diff --git a/docs/release-control/v6/internal/subsystems/agent-lifecycle.md b/docs/release-control/v6/internal/subsystems/agent-lifecycle.md
index 23a61ce22..a3903ee8a 100644
--- a/docs/release-control/v6/internal/subsystems/agent-lifecycle.md
+++ b/docs/release-control/v6/internal/subsystems/agent-lifecycle.md
@@ -15,6 +15,11 @@
 
 ## Purpose
 
+First-run security setup persists the canonical authentication environment file
+before activating runtime credentials for every deployment shape. A systemd
+override may additionally bind service startup, but agent and server lifecycle
+must not depend on successful service-name detection to retain authentication.
+
 API-token names are operator-facing metadata, not agent identity. Renaming an
 existing token must preserve its ID, secret hash, scopes, expiry, and connected
 agent sessions, so lifecycle continuity never depends on a display label.
diff --git a/docs/release-control/v6/internal/subsystems/api-contracts.md b/docs/release-control/v6/internal/subsystems/api-contracts.md
index a12427d5e..52cda5f0a 100644
--- a/docs/release-control/v6/internal/subsystems/api-contracts.md
+++ b/docs/release-control/v6/internal/subsystems/api-contracts.md
@@ -20,6 +20,11 @@
 
 ## Purpose
 
+Successful quick security setup is durable before its success response is
+emitted: Pulse writes the canonical auth environment file, activates the same
+hashed credentials in memory, and for root systemd installs reports both the
+canonical `envFile` and the supplemental service override behavior.
+
 `PATCH /api/security/tokens/{id}` supports bounded metadata updates. A nonblank
 `name` renames the record without rotating its secret or changing scopes; a
 `scopes` update retains the existing delegation checks, and omitted fields are
diff --git a/docs/release-control/v6/internal/subsystems/storage-recovery.md b/docs/release-control/v6/internal/subsystems/storage-recovery.md
index 6208c1542..dbc0998c8 100644
--- a/docs/release-control/v6/internal/subsystems/storage-recovery.md
+++ b/docs/release-control/v6/internal/subsystems/storage-recovery.md
@@ -21,6 +21,11 @@
 
 ## Purpose
 
+First-run authentication always writes the canonical `.env` persistence
+artifact before runtime state changes. Root systemd installation may also
+write a service override, but reload, restart, backup, and recovery remain
+anchored to the canonical data/config-path file rather than service discovery.
+
 Token display-name changes use the existing API-token persistence boundary.
 The in-memory record must roll back if persistence fails, while the token ID,
 secret hash, scopes, and expiry remain intact so restart and restore preserve
diff --git a/internal/api/contract_test.go b/internal/api/contract_test.go
index 0c9349569..e34209f8e 100644
--- a/internal/api/contract_test.go
+++ b/internal/api/contract_test.go
@@ -10590,6 +10590,54 @@ func TestContract_QuickSecuritySetupBootstrapRetrievalGuidance(t *testing.T) {
 	}
 }
 
+func TestContract_QuickSecuritySetupPersistsCanonicalAuthEnvironment(t *testing.T) {
+	resetPersistentAuthStoresForTests()
+	t.Cleanup(resetPersistentAuthStoresForTests)
+
+	tempDir := t.TempDir()
+	cfg := &config.Config{
+		DataPath:   tempDir,
+		ConfigPath: tempDir,
+	}
+	router := &Router{
+		config:      cfg,
+		persistence: config.NewConfigPersistence(cfg.DataPath),
+	}
+	router.initializeBootstrapToken()
+	InitPersistentAuthStores(tempDir)
+
+	token, _, _, err := loadOrCreateBootstrapToken(tempDir)
+	if err != nil {
+		t.Fatalf("loadOrCreateBootstrapToken: %v", err)
+	}
+	body := `{"username":"canonical-admin","password":"StrongPass!1","apiToken":"` + strings.Repeat("ac", 32) + `"}`
+	req := httptest.NewRequest(http.MethodPost, "/api/security/quick-setup", strings.NewReader(body))
+	req.RemoteAddr = "127.0.0.1:54321"
+	req.Header.Set(bootstrapTokenHeader, token)
+	rec := httptest.NewRecorder()
+
+	authLimiter.Reset("127.0.0.1")
+	handleQuickSecuritySetupFixed(router)(rec, req)
+	if rec.Code != http.StatusOK {
+		t.Fatalf("quick setup status = %d, want 200 (%s)", rec.Code, rec.Body.String())
+	}
+
+	authEnv, err := os.ReadFile(resolveAuthEnvPath(cfg.ConfigPath))
+	if err != nil {
+		t.Fatalf("read canonical auth environment: %v", err)
+	}
+	authText := string(authEnv)
+	if !strings.Contains(authText, "PULSE_AUTH_USER='canonical-admin'\n") {
+		t.Fatalf("canonical auth environment missing username")
+	}
+	if !strings.Contains(authText, "PULSE_AUTH_PASS='$2") {
+		t.Fatalf("canonical auth environment missing password hash")
+	}
+	if strings.Contains(authText, "StrongPass!1") {
+		t.Fatal("canonical auth environment stored the plaintext password")
+	}
+}
+
 // A valid bootstrap token authorizes quick setup from any origin — the token
 // is the security boundary, and it's only readable by callers with filesystem
 // access to the Pulse data directory. The loopback-only path remains for the
diff --git a/internal/api/security_setup_fix.go b/internal/api/security_setup_fix.go
index 4737f56f2..1b26dc2f1 100644
--- a/internal/api/security_setup_fix.go
+++ b/internal/api/security_setup_fix.go
@@ -484,6 +484,17 @@ func handleQuickSecuritySetupFixed(r *Router) http.HandlerFunc {
 		}
 		setAPITokenOwnerUserID(tokenRecord, setupRequest.Username)
 
+		// Persist the canonical auth file for every deployment type before
+		// updating runtime state. Systemd root installs also write an override
+		// below, but the canonical file keeps config reloads and recovery
+		// independent of service-name detection.
+		envPath, err := writeAuthEnvFile(r.config.ConfigPath, r.config.DataPath, authEnvContent)
+		if err != nil {
+			log.Error().Err(err).Msg("Failed to write authentication configuration")
+			http.Error(w, "Failed to save security configuration", http.StatusInternalServerError)
+			return
+		}
+
 		if r.config.HasAPITokens() && r.config.AuthUser == "" && r.config.AuthPass == "" {
 			// We had API-only access before, now replacing with full security
 			log.Info().Msg("Replacing API-only token with new secure token")
@@ -545,13 +556,6 @@ func handleQuickSecuritySetupFixed(r *Router) http.HandlerFunc {
 
 		// Choose appropriate method based on environment
 		if isDocker {
-			envPath, err := writeAuthEnvFile(r.config.ConfigPath, r.config.DataPath, authEnvContent)
-			if err != nil {
-				log.Error().Err(err).Msg("Failed to write .env file in Docker")
-				http.Error(w, "Failed to save security configuration", http.StatusInternalServerError)
-				return
-			}
-
 			log.Info().Str("path", envPath).Msg("Docker security configuration saved")
 
 			response := map[string]interface{}{
@@ -571,13 +575,6 @@ func handleQuickSecuritySetupFixed(r *Router) http.HandlerFunc {
 			// Systemd but not root (ProxmoxVE script scenario)
 			// Don't attempt sudo, just save config and provide instructions
 
-			envPath, err := writeAuthEnvFile(r.config.ConfigPath, r.config.DataPath, authEnvContent)
-			if err != nil {
-				log.Error().Err(err).Msg("Failed to write .env file")
-				http.Error(w, "Failed to save security configuration", http.StatusInternalServerError)
-				return
-			}
-
 			// Create response - security is active immediately
 			response := map[string]interface{}{
 				"success":               true,
@@ -629,11 +626,12 @@ func handleQuickSecuritySetupFixed(r *Router) http.HandlerFunc {
 				"success":               true,
 				"method":                "systemd-root",
 				"serviceName":           serviceName,
+				"envFile":               envPath,
 				"deploymentType":        updates.GetDeploymentType(),
 				"automatic":             true,
 				"requiresManualRestart": false,
 				"message":               "Security enabled immediately! Your settings are saved and active.",
-				"note":                  "Systemd override created for persistence across restarts.",
+				"note":                  "Authentication file and systemd override created for persistence across restarts.",
 			}
 
 			w.Header().Set("Content-Type", "application/json")
@@ -642,12 +640,6 @@ func handleQuickSecuritySetupFixed(r *Router) http.HandlerFunc {
 
 		} else {
 			// Manual installation or development
-			envPath, err := writeAuthEnvFile(r.config.ConfigPath, r.config.DataPath, authEnvContent)
-			if err != nil {
-				log.Error().Err(err).Msg("Failed to write .env file")
-				// Still return success with manual instructions
-			}
-
 			// Get deployment type for restart instructions
 			deploymentType := updates.GetDeploymentType()
 
diff --git a/internal/api/security_setup_fix_test.go b/internal/api/security_setup_fix_test.go
index c32fe659e..071c6d7d1 100644
--- a/internal/api/security_setup_fix_test.go
+++ b/internal/api/security_setup_fix_test.go
@@ -147,6 +147,18 @@ func TestQuickSecuritySetupRequiresBootstrapToken(t *testing.T) {
 	if router.bootstrapTokenHash != "" {
 		t.Fatalf("expected bootstrap token hash to be cleared after successful setup")
 	}
+
+	authEnv, err := os.ReadFile(resolveAuthEnvPath(cfg.ConfigPath))
+	if err != nil {
+		t.Fatalf("read persisted authentication configuration: %v", err)
+	}
+	authEnvText := string(authEnv)
+	if !strings.Contains(authEnvText, "PULSE_AUTH_USER='bootstrap'\n") {
+		t.Fatalf("persisted authentication configuration missing username:\n%s", authEnvText)
+	}
+	if !strings.Contains(authEnvText, "PULSE_AUTH_PASS='$2") {
+		t.Fatalf("persisted authentication configuration missing password hash:\n%s", authEnvText)
+	}
 }
 
 func TestQuickSecuritySetupRejectsUnsafeUsernamesBeforeStateChanges(t *testing.T) {