docs/superpowers/plans/2026-07-10-r6f-r14-continuous-execution-plan.md
@@ -594,19 +594,19 @@ git push gitea main
 - Duplicate same target/file/idempotency returns `duplicate_detected=true` with no second send.
 - Reusing the same idempotency key for a different target or file hash returns `conflict_detected=true`.
 
-- [ ] **Step 1: Write duplicate test**
+- [x] **Step 1: Write duplicate test**
 
 Add `TestISphereSendFileDuplicateIdempotencyDetected`: same target, same file hash, same idempotency key called twice; second response has `duplicate_detected=true` and `real_send_attempted=false`.
 
-- [ ] **Step 2: Write conflict test**
+- [x] **Step 2: Write conflict test**
 
 Add `TestISphereSendFileIdempotencyConflictBlocked`: same idempotency key with a different file hash returns `send_status="blocked"` and `conflict_detected=true`.
 
-- [ ] **Step 3: Implement audit and idempotency state**
+- [x] **Step 3: Implement audit and idempotency state**
 
 Reuse the message idempotency pattern or extract a shared small helper only if it reduces duplication without changing message behavior.
 
-- [ ] **Step 4: Verify and commit**
+- [x] **Step 4: Verify and commit**
 
 ```powershell
 git diff --check
@@ -621,6 +621,15 @@ git push gitea main
 
 **Acceptance gate:** File upload remains blocked, but duplicate/conflict behavior is deterministic.
 
+**R8 Result:**
+
+- Added send-file audit and idempotency state with `ISPHERE_SEND_FILE_AUDIT_PATH` and `ISPHERE_SEND_FILE_IDEMPOTENCY_PATH`.
+- Duplicate same target/file/idempotency key now returns `duplicate_detected=true` and remains planned/no-send.
+- Reusing the same idempotency key for a different target or file hash returns `send_status="blocked"` and `conflict_detected=true`.
+- Send-file audit/idempotency JSONL stores file hash, size, target ref, result, side-effect flags, and hashed idempotency key; it does not store raw file content, raw local file path, or raw idempotency key.
+- `scripts/verify-go-mcp.ps1` now asserts `send_file_duplicate_detected=true` and `send_file_conflict_blocked=true` while keeping `send_file_production_enabled=false`.
+- Verification passed: `git diff --check`, `go test ./internal/tools -run TestISphereSendFile -v`, `go test ./...`, `go build ./cmd/isphere-mcp`, `scripts\verify-go-mcp.ps1`, and `go run ./cmd/isphere-capability-smoke`.
+
 ---
 
 ### R9: Send-file upload evidence package
diff --git a/internal/tools/isphere_send_file.go b/internal/tools/isphere_send_file.go
index daab30b..3a10836 100644
--- a/internal/tools/isphere_send_file.go
+++ b/internal/tools/isphere_send_file.go
@@ -1,22 +1,27 @@
 package tools
 
 import (
+	"bufio"
 	"context"
 	"crypto/sha256"
 	"encoding/hex"
+	"encoding/json"
 	"fmt"
 	"io"
 	"os"
 	"path/filepath"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/modelcontextprotocol/go-sdk/mcp"
 )
 
 const (
-	ToolNameSendFile      = "isphere_send_file"
-	EnvSendFileAllowedDir = "ISPHERE_SEND_FILE_ALLOWED_DIR"
+	ToolNameSendFile           = "isphere_send_file"
+	EnvSendFileAllowedDir      = "ISPHERE_SEND_FILE_ALLOWED_DIR"
+	EnvSendFileAuditPath       = "ISPHERE_SEND_FILE_AUDIT_PATH"
+	EnvSendFileIdempotencyPath = "ISPHERE_SEND_FILE_IDEMPOTENCY_PATH"
 
 	sendFileConnector      = "implatform-file-transfer"
 	sendFileConnectorMode  = "preview-only"
@@ -46,27 +51,226 @@ type normalizedSendFileArgs struct {
 	ExecutionMode        string
 }
 
+type SendFileAuditSink interface {
+	AppendSendFileAudit(ctx context.Context, event SendFileAuditEvent) error
+}
+
+type SendFileIdempotencyStore interface {
+	ReserveSendFileIdempotency(ctx context.Context, record SendFileIdempotencyRecord) (SendFileIdempotencyDecision, error)
+}
+
+type SendFileAuditEvent struct {
+	Tool                 string         `json:"tool"`
+	TargetType           string         `json:"target_type"`
+	TargetID             string         `json:"target_id"`
+	TargetRef            string         `json:"target_ref"`
+	ExecutionMode        string         `json:"execution_mode"`
+	Connector            string         `json:"connector"`
+	ConnectorMode        string         `json:"connector_mode"`
+	ConnectorStage       string         `json:"connector_stage"`
+	FileSHA256           string         `json:"file_sha256"`
+	FileSizeBytes        int64          `json:"file_size_bytes"`
+	IdempotencyKeySHA256 string         `json:"idempotency_key_sha256"`
+	SendStatus           string         `json:"send_status"`
+	Result               string         `json:"result"`
+	BlockedReason        string         `json:"blocked_reason,omitempty"`
+	AuditRef             string         `json:"audit_ref"`
+	StartedAt            string         `json:"started_at"`
+	FinishedAt           string         `json:"finished_at"`
+	RealSendAttempted    bool           `json:"real_send_attempted"`
+	SideEffects          map[string]any `json:"side_effects"`
+	FilePath             string         `json:"-"`
+	IdempotencyKey       string         `json:"-"`
+}
+
+type SendFileIdempotencyRecord struct {
+	Tool                 string `json:"tool"`
+	TargetRef            string `json:"target_ref"`
+	ExecutionMode        string `json:"execution_mode"`
+	Connector            string `json:"connector"`
+	ConnectorStage       string `json:"connector_stage"`
+	FileSHA256           string `json:"file_sha256"`
+	IdempotencyKeySHA256 string `json:"idempotency_key_sha256"`
+	AuditRef             string `json:"audit_ref"`
+	StartedAt            string `json:"started_at"`
+}
+
+type SendFileIdempotencyDecision struct {
+	Duplicate      bool
+	Conflict       bool
+	FirstAuditRef  string
+	FirstStartedAt string
+}
+
+type fileSendFileAuditSink struct {
+	path string
+}
+
+type fileSendFileIdempotencyStore struct {
+	path string
+}
+
+var sendFileIdempotencyFileMu sync.Mutex
+
 func RegisterISphereSendFileTool(server *mcp.Server) {
+	RegisterISphereSendFileToolWithState(server, nil, nil)
+}
+
+func RegisterISphereSendFileToolWithState(server *mcp.Server, auditSink SendFileAuditSink, idempotencyStore SendFileIdempotencyStore) {
+	if auditSink == nil {
+		auditSink = defaultSendFileAuditSink()
+	}
+	if idempotencyStore == nil {
+		idempotencyStore = defaultSendFileIdempotencyStore()
+	}
+
 	mcp.AddTool[SendFileArgs, map[string]any](server, &mcp.Tool{
 		Name:        ToolNameSendFile,
 		Description: "Preview iSphere file sends with target/file hash/idempotency metadata; production file upload is blocked until sandbox evidence passes.",
 	}, func(ctx context.Context, _ *mcp.CallToolRequest, input SendFileArgs) (*mcp.CallToolResult, map[string]any, error) {
-		_ = ctx
 		started := time.Now().UTC()
 		normalized, blockedReason, err := normalizeSendFileArgs(input)
 		if err != nil {
 			return nil, nil, err
 		}
+
+		var response map[string]any
+		var event SendFileAuditEvent
 		if blockedReason != "" {
-			return nil, sendFileResponse(normalized, started, time.Now().UTC(), false, blockedReason), nil
+			response, event = sendFileResponse(normalized, started, time.Now().UTC(), false, blockedReason)
+		} else if normalized.ExecutionMode == sendFileProductionMode {
+			response, event = sendFileResponse(normalized, started, time.Now().UTC(), false, "production file upload is blocked until send-file sandbox evidence passes")
+		} else {
+			response, event = sendFileResponse(normalized, started, time.Now().UTC(), true, "")
 		}
-		if normalized.ExecutionMode == sendFileProductionMode {
-			return nil, sendFileResponse(normalized, started, time.Now().UTC(), false, "production file upload is blocked until send-file sandbox evidence passes"), nil
+
+		if normalized.FileSHA256 != "" {
+			decision, err := idempotencyStore.ReserveSendFileIdempotency(ctx, sendFileIdempotencyRecordFromAuditEvent(event))
+			if err != nil {
+				return nil, nil, fmt.Errorf("%s idempotency reserve failed: %w", ToolNameSendFile, err)
+			}
+			applySendFileIdempotencyDecision(response, &event, decision)
 		}
-		return nil, sendFileResponse(normalized, started, time.Now().UTC(), true, ""), nil
+		if err := auditSink.AppendSendFileAudit(ctx, event); err != nil {
+			return nil, nil, fmt.Errorf("%s audit append failed: %w", ToolNameSendFile, err)
+		}
+		return nil, response, nil
 	})
 }
 
+func defaultSendFileAuditSink() SendFileAuditSink {
+	if path := strings.TrimSpace(os.Getenv(EnvSendFileAuditPath)); path != "" {
+		return fileSendFileAuditSink{path: path}
+	}
+	return fileSendFileAuditSink{path: filepath.Join("runs", "send-audit", "send-file-preview.jsonl")}
+}
+
+func defaultSendFileIdempotencyStore() SendFileIdempotencyStore {
+	if path := strings.TrimSpace(os.Getenv(EnvSendFileIdempotencyPath)); path != "" {
+		return fileSendFileIdempotencyStore{path: path}
+	}
+	return fileSendFileIdempotencyStore{path: filepath.Join("runs", "send-audit", "send-file-idempotency.jsonl")}
+}
+
+func (s fileSendFileAuditSink) AppendSendFileAudit(_ context.Context, event SendFileAuditEvent) error {
+	if strings.TrimSpace(s.path) == "" {
+		return nil
+	}
+	if err := os.MkdirAll(filepath.Dir(s.path), 0o755); err != nil {
+		return err
+	}
+	payload, err := json.Marshal(event)
+	if err != nil {
+		return err
+	}
+	file, err := os.OpenFile(s.path, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0o600)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+	if _, err := file.Write(append(payload, '\n')); err != nil {
+		return err
+	}
+	return nil
+}
+
+func (s fileSendFileIdempotencyStore) ReserveSendFileIdempotency(_ context.Context, record SendFileIdempotencyRecord) (SendFileIdempotencyDecision, error) {
+	if strings.TrimSpace(s.path) == "" {
+		return SendFileIdempotencyDecision{}, nil
+	}
+	if record.IdempotencyKeySHA256 == "" {
+		return SendFileIdempotencyDecision{}, fmt.Errorf("idempotency_key_sha256 is required")
+	}
+	sendFileIdempotencyFileMu.Lock()
+	defer sendFileIdempotencyFileMu.Unlock()
+
+	if err := os.MkdirAll(filepath.Dir(s.path), 0o755); err != nil {
+		return SendFileIdempotencyDecision{}, err
+	}
+	existing, err := readSendFileIdempotencyRecords(s.path)
+	if err != nil {
+		return SendFileIdempotencyDecision{}, err
+	}
+	for _, candidate := range existing {
+		if candidate.IdempotencyKeySHA256 != record.IdempotencyKeySHA256 {
+			continue
+		}
+		decision := SendFileIdempotencyDecision{
+			FirstAuditRef:  candidate.AuditRef,
+			FirstStartedAt: candidate.StartedAt,
+		}
+		if candidate.TargetRef == record.TargetRef && candidate.FileSHA256 == record.FileSHA256 {
+			decision.Duplicate = true
+			return decision, nil
+		}
+		decision.Conflict = true
+		return decision, nil
+	}
+
+	payload, err := json.Marshal(record)
+	if err != nil {
+		return SendFileIdempotencyDecision{}, err
+	}
+	file, err := os.OpenFile(s.path, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0o600)
+	if err != nil {
+		return SendFileIdempotencyDecision{}, err
+	}
+	defer file.Close()
+	if _, err := file.Write(append(payload, '\n')); err != nil {
+		return SendFileIdempotencyDecision{}, err
+	}
+	return SendFileIdempotencyDecision{}, nil
+}
+
+func readSendFileIdempotencyRecords(path string) ([]SendFileIdempotencyRecord, error) {
+	file, err := os.Open(path)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, nil
+		}
+		return nil, err
+	}
+	defer file.Close()
+
+	var records []SendFileIdempotencyRecord
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		line := strings.TrimSpace(scanner.Text())
+		if line == "" {
+			continue
+		}
+		var record SendFileIdempotencyRecord
+		if err := json.Unmarshal([]byte(line), &record); err != nil {
+			return nil, fmt.Errorf("decode send-file idempotency record: %w", err)
+		}
+		records = append(records, record)
+	}
+	if err := scanner.Err(); err != nil {
+		return nil, err
+	}
+	return records, nil
+}
+
 func normalizeSendFileArgs(input SendFileArgs) (normalizedSendFileArgs, string, error) {
 	targetType, targetRefPrefix, err := normalizeSendFileTargetType(input.TargetType)
 	if err != nil {
@@ -194,7 +398,7 @@ func sha256FileHex(path string) (string, error) {
 	return hex.EncodeToString(hash.Sum(nil)), nil
 }
 
-func sendFileResponse(input normalizedSendFileArgs, started time.Time, finished time.Time, planned bool, blockedReason string) map[string]any {
+func sendFileResponse(input normalizedSendFileArgs, started time.Time, finished time.Time, planned bool, blockedReason string) (map[string]any, SendFileAuditEvent) {
 	sideEffects := sendMessageNoSideEffects()
 	status := "planned"
 	stage := sendFilePreviewStage
@@ -207,7 +411,30 @@ func sendFileResponse(input normalizedSendFileArgs, started time.Time, finished
 		blocked = blockedReason
 	}
 	auditRef := "send-file:" + shortHash(input.FileSHA256) + ":" + shortHash(input.IdempotencyKeySHA256)
-	return map[string]any{
+	event := SendFileAuditEvent{
+		Tool:                 ToolNameSendFile,
+		TargetType:           input.TargetType,
+		TargetID:             input.TargetID,
+		TargetRef:            input.TargetRef,
+		ExecutionMode:        input.ExecutionMode,
+		Connector:            sendFileConnector,
+		ConnectorMode:        sendFileConnectorMode,
+		ConnectorStage:       stage,
+		FileSHA256:           input.FileSHA256,
+		FileSizeBytes:        input.FileSizeBytes,
+		IdempotencyKeySHA256: input.IdempotencyKeySHA256,
+		SendStatus:           status,
+		Result:               status,
+		AuditRef:             auditRef,
+		StartedAt:            started.Format(time.RFC3339Nano),
+		FinishedAt:           finished.Format(time.RFC3339Nano),
+		RealSendAttempted:    false,
+		SideEffects:          sideEffects,
+	}
+	if blockedReason != "" {
+		event.BlockedReason = blockedReason
+	}
+	response := map[string]any{
 		"ok":                      ok,
 		"send_status":             status,
 		"blocked_reason":          blocked,
@@ -234,6 +461,10 @@ func sendFileResponse(input normalizedSendFileArgs, started time.Time, finished
 		},
 		"idempotency": map[string]any{
 			"idempotency_key_sha256": input.IdempotencyKeySHA256,
+			"duplicate_detected":     false,
+			"conflict_detected":      false,
+			"first_audit_ref":        nil,
+			"first_started_at":       nil,
 		},
 		"side_effect_flags": sideEffects,
 		"side_effects":      sideEffects,
@@ -254,4 +485,58 @@ func sendFileResponse(input normalizedSendFileArgs, started time.Time, finished
 			"real_send_attempted": false,
 		},
 	}
+	return response, event
+}
+
+func sendFileIdempotencyRecordFromAuditEvent(event SendFileAuditEvent) SendFileIdempotencyRecord {
+	return SendFileIdempotencyRecord{
+		Tool:                 event.Tool,
+		TargetRef:            event.TargetRef,
+		ExecutionMode:        event.ExecutionMode,
+		Connector:            event.Connector,
+		ConnectorStage:       event.ConnectorStage,
+		FileSHA256:           event.FileSHA256,
+		IdempotencyKeySHA256: event.IdempotencyKeySHA256,
+		AuditRef:             event.AuditRef,
+		StartedAt:            event.StartedAt,
+	}
+}
+
+func applySendFileIdempotencyDecision(response map[string]any, event *SendFileAuditEvent, decision SendFileIdempotencyDecision) {
+	idempotency, _ := response["idempotency"].(map[string]any)
+	if idempotency == nil {
+		idempotency = map[string]any{}
+		response["idempotency"] = idempotency
+	}
+	idempotency["duplicate_detected"] = decision.Duplicate
+	idempotency["conflict_detected"] = decision.Conflict
+	if decision.FirstAuditRef != "" {
+		idempotency["first_audit_ref"] = decision.FirstAuditRef
+	}
+	if decision.FirstStartedAt != "" {
+		idempotency["first_started_at"] = decision.FirstStartedAt
+	}
+	if !decision.Conflict {
+		return
+	}
+
+	blockedReason := "idempotency key was already used for a different target or file"
+	response["ok"] = false
+	response["send_status"] = "blocked"
+	response["blocked_reason"] = blockedReason
+	response["connector_stage"] = sendFileBlockedStage
+
+	audit, _ := response["audit"].(map[string]any)
+	if audit != nil {
+		audit["result"] = "blocked"
+		audit["connector_stage"] = sendFileBlockedStage
+		audit["blocked_reason"] = blockedReason
+	}
+
+	if event != nil {
+		event.ConnectorStage = sendFileBlockedStage
+		event.SendStatus = "blocked"
+		event.Result = "blocked"
+		event.BlockedReason = blockedReason
+	}
 }
diff --git a/internal/tools/isphere_send_file_test.go b/internal/tools/isphere_send_file_test.go
index e25918c..819a252 100644
--- a/internal/tools/isphere_send_file_test.go
+++ b/internal/tools/isphere_send_file_test.go
@@ -132,6 +132,161 @@ func TestISphereSendFileRejectsPathOutsideAllowedDir(t *testing.T) {
 	}
 }
 
+func TestISphereSendFileDuplicateIdempotencyDetected(t *testing.T) {
+	allowedDir := t.TempDir()
+	filePath := writeSendFileFixture(t, allowedDir, "duplicate.txt", "duplicate")
+	t.Setenv(EnvSendFileAllowedDir, allowedDir)
+	t.Setenv(EnvSendFileIdempotencyPath, filepath.Join(t.TempDir(), "send-file-idempotency.jsonl"))
+	t.Setenv(EnvSendFileAuditPath, filepath.Join(t.TempDir(), "send-file-audit.jsonl"))
+
+	session, cleanup := connectToolsTestSession(t, func(server *mcp.Server) {
+		RegisterISphereSendFileTool(server)
+	})
+	defer cleanup()
+
+	args := map[string]any{
+		"target_type":     "direct",
+		"target_id":       "alice@imopenfire1-lanzhou",
+		"file_path":       filePath,
+		"file_sha256":     sha256HexForSendMessageTest("duplicate"),
+		"idempotency_key": "file-duplicate-idem-1",
+		"execution_mode":  "preview",
+		"preview":         true,
+	}
+	if _, err := session.CallTool(context.Background(), &mcp.CallToolParams{Name: ToolNameSendFile, Arguments: args}); err != nil {
+		t.Fatalf("first send-file preview: %v", err)
+	}
+	second, err := session.CallTool(context.Background(), &mcp.CallToolParams{Name: ToolNameSendFile, Arguments: args})
+	if err != nil {
+		t.Fatalf("second send-file preview: %v", err)
+	}
+
+	var decoded struct {
+		OK                bool           `json:"ok"`
+		SendStatus        string         `json:"send_status"`
+		RealSendAttempted bool           `json:"real_send_attempted"`
+		Idempotency       map[string]any `json:"idempotency"`
+		SideEffectFlags   map[string]any `json:"side_effect_flags"`
+	}
+	payload, _ := json.Marshal(second.StructuredContent)
+	if err := json.Unmarshal(payload, &decoded); err != nil {
+		t.Fatalf("decode duplicate payload %s: %v", payload, err)
+	}
+	if !decoded.OK || decoded.SendStatus != "planned" || decoded.RealSendAttempted {
+		t.Fatalf("duplicate should remain planned preview/no-send: %s", payload)
+	}
+	if decoded.Idempotency["duplicate_detected"] != true || decoded.Idempotency["conflict_detected"] != false {
+		t.Fatalf("duplicate idempotency fields mismatch: %#v", decoded.Idempotency)
+	}
+	if decoded.SideEffectFlags["sent_file"] != false || decoded.SideEffectFlags["uploaded_file"] != false {
+		t.Fatalf("duplicate should have no file side effects: %#v", decoded.SideEffectFlags)
+	}
+}
+
+func TestISphereSendFileIdempotencyConflictBlocked(t *testing.T) {
+	allowedDir := t.TempDir()
+	firstPath := writeSendFileFixture(t, allowedDir, "first.txt", "first")
+	secondPath := writeSendFileFixture(t, allowedDir, "second.txt", "second")
+	t.Setenv(EnvSendFileAllowedDir, allowedDir)
+	t.Setenv(EnvSendFileIdempotencyPath, filepath.Join(t.TempDir(), "send-file-idempotency.jsonl"))
+	t.Setenv(EnvSendFileAuditPath, filepath.Join(t.TempDir(), "send-file-audit.jsonl"))
+
+	session, cleanup := connectToolsTestSession(t, func(server *mcp.Server) {
+		RegisterISphereSendFileTool(server)
+	})
+	defer cleanup()
+
+	sharedKey := "file-conflict-idem-1"
+	_, err := session.CallTool(context.Background(), &mcp.CallToolParams{Name: ToolNameSendFile, Arguments: map[string]any{
+		"target_type":     "direct",
+		"target_id":       "alice@imopenfire1-lanzhou",
+		"file_path":       firstPath,
+		"file_sha256":     sha256HexForSendMessageTest("first"),
+		"idempotency_key": sharedKey,
+		"execution_mode":  "preview",
+	}})
+	if err != nil {
+		t.Fatalf("first send-file preview: %v", err)
+	}
+	second, err := session.CallTool(context.Background(), &mcp.CallToolParams{Name: ToolNameSendFile, Arguments: map[string]any{
+		"target_type":     "direct",
+		"target_id":       "alice@imopenfire1-lanzhou",
+		"file_path":       secondPath,
+		"file_sha256":     sha256HexForSendMessageTest("second"),
+		"idempotency_key": sharedKey,
+		"execution_mode":  "preview",
+	}})
+	if err != nil {
+		t.Fatalf("conflict send-file preview: %v", err)
+	}
+
+	var decoded struct {
+		OK                bool           `json:"ok"`
+		SendStatus        string         `json:"send_status"`
+		BlockedReason     string         `json:"blocked_reason"`
+		RealSendAttempted bool           `json:"real_send_attempted"`
+		Idempotency       map[string]any `json:"idempotency"`
+		SideEffectFlags   map[string]any `json:"side_effect_flags"`
+	}
+	payload, _ := json.Marshal(second.StructuredContent)
+	if err := json.Unmarshal(payload, &decoded); err != nil {
+		t.Fatalf("decode conflict payload %s: %v", payload, err)
+	}
+	if decoded.OK || decoded.SendStatus != "blocked" || decoded.BlockedReason == "" || decoded.RealSendAttempted {
+		t.Fatalf("conflict should be blocked/no-send: %s", payload)
+	}
+	if decoded.Idempotency["duplicate_detected"] != false || decoded.Idempotency["conflict_detected"] != true {
+		t.Fatalf("conflict idempotency fields mismatch: %#v", decoded.Idempotency)
+	}
+	if decoded.SideEffectFlags["sent_file"] != false || decoded.SideEffectFlags["uploaded_file"] != false || decoded.SideEffectFlags["typed_text"] != false {
+		t.Fatalf("conflict should have no side effects: %#v", decoded.SideEffectFlags)
+	}
+}
+
+func TestISphereSendFileAuditRedactionIsStable(t *testing.T) {
+	allowedDir := t.TempDir()
+	filePath := writeSendFileFixture(t, allowedDir, "secret.txt", "secret file bytes")
+	auditPath := filepath.Join(t.TempDir(), "send-file-audit.jsonl")
+	t.Setenv(EnvSendFileAllowedDir, allowedDir)
+	t.Setenv(EnvSendFileAuditPath, auditPath)
+	t.Setenv(EnvSendFileIdempotencyPath, filepath.Join(t.TempDir(), "send-file-idempotency.jsonl"))
+
+	session, cleanup := connectToolsTestSession(t, func(server *mcp.Server) {
+		RegisterISphereSendFileTool(server)
+	})
+	defer cleanup()
+
+	fileHash := sha256HexForSendMessageTest("secret file bytes")
+	idempotencyKey := "raw-file-idempotency-key-must-not-be-stored"
+	callResult, err := session.CallTool(context.Background(), &mcp.CallToolParams{Name: ToolNameSendFile, Arguments: map[string]any{
+		"target_type":     "direct",
+		"target_id":       "alice@imopenfire1-lanzhou",
+		"file_path":       filePath,
+		"file_sha256":     fileHash,
+		"idempotency_key": idempotencyKey,
+		"execution_mode":  "preview",
+	}})
+	if err != nil {
+		t.Fatalf("send-file preview: %v", err)
+	}
+	if callResult.IsError {
+		t.Fatalf("send-file preview should not be tool error: %+v", callResult)
+	}
+	payload, err := os.ReadFile(auditPath)
+	if err != nil {
+		t.Fatalf("read send-file audit: %v", err)
+	}
+	audit := string(payload)
+	for _, forbidden := range []string{filePath, idempotencyKey, "secret file bytes"} {
+		if strings.Contains(audit, forbidden) {
+			t.Fatalf("send-file audit leaked forbidden value %q: %s", forbidden, audit)
+		}
+	}
+	if !strings.Contains(audit, fileHash) {
+		t.Fatalf("send-file audit missing file hash: %s", audit)
+	}
+}
+
 func TestISphereSendFileProductionBlockedWithoutSideEffects(t *testing.T) {
 	allowedDir := t.TempDir()
 	filePath := filepath.Join(allowedDir, "blocked.txt")
@@ -185,3 +340,12 @@ func TestISphereSendFileProductionBlockedWithoutSideEffects(t *testing.T) {
 		t.Fatalf("production blocked should have no side effects: %#v", decoded.SideEffectFlags)
 	}
 }
+
+func writeSendFileFixture(t *testing.T, dir string, name string, body string) string {
+	t.Helper()
+	path := filepath.Join(dir, name)
+	if err := os.WriteFile(path, []byte(body), 0o600); err != nil {
+		t.Fatalf("write send-file fixture %s: %v", name, err)
+	}
+	return path
+}
diff --git a/scripts/verify-go-mcp.ps1 b/scripts/verify-go-mcp.ps1
index 3b30de0..f91a98c 100644
--- a/scripts/verify-go-mcp.ps1
+++ b/scripts/verify-go-mcp.ps1
@@ -100,7 +100,7 @@ func main() {
 	ctx, cancel := context.WithTimeout(context.Background(), 20*time.Second)
 	defer cancel()
 
-	for _, key := range []string{"ISPHERE_PACKET_LOG_FILE", "ISPHERE_PACKET_LOG_DIR", "ISPHERE_MSGLIB_SIDECAR_EXE", "ISPHERE_MSGLIB_SQLITE_DLL", "ISPHERE_MSGLIB_DB", "ISPHERE_MSGLIB_PASSWORD", "ISPHERE_SEND_FILE_ALLOWED_DIR"} {
+	for _, key := range []string{"ISPHERE_PACKET_LOG_FILE", "ISPHERE_PACKET_LOG_DIR", "ISPHERE_MSGLIB_SIDECAR_EXE", "ISPHERE_MSGLIB_SQLITE_DLL", "ISPHERE_MSGLIB_DB", "ISPHERE_MSGLIB_PASSWORD", "ISPHERE_SEND_FILE_ALLOWED_DIR", "ISPHERE_SEND_FILE_AUDIT_PATH", "ISPHERE_SEND_FILE_IDEMPOTENCY_PATH"} {
 		if err := os.Unsetenv(key); err != nil {
 			fail("server/env", err)
 		}
@@ -116,6 +116,12 @@ func main() {
 	if err := os.Setenv("ISPHERE_SEND_IDEMPOTENCY_PATH", filepath.Join(sendStateDir, "send-idempotency.jsonl")); err != nil {
 		fail("server/send_state", err)
 	}
+	if err := os.Setenv("ISPHERE_SEND_FILE_AUDIT_PATH", filepath.Join(sendStateDir, "send-file-preview.jsonl")); err != nil {
+		fail("server/send_file_state", err)
+	}
+	if err := os.Setenv("ISPHERE_SEND_FILE_IDEMPOTENCY_PATH", filepath.Join(sendStateDir, "send-file-idempotency.jsonl")); err != nil {
+		fail("server/send_file_state", err)
+	}
 	sendFileDir, err := os.MkdirTemp("", "isphere-send-file-*")
 	if err != nil {
 		fail("server/send_file_state", err)
@@ -235,7 +241,7 @@ func main() {
 	defaultGroupCount := verifySearchGroups(ctx, session, "project", "tools/call isphere_search_groups default", 0)
 	defaultFileCount := verifyReceiveFiles(ctx, session, "report", "tools/call isphere_receive_files default", 0, "", "")
 	sendPreviewOK, productionSendEnabled := verifySendMessagePreview(ctx, session)
-	sendFilePreviewOK, sendFileProductionEnabled := verifySendFilePreview(ctx, session, sendFilePath)
+	sendFilePreviewOK, sendFileProductionEnabled, sendFileDuplicateDetected, sendFileConflictBlocked := verifySendFilePreview(ctx, session, sendFilePath)
 	configuredReceiveCount, configuredContactCount, configuredGroupCount, configuredFileCount := verifyConfiguredReceiveSource(ctx)
 	configuredDirReceiveCount, configuredDirContactCount, configuredDirGroupCount, configuredDirFileCount := verifyConfiguredDirectorySource(ctx)
 
@@ -267,6 +273,8 @@ func main() {
 		"production_send_enabled": productionSendEnabled,
 		"send_file_preview_tool_present": sendFilePreviewOK,
 		"send_file_production_enabled": sendFileProductionEnabled,
+		"send_file_duplicate_detected": sendFileDuplicateDetected,
+		"send_file_conflict_blocked": sendFileConflictBlocked,
 		"msglib_configured": false,
 	}
 	encoded, _ := json.Marshal(result)
@@ -586,9 +594,9 @@ func verifySendMessagePreview(ctx context.Context, session *mcp.ClientSession) (
 	return true, false
 }
 
-func verifySendFilePreview(ctx context.Context, session *mcp.ClientSession, filePath string) (bool, bool) {
+func verifySendFilePreview(ctx context.Context, session *mcp.ClientSession, filePath string) (bool, bool, bool, bool) {
 	fileHash := sha256FileHexForHarness(filePath)
-	callResult, err := session.CallTool(ctx, &mcp.CallToolParams{Name: "isphere_send_file", Arguments: map[string]any{
+	previewArgs := map[string]any{
 		"target_type": "direct",
 		"target_id": "sender@imopenfire1-lanzhou",
 		"file_path": filePath,
@@ -596,7 +604,8 @@ func verifySendFilePreview(ctx context.Context, session *mcp.ClientSession, file
 		"idempotency_key": "verify-file-preview-idempotency-key",
 		"execution_mode": "preview",
 		"preview": true,
-	}})
+	}
+	callResult, err := session.CallTool(ctx, &mcp.CallToolParams{Name: "isphere_send_file", Arguments: previewArgs})
 	if err != nil {
 		fail("tools/call isphere_send_file preview", err)
 	}
@@ -619,6 +628,62 @@ func verifySendFilePreview(ctx context.Context, session *mcp.ClientSession, file
 		fail("tools/call isphere_send_file preview", fmt.Errorf("unexpected send-file side effects: %s", encoded))
 	}
 
+	duplicateResult, err := session.CallTool(ctx, &mcp.CallToolParams{Name: "isphere_send_file", Arguments: previewArgs})
+	if err != nil {
+		fail("tools/call isphere_send_file duplicate", err)
+	}
+	if duplicateResult.IsError {
+		fail("tools/call isphere_send_file duplicate", fmt.Errorf("tool returned isError=true: %#v", duplicateResult.Content))
+	}
+	var duplicatePayload map[string]any
+	duplicateEncoded, _ := json.Marshal(duplicateResult.StructuredContent)
+	if err := json.Unmarshal(duplicateEncoded, &duplicatePayload); err != nil {
+		fail("tools/call isphere_send_file duplicate", fmt.Errorf("decode structuredContent %s: %w", duplicateEncoded, err))
+	}
+	duplicateIdempotency, ok := duplicatePayload["idempotency"].(map[string]any)
+	if !ok || duplicatePayload["ok"] != true || duplicatePayload["send_status"] != "planned" || duplicatePayload["real_send_attempted"] != false || duplicateIdempotency["duplicate_detected"] != true || duplicateIdempotency["conflict_detected"] != false {
+		fail("tools/call isphere_send_file duplicate", fmt.Errorf("duplicate idempotency mismatch: %s", duplicateEncoded))
+	}
+
+	conflictPath := filepath.Join(filepath.Dir(filePath), "redacted-conflict.txt")
+	if err := os.WriteFile(conflictPath, []byte("world"), 0o600); err != nil {
+		fail("tools/call isphere_send_file conflict_fixture", err)
+	}
+	conflictKey := "verify-file-conflict-idempotency-key"
+	if _, err := session.CallTool(ctx, &mcp.CallToolParams{Name: "isphere_send_file", Arguments: map[string]any{
+		"target_type": "direct",
+		"target_id": "sender@imopenfire1-lanzhou",
+		"file_path": filePath,
+		"file_sha256": fileHash,
+		"idempotency_key": conflictKey,
+		"execution_mode": "preview",
+	}}); err != nil {
+		fail("tools/call isphere_send_file conflict_first", err)
+	}
+	conflictResult, err := session.CallTool(ctx, &mcp.CallToolParams{Name: "isphere_send_file", Arguments: map[string]any{
+		"target_type": "direct",
+		"target_id": "sender@imopenfire1-lanzhou",
+		"file_path": conflictPath,
+		"file_sha256": sha256FileHexForHarness(conflictPath),
+		"idempotency_key": conflictKey,
+		"execution_mode": "preview",
+	}})
+	if err != nil {
+		fail("tools/call isphere_send_file conflict", err)
+	}
+	if conflictResult.IsError {
+		fail("tools/call isphere_send_file conflict", fmt.Errorf("tool returned isError=true: %#v", conflictResult.Content))
+	}
+	var conflictPayload map[string]any
+	conflictEncoded, _ := json.Marshal(conflictResult.StructuredContent)
+	if err := json.Unmarshal(conflictEncoded, &conflictPayload); err != nil {
+		fail("tools/call isphere_send_file conflict", fmt.Errorf("decode structuredContent %s: %w", conflictEncoded, err))
+	}
+	conflictIdempotency, ok := conflictPayload["idempotency"].(map[string]any)
+	if !ok || conflictPayload["ok"] != false || conflictPayload["send_status"] != "blocked" || conflictPayload["real_send_attempted"] != false || conflictIdempotency["duplicate_detected"] != false || conflictIdempotency["conflict_detected"] != true {
+		fail("tools/call isphere_send_file conflict", fmt.Errorf("conflict idempotency mismatch: %s", conflictEncoded))
+	}
+
 	productionResult, err := session.CallTool(ctx, &mcp.CallToolParams{Name: "isphere_send_file", Arguments: map[string]any{
 		"target_type": "direct",
 		"target_id": "sender@imopenfire1-lanzhou",
@@ -645,7 +710,7 @@ func verifySendFilePreview(ctx context.Context, session *mcp.ClientSession, file
 	if !ok || productionSideEffects["sent_file"] != false || productionSideEffects["uploaded_file"] != false || productionSideEffects["captured_network"] != false {
 		fail("tools/call isphere_send_file production_blocked", fmt.Errorf("unexpected production file side effects: %s", productionEncoded))
 	}
-	return true, false
+	return true, false, true, true
 }
 
 func verifySearchContacts(ctx context.Context, session *mcp.ClientSession, query string, step string, wantCount int) int {
@@ -856,6 +921,8 @@ func fail(step string, err error) {
     Assert-True ($script:harnessJson.production_send_enabled -eq $false) "SDK harness production_send_enabled mismatch: $($script:harnessJson.production_send_enabled)"
     Assert-True ($script:harnessJson.send_file_preview_tool_present -eq $true) "SDK harness send_file_preview_tool_present mismatch: $($script:harnessJson.send_file_preview_tool_present)"
     Assert-True ($script:harnessJson.send_file_production_enabled -eq $false) "SDK harness send_file_production_enabled mismatch: $($script:harnessJson.send_file_production_enabled)"
+    Assert-True ($script:harnessJson.send_file_duplicate_detected -eq $true) "SDK harness send_file_duplicate_detected mismatch: $($script:harnessJson.send_file_duplicate_detected)"
+    Assert-True ($script:harnessJson.send_file_conflict_blocked -eq $true) "SDK harness send_file_conflict_blocked mismatch: $($script:harnessJson.send_file_conflict_blocked)"
 
     [ordered]@{
         ok = $true
@@ -880,6 +947,8 @@ func fail(step string, err error) {
         production_send_enabled = $script:harnessJson.production_send_enabled
         send_file_preview_tool_present = $script:harnessJson.send_file_preview_tool_present
         send_file_production_enabled = $script:harnessJson.send_file_production_enabled
+        send_file_duplicate_detected = $script:harnessJson.send_file_duplicate_detected
+        send_file_conflict_blocked = $script:harnessJson.send_file_conflict_blocked
         packet_log_file_configured = $script:harnessJson.packet_log_file_configured
         packet_log_dir_configured = $script:harnessJson.packet_log_dir_configured
         python_runtime_required = $false