diff --git a/backend/src/app.ts b/backend/src/app.ts
index 9b5d935f..3aa448b1 100644
--- a/backend/src/app.ts
+++ b/backend/src/app.ts
@@ -15,6 +15,7 @@ import { settingsRoutes, effectiveSettings } from "./routes/settings.js";
 import { createPiModelLister } from "./pi/list-models.js";
 import { loadSettings, type Settings } from "./settings/settings-store.js";
 import { ReadinessManager } from "./runtime/readiness-manager.js";
+import { createMaintenanceGate } from "./runtime/maintenance-gate.js";
 import { WorkspaceRegistry } from "./workspaces/registry.js";
 import { createProductionWorkspaceDiagnoser } from "./workspaces/diagnostics.js";
 import { workspaceRoutes, type WorkspaceDiagnoser } from "./routes/workspaces.js";
@@ -32,6 +33,8 @@ export interface BuildAppDeps {
   workspaceRegistry?: WorkspaceRegistry;
   workspaceDiagnoser?: WorkspaceDiagnoser;
   workspaceRuntimeSupport?: (workspace: WorkspaceDescriptor) => boolean;
+  /** Returns true while a host maintenance transaction is preventing new runtimes. */
+  maintenanceGate?: () => boolean;
 }
 
 export function buildApp(config: AppConfig, deps?: BuildAppDeps): FastifyInstance {
@@ -99,6 +102,7 @@ export function buildApp(config: AppConfig, deps?: BuildAppDeps): FastifyInstanc
     dwhPrecheck: config.dwhPrecheck,
     legacyWorkspaceMode: config.legacyWorkspaceMode,
     workspaceRuntimeSupport,
+    maintenanceGate: deps?.maintenanceGate ?? createMaintenanceGate(config.maintenanceFile),
   });
   sqlRoutes(app, { tht: tht as ThtRunner, getSettings });
   metaRoutes(app, { harnessDir: config.harnessDir, listModels });
diff --git a/backend/src/config.ts b/backend/src/config.ts
index 4a663c25..b7f87ec7 100644
--- a/backend/src/config.ts
+++ b/backend/src/config.ts
@@ -12,6 +12,7 @@ export interface AppConfig {
   defaults: { provider?: string; model?: string; thinking?: string };
   maxPiProcesses: number;
   settingsFile: string;
+  maintenanceFile: string;
   dataRoot?: string;
   ollamaEnsureTimeoutMs: number;
   secretsFile?: string;
@@ -206,6 +207,7 @@ export function loadConfig(env: Record<string, string | undefined>): AppConfig {
     defaults: { provider: env.PI_PROVIDER, model: env.PI_MODEL, thinking: env.PI_THINKING },
     maxPiProcesses: Number(env.MAX_PI_PROCESSES ?? 4),
     settingsFile: env.SETTINGS_FILE ?? "data/settings.json",
+    maintenanceFile: env.THT_MAINTENANCE_FILE ?? "data/maintenance.json",
     dataRoot: env.THT_DATA_ROOT,
     ollamaEnsureTimeoutMs: Number(env.OLLAMA_ENSURE_TIMEOUT_MS ?? 60000),
     secretsFile,
diff --git a/backend/src/routes/sessions.ts b/backend/src/routes/sessions.ts
index 136af41e..e8086c47 100644
--- a/backend/src/routes/sessions.ts
+++ b/backend/src/routes/sessions.ts
@@ -37,6 +37,8 @@ export function sessionRoutes(
     legacyWorkspaceMode?: boolean;
     /** Fail-closed installation/runtime transport capability check. */
     workspaceRuntimeSupport: (workspace: WorkspaceDescriptor) => boolean;
+    /** Host-controlled admission guard. Existing runtimes deliberately continue. */
+    maintenanceGate: () => boolean;
   },
 ) {
   const lifecycleTails = new Map<string, Promise<void>>();
@@ -75,6 +77,11 @@ export function sessionRoutes(
     return typeof runner.withPrincipal === "function" ? runner.withPrincipal(principal) : runner;
   };
 
+  const maintenanceReply = (reply: any) => reply.code(503).send({
+    code: "maintenance",
+    error: "Session admission is temporarily paused for maintenance. Try again shortly.",
+  });
+
   /** Include retained historical descriptors so removed workspaces remain resumable. */
   const sessionRevisions = async () => {
     const registry = d.workspaceRegistry as Partial<WorkspaceRegistry>;
@@ -272,6 +279,7 @@ export function sessionRoutes(
   });
 
   app.post("/sessions", async (req, reply) => {
+    if (d.maintenanceGate()) return maintenanceReply(reply);
     const b = req.body as {
       question: string; name?: string; workspace?: string; workspaceId?: string;
       provider?: string; model?: string; thinking?: string;
@@ -502,6 +510,7 @@ export function sessionRoutes(
     return reply.code(204).send();
   });
   app.post("/sessions/:id/resume", async (req, reply) => {
+    if (d.maintenanceGate()) return maintenanceReply(reply);
     const id = (req.params as any).id;
     const principal = getPrincipal(req);
     return withSessionLifecycle(id, async () => {
diff --git a/backend/src/runtime/maintenance-gate.ts b/backend/src/runtime/maintenance-gate.ts
new file mode 100644
index 00000000..2fa02fa2
--- /dev/null
+++ b/backend/src/runtime/maintenance-gate.ts
@@ -0,0 +1,10 @@
+import { existsSync } from "node:fs";
+
+/**
+ * A host-side lifecycle transaction creates this marker before it checks for active sessions.
+ * The marker is intentionally only an admission gate: it must never terminate existing Pi
+ * processes or make their in-flight work unavailable.
+ */
+export function createMaintenanceGate(markerFile: string): () => boolean {
+  return () => existsSync(markerFile);
+}
diff --git a/backend/src/settings/settings-cli.ts b/backend/src/settings/settings-cli.ts
new file mode 100644
index 00000000..87598732
--- /dev/null
+++ b/backend/src/settings/settings-cli.ts
@@ -0,0 +1,30 @@
+/* Core-side, non-interactive installation-default writer used only through compose exec.
+ * It accepts no credentials and writes the same SETTINGS_FILE consumed by session creation. */
+import { loadConfig } from "../config.js";
+import { loadSettings, saveSettings, type Settings } from "./settings-store.js";
+
+const choice = /^[A-Za-z0-9][A-Za-z0-9._/-]{0,127}$/;
+
+function value(args: string[], flag: string): string {
+  const at = args.indexOf(flag);
+  if (at < 0 || at + 1 >= args.length || args.filter((part) => part === flag).length !== 1) {
+    throw new Error(`missing ${flag}`);
+  }
+  return args[at + 1];
+}
+
+try {
+  const args = process.argv.slice(2);
+  if (args.length !== 6) throw new Error("only provider, model, and thinking may be configured");
+  const provider = value(args, "--provider");
+  const model = value(args, "--model");
+  const thinking = value(args, "--thinking");
+  if (!choice.test(provider) || !choice.test(model)) throw new Error("invalid provider or model");
+  if (!["low", "medium", "high"].includes(thinking)) throw new Error("invalid thinking level");
+  const cfg = loadConfig(process.env);
+  const next: Settings = { ...loadSettings(cfg), provider, model, thinking };
+  saveSettings(cfg, next);
+} catch (error) {
+  process.stderr.write(`settings-cli: ${error instanceof Error ? error.message : "invalid configuration"}\n`);
+  process.exitCode = 2;
+}
diff --git a/backend/src/settings/settings-store.ts b/backend/src/settings/settings-store.ts
index e09d417e..ba880f0b 100644
--- a/backend/src/settings/settings-store.ts
+++ b/backend/src/settings/settings-store.ts
@@ -1,4 +1,4 @@
-import { mkdirSync, readFileSync, writeFileSync } from "node:fs";
+import { closeSync, fsyncSync, mkdirSync, openSync, readFileSync, renameSync, writeFileSync } from "node:fs";
 import { dirname } from "node:path";
 import type { AppConfig } from "../config.js";
 
@@ -29,6 +29,21 @@ export function loadSettings(cfg: AppConfig): Settings {
 /** Persist settings (pretty JSON). Creates the parent directory if needed. */
 export function saveSettings(cfg: AppConfig, s: Settings): Settings {
   mkdirSync(dirname(cfg.settingsFile), { recursive: true });
-  writeFileSync(cfg.settingsFile, JSON.stringify(s, null, 2) + "\n", "utf8");
+  const directory = dirname(cfg.settingsFile);
+  const temporary = `${cfg.settingsFile}.tmp-${process.pid}-${Date.now()}`;
+  const fd = openSync(temporary, "wx", 0o600);
+  try {
+    writeFileSync(fd, JSON.stringify(s, null, 2) + "\n", "utf8");
+    fsyncSync(fd);
+  } finally {
+    closeSync(fd);
+  }
+  renameSync(temporary, cfg.settingsFile);
+  // The core image runs Linux. Keep the directory acknowledgement explicit there; Windows
+  // filesystem replacement semantics are delegated to the host-side Go durable writer.
+  if (process.platform !== "win32") {
+    const dirFd = openSync(directory, "r");
+    try { fsyncSync(dirFd); } finally { closeSync(dirFd); }
+  }
   return s;
 }
diff --git a/backend/test/routes-sessions.test.ts b/backend/test/routes-sessions.test.ts
index 5610c95d..3ad07a49 100644
--- a/backend/test/routes-sessions.test.ts
+++ b/backend/test/routes-sessions.test.ts
@@ -2,7 +2,8 @@ import { test, expect, vi } from "vitest";
 import { spawn as nodeSpawn } from "node:child_process";
 import path from "node:path";
 import os from "node:os";
-import { chmodSync, unlinkSync, writeFileSync } from "node:fs";
+import { chmodSync, unlinkSync, writeFileSync, mkdtempSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
 import { buildApp as buildRealApp } from "../src/app.js";
 import { loadConfig } from "../src/config.js";
 import { SseHub } from "../src/sse/sse-hub.js";
@@ -74,6 +75,43 @@ test("upstream requests without a principal fail before a Pi runtime can be crea
   expect(created).toBe(false);
 });
 
+test("maintenance rejects new and resumed session admission without interrupting running sessions", async () => {
+  const app = buildApp(loadConfig({ AUTH_MODE: "upstream", THT_HARNESS_DIR: "../harness" }), {
+    maintenanceGate: () => true,
+    thtRunner: { withPrincipal: () => ({ sessionShow: async () => ({ id: "open", status: "open" }) }) } as any,
+  });
+
+  const create = await app.inject({
+    method: "POST", url: "/sessions", headers: aliceHeaders, payload: { question: "q" },
+  });
+  const resume = await app.inject({ method: "POST", url: "/sessions/open/resume", headers: aliceHeaders });
+
+  expect(create.statusCode).toBe(503);
+  expect(resume.statusCode).toBe(503);
+  expect(create.json()).toEqual({
+    code: "maintenance", error: "Session admission is temporarily paused for maintenance. Try again shortly.",
+  });
+  expect(resume.json()).toEqual(create.json());
+});
+
+test("the on-disk maintenance marker gates admission in an upstream server profile", async () => {
+  const dir = mkdtempSync(path.join(tmpdir(), "tht-maintenance-"));
+  try {
+    const marker = path.join(dir, "maintenance.json");
+    writeFileSync(marker, '{"transaction":"test"}\n');
+    const app = buildApp(loadConfig({
+      AUTH_MODE: "upstream", THT_HARNESS_DIR: "../harness", THT_MAINTENANCE_FILE: marker,
+    }), { thtRunner: {} as any });
+    const response = await app.inject({
+      method: "POST", url: "/sessions", headers: aliceHeaders, payload: { question: "q" },
+    });
+    expect(response.statusCode).toBe(503);
+    expect(response.json().code).toBe("maintenance");
+  } finally {
+    rmSync(dir, { recursive: true, force: true });
+  }
+});
+
 test("session routes conceal foreign or missing sessions and deny SSE before it subscribes", async () => {
   let subscribed = false;
   const app = buildApp(loadConfig({ AUTH_MODE: "upstream", THT_HARNESS_DIR: "../harness" }), {
diff --git a/compose.yaml b/compose.yaml
index cf733104..3eec4da0 100644
--- a/compose.yaml
+++ b/compose.yaml
@@ -13,6 +13,7 @@ services:
       THT_BIN: /opt/venv/bin/tht
       THT_DATA_ROOT: /data
       SETTINGS_FILE: /data/settings/settings.json
+      THT_MAINTENANCE_FILE: /data/settings/maintenance.json
       THT_WORKSPACE_REGISTRY_ROOT: /data/workspace-registry
       THT_WORKSPACE_GIT_REMOTE: ${THT_WORKSPACE_GIT_REMOTE:?set THT_WORKSPACE_GIT_REMOTE}
       THT_WORKSPACE_GIT_BRANCH: ${THT_WORKSPACE_GIT_BRANCH:-main}
diff --git a/tools/thothctl/cmd/thothctl/main.go b/tools/thothctl/cmd/thothctl/main.go
index 3e5ed0fc..e2293da7 100644
--- a/tools/thothctl/cmd/thothctl/main.go
+++ b/tools/thothctl/cmd/thothctl/main.go
@@ -23,7 +23,7 @@ const usage = `Usage: thothctl --installation <absolute-path>/thothii-installati
 Commands:
   status              Show the Compose service state.
   doctor              Validate Docker, Compose, rendered configuration, line endings, volumes, and health.
-  logs [--follow]     Show sanitized service logs (the default is the latest 200 lines).
+  logs                Show the latest 200 sanitized service log lines.
   start               Start the installation in the background.
   stop                Stop the installation.
   update --check-only Validate the current installation without changing containers.
@@ -31,8 +31,8 @@ Commands:
   pi doctor           Check Pi preconditions without changing the installation.
   pi test             Run the temporary Pi/core smoke checks.
   pi check            Alias for pi test.
-  pi configure        Store non-secret Pi defaults (credentials stay in PI_AUTH_FILE).
-  pi update           Rebuild or pull a pinned Pi image (requires --yes).
+  pi configure        Apply non-secret provider/model/thinking defaults to core (credentials stay in PI_AUTH_FILE).
+  pi update           Rebuild or pull a pinned Pi image (--source build|pull and --yes required).
   pi rollback --yes   Restore the image recorded by the latest Pi update.
   pi logs             Show the latest sanitized core logs.
 `
@@ -169,10 +169,10 @@ func piCommand(ctx context.Context, installation config.Installation, runner com
 		if err != nil {
 			return commandUsageError(stderr, err.Error())
 		}
-		if err := pi.Configure(ctx, controlled, filepath.Join(installation.ProjectDirectory, ".thothctl", "pi-defaults.json"), defaults); err != nil {
+		if err := pi.Configure(ctx, controlled, defaults); err != nil {
 			return piFailure(stderr, err, secretValues)
 		}
-		fmt.Fprintln(stdout, "Pi defaults saved. Put credentials only in the configured PI_AUTH_FILE (mode 0600).")
+		fmt.Fprintln(stdout, "Pi defaults applied and read back. Put credentials only in PI_AUTH_FILE (/home/thoth/.pi/agent/auth.json, mode 0600); never pass credentials to thothctl.")
 		return 0
 	case "update":
 		request, err := parsePiUpdateArgs(args[1:], filepath.Join(installation.ProjectDirectory, ".thothctl", "update-state.json"))
@@ -219,20 +219,18 @@ func parsePiConfigureArgs(args []string) (pi.Defaults, error) {
 			value.Model = v
 		case "--thinking":
 			value.Thinking = v
-		case "--llm-url":
-			value.LLMURL = v
 		default:
 			return pi.Defaults{}, fmt.Errorf("unknown pi configure option %q", key)
 		}
 	}
-	if value.Provider == "" || value.Model == "" || value.Thinking == "" || value.LLMURL == "" {
-		return pi.Defaults{}, errors.New("pi configure requires --provider --model --thinking --llm-url")
+	if value.Provider == "" || value.Model == "" || value.Thinking == "" {
+		return pi.Defaults{}, errors.New("pi configure requires --provider --model --thinking; THT_LLM_URL stays Compose-managed")
 	}
 	return value, nil
 }
 
 func parsePiUpdateArgs(args []string, statePath string) (pi.Request, error) {
-	request := pi.Request{StatePath: statePath, Source: pi.BuildSource}
+	request := pi.Request{StatePath: statePath}
 	for len(args) > 0 {
 		switch args[0] {
 		case "--version":
@@ -264,15 +262,17 @@ func parsePiUpdateArgs(args []string, statePath string) (pi.Request, error) {
 			return pi.Request{}, fmt.Errorf("unknown pi update option %q", args[0])
 		}
 	}
-	if request.Version == "" {
-		return pi.Request{}, errors.New("pi update requires --version <pinned-version>")
-	}
+	if request.Version == "" { return pi.Request{}, errors.New("pi update requires --version <pinned-version>") }
+	if request.Source == "" { return pi.Request{}, errors.New("pi update requires explicit --source build or pull") }
+	if request.Source != pi.BuildSource && request.Source != pi.PullSource { return pi.Request{}, errors.New("--source requires build or pull") }
+	if request.Source == pi.PullSource && request.Image == "" { return pi.Request{}, errors.New("--source pull requires --image <digest-reference>") }
+	if request.Source == pi.BuildSource && request.Image != "" { return pi.Request{}, errors.New("--image is valid only with --source pull") }
 	return request, nil
 }
 
 func piFailure(stderr io.Writer, err error, secretValues []string) int {
 	code := 1
-	if errors.Is(err, pi.ErrConfirmationRequired) || errors.Is(err, pi.ErrActiveSessions) || errors.Is(err, pi.ErrInterruptedUpdate) {
+	if errors.Is(err, pi.ErrConfirmationRequired) || errors.Is(err, pi.ErrInvalidRequest) {
 		code = 2
 	}
 	var childExit interface{ ExitCode() int }
diff --git a/tools/thothctl/cmd/thothctl/main_test.go b/tools/thothctl/cmd/thothctl/main_test.go
index 64e26d16..3f12f688 100644
--- a/tools/thothctl/cmd/thothctl/main_test.go
+++ b/tools/thothctl/cmd/thothctl/main_test.go
@@ -368,7 +368,7 @@ func TestRunPiUpdateRequiresExplicitConfirmationWithoutInvokingDocker(t *testing
 	fixture.setEnvironment(t)
 
 	var stdout, stderr bytes.Buffer
-	exitCode := run(context.Background(), []string{"--installation", fixture.installationPath, "pi", "update", "--version", "0.81.0"}, &stdout, &stderr)
+	exitCode := run(context.Background(), []string{"--installation", fixture.installationPath, "pi", "update", "--version", "0.81.0", "--source", "build"}, &stdout, &stderr)
 
 	if exitCode != 2 {
 		t.Errorf("run() exit code = %d, want 2", exitCode)
diff --git a/tools/thothctl/go.mod b/tools/thothctl/go.mod
index 72316e51..9c44d308 100644
--- a/tools/thothctl/go.mod
+++ b/tools/thothctl/go.mod
@@ -6,6 +6,9 @@ require gopkg.in/yaml.v3 v3.0.1
 
 require (
 	github.com/compose-spec/compose-go/v2 v2.14.0
+	github.com/distribution/reference v0.6.0
 	github.com/sirupsen/logrus v1.9.0
 	golang.org/x/sys v0.5.0
 )
+
+require github.com/opencontainers/go-digest v1.0.0 // indirect
diff --git a/tools/thothctl/go.sum b/tools/thothctl/go.sum
index 593ae01e..b2b7a409 100644
--- a/tools/thothctl/go.sum
+++ b/tools/thothctl/go.sum
@@ -3,8 +3,12 @@ github.com/compose-spec/compose-go/v2 v2.14.0/go.mod h1:ZU6zlcweCZKyiB7BVfCizQT9
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/distribution/reference v0.6.0 h1:0IXCQ5g4/QMHHkarYzh5l+u8T3t73zM5QvfrDyIgxBk=
+github.com/distribution/reference v0.6.0/go.mod h1:BbU0aIcezP1/5jX/8MP0YiH4SdvB5Y4f/wlDRiLyi3E=
 github.com/google/go-cmp v0.5.9 h1:O2Tfq5qg4qc4AmwVlvv0oLiVAGB7enBSJ2x2DqQFi38=
 github.com/google/go-cmp v0.5.9/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
+github.com/opencontainers/go-digest v1.0.0 h1:apOUWs51W5PlhuyGyz9FCeeBIOUDA/6nW8Oi/yOhh5U=
+github.com/opencontainers/go-digest v1.0.0/go.mod h1:0JzlMkj0TRzQZfJkVvzbP0HBR3IKzErnv2BNG4W4MAM=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/sirupsen/logrus v1.9.0 h1:trlNQbNUG3OdDrDil03MCb1H2o9nJ1x4/5LYw7byDE0=
diff --git a/tools/thothctl/internal/pi/commands.go b/tools/thothctl/internal/pi/commands.go
index 9f5b0a98..650c731e 100644
--- a/tools/thothctl/internal/pi/commands.go
+++ b/tools/thothctl/internal/pi/commands.go
@@ -7,9 +7,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"net/url"
-	"os"
-	"path/filepath"
 	"regexp"
 	"strings"
 
@@ -22,22 +19,29 @@ type Defaults struct {
 	Provider string `json:"provider"`
 	Model    string `json:"model"`
 	Thinking string `json:"thinking"`
-	LLMURL   string `json:"llm_url"`
 }
 
-// Configure validates and atomically stores only local non-secret Pi defaults.
-func Configure(ctx context.Context, runner Runner, path string, value Defaults) error {
+var internalIdentityHeaders = []string{
+	"-H", "x-thoth-principal-issuer: thothctl",
+	"-H", "x-thoth-principal-subject: thothctl-maintenance",
+	"-H", "x-thoth-principal-display-name: Thothctl maintenance",
+	"-H", "x-thoth-is-admin: 1",
+}
+
+// Configure changes the backend's real installation settings through a core-side helper. It
+// deliberately has no secret or endpoint input: external endpoints remain Compose-owned.
+func Configure(ctx context.Context, runner Runner, value Defaults) error {
 	if !choicePattern.MatchString(value.Provider) || !choicePattern.MatchString(value.Model) {
 		return errors.New("provider and model must be supported identifiers")
 	}
 	if value.Thinking != "low" && value.Thinking != "medium" && value.Thinking != "high" {
 		return errors.New("thinking must be low, medium, or high")
 	}
-	u, err := url.Parse(value.LLMURL)
-	if err != nil || (u.Scheme != "https" && u.Scheme != "http") || u.Host == "" || u.User != nil || u.RawQuery != "" || u.Fragment != "" {
-		return errors.New("LLM endpoint must be an http(s) URL without credentials, query, or fragment")
-	}
-	models, err := runCompose(ctx, runner, "exec", "-T", "core", "curl", "-fsS", "http://127.0.0.1:8787/models")
+	before, err := renderedCore(ctx, runner)
+	if err != nil { return err }
+	args := append([]string{"exec", "-T", "core", "curl", "-fsS"}, internalIdentityHeaders...)
+	args = append(args, "http://127.0.0.1:8787/models")
+	models, err := runCompose(ctx, runner, args...)
 	if err != nil {
 		return commandError("Pi options check", models, err)
 	}
@@ -59,39 +63,19 @@ func Configure(ctx context.Context, runner Runner, path string, value Defaults)
 	if !found {
 		return errors.New("provider/model is not in Pi options")
 	}
-	return writeJSON(path, value)
-}
-
-func writeJSON(path string, value any) error {
-	contents, err := json.MarshalIndent(value, "", "  ")
-	if err != nil {
-		return err
-	}
-	contents = append(contents, '\n')
-	if err = os.MkdirAll(filepath.Dir(path), 0o700); err != nil {
-		return errors.New("could not create Pi configuration directory")
-	}
-	temporary, err := os.CreateTemp(filepath.Dir(path), ".pi-defaults-*.tmp")
-	if err != nil {
-		return errors.New("could not write Pi configuration")
-	}
-	name := temporary.Name()
-	defer os.Remove(name)
-	if err = temporary.Chmod(0o600); err == nil {
-		_, err = temporary.Write(contents)
-	}
-	if err == nil {
-		err = temporary.Sync()
-	}
-	if closeErr := temporary.Close(); err == nil {
-		err = closeErr
-	}
-	if err == nil {
-		err = os.Rename(name, path)
-	}
-	if err != nil {
-		return errors.New("could not atomically write Pi configuration")
+	result, err := runCompose(ctx, runner, "exec", "-T", "core", "node", "/app/backend/dist/settings/settings-cli.js", "--provider", value.Provider, "--model", value.Model, "--thinking", value.Thinking)
+	if err != nil { return commandError("Pi installation settings write", result, err) }
+	settingsArgs := append([]string{"exec", "-T", "core", "curl", "-fsS"}, internalIdentityHeaders...)
+	settingsArgs = append(settingsArgs, "http://127.0.0.1:8787/settings")
+	settings, err := runCompose(ctx, runner, settingsArgs...)
+	if err != nil { return commandError("Pi installation settings read-back", settings, err) }
+	var saved Defaults
+	if json.Unmarshal([]byte(settings.Stdout), &saved) != nil || saved.Provider != value.Provider || saved.Model != value.Model || saved.Thinking != value.Thinking {
+		return errors.New("Pi installation settings read-back did not match requested provider, model, and thinking")
 	}
+	after, err := renderedCore(ctx, runner)
+	if err != nil { return err }
+	if before.ConfigurationSHA != after.ConfigurationSHA { return errors.New("external endpoint configuration changed while configuring Pi") }
 	return nil
 }
 
@@ -131,7 +115,7 @@ func Doctor(ctx context.Context, runner Runner) error {
 			return commandError("Pi preflight check", result, err)
 		}
 	}
-	return nil
+	return Test(ctx, runner)
 }
 
 // Test performs the pre-Task-8 composite smoke through core's private loopback endpoint.
@@ -140,7 +124,10 @@ func Test(ctx context.Context, runner Runner) error {
 		return err
 	}
 	for _, path := range []string{"health", "models", "settings"} {
-		result, err := runCompose(ctx, runner, "exec", "-T", "core", "curl", "-fsS", "http://127.0.0.1:8787/"+path)
+		args := []string{"exec", "-T", "core", "curl", "-fsS"}
+		if path != "health" { args = append(args, internalIdentityHeaders...) }
+		args = append(args, "http://127.0.0.1:8787/"+path)
+		result, err := runCompose(ctx, runner, args...)
 		if err != nil {
 			return commandError("Pi smoke check", result, err)
 		}
@@ -148,13 +135,28 @@ func Test(ctx context.Context, runner Runner) error {
 		if err := json.Unmarshal([]byte(result.Stdout), &payload); err != nil {
 			return fmt.Errorf("Pi smoke check returned invalid %s response", path)
 		}
-		if _, ok := payload.(map[string]any); !ok {
+		object, ok := payload.(map[string]any)
+		if !ok {
 			return fmt.Errorf("Pi smoke check returned invalid %s response", path)
 		}
+		switch path {
+		case "health":
+			if object["status"] != "ok" { return errors.New("Pi smoke health response is not ready") }
+		case "models":
+			models, ok := object["models"].([]any)
+			if !ok || len(models) == 0 { return errors.New("Pi smoke models response is empty") }
+			valid := false
+			for _, item := range models { if model, ok := item.(map[string]any); ok && stringField(model, "provider") != "" && stringField(model, "id") != "" { valid = true; break } }
+			if !valid { return errors.New("Pi smoke models response has no provider/model choices") }
+		case "settings":
+			if stringField(object, "provider") == "" || stringField(object, "model") == "" || stringField(object, "thinking") == "" { return errors.New("Pi smoke settings response is incomplete") }
+		}
 	}
 	return nil
 }
 
+func stringField(value map[string]any, key string) string { text, _ := value[key].(string); return strings.TrimSpace(text) }
+
 func renderedCore(ctx context.Context, runner Runner) (Image, error) {
 	result, err := runCompose(ctx, runner, "config", "--format", "json")
 	if err != nil {
diff --git a/tools/thothctl/internal/pi/commands_test.go b/tools/thothctl/internal/pi/commands_test.go
index 90e7ef04..45d99a81 100644
--- a/tools/thothctl/internal/pi/commands_test.go
+++ b/tools/thothctl/internal/pi/commands_test.go
@@ -2,7 +2,6 @@ package pi
 
 import (
 	"context"
-	"path/filepath"
 	"strings"
 	"testing"
 )
@@ -17,16 +16,17 @@ func TestDoctorRequiresExternalEndpointAuthPiStateAndHealth(t *testing.T) {
 	}
 }
 
-func TestConfigureValidatesBackendModelOptionsAndWritesNoSecrets(t *testing.T) {
+func TestConfigureValidatesBackendModelOptionsWritesRealCoreSettingsAndUsesUpstreamIdentity(t *testing.T) {
 	fake := newFakeRunner()
-	path := filepath.Join(t.TempDir(), "pi-defaults.json")
-	if err := Configure(context.Background(), fake, path, Defaults{Provider: "provider", Model: "model", Thinking: "medium", LLMURL: "https://llm.example.invalid"}); err != nil {
+	if err := Configure(context.Background(), fake, Defaults{Provider: "provider", Model: "model", Thinking: "medium"}); err != nil {
 		t.Fatal(err)
 	}
-	if got := string(readStateBytes(t, path)); strings.Contains(got, "secret") || !strings.Contains(got, "llm.example.invalid") {
-		t.Fatalf("defaults=%q", got)
+	assertCalled(t, fake.calls, "node /app/backend/dist/settings/settings-cli.js --provider provider --model model --thinking medium")
+	assertCalled(t, fake.calls, "x-thoth-principal-subject: thothctl-maintenance")
+	if got := strings.Join(fake.calls, "\n"); strings.Contains(got, "pi-defaults.json") || strings.Contains(got, "secret") {
+		t.Fatalf("commands=%q", got)
 	}
-	if err := Configure(context.Background(), fake, path, Defaults{Provider: "provider", Model: "unknown", Thinking: "medium", LLMURL: "https://llm.example.invalid"}); err == nil {
+	if err := Configure(context.Background(), fake, Defaults{Provider: "provider", Model: "unknown", Thinking: "medium"}); err == nil {
 		t.Fatal("expected unknown model rejection")
 	}
 }
diff --git a/tools/thothctl/internal/pi/durable_unix.go b/tools/thothctl/internal/pi/durable_unix.go
new file mode 100644
index 00000000..8f4c0d31
--- /dev/null
+++ b/tools/thothctl/internal/pi/durable_unix.go
@@ -0,0 +1,15 @@
+//go:build !windows
+
+package pi
+
+import "os"
+
+// durableReplace acknowledges both the data file and its directory entry. A successful return
+// is the strongest atomic replacement guarantee supported by Unix filesystems.
+func durableReplace(temporary, target, directory string) error {
+	if err := os.Rename(temporary, target); err != nil { return err }
+	dir, err := os.Open(directory)
+	if err != nil { return err }
+	defer dir.Close()
+	return dir.Sync()
+}
diff --git a/tools/thothctl/internal/pi/durable_windows.go b/tools/thothctl/internal/pi/durable_windows.go
new file mode 100644
index 00000000..cd664a3a
--- /dev/null
+++ b/tools/thothctl/internal/pi/durable_windows.go
@@ -0,0 +1,15 @@
+//go:build windows
+
+package pi
+
+import "golang.org/x/sys/windows"
+
+// MoveFileEx requests replacement and write-through on Windows. Directory fsync is not exposed
+// by the Windows API in the same form as Unix, so callers must not claim a stronger guarantee.
+func durableReplace(temporary, target, _ string) error {
+	from, err := windows.UTF16PtrFromString(temporary)
+	if err != nil { return err }
+	to, err := windows.UTF16PtrFromString(target)
+	if err != nil { return err }
+	return windows.MoveFileEx(from, to, windows.MOVEFILE_REPLACE_EXISTING|windows.MOVEFILE_WRITE_THROUGH)
+}
diff --git a/tools/thothctl/internal/pi/process_unix.go b/tools/thothctl/internal/pi/process_unix.go
new file mode 100644
index 00000000..cb158ea3
--- /dev/null
+++ b/tools/thothctl/internal/pi/process_unix.go
@@ -0,0 +1,16 @@
+//go:build !windows
+
+package pi
+
+import (
+	"errors"
+	"os"
+	"syscall"
+)
+
+func processAlive(pid int) bool {
+	process, err := os.FindProcess(pid)
+	if err != nil { return false }
+	err = process.Signal(syscall.Signal(0))
+	return err == nil || errors.Is(err, syscall.EPERM)
+}
diff --git a/tools/thothctl/internal/pi/process_windows.go b/tools/thothctl/internal/pi/process_windows.go
new file mode 100644
index 00000000..8af08940
--- /dev/null
+++ b/tools/thothctl/internal/pi/process_windows.go
@@ -0,0 +1,14 @@
+//go:build windows
+
+package pi
+
+import "golang.org/x/sys/windows"
+
+func processAlive(pid int) bool {
+	handle, err := windows.OpenProcess(windows.PROCESS_QUERY_LIMITED_INFORMATION, false, uint32(pid))
+	if err != nil { return err == windows.ERROR_ACCESS_DENIED }
+	defer windows.CloseHandle(handle)
+	var code uint32
+	if windows.GetExitCodeProcess(handle, &code) != nil { return true }
+	return code == 259 // STILL_ACTIVE
+}
diff --git a/tools/thothctl/internal/pi/state.go b/tools/thothctl/internal/pi/state.go
index 7931c702..3bf89c3c 100644
--- a/tools/thothctl/internal/pi/state.go
+++ b/tools/thothctl/internal/pi/state.go
@@ -5,13 +5,15 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"crypto/sha256"
 	"os"
 	"path/filepath"
-	"runtime"
+	"sort"
+	"strings"
 	"time"
 )
 
-const stateFileVersion = 1
+const stateFileVersion = 2
 
 // Phase describes the durable point reached by a Pi update.
 type Phase string
@@ -32,6 +34,7 @@ type Image struct {
 	Reference        string   `json:"reference"`
 	Volumes          []string `json:"volumes"`
 	Mounts           []Mount  `json:"mounts"`
+	MountFingerprint string   `json:"mount_fingerprint"`
 	ConfigurationSHA string   `json:"configuration_sha256,omitempty"`
 }
 
@@ -39,9 +42,10 @@ type Image struct {
 type Mount struct {
 	Type        string `json:"type"`
 	Name        string `json:"name,omitempty"`
-	Source      string `json:"source"`
+	SourceSHA256 string `json:"source_sha256"`
 	Destination string `json:"destination"`
 	RW          bool   `json:"rw"`
+	Options     string `json:"options,omitempty"`
 }
 
 // Target records the immutable input selected by the operator. Source is either build or a
@@ -72,14 +76,14 @@ func readState(path string) (State, error) {
 	if err := json.Unmarshal(contents, &state); err != nil {
 		return State{}, errors.New("update recovery state is invalid")
 	}
-	if state.Version != stateFileVersion || state.Previous.ID == "" || state.Previous.Reference == "" {
+	if state.Version != stateFileVersion || state.Previous.ID == "" || state.Previous.Reference == "" || state.Previous.MountFingerprint == "" {
 		return State{}, errors.New("update recovery state is incomplete")
 	}
 	return state, nil
 }
 
 func writeState(path string, state State) error {
-	if state.Previous.ID == "" || state.Previous.Reference == "" {
+	if state.Previous.ID == "" || state.Previous.Reference == "" || state.Previous.MountFingerprint == "" {
 		return errors.New("refusing to write incomplete update recovery state")
 	}
 	state.Version = stateFileVersion
@@ -89,45 +93,52 @@ func writeState(path string, state State) error {
 		return fmt.Errorf("encode update recovery state: %w", err)
 	}
 	contents = append(contents, '\n')
-	directory := filepath.Dir(path)
-	if err := os.MkdirAll(directory, 0o700); err != nil {
-		return errors.New("could not create update recovery directory")
-	}
-	temporary, err := os.CreateTemp(directory, ".update-state-*.tmp")
-	if err != nil {
-		return errors.New("could not write update recovery state")
-	}
-	temporaryName := temporary.Name()
-	defer os.Remove(temporaryName)
-	if err := temporary.Chmod(0o600); err != nil {
-		temporary.Close()
-		return errors.New("could not protect update recovery state")
-	}
-	if _, err := temporary.Write(contents); err != nil {
-		temporary.Close()
-		return errors.New("could not write update recovery state")
-	}
-	if err := temporary.Sync(); err != nil {
-		temporary.Close()
-		return errors.New("could not durably write update recovery state")
-	}
-	if err := temporary.Close(); err != nil {
-		return errors.New("could not write update recovery state")
-	}
-	if err := os.Rename(temporaryName, path); err != nil {
-		return errors.New("could not finalize update recovery state")
-	}
-	if runtime.GOOS != "windows" {
-		if directoryHandle, err := os.Open(directory); err == nil {
-			_ = directoryHandle.Sync()
-			_ = directoryHandle.Close()
-		}
+	if err := writeFileDurably(path, ".update-state-", contents); err != nil {
+		return fmt.Errorf("could not durably write update recovery state: %w", err)
 	}
 	return nil
 }
 
+func writeFileDurably(path, prefix string, contents []byte) error {
+	directory := filepath.Dir(path)
+	if err := os.MkdirAll(directory, 0o700); err != nil { return err }
+	temporary, err := os.CreateTemp(directory, prefix+"*.tmp")
+	if err != nil { return err }
+	temporaryName := temporary.Name()
+	defer os.Remove(temporaryName)
+	if err := temporary.Chmod(0o600); err != nil { temporary.Close(); return err }
+	if _, err := temporary.Write(contents); err != nil { temporary.Close(); return err }
+	if err := temporary.Sync(); err != nil { temporary.Close(); return err }
+	if err := temporary.Close(); err != nil { return err }
+	return durableReplace(temporaryName, path, directory)
+}
+
+func mountSourceHash(source string) string {
+	sum := sha256.Sum256([]byte(source))
+	return fmt.Sprintf("%x", sum[:])
+}
+
+func mountFingerprint(mounts []Mount) string {
+	values := make([]string, len(mounts))
+	for i, mount := range mounts {
+		values[i] = strings.Join([]string{mount.Type, mount.Name, mount.SourceSHA256, mount.Destination, fmt.Sprint(mount.RW), mount.Options}, "\x00")
+	}
+	sort.Strings(values)
+	sum := sha256.Sum256([]byte(strings.Join(values, "\n")))
+	return fmt.Sprintf("%x", sum[:])
+}
+
+type lockOwner struct {
+	PID         int       `json:"pid"`
+	Host        string    `json:"host"`
+	StartedAt   time.Time `json:"started_at"`
+	Transaction string    `json:"transaction"`
+}
+
 type updateLock struct{ path string }
 
+var ErrLockHeld = errors.New("another Pi update or rollback is already in progress")
+
 func acquireLock(statePath string) (*updateLock, error) {
 	if err := os.MkdirAll(filepath.Dir(statePath), 0o700); err != nil {
 		return nil, errors.New("could not create Pi update recovery directory")
@@ -135,10 +146,36 @@ func acquireLock(statePath string) (*updateLock, error) {
 	path := statePath + ".lock"
 	if err := os.Mkdir(path, 0o700); err != nil {
 		if errors.Is(err, os.ErrExist) {
-			return nil, errors.New("another Pi update or rollback is already in progress; recovery lock retained")
+			if reclaimDeadLocalLock(path) {
+				return acquireLock(statePath)
+			}
+			return nil, ErrLockHeld
 		}
 		return nil, errors.New("could not acquire Pi update lock")
 	}
+	host, err := os.Hostname()
+	if err != nil { _ = os.Remove(path); return nil, errors.New("could not identify Pi update lock owner") }
+	owner := lockOwner{PID: os.Getpid(), Host: host, StartedAt: time.Now().UTC(), Transaction: fmt.Sprintf("%d-%d", os.Getpid(), time.Now().UnixNano())}
+	contents, err := json.Marshal(owner)
+	if err != nil { _ = os.Remove(path); return nil, errors.New("could not record Pi update lock owner") }
+	if err := writeFileDurably(filepath.Join(path, "owner.json"), ".owner-", append(contents, '\n')); err != nil {
+		_ = os.Remove(path)
+		return nil, errors.New("could not record Pi update lock owner")
+	}
 	return &updateLock{path: path}, nil
 }
-func (l *updateLock) Release() { _ = os.Remove(l.path) }
+func (l *updateLock) Release() { _ = os.Remove(filepath.Join(l.path, "owner.json")); _ = os.Remove(l.path) }
+
+// reclaimDeadLocalLock is deliberately conservative: a malformed, remote, or merely old lock
+// is recovery-required. Only a process we can prove is gone on this machine is reclaimed.
+func reclaimDeadLocalLock(path string) bool {
+	contents, err := os.ReadFile(filepath.Join(path, "owner.json"))
+	if err != nil { return false }
+	var owner lockOwner
+	if json.Unmarshal(contents, &owner) != nil || owner.PID <= 0 || owner.Host == "" { return false }
+	host, err := os.Hostname()
+	if err != nil || owner.Host != host { return false }
+	if processAlive(owner.PID) { return false }
+	if err := os.Remove(filepath.Join(path, "owner.json")); err != nil { return false }
+	return os.Remove(path) == nil
+}
diff --git a/tools/thothctl/internal/pi/update.go b/tools/thothctl/internal/pi/update.go
index 42b293c6..f410c66b 100644
--- a/tools/thothctl/internal/pi/update.go
+++ b/tools/thothctl/internal/pi/update.go
@@ -10,14 +10,16 @@ import (
 	"sort"
 	"strings"
 	"time"
+
+	"github.com/distribution/reference"
 )
 
 var (
 	ErrConfirmationRequired = errors.New("update requires --yes after reviewing the planned Pi version")
 	ErrActiveSessions       = errors.New("active sessions must be drained before updating Pi; use --drain only after they are complete")
 	ErrInterruptedUpdate    = errors.New("a previous Pi update is incomplete; run pi rollback --yes before starting another update")
+	ErrInvalidRequest       = errors.New("invalid Pi lifecycle request")
 	versionPattern          = regexp.MustCompile(`^[0-9]+(?:\.[0-9]+){1,3}(?:[-+][0-9A-Za-z.-]+)?$`)
-	digestPattern           = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9._/:@-]*@sha256:[a-f0-9]{64}$`)
 )
 
 // Source chooses whether the candidate is built from this checkout or pulled from an immutable image.
@@ -45,7 +47,7 @@ type Result struct {
 }
 
 // Update performs a recoverable core-only Pi update using the default Compose command layout.
-func Update(ctx context.Context, runner Runner, request Request) (Result, error) {
+func Update(ctx context.Context, runner Runner, request Request) (result Result, retErr error) {
 	lock, err := acquireLock(request.StatePath)
 	if err != nil {
 		return Result{StatePath: request.StatePath}, err
@@ -58,42 +60,39 @@ func Update(ctx context.Context, runner Runner, request Request) (Result, error)
 		return Result{StatePath: request.StatePath}, ErrConfirmationRequired
 	}
 	if !versionPattern.MatchString(request.Version) {
-		return Result{StatePath: request.StatePath}, errors.New("Pi version must be an explicit pinned version")
-	}
-	if request.Source == "" {
-		request.Source = BuildSource
+		return Result{StatePath: request.StatePath}, fmt.Errorf("%w: Pi version must be an explicit pinned version", ErrInvalidRequest)
 	}
+	if request.Source == "" { return Result{StatePath: request.StatePath}, fmt.Errorf("%w: Pi update requires an explicit source: build or pull", ErrInvalidRequest) }
 	if request.Source != BuildSource && request.Source != PullSource {
-		return Result{StatePath: request.StatePath}, errors.New("Pi update source must be build or pull")
+		return Result{StatePath: request.StatePath}, fmt.Errorf("%w: Pi update source must be build or pull", ErrInvalidRequest)
 	}
-	if request.Source == PullSource && !digestPattern.MatchString(request.Image) {
-		return Result{StatePath: request.StatePath}, errors.New("pulled Pi image must use an immutable sha256 digest")
+	if request.Source == PullSource {
+		canonical, err := canonicalDigestReference(request.Image)
+		if err != nil { return Result{StatePath: request.StatePath}, fmt.Errorf("%w: %v", ErrInvalidRequest, err) }
+		request.Image = canonical
 	}
 	if old, err := readState(request.StatePath); err == nil && old.Phase != PhaseVerified && old.Phase != PhaseRolledBack && old.Phase != PhaseNoop {
 		return Result{StatePath: request.StatePath}, ErrInterruptedUpdate
 	} else if err != nil && !errors.Is(err, os.ErrNotExist) {
 		return Result{StatePath: request.StatePath}, err
 	}
+	if err := setMaintenance(ctx, runner, true); err != nil { return Result{StatePath: request.StatePath}, err }
+	defer func() {
+		if clearErr := setMaintenance(context.Background(), runner, false); clearErr != nil {
+			result = Result{Phase: PhaseFailed, StatePath: request.StatePath}
+			if retErr == nil { retErr = errors.New("maintenance admission gate could not be cleared: recovery required")
+			} else { retErr = fmt.Errorf("%w; maintenance admission gate could not be cleared: recovery required", retErr) }
+		}
+	}()
 
 	running, err := activeSessions(ctx, runner)
 	if err != nil {
 		return Result{StatePath: request.StatePath}, err
 	}
-	frontendStopped := false
 	if running {
 		if !request.Drain {
 			return Result{StatePath: request.StatePath}, ErrActiveSessions
 		}
-		stopped, stopErr := runCompose(ctx, runner, "stop", "frontend")
-		if stopErr != nil {
-			return Result{StatePath: request.StatePath}, commandError("frontend admission gate", stopped, stopErr)
-		}
-		frontendStopped = true
-		defer func() {
-			if frontendStopped {
-				_, _ = runCompose(context.Background(), runner, "up", "--detach", "frontend")
-			}
-		}()
 		for attempts := 0; attempts < 30; attempts++ {
 			running, err = activeSessions(ctx, runner)
 			if err != nil {
@@ -134,41 +133,34 @@ func Update(ctx context.Context, runner Runner, request Request) (Result, error)
 	}
 
 	state.Phase = PhaseBuilding
-	if err := writeState(request.StatePath, state); err != nil {
-		return Result{StatePath: request.StatePath}, err
-	}
+	if err := writeState(request.StatePath, state); err != nil { return Result{Phase: PhaseFailed, StatePath: request.StatePath}, err }
 	if err := prepareCandidate(ctx, runner, request, previous.Reference); err != nil {
-		state.Phase, state.Error = PhaseFailed, "candidate image preparation failed"
-		_ = writeState(request.StatePath, state)
-		return Result{Phase: PhaseFailed, StatePath: request.StatePath}, err
+		return compensate(ctx, runner, request.StatePath, state, err)
 	}
-	if frontendStopped {
+	if request.Drain {
 		running, err = activeSessions(ctx, runner)
 		if err != nil {
-			return Result{Phase: PhaseFailed, StatePath: request.StatePath}, err
+			return compensate(ctx, runner, request.StatePath, state, err)
 		}
 		if running {
-			state.Phase, state.Error = PhaseFailed, "new session admitted while draining"
-			_ = writeState(request.StatePath, state)
-			return Result{Phase: PhaseFailed, StatePath: request.StatePath}, ErrActiveSessions
+			return compensate(ctx, runner, request.StatePath, state, ErrActiveSessions)
 		}
 	}
 	if err := recreateCore(ctx, runner); err != nil {
-		state.Phase, state.Error = PhaseFailed, "core recreation failed"
-		_ = writeState(request.StatePath, state)
-		return Result{Phase: PhaseFailed, StatePath: request.StatePath}, err
+		return compensate(ctx, runner, request.StatePath, state, err)
 	}
 	state.Phase = PhaseRecreated
-	state.Candidate, _ = runningImage(ctx, runner, previous.Reference)
+	state.Candidate, err = runningImage(ctx, runner, previous.Reference)
+	if err != nil { return compensate(ctx, runner, request.StatePath, state, err) }
 	if err := writeState(request.StatePath, state); err != nil {
-		return Result{Phase: PhaseRecreated, StatePath: request.StatePath}, err
+		return compensate(ctx, runner, request.StatePath, state, err)
 	}
 	if err := verifyCandidate(ctx, runner, request.Version, previous); err != nil {
-		return rollbackAfterFailure(ctx, runner, request.StatePath, state, err)
+		return compensate(ctx, runner, request.StatePath, state, err)
 	}
 	state.Phase, state.Error = PhaseVerified, ""
 	if err := writeState(request.StatePath, state); err != nil {
-		return Result{Phase: PhaseVerified, StatePath: request.StatePath}, err
+		return compensate(ctx, runner, request.StatePath, state, err)
 	}
 	return Result{Phase: PhaseVerified, StatePath: request.StatePath}, nil
 }
@@ -189,25 +181,35 @@ func Rollback(ctx context.Context, runner Runner, statePath string, confirm bool
 	}
 	if err := restore(ctx, runner, state.Previous); err != nil {
 		state.Phase, state.Error = PhaseFailed, "rollback failed"
-		_ = writeState(statePath, state)
+		if writeErr := writeState(statePath, state); writeErr != nil { return Result{Phase: PhaseFailed, StatePath: statePath}, errors.New("rollback failed and recovery state could not be persisted") }
 		return Result{Phase: PhaseFailed, StatePath: statePath}, err
 	}
 	state.Phase, state.Error = PhaseRolledBack, ""
 	if err := writeState(statePath, state); err != nil {
-		return Result{Phase: PhaseRolledBack, StatePath: statePath}, err
+		return Result{Phase: PhaseFailed, StatePath: statePath}, errors.New("rollback restored the core but recovery state could not be persisted")
 	}
 	return Result{Phase: PhaseRolledBack, StatePath: statePath}, nil
 }
 
-func rollbackAfterFailure(ctx context.Context, runner Runner, statePath string, state State, cause error) (Result, error) {
+func compensate(ctx context.Context, runner Runner, statePath string, state State, cause error) (Result, error) {
 	if restoreErr := restore(ctx, runner, state.Previous); restoreErr != nil {
 		state.Phase, state.Error = PhaseFailed, "candidate verification and automatic rollback failed"
-		_ = writeState(statePath, state)
-		return Result{Phase: PhaseFailed, StatePath: statePath}, fmt.Errorf("candidate verification failed; automatic rollback also failed")
+		if writeErr := writeState(statePath, state); writeErr != nil {
+			return Result{Phase: PhaseFailed, StatePath: statePath}, fmt.Errorf("update failed and rollback proof failed; recovery state could not be persisted")
+		}
+		return Result{Phase: PhaseFailed, StatePath: statePath}, fmt.Errorf("update failed; automatic rollback also failed: recovery required")
 	}
 	state.Phase, state.Error = PhaseRolledBack, ""
-	_ = writeState(statePath, state)
-	return Result{Phase: PhaseRolledBack, StatePath: statePath}, fmt.Errorf("candidate verification failed; previous core image was restored")
+	if writeErr := writeState(statePath, state); writeErr != nil {
+		return Result{Phase: PhaseFailed, StatePath: statePath}, fmt.Errorf("previous core image was restored but recovery state write failed: recovery required")
+	}
+	return Result{Phase: PhaseRolledBack, StatePath: statePath}, fmt.Errorf("update failed; previous core image was restored")
+}
+
+func recordFailure(path string, state State, label string, cause error) error {
+	state.Phase, state.Error = PhaseFailed, label
+	if err := writeState(path, state); err != nil { return fmt.Errorf("%w; recovery state write failed", cause) }
+	return cause
 }
 
 func sourceValue(request Request) string {
@@ -217,6 +219,29 @@ func sourceValue(request Request) string {
 	return string(BuildSource)
 }
 
+func canonicalDigestReference(value string) (string, error) {
+	if strings.Contains(value, "://") || strings.ContainsAny(value, "?#") || strings.Contains(value, "@") && strings.Contains(strings.Split(value, "@")[0], ":") && strings.Contains(strings.Split(value, "@")[0], "//") {
+		return "", errors.New("pulled Pi image must be a credential-free canonical sha256 digest reference")
+	}
+	parsed, err := reference.ParseAnyReference(value)
+	if err != nil { return "", errors.New("pulled Pi image must be a valid canonical sha256 digest reference") }
+	canonical, ok := parsed.(reference.Canonical)
+	if !ok || canonical.Digest().Algorithm().String() != "sha256" || len(canonical.Digest().Encoded()) != 64 {
+		return "", errors.New("pulled Pi image must use an immutable sha256 digest")
+	}
+	return reference.FamiliarString(canonical), nil
+}
+
+// The command text is fixed; no operator input or host path is interpolated into the core shell.
+// The marker lives alongside SETTINGS_FILE's named/bind-mounted directory and is read by backend.
+func setMaintenance(ctx context.Context, runner Runner, enabled bool) error {
+	command := "mkdir -p /data/settings && : > /data/settings/maintenance.json && chmod 600 /data/settings/maintenance.json"
+	if !enabled { command = "rm -f /data/settings/maintenance.json" }
+	result, err := runCompose(ctx, runner, "exec", "-T", "core", "sh", "-ceu", command)
+	if err != nil { return commandError("maintenance admission gate", result, err) }
+	return nil
+}
+
 func activeSessions(ctx context.Context, runner Runner) (bool, error) {
 	result, err := runCompose(ctx, runner, "exec", "-T", "core", "tht", "session", "list", "--json")
 	if err != nil {
@@ -251,20 +276,27 @@ func runningImage(ctx context.Context, runner Runner, reference string) (Image,
 	if err != nil {
 		return Image{}, commandError("core volume check", mounts, err)
 	}
-	var contract []Mount
-	if err := json.Unmarshal([]byte(mounts.Stdout), &contract); err != nil {
+	var raw []struct {
+		Type string `json:"Type"`; Name string `json:"Name"`; Source string `json:"Source"`
+		Destination string `json:"Destination"`; RW bool `json:"RW"`; Mode string `json:"Mode"`
+		Propagation string `json:"Propagation"`; Driver string `json:"Driver"`
+	}
+	if err := json.Unmarshal([]byte(mounts.Stdout), &raw); err != nil {
 		return Image{}, errors.New("core returned invalid persistence mount data")
 	}
-	if len(contract) == 0 {
+	if len(raw) == 0 {
 		return Image{}, errors.New("core has no persistence mounts to preserve")
 	}
-	volumes := make([]string, 0, len(contract))
-	for _, mount := range contract {
+	contract := make([]Mount, 0, len(raw))
+	volumes := make([]string, 0, len(raw))
+	for _, mount := range raw {
+		if mount.Type == "" || mount.Source == "" || mount.Destination == "" { return Image{}, errors.New("core returned incomplete persistence mount data") }
+		contract = append(contract, Mount{Type: mount.Type, Name: mount.Name, SourceSHA256: mountSourceHash(mount.Source), Destination: mount.Destination, RW: mount.RW, Options: strings.Join([]string{mount.Mode, mount.Propagation, mount.Driver}, "\x00")})
 		if mount.Type == "volume" && mount.Name != "" {
 			volumes = append(volumes, mount.Name)
 		}
 	}
-	return Image{ID: strings.TrimSpace(image.Stdout), Reference: reference, Volumes: volumes, Mounts: contract}, nil
+	return Image{ID: strings.TrimSpace(image.Stdout), Reference: reference, Volumes: volumes, Mounts: contract, MountFingerprint: mountFingerprint(contract)}, nil
 }
 
 func prepareCandidate(ctx context.Context, runner Runner, request Request, reference string) error {
@@ -382,7 +414,7 @@ func sameMounts(left, right []Mount) bool {
 		return false
 	}
 	key := func(m Mount) string {
-		return m.Type + "\x00" + m.Name + "\x00" + m.Source + "\x00" + m.Destination + "\x00" + fmt.Sprint(m.RW)
+		return m.Type + "\x00" + m.Name + "\x00" + m.SourceSHA256 + "\x00" + m.Destination + "\x00" + fmt.Sprint(m.RW) + "\x00" + m.Options
 	}
 	a, b := make([]string, len(left)), make([]string, len(right))
 	for i := range left {
diff --git a/tools/thothctl/internal/pi/update_test.go b/tools/thothctl/internal/pi/update_test.go
index 054b1ee0..c7e9e901 100644
--- a/tools/thothctl/internal/pi/update_test.go
+++ b/tools/thothctl/internal/pi/update_test.go
@@ -3,6 +3,7 @@ package pi
 import (
 	"context"
 	"errors"
+	"fmt"
 	"io"
 	"os"
 	"path/filepath"
@@ -103,10 +104,9 @@ func TestUpdateDoesNotRecreateWhenPreflightOrBuildFails(t *testing.T) {
 			if err == nil {
 				t.Fatal("Update() error = nil, want failure")
 			}
-			if result.Phase == PhaseRolledBack {
-				t.Fatalf("pre-recreate failure unexpectedly rolled back: %+v", result)
-			}
-			assertNotCalled(t, fake.calls, "force-recreate")
+			if failure == "preflight" && result.Phase == PhaseRolledBack { t.Fatalf("preflight failure unexpectedly rolled back: %+v", result) }
+			if failure == "build" && result.Phase != PhaseRolledBack { t.Fatalf("candidate build failure must compensate: %+v", result) }
+			if failure == "preflight" { assertNotCalled(t, fake.calls, "force-recreate") }
 		})
 	}
 }
@@ -162,7 +162,7 @@ func TestRollbackRestoresInterruptedOrPreviouslyRecordedState(t *testing.T) {
 func TestUpdateRefusesToOverwriteInterruptedRecoveryState(t *testing.T) {
 	fake := newFakeRunner()
 	statePath := filepath.Join(t.TempDir(), "state.json")
-	writeStateForTest(t, statePath, State{Phase: PhaseRecreated, Previous: Image{ID: "sha256:old", Reference: "thothii-core:local", Volumes: []string{"settings"}}})
+	writeStateForTest(t, statePath, State{Phase: PhaseRecreated, Previous: Image{ID: "sha256:old", Reference: "thothii-core:local", Volumes: []string{"settings"}, MountFingerprint: "recorded"}})
 	_, err := Update(context.Background(), fake, Request{StatePath: statePath, Version: "0.81.0", Source: BuildSource, Confirm: true})
 	if !errors.Is(err, ErrInterruptedUpdate) {
 		t.Fatalf("Update() error = %v, want interrupted update error", err)
@@ -180,6 +180,17 @@ func TestRunningImageCapturesServerBindAndNamedMountIdentity(t *testing.T) {
 	if len(image.Mounts) != 3 || image.Mounts[0].Type != "bind" || image.Mounts[0].Destination != "/data" {
 		t.Fatalf("mounts = %#v", image.Mounts)
 	}
+	if strings.Contains(fmt.Sprint(image), "/srv/thothii") || image.Mounts[0].SourceSHA256 == "" || image.MountFingerprint == "" {
+		t.Fatalf("mount contract leaked a server source or lacks a safe fingerprint: %#v", image)
+	}
+}
+
+func TestCanonicalDigestReferenceRejectsCredentialsAndURLForms(t *testing.T) {
+	valid := "registry.example.invalid/thothii-core@sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+	if got, err := canonicalDigestReference(valid); err != nil || got != valid { t.Fatalf("canonicalDigestReference() = %q, %v", got, err) }
+	for _, invalid := range []string{"https://registry.example.invalid/a@sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa", "user:pass@registry.example/a@sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa", "registry.example/a@sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa?token=x"} {
+		if _, err := canonicalDigestReference(invalid); err == nil { t.Fatalf("accepted unsafe reference %q", invalid) }
+	}
 }
 
 type fakeRunner struct {
@@ -188,12 +199,13 @@ type fakeRunner struct {
 	version        string
 	activeSessions bool
 	built          bool
+	currentImage   string
 	volumes        []string
 	mountsJSON     string
 }
 
 func newFakeRunner() *fakeRunner {
-	return &fakeRunner{version: "0.80.3", volumes: []string{"settings", "pi-state", "sessions", "workspace-registry"}}
+	return &fakeRunner{version: "0.80.3", currentImage: "sha256:old", volumes: []string{"settings", "pi-state", "sessions", "workspace-registry"}}
 }
 
 func (f *fakeRunner) Run(_ context.Context, args []string, _ io.Reader) (compose.Result, error) {
@@ -201,6 +213,7 @@ func (f *fakeRunner) Run(_ context.Context, args []string, _ io.Reader) (compose
 	f.calls = append(f.calls, call)
 	if strings.Contains(call, "image tag sha256:old") {
 		f.fail = ""
+		f.currentImage = "sha256:old"
 	}
 	if f.fail == "preflight" && strings.Contains(call, "config --format json") {
 		return compose.Result{ExitCode: 1}, errors.New("provider token=secret")
@@ -214,7 +227,7 @@ func (f *fakeRunner) Run(_ context.Context, args []string, _ io.Reader) (compose
 	if f.fail == "version" && f.built && strings.Contains(call, "pi --version") && strings.Contains(call, "exec") {
 		return compose.Result{ExitCode: 1}, errors.New("version token=secret")
 	}
-	if f.fail == "smoke" && strings.Contains(call, "curl -fsS http://127.0.0.1:8787/models") {
+	if f.fail == "smoke" && f.built && strings.Contains(call, "127.0.0.1:8787/models") {
 		return compose.Result{ExitCode: 1}, errors.New("smoke token=secret")
 	}
 	switch {
@@ -223,7 +236,7 @@ func (f *fakeRunner) Run(_ context.Context, args []string, _ io.Reader) (compose
 	case strings.Contains(call, "ps -q core"):
 		return compose.Result{Stdout: "core-container\n"}, nil
 	case strings.Contains(call, "inspect --format {{.Image}}"):
-		return compose.Result{Stdout: "sha256:old\n"}, nil
+		return compose.Result{Stdout: f.currentImage + "\n"}, nil
 	case strings.Contains(call, "inspect --format {{json .Mounts}}"):
 		if f.mountsJSON != "" {
 			return compose.Result{Stdout: f.mountsJSON}, nil
@@ -238,6 +251,7 @@ func (f *fakeRunner) Run(_ context.Context, args []string, _ io.Reader) (compose
 	case strings.Contains(call, "compose build"):
 		f.built = true
 		f.version = "0.81.0"
+		f.currentImage = "sha256:candidate"
 		return compose.Result{}, nil
 	case strings.Contains(call, "pi --version"):
 		return compose.Result{Stdout: f.version + "\n"}, nil