diff --git a/apps/api/src/local-data-root.ts b/apps/api/src/local-data-root.ts
index 68c3959..33d9f22 100644
--- a/apps/api/src/local-data-root.ts
+++ b/apps/api/src/local-data-root.ts
@@ -69,6 +69,13 @@ interface InstanceConfiguration {
   schema_version: 1;
 }
 
+export function readConfiguredLocalDataRoot(configFile = defaultInstanceConfigPath()) {
+  const configuration = JSON.parse(readFileSync(configFile, "utf8")) as Record<string, unknown>;
+  const candidate = configuration.data_root ?? configuration.local_data_root;
+  if (typeof candidate !== "string" || !isAbsolute(candidate)) throw new Error("data_root_configuration_invalid");
+  return resolve(candidate);
+}
+
 export interface ValidatedReadOnlyAssetRoot {
   absolute_root: string;
   ok: true;
diff --git a/apps/api/src/main.ts b/apps/api/src/main.ts
index 24dbac5..416f9bc 100644
--- a/apps/api/src/main.ts
+++ b/apps/api/src/main.ts
@@ -1,7 +1,10 @@
-import { resolve } from "node:path";
+import { join, resolve } from "node:path";
 
 import { createApp } from "./app.js";
 import { readBrowserSupportRelease } from "./browser-support.js";
+import { readConfiguredLocalDataRoot } from "./local-data-root.js";
+import { ManagedStorage } from "./managed-storage.js";
+import { StructuredJsonlLogger } from "./structured-log.js";
 import { attachApiSupervisorControl, initializeApiCredentialClients, receiveApiCredentials } from "./supervisor-channel.js";
 
 const credentialChannelEnabled = process.argv.includes("--dada-credential-stdin");
@@ -21,5 +24,27 @@ const controlPipeIndex = process.argv.indexOf("--dada-control-pipe");
 if (controlPipeIndex >= 0) {
   const controlPipe = process.argv[controlPipeIndex + 1];
   if (!controlPipe) throw new Error("Supervisor control pipe name is required.");
-  attachApiSupervisorControl(controlPipe, () => app.close());
+  let storage: ManagedStorage | undefined;
+  const control = attachApiSupervisorControl(controlPipe, async () => {
+    await app.close();
+    storage?.close();
+  });
+  try {
+    const dataRoot = readConfiguredLocalDataRoot();
+    storage = new ManagedStorage({ dataRoot, databasePath: join(dataRoot, "db", "dada.sqlite3") });
+    const logger = new StructuredJsonlLogger({
+      component: "api",
+      directory: join(dataRoot, "logs", "api"),
+      onWriteFailure: () => {
+        try {
+          storage?.setLogAvailability(false);
+        } finally {
+          control.reportStatus("storage_unavailable");
+        }
+      },
+    });
+    logger.write({ error_category: "none", status_category: "ready" });
+  } catch {
+    control.reportStatus("storage_unavailable");
+  }
 }
diff --git a/apps/api/src/managed-storage.ts b/apps/api/src/managed-storage.ts
index 6dd08b7..58af953 100644
--- a/apps/api/src/managed-storage.ts
+++ b/apps/api/src/managed-storage.ts
@@ -134,6 +134,7 @@ export class ManagedStorage {
   private readonly database: BetterSqlite3.Database;
   private dataRootWritable = true;
   private diskSpaceAvailable = true;
+  private logWritable = true;
   private sqliteWritable = true;
   private measurementBaselineBytes = 0;
   private recoveryRequiresRemeasure = false;
@@ -241,7 +242,7 @@ export class ManagedStorage {
   getState(): StorageStateRow {
     const state = this.database.prepare("SELECT * FROM local_backend_storage_state WHERE singleton = 1").get() as Omit<StorageStateRow, "active_storage_reservations_bytes">;
     const withReservations = { ...state, active_storage_reservations_bytes: this.activeReservationBytes() };
-    if (!this.dataRootWritable || !this.diskSpaceAvailable || !this.sqliteWritable) {
+    if (!this.dataRootWritable || !this.diskSpaceAvailable || !this.sqliteWritable || !this.logWritable) {
       return { ...withReservations, storage_status: "unavailable" };
     }
     return withReservations;
@@ -260,7 +261,7 @@ export class ManagedStorage {
     if (!this.sqliteWritable) return;
     const state = this.database.prepare("SELECT managed_content_bytes FROM local_backend_storage_state WHERE singleton = 1").get() as { managed_content_bytes: number };
     const classification = classifyCapacity(state.managed_content_bytes, this.activeReservationBytes());
-    const storageStatus = !this.dataRootWritable || !this.diskSpaceAvailable || this.recoveryRequiresRemeasure
+    const storageStatus = !this.dataRootWritable || !this.diskSpaceAvailable || !this.logWritable || this.recoveryRequiresRemeasure
       ? "unavailable"
       : classification.storage_status;
     this.database.prepare(`
@@ -291,6 +292,12 @@ export class ManagedStorage {
     this.refreshState();
   }
 
+  setLogAvailability(writable: boolean) {
+    this.logWritable = writable;
+    if (!writable) this.recoveryRequiresRemeasure = true;
+    this.refreshState();
+  }
+
   private physicalManagedBytes() {
     return ["content", "managed-assets", "derived-assets"]
       .flatMap((root) => listFiles(resolvePathWithinRoot(this.dataRoot, root)))
diff --git a/apps/api/src/structured-log.ts b/apps/api/src/structured-log.ts
new file mode 100644
index 0000000..47e606b
--- /dev/null
+++ b/apps/api/src/structured-log.ts
@@ -0,0 +1,165 @@
+import {
+  appendFileSync,
+  existsSync,
+  mkdirSync,
+  readdirSync,
+  renameSync,
+  rmSync,
+  statSync,
+} from "node:fs";
+import { join } from "node:path";
+
+export const LOG_SIZE_LIMIT_BYTES = 10 * 1024 * 1024;
+export const LOG_FILE_LIMIT = 10;
+export const LOG_RETENTION_DAYS = 30;
+
+const statusCategories = new Set([
+  "starting", "ready", "completed", "failed", "unavailable", "degraded",
+  "blocked", "stopping", "stopped",
+]);
+const errorCategories = new Set([
+  "none", "invalid_input", "storage_unavailable", "log_write_failed",
+  "service_unavailable", "timeout", "internal_error",
+]);
+const identifierPattern = /^[a-zA-Z0-9][a-zA-Z0-9_-]{0,63}$/;
+const codePattern = /^[a-z][a-z0-9_]{0,63}$/;
+
+export interface StructuredLogInput {
+  correlation_id?: string;
+  duration_ms?: number;
+  error_category?: string;
+  object_id?: string;
+  status_category: string;
+}
+
+export interface StructuredJsonlLoggerOptions {
+  component: "api";
+  directory: string;
+  now?: () => Date;
+  onWriteFailure?: () => void;
+}
+
+export class LogWriteError extends Error {
+  constructor(options?: ErrorOptions) {
+    super("log_write_failed", options);
+  }
+}
+
+export class StructuredJsonlLogger {
+  private readonly component: "api";
+  private readonly directory: string;
+  private readonly now: () => Date;
+  private readonly onWriteFailure: () => void;
+  private initialized = false;
+  private currentSize = 0;
+
+  constructor(options: StructuredJsonlLoggerOptions) {
+    this.component = options.component;
+    this.directory = options.directory;
+    this.now = options.now ?? (() => new Date());
+    this.onWriteFailure = options.onWriteFailure ?? (() => undefined);
+  }
+
+  write(input: StructuredLogInput | Record<string, unknown>) {
+    try {
+      this.initialize();
+      const line = `${JSON.stringify(sanitizeLogEntry(this.component, input, this.now()))}\n`;
+      const bytes = Buffer.byteLength(line);
+      if (bytes > LOG_SIZE_LIMIT_BYTES) throw new Error("log_entry_too_large");
+      if (this.currentSize > 0 && this.currentSize + bytes > LOG_SIZE_LIMIT_BYTES) this.rotate();
+      appendFileSync(this.activePath(), line, { encoding: "utf8" });
+      this.currentSize += bytes;
+    } catch (error) {
+      if (error instanceof LogWriteError) throw error;
+      this.fail(error);
+    }
+  }
+
+  maintain() {
+    try {
+      mkdirSync(this.directory, { recursive: true });
+      this.maintainFiles();
+      this.currentSize = existsSync(this.activePath()) ? statSync(this.activePath()).size : 0;
+      this.initialized = true;
+    } catch (error) {
+      if (error instanceof LogWriteError) throw error;
+      this.fail(error);
+    }
+  }
+
+  private initialize() {
+    if (!this.initialized) this.maintain();
+  }
+
+  private maintainFiles() {
+    const cutoff = this.now().getTime() - LOG_RETENTION_DAYS * 24 * 60 * 60 * 1000;
+    for (const file of this.files()) {
+      const path = join(this.directory, file.name);
+      if (file.index > LOG_FILE_LIMIT - 1 || statSync(path).mtimeMs < cutoff) rmSync(path, { force: true });
+    }
+    const remaining = this.files();
+    for (const file of remaining.slice(LOG_FILE_LIMIT)) rmSync(join(this.directory, file.name), { force: true });
+  }
+
+  private rotate() {
+    const last = join(this.directory, `${this.component}.${LOG_FILE_LIMIT - 1}.jsonl`);
+    rmSync(last, { force: true });
+    for (let index = LOG_FILE_LIMIT - 2; index >= 1; index -= 1) {
+      const source = join(this.directory, `${this.component}.${index}.jsonl`);
+      if (existsSync(source)) renameSync(source, join(this.directory, `${this.component}.${index + 1}.jsonl`));
+    }
+    if (existsSync(this.activePath())) renameSync(this.activePath(), join(this.directory, `${this.component}.1.jsonl`));
+    this.currentSize = 0;
+  }
+
+  private files() {
+    if (!existsSync(this.directory)) return [];
+    const pattern = new RegExp(`^${this.component}(?:\\.(\\d+))?\\.jsonl$`);
+    return readdirSync(this.directory)
+      .map((name) => ({ match: pattern.exec(name), name }))
+      .filter((entry): entry is { match: RegExpExecArray; name: string } => entry.match !== null)
+      .map(({ match, name }) => ({ index: match[1] === undefined ? 0 : Number(match[1]), name }))
+      .sort((left, right) => left.index - right.index);
+  }
+
+  private activePath() {
+    return join(this.directory, `${this.component}.jsonl`);
+  }
+
+  private fail(error: unknown): never {
+    try {
+      this.onWriteFailure();
+    } catch {
+      // State persistence failure must not replace the stable redacted error.
+    }
+    throw new LogWriteError({ cause: error });
+  }
+}
+
+export function sanitizeLogEntry(component: "api", input: StructuredLogInput | Record<string, unknown>, now: Date) {
+  const value = input as Record<string, unknown>;
+  const entry: Record<string, unknown> = {
+    component,
+    schema_version: "1.0",
+    status_category: statusCategories.has(String(value.status_category)) ? value.status_category : "failed",
+    timestamp: now.toISOString(),
+  };
+  if (typeof value.correlation_id === "string" && identifierPattern.test(value.correlation_id)) entry.correlation_id = value.correlation_id;
+  if (typeof value.object_id === "string" && identifierPattern.test(value.object_id)) entry.object_id = value.object_id;
+  if (typeof value.duration_ms === "number" && Number.isSafeInteger(value.duration_ms) && value.duration_ms >= 0) entry.duration_ms = value.duration_ms;
+  if (typeof value.error_category === "string") {
+    entry.error_category = errorCategories.has(value.error_category) ? value.error_category : "internal_error";
+  }
+  return entry;
+}
+
+export function sanitizeDiagnosticRecord(input: Record<string, unknown>) {
+  return {
+    app_version: typeof input.app_version === "string" && /^[0-9]+(?:\.[0-9]+){2,3}$/.test(input.app_version) ? input.app_version : "0.0.0",
+    checked_at: typeof input.checked_at === "string" && !Number.isNaN(Date.parse(input.checked_at)) ? input.checked_at : new Date(0).toISOString(),
+    component: input.component === "api" || input.component === "worker" || input.component === "supervisor" ? input.component : "supervisor",
+    message_key: typeof input.message_key === "string" && codePattern.test(input.message_key) ? input.message_key : "diagnostic_redacted",
+    result: input.result === "pass" || input.result === "warning" || input.result === "fail" ? input.result : "fail",
+    stable_check_code: typeof input.stable_check_code === "string" && codePattern.test(input.stable_check_code) ? input.stable_check_code : "invalid_check",
+  };
+}
diff --git a/apps/api/src/supervisor-channel.ts b/apps/api/src/supervisor-channel.ts
index 41a68b3..45f41f4 100644
--- a/apps/api/src/supervisor-channel.ts
+++ b/apps/api/src/supervisor-channel.ts
@@ -33,8 +33,14 @@ export function initializeApiCredentialClients(credentials: Record<(typeof API_C
 export function attachApiSupervisorControl(pipeName: string, shutdown: () => Promise<void>) {
   const socket = createConnection(`\\\\.\\pipe\\${pipeName}`);
   let pending = "";
+  let connected = false;
+  const pendingStatuses: string[] = [];
   socket.setEncoding("utf8");
-  socket.on("connect", () => socket.write("ready\n"));
+  socket.on("connect", () => {
+    connected = true;
+    socket.write("ready\n");
+    for (const status of pendingStatuses.splice(0)) socket.write(`${status}\n`);
+  });
   socket.on("data", (chunk) => {
     pending += chunk;
     if (!pending.includes("\n")) return;
@@ -42,5 +48,11 @@ export function attachApiSupervisorControl(pipeName: string, shutdown: () => Pro
     pending = "";
     if (command === "shutdown") void shutdown().finally(() => socket.end());
   });
-  return socket;
+  return {
+    reportStatus(status: "storage_unavailable") {
+      if (socket.destroyed) return;
+      if (connected) socket.write(`${status}\n`); else pendingStatuses.push(status);
+    },
+    socket,
+  };
 }
diff --git a/apps/worker/src/ai-call-gate.ts b/apps/worker/src/ai-call-gate.ts
new file mode 100644
index 0000000..741fc58
--- /dev/null
+++ b/apps/worker/src/ai-call-gate.ts
@@ -0,0 +1,47 @@
+import type { StructuredJsonlLogger } from "./structured-log.js";
+
+export class WorkerAiCallGate {
+  private readonly getStorageStatus: () => "active" | "full" | "unavailable";
+  private readonly logger: StructuredJsonlLogger;
+
+  constructor(input: {
+    getStorageStatus: () => "active" | "full" | "unavailable";
+    logger: StructuredJsonlLogger;
+  }) {
+    this.getStorageStatus = input.getStorageStatus;
+    this.logger = input.logger;
+  }
+
+  async execute<T>(correlationId: string, objectId: string, externalCall: () => Promise<T>) {
+    const initialStatus = this.getStorageStatus();
+    if (initialStatus === "full") return { reason: "storage_full" as const, status: "blocked" as const };
+    if (initialStatus === "unavailable") return { reason: "storage_unavailable" as const, status: "blocked" as const };
+    try {
+      this.logger.write({
+        correlation_id: correlationId,
+        error_category: "none",
+        object_id: objectId,
+        status_category: "starting",
+      });
+    } catch {
+      return { reason: "storage_unavailable" as const, status: "blocked" as const };
+    }
+    const statusAfterLog = this.getStorageStatus();
+    if (statusAfterLog === "full") return { reason: "storage_full" as const, status: "blocked" as const };
+    if (statusAfterLog === "unavailable") return { reason: "storage_unavailable" as const, status: "blocked" as const };
+    const started = Date.now();
+    const value = await externalCall();
+    try {
+      this.logger.write({
+        correlation_id: correlationId,
+        duration_ms: Date.now() - started,
+        error_category: "none",
+        object_id: objectId,
+        status_category: "completed",
+      });
+    } catch {
+      // The completed call cannot be undone; the write failure blocks every later call.
+    }
+    return { status: "completed" as const, value };
+  }
+}
diff --git a/apps/worker/src/runtime-config.ts b/apps/worker/src/runtime-config.ts
new file mode 100644
index 0000000..4a4abcd
--- /dev/null
+++ b/apps/worker/src/runtime-config.ts
@@ -0,0 +1,12 @@
+import { readFileSync } from "node:fs";
+import { isAbsolute, join, resolve } from "node:path";
+
+export function readConfiguredLocalDataRoot(environment: NodeJS.ProcessEnv = process.env) {
+  const localAppData = environment.LOCALAPPDATA;
+  if (!localAppData || !isAbsolute(localAppData)) throw new Error("local_app_data_unavailable");
+  const configFile = join(localAppData, "Dada", "P0A", "config", "instance.json");
+  const configuration = JSON.parse(readFileSync(configFile, "utf8")) as Record<string, unknown>;
+  const candidate = configuration.data_root ?? configuration.local_data_root;
+  if (typeof candidate !== "string" || !isAbsolute(candidate)) throw new Error("data_root_configuration_invalid");
+  return resolve(candidate);
+}
diff --git a/apps/worker/src/storage-status.ts b/apps/worker/src/storage-status.ts
new file mode 100644
index 0000000..b8d0444
--- /dev/null
+++ b/apps/worker/src/storage-status.ts
@@ -0,0 +1,32 @@
+import { createRequire } from "node:module";
+
+import type BetterSqlite3 from "better-sqlite3";
+
+const require = createRequire(import.meta.url);
+const Database = require("better-sqlite3") as typeof BetterSqlite3;
+
+export class WorkerStorageStatus {
+  private readonly database: BetterSqlite3.Database;
+
+  constructor(databasePath: string) {
+    this.database = new Database(databasePath);
+    this.database.pragma("busy_timeout = 5000");
+  }
+
+  getStatus(): "active" | "full" | "unavailable" {
+    const row = this.database.prepare("SELECT storage_status FROM local_backend_storage_state WHERE singleton = 1").get() as { storage_status: "active" | "full" | "unavailable" };
+    return row.storage_status;
+  }
+
+  markLogUnavailable() {
+    this.database.prepare(`
+      UPDATE local_backend_storage_state
+      SET storage_status = 'unavailable', measured_at = ?, version = version + 1
+      WHERE singleton = 1
+    `).run(new Date().toISOString());
+  }
+
+  close() {
+    this.database.close();
+  }
+}
diff --git a/apps/worker/src/structured-log.ts b/apps/worker/src/structured-log.ts
new file mode 100644
index 0000000..290bb3e
--- /dev/null
+++ b/apps/worker/src/structured-log.ts
@@ -0,0 +1,129 @@
+import {
+  appendFileSync,
+  existsSync,
+  mkdirSync,
+  readdirSync,
+  renameSync,
+  rmSync,
+  statSync,
+} from "node:fs";
+import { join } from "node:path";
+
+export const LOG_SIZE_LIMIT_BYTES = 10 * 1024 * 1024;
+export const LOG_FILE_LIMIT = 10;
+export const LOG_RETENTION_DAYS = 30;
+
+const statusCategories = new Set(["starting", "ready", "completed", "failed", "unavailable", "degraded", "blocked", "stopping", "stopped"]);
+const errorCategories = new Set(["none", "invalid_input", "storage_unavailable", "log_write_failed", "service_unavailable", "timeout", "internal_error"]);
+const identifierPattern = /^[a-zA-Z0-9][a-zA-Z0-9_-]{0,63}$/;
+
+export interface StructuredLogInput {
+  correlation_id?: string;
+  duration_ms?: number;
+  error_category?: string;
+  object_id?: string;
+  status_category: string;
+}
+
+export class LogWriteError extends Error {
+  constructor(options?: ErrorOptions) {
+    super("log_write_failed", options);
+  }
+}
+
+export class StructuredJsonlLogger {
+  private readonly directory: string;
+  private readonly now: () => Date;
+  private readonly onWriteFailure: () => void;
+  private initialized = false;
+  private currentSize = 0;
+
+  constructor(options: { component: "worker"; directory: string; now?: () => Date; onWriteFailure?: () => void }) {
+    this.directory = options.directory;
+    this.now = options.now ?? (() => new Date());
+    this.onWriteFailure = options.onWriteFailure ?? (() => undefined);
+  }
+
+  write(input: StructuredLogInput | Record<string, unknown>) {
+    try {
+      this.initialize();
+      const line = `${JSON.stringify(sanitizeWorkerLogEntry(input, this.now()))}\n`;
+      const bytes = Buffer.byteLength(line);
+      if (bytes > LOG_SIZE_LIMIT_BYTES) throw new Error("log_entry_too_large");
+      if (this.currentSize > 0 && this.currentSize + bytes > LOG_SIZE_LIMIT_BYTES) this.rotate();
+      appendFileSync(this.activePath(), line, { encoding: "utf8" });
+      this.currentSize += bytes;
+    } catch (error) {
+      if (error instanceof LogWriteError) throw error;
+      this.fail(error);
+    }
+  }
+
+  maintain() {
+    try {
+      mkdirSync(this.directory, { recursive: true });
+      const cutoff = this.now().getTime() - LOG_RETENTION_DAYS * 24 * 60 * 60 * 1000;
+      for (const file of this.files()) {
+        const path = join(this.directory, file.name);
+        if (file.index > LOG_FILE_LIMIT - 1 || statSync(path).mtimeMs < cutoff) rmSync(path, { force: true });
+      }
+      for (const file of this.files().slice(LOG_FILE_LIMIT)) rmSync(join(this.directory, file.name), { force: true });
+      this.currentSize = existsSync(this.activePath()) ? statSync(this.activePath()).size : 0;
+      this.initialized = true;
+    } catch (error) {
+      if (error instanceof LogWriteError) throw error;
+      this.fail(error);
+    }
+  }
+
+  private initialize() {
+    if (!this.initialized) this.maintain();
+  }
+
+  private rotate() {
+    rmSync(join(this.directory, `worker.${LOG_FILE_LIMIT - 1}.jsonl`), { force: true });
+    for (let index = LOG_FILE_LIMIT - 2; index >= 1; index -= 1) {
+      const source = join(this.directory, `worker.${index}.jsonl`);
+      if (existsSync(source)) renameSync(source, join(this.directory, `worker.${index + 1}.jsonl`));
+    }
+    if (existsSync(this.activePath())) renameSync(this.activePath(), join(this.directory, "worker.1.jsonl"));
+    this.currentSize = 0;
+  }
+
+  private files() {
+    if (!existsSync(this.directory)) return [];
+    return readdirSync(this.directory)
+      .map((name) => ({ match: /^worker(?:\.(\d+))?\.jsonl$/.exec(name), name }))
+      .filter((entry): entry is { match: RegExpExecArray; name: string } => entry.match !== null)
+      .map(({ match, name }) => ({ index: match[1] === undefined ? 0 : Number(match[1]), name }))
+      .sort((left, right) => left.index - right.index);
+  }
+
+  private activePath() {
+    return join(this.directory, "worker.jsonl");
+  }
+
+  private fail(error: unknown): never {
+    try {
+      this.onWriteFailure();
+    } catch {
+      // State persistence failure must not replace the stable redacted error.
+    }
+    throw new LogWriteError({ cause: error });
+  }
+}
+
+function sanitizeWorkerLogEntry(input: StructuredLogInput | Record<string, unknown>, now: Date) {
+  const value = input as Record<string, unknown>;
+  const entry: Record<string, unknown> = {
+    component: "worker",
+    schema_version: "1.0",
+    status_category: statusCategories.has(String(value.status_category)) ? value.status_category : "failed",
+    timestamp: now.toISOString(),
+  };
+  if (typeof value.correlation_id === "string" && identifierPattern.test(value.correlation_id)) entry.correlation_id = value.correlation_id;
+  if (typeof value.object_id === "string" && identifierPattern.test(value.object_id)) entry.object_id = value.object_id;
+  if (typeof value.duration_ms === "number" && Number.isSafeInteger(value.duration_ms) && value.duration_ms >= 0) entry.duration_ms = value.duration_ms;
+  if (typeof value.error_category === "string") entry.error_category = errorCategories.has(value.error_category) ? value.error_category : "internal_error";
+  return entry;
+}
diff --git a/apps/worker/src/supervisor-channel.ts b/apps/worker/src/supervisor-channel.ts
index c06e1b2..dc6d17e 100644
--- a/apps/worker/src/supervisor-channel.ts
+++ b/apps/worker/src/supervisor-channel.ts
@@ -33,8 +33,14 @@ export function initializeWorkerCredentialClient(credentials: Record<(typeof WOR
 export function attachWorkerSupervisorControl(pipeName: string, shutdown: () => Promise<void> | void) {
   const socket = createConnection(`\\\\.\\pipe\\${pipeName}`);
   let pending = "";
+  let connected = false;
+  const pendingStatuses: string[] = [];
   socket.setEncoding("utf8");
-  socket.on("connect", () => socket.write("ready\n"));
+  socket.on("connect", () => {
+    connected = true;
+    socket.write("ready\n");
+    for (const status of pendingStatuses.splice(0)) socket.write(`${status}\n`);
+  });
   socket.on("data", (chunk) => {
     pending += chunk;
     if (!pending.includes("\n")) return;
@@ -42,5 +48,11 @@ export function attachWorkerSupervisorControl(pipeName: string, shutdown: () =>
     pending = "";
     if (command === "shutdown") void Promise.resolve(shutdown()).finally(() => socket.end());
   });
-  return socket;
+  return {
+    reportStatus(status: "storage_unavailable") {
+      if (socket.destroyed) return;
+      if (connected) socket.write(`${status}\n`); else pendingStatuses.push(status);
+    },
+    socket,
+  };
 }
diff --git a/apps/worker/src/worker.ts b/apps/worker/src/worker.ts
index 8a288f0..5144815 100644
--- a/apps/worker/src/worker.ts
+++ b/apps/worker/src/worker.ts
@@ -1,5 +1,10 @@
 import { parentPort } from "node:worker_threads";
+import { join } from "node:path";
 
+import { WorkerAiCallGate } from "./ai-call-gate.js";
+import { readConfiguredLocalDataRoot } from "./runtime-config.js";
+import { StructuredJsonlLogger } from "./structured-log.js";
+import { WorkerStorageStatus } from "./storage-status.js";
 import { attachWorkerSupervisorControl, initializeWorkerCredentialClient, receiveWorkerCredentials } from "./supervisor-channel.js";
 
 export function handleWorkerProbe(message: unknown) {
@@ -20,5 +25,31 @@ if (!workerPort && process.argv.includes("--dada-credential-stdin")) {
   const controlPipe = process.argv[controlPipeIndex + 1];
   if (controlPipeIndex < 0 || !controlPipe) throw new Error("Supervisor control pipe name is required.");
   const keepAlive = setInterval(() => undefined, 30_000);
-  attachWorkerSupervisorControl(controlPipe, () => clearInterval(keepAlive));
+  let storage: WorkerStorageStatus | undefined;
+  const control = attachWorkerSupervisorControl(controlPipe, () => {
+    clearInterval(keepAlive);
+    storage?.close();
+  });
+  let storageStatus: "active" | "unavailable" = "active";
+  try {
+    const dataRoot = readConfiguredLocalDataRoot();
+    storage = new WorkerStorageStatus(join(dataRoot, "db", "dada.sqlite3"));
+    const logger = new StructuredJsonlLogger({
+      component: "worker",
+      directory: join(dataRoot, "logs", "worker"),
+      onWriteFailure: () => {
+        storageStatus = "unavailable";
+        try {
+          storage?.markLogUnavailable();
+        } finally {
+          control.reportStatus("storage_unavailable");
+        }
+      },
+    });
+    logger.write({ error_category: "none", status_category: "ready" });
+    new WorkerAiCallGate({ getStorageStatus: () => storageStatus === "unavailable" ? storageStatus : (storage?.getStatus() ?? "unavailable"), logger });
+  } catch {
+    storageStatus = "unavailable";
+    control.reportStatus("storage_unavailable");
+  }
 }
diff --git a/package.json b/package.json
index 0204a36..d7d7f60 100644
--- a/package.json
+++ b/package.json
@@ -34,7 +34,9 @@
     "test:wp0-06": "node scripts/run-wp0-06-validation.mjs",
     "test:wp0-06:red": "node scripts/run-wp0-06-validation.mjs --phase red",
     "test:wp0-07": "node scripts/run-wp0-07-validation.mjs",
-    "test:wp0-07:red": "node scripts/run-wp0-07-validation.mjs --phase red"
+    "test:wp0-07:red": "node scripts/run-wp0-07-validation.mjs --phase red",
+    "test:wp0-08": "node scripts/run-wp0-08-validation.mjs",
+    "test:wp0-08:red": "node scripts/run-wp0-08-validation.mjs --phase red"
   },
   "devDependencies": {
     "@playwright/test": "1.62.0",
diff --git a/scripts/run-wp0-08-validation.mjs b/scripts/run-wp0-08-validation.mjs
new file mode 100644
index 0000000..1fbe274
--- /dev/null
+++ b/scripts/run-wp0-08-validation.mjs
@@ -0,0 +1,79 @@
+import { createHash } from "node:crypto";
+import { spawnSync } from "node:child_process";
+import { existsSync, mkdirSync, readFileSync, writeFileSync } from "node:fs";
+import { resolve } from "node:path";
+
+const phaseIndex = process.argv.indexOf("--phase");
+const phase = phaseIndex >= 0 ? process.argv[phaseIndex + 1] : "green";
+if (!["red", "green"].includes(phase)) throw new Error(`Unsupported phase: ${phase}`);
+const runId = process.env.DADA_TDD_RUN_ID ?? `wp0-08-${phase}-${new Date().toISOString().replace(/[^0-9]/g, "")}`;
+const runDirectory = resolve("artifacts", "tdd", runId);
+const caseId = "TDD-WP0-LOG-001-rotation-redaction";
+const caseDirectory = resolve(runDirectory, "cases", caseId);
+const uiDirectory = resolve(runDirectory, "ui", "system-ui", "unavailable");
+if (existsSync(runDirectory)) throw new Error(`Evidence run already exists: ${runId}`);
+mkdirSync(caseDirectory, { recursive: true });
+mkdirSync(uiDirectory, { recursive: true });
+
+const commandSpecs = phase === "red"
+  ? [
+      ["pnpm exec vitest run tests/integration/wp0-08-structured-log.test.ts", ["exec", "vitest", "run", "tests/integration/wp0-08-structured-log.test.ts"]],
+      ["pnpm exec vitest run tests/worker/wp0-08-log-availability.test.ts", ["exec", "vitest", "run", "tests/worker/wp0-08-log-availability.test.ts"]],
+    ]
+  : [
+      ["pnpm test:integration", ["test:integration"]],
+      ["pnpm test:worker", ["test:worker"]],
+      ["pnpm test:security", ["test:security"]],
+      ["pnpm test:package", ["test:package"]],
+      ["pnpm validate:tdd-trace", ["validate:tdd-trace"]],
+    ];
+const environment = { ...process.env, DADA_EVIDENCE_DIR_LOG: caseDirectory, DADA_EVIDENCE_DIR_SUP: uiDirectory };
+const startedAt = new Date().toISOString();
+const commands = [];
+for (const [command, args] of commandSpecs) {
+  const started_at = new Date().toISOString();
+  const executable = process.platform === "win32" ? (process.env.ComSpec ?? "cmd.exe") : "pnpm";
+  const actualArgs = process.platform === "win32" ? ["/d", "/s", "/c", `pnpm ${args.join(" ")}`] : args;
+  const execution = spawnSync(executable, actualArgs, { encoding: "utf8", env: environment });
+  if (execution.stdout) process.stdout.write(execution.stdout);
+  if (execution.stderr) process.stderr.write(execution.stderr);
+  commands.push({ command, exit_code: execution.status ?? 1, finished_at: new Date().toISOString(), started_at });
+}
+
+writeFileSync(resolve(caseDirectory, "commands.json"), `${JSON.stringify({ commands, phase, run_id: runId, schema_version: "1.0" }, null, 2)}\n`);
+const evidenceRefs = ["log-manifest.json", "redaction.json", "response.json", "external-calls.json"];
+const missingEvidence = phase === "green" ? evidenceRefs.filter((path) => !existsSync(resolve(caseDirectory, path))) : [];
+const uiEvidenceRefs = ["ui/system-ui/unavailable/screenshots/storage-unavailable.png"];
+const missingUiEvidence = phase === "green" ? uiEvidenceRefs.filter((path) => !existsSync(resolve(runDirectory, path))) : [];
+const commandState = phase === "red" ? commands.every((item) => item.exit_code !== 0) : commands.every((item) => item.exit_code === 0);
+const status = phase === "red" ? (commandState ? "red_confirmed" : "failed") : (commandState && missingEvidence.length === 0 && missingUiEvidence.length === 0 ? "passed" : "failed");
+const result = {
+  acceptance_criteria: ["AC-41", "AC-56"],
+  automation: ["automated"],
+  commit: spawnSync("git", ["rev-parse", "--short", "HEAD"], { encoding: "utf8" }).stdout.trim(),
+  environment: { arch: process.arch, node: process.version.slice(1), os: process.platform },
+  evidence_refs: evidenceRefs,
+  finished_at: new Date().toISOString(),
+  layer: ["DB", "WORKER", "PACKAGE_SECURITY"],
+  manifest: { path: "tasks.manifest.json", sha256: createHash("sha256").update(readFileSync("tasks.manifest.json")).digest("hex").toUpperCase() },
+  missing_evidence: missingEvidence,
+  missing_ui_evidence: missingUiEvidence,
+  parent_family: "TDD-WP0-LOG-001",
+  phase,
+  release_gate: ["work_package:WP-0", "release:P0-A"],
+  requirements: ["NFR-09", "PRIV-01", "PRIV-02"],
+  run_id: runId,
+  schema_version: "1.0",
+  started_at: startedAt,
+  status,
+  task_id: "TASK-WP0-08",
+  test_id: caseId,
+  ui_evidence_refs: uiEvidenceRefs,
+  work_package: "WP-0",
+  worktree_under_test: spawnSync("git", ["status", "--porcelain"], { encoding: "utf8" }).stdout.trim() ? "uncommitted implementation" : "clean committed implementation",
+};
+writeFileSync(resolve(caseDirectory, "result.json"), `${JSON.stringify(result, null, 2)}\n`);
+const summary = { cases: [{ missing_evidence: missingEvidence, status, test_id: caseId }], phase, run_id: runId, status };
+writeFileSync(resolve(runDirectory, "evidence.json"), `${JSON.stringify(summary, null, 2)}\n`);
+console.log(JSON.stringify(summary, null, 2));
+if (status !== (phase === "red" ? "red_confirmed" : "passed")) process.exit(1);
diff --git a/supervisor/Dada.Supervisor.Tests/Program.cs b/supervisor/Dada.Supervisor.Tests/Program.cs
index 8b80f03..0851980 100644
--- a/supervisor/Dada.Supervisor.Tests/Program.cs
+++ b/supervisor/Dada.Supervisor.Tests/Program.cs
@@ -32,6 +32,7 @@ internal static class Program
         {
             var security = await TestCredentialBoundaryAsync();
             var supervisor = await TestSupervisorLifecycleAsync();
+            TestStructuredLogging();
             WriteEvidence(Environment.GetEnvironmentVariable("DADA_EVIDENCE_DIR_SEC"), security);
             WriteEvidence(Environment.GetEnvironmentVariable("DADA_EVIDENCE_DIR_SUP"), supervisor);
             Console.WriteLine(JsonSerializer.Serialize(new { security = "passed", supervisor = "passed" }, JsonOptions));
@@ -44,6 +45,35 @@ internal static class Program
         }
     }
 
+    private static void TestStructuredLogging()
+    {
+        Equal(10 * 1024 * 1024L, StructuredJsonlLogger.SizeLimitBytes, "Supervisor log byte limit");
+        Equal(10, StructuredJsonlLogger.FileLimit, "Supervisor log file limit");
+        Equal(30, StructuredJsonlLogger.RetentionDays, "Supervisor log retention");
+        var directory = Path.Combine(Path.GetTempPath(), $"dada-supervisor-log-{Guid.NewGuid():N}");
+        try
+        {
+            var logger = new StructuredJsonlLogger(directory, "supervisor", sizeLimitBytes: 512, fileLimit: 10);
+            for (var index = 0; index < 40; index++)
+            {
+                logger.Write(new StructuredLogEvent("completed", $"corr_{index}", $"obj_{index}", index, "none"));
+            }
+            var files = Directory.GetFiles(directory, "*.jsonl");
+            True(files.Length <= StructuredJsonlLogger.FileLimit, "Supervisor log file cap");
+            True(files.All(path => new FileInfo(path).Length <= 512), "Supervisor log rotation byte boundary");
+            foreach (var line in files.SelectMany(File.ReadLines))
+            {
+                using var document = JsonDocument.Parse(line);
+                var keys = document.RootElement.EnumerateObject().Select(property => property.Name).ToHashSet(StringComparer.Ordinal);
+                True(keys.IsSubsetOf(["schema_version", "timestamp", "component", "status_category", "correlation_id", "object_id", "duration_ms", "error_category"]), "Supervisor log field allowlist");
+            }
+        }
+        finally
+        {
+            if (Directory.Exists(directory)) Directory.Delete(directory, recursive: true);
+        }
+    }
+
     private static async Task<object> TestCredentialBoundaryAsync()
     {
         var store = new TestCredentialStore();
@@ -184,6 +214,11 @@ internal static class Program
         {
             EqualSequence(new[] { "打开 Dada", "运行状态", "打开诊断", "重新启动服务", "退出 Dada" }, menuForm.TrayMenuLabels, "tray menu order");
         }
+        using (var diagnostics = new DiagnosticsForm(SupervisorState.StorageUnavailable))
+        {
+            True(diagnostics.CopyPayload.Contains("log_write_failed", StringComparison.Ordinal), "diagnostic log status");
+            False(diagnostics.CopyPayload.Contains("CredentialBlob", StringComparison.Ordinal), "diagnostic credential redaction");
+        }
 
         var screenshotPath = Path.Combine(Environment.GetEnvironmentVariable("DADA_EVIDENCE_DIR_SUP") ?? Path.GetTempPath(), "screenshots", "system-ui.png");
         Directory.CreateDirectory(Path.GetDirectoryName(screenshotPath)!);
diff --git a/supervisor/Dada.Supervisor/Diagnostics.cs b/supervisor/Dada.Supervisor/Diagnostics.cs
index 158ee22..aae58b3 100644
--- a/supervisor/Dada.Supervisor/Diagnostics.cs
+++ b/supervisor/Dada.Supervisor/Diagnostics.cs
@@ -9,9 +9,12 @@ internal enum DiagnosticResult
 
 internal sealed record DiagnosticCheck(string CheckCode, DiagnosticResult Result, string MessageKey, DateTimeOffset CheckedAt)
 {
-    internal static DiagnosticCheck Pass(string checkCode, string messageKey) => new(checkCode, DiagnosticResult.Pass, messageKey, DateTimeOffset.UtcNow);
-    internal static DiagnosticCheck Warning(string checkCode, string messageKey) => new(checkCode, DiagnosticResult.Warning, messageKey, DateTimeOffset.UtcNow);
-    internal static DiagnosticCheck Fail(string checkCode, string messageKey) => new(checkCode, DiagnosticResult.Fail, messageKey, DateTimeOffset.UtcNow);
+    internal static DiagnosticCheck Pass(string checkCode, string messageKey) => Create(checkCode, DiagnosticResult.Pass, messageKey);
+    internal static DiagnosticCheck Warning(string checkCode, string messageKey) => Create(checkCode, DiagnosticResult.Warning, messageKey);
+    internal static DiagnosticCheck Fail(string checkCode, string messageKey) => Create(checkCode, DiagnosticResult.Fail, messageKey);
+
+    private static DiagnosticCheck Create(string checkCode, DiagnosticResult result, string messageKey) =>
+        new(RedactionPolicy.Code(checkCode, "invalid_check"), result, RedactionPolicy.Code(messageKey, "diagnostic_redacted"), DateTimeOffset.UtcNow);
 }
 
 internal sealed record DiagnosticStorageSummary(long UsedBytes, long CapacityBytes, long ReclaimableBytes);
diff --git a/supervisor/Dada.Supervisor/ManagedChildProcess.cs b/supervisor/Dada.Supervisor/ManagedChildProcess.cs
index 953c42b..8f4a646 100644
--- a/supervisor/Dada.Supervisor/ManagedChildProcess.cs
+++ b/supervisor/Dada.Supervisor/ManagedChildProcess.cs
@@ -8,18 +8,32 @@ internal sealed class ManagedChildProcess : IAsyncDisposable
 {
     private readonly NamedPipeServerStream controlPipe;
     private readonly StreamWriter controlWriter;
+    private readonly StreamReader controlReader;
+    private Action<string>? statusReceived;
     private bool stopping;
 
-    private ManagedChildProcess(Process process, NamedPipeServerStream controlPipe, StreamWriter controlWriter)
+    private ManagedChildProcess(Process process, NamedPipeServerStream controlPipe, StreamReader controlReader, StreamWriter controlWriter)
     {
         Process = process;
         this.controlPipe = controlPipe;
+        this.controlReader = controlReader;
         this.controlWriter = controlWriter;
+        _ = ListenForStatusAsync();
     }
 
     internal Process Process { get; }
     internal bool IsStopping => stopping;
     internal static TimeSpan ShutdownDeadline { get; } = TimeSpan.FromSeconds(15);
+    internal string? LastStatus { get; private set; }
+    internal event Action<string> StatusReceived
+    {
+        add
+        {
+            statusReceived += value;
+            if (LastStatus is not null) value(LastStatus);
+        }
+        remove => statusReceived -= value;
+    }
 
     internal static async Task<ManagedChildProcess> StartAsync(
         ProcessStartInfo startInfo,
@@ -48,7 +62,7 @@ internal sealed class ManagedChildProcess : IAsyncDisposable
             var ready = await reader.ReadLineAsync(timeout.Token);
             if (!string.Equals(ready, "ready", StringComparison.Ordinal)) throw new InvalidOperationException("Managed child did not report ready.");
             var writer = new StreamWriter(pipe, new UTF8Encoding(false), leaveOpen: true) { AutoFlush = true };
-            return new ManagedChildProcess(process, pipe, writer);
+            return new ManagedChildProcess(process, pipe, reader, writer);
         }
         catch
         {
@@ -59,6 +73,23 @@ internal sealed class ManagedChildProcess : IAsyncDisposable
         }
     }
 
+    private async Task ListenForStatusAsync()
+    {
+        try
+        {
+            while (controlPipe.IsConnected && !Process.HasExited)
+            {
+                var status = await controlReader.ReadLineAsync();
+                if (status is null) return;
+                LastStatus = status;
+                statusReceived?.Invoke(status);
+            }
+        }
+        catch (IOException) when (stopping || Process.HasExited)
+        {
+        }
+    }
+
     internal async Task StopAsync(TimeSpan? timeout = null, CancellationToken cancellationToken = default)
     {
         if (stopping || Process.HasExited) return;
@@ -77,6 +108,7 @@ internal sealed class ManagedChildProcess : IAsyncDisposable
     {
         if (!Process.HasExited) await StopAsync();
         controlWriter.Dispose();
+        controlReader.Dispose();
         controlPipe.Dispose();
         Process.Dispose();
     }
diff --git a/supervisor/Dada.Supervisor/StructuredJsonlLogger.cs b/supervisor/Dada.Supervisor/StructuredJsonlLogger.cs
new file mode 100644
index 0000000..3b4adea
--- /dev/null
+++ b/supervisor/Dada.Supervisor/StructuredJsonlLogger.cs
@@ -0,0 +1,158 @@
+using System.Text.Json;
+
+namespace Dada.Supervisor;
+
+internal sealed record StructuredLogEvent(
+    string StatusCategory,
+    string? CorrelationId = null,
+    string? ObjectId = null,
+    long? DurationMs = null,
+    string? ErrorCategory = null);
+
+internal static class RedactionPolicy
+{
+    private static readonly HashSet<string> StatusCategories =
+        ["starting", "ready", "completed", "failed", "unavailable", "degraded", "blocked", "stopping", "stopped"];
+    private static readonly HashSet<string> ErrorCategories =
+        ["none", "invalid_input", "storage_unavailable", "log_write_failed", "service_unavailable", "timeout", "internal_error"];
+
+    internal static string StatusCategory(string value) => StatusCategories.Contains(value) ? value : "failed";
+    internal static string ErrorCategory(string value) => ErrorCategories.Contains(value) ? value : "internal_error";
+    internal static string Code(string value, string fallback) =>
+        value.Length is > 0 and <= 64 && value[0] is >= 'a' and <= 'z' && value.All(character => character is >= 'a' and <= 'z' or >= '0' and <= '9' or '_')
+            ? value
+            : fallback;
+    internal static string? Identifier(string? value) =>
+        value is { Length: > 0 and <= 64 } && value.All(character => char.IsAsciiLetterOrDigit(character) || character is '_' or '-')
+            ? value
+            : null;
+}
+
+internal sealed class StructuredJsonlLogger
+{
+    internal const long SizeLimitBytes = 10 * 1024 * 1024;
+    internal const int FileLimit = 10;
+    internal const int RetentionDays = 30;
+
+    private static readonly JsonSerializerOptions JsonOptions = new()
+    {
+        PropertyNamingPolicy = JsonNamingPolicy.SnakeCaseLower,
+    };
+
+    private readonly string directory;
+    private readonly string component;
+    private readonly long sizeLimitBytes;
+    private readonly int fileLimit;
+    private readonly Func<DateTimeOffset> now;
+    private readonly Action onWriteFailure;
+    private static readonly System.Text.Encoding Utf8WithoutBom = new System.Text.UTF8Encoding(false);
+    private bool initialized;
+    private long currentSize;
+
+    internal StructuredJsonlLogger(
+        string directory,
+        string component,
+        Action? onWriteFailure = null,
+        Func<DateTimeOffset>? now = null,
+        long sizeLimitBytes = SizeLimitBytes,
+        int fileLimit = FileLimit)
+    {
+        this.directory = directory;
+        this.component = component is "api" or "worker" or "supervisor" ? component : "supervisor";
+        this.onWriteFailure = onWriteFailure ?? (() => { });
+        this.now = now ?? (() => DateTimeOffset.UtcNow);
+        this.sizeLimitBytes = sizeLimitBytes;
+        this.fileLimit = fileLimit;
+    }
+
+    internal void Write(StructuredLogEvent input)
+    {
+        try
+        {
+            Initialize();
+            var entry = new Dictionary<string, object?>
+            {
+                ["schema_version"] = "1.0",
+                ["timestamp"] = now().ToString("O"),
+                ["component"] = component,
+                ["status_category"] = RedactionPolicy.StatusCategory(input.StatusCategory),
+            };
+            var correlationId = RedactionPolicy.Identifier(input.CorrelationId);
+            var objectId = RedactionPolicy.Identifier(input.ObjectId);
+            if (correlationId is not null) entry["correlation_id"] = correlationId;
+            if (objectId is not null) entry["object_id"] = objectId;
+            if (input.DurationMs is >= 0) entry["duration_ms"] = input.DurationMs;
+            if (input.ErrorCategory is not null) entry["error_category"] = RedactionPolicy.ErrorCategory(input.ErrorCategory);
+            var line = JsonSerializer.Serialize(entry, JsonOptions) + Environment.NewLine;
+            var bytes = System.Text.Encoding.UTF8.GetByteCount(line);
+            if (bytes > sizeLimitBytes) throw new InvalidOperationException("log_entry_too_large");
+            if (currentSize > 0 && currentSize + bytes > sizeLimitBytes) Rotate();
+            File.AppendAllText(ActivePath(), line, Utf8WithoutBom);
+            currentSize += bytes;
+        }
+        catch (Exception exception) when (exception is not LogWriteException)
+        {
+            try { onWriteFailure(); } catch { }
+            throw new LogWriteException(exception);
+        }
+    }
+
+    internal void Maintain()
+    {
+        try
+        {
+            Directory.CreateDirectory(directory);
+            var cutoff = now().AddDays(-RetentionDays);
+            foreach (var file in Files())
+            {
+                if (file.Index > fileLimit - 1 || file.Info.LastWriteTimeUtc < cutoff.UtcDateTime) file.Info.Delete();
+            }
+            foreach (var file in Files().Skip(fileLimit)) file.Info.Delete();
+            currentSize = File.Exists(ActivePath()) ? new FileInfo(ActivePath()).Length : 0;
+            initialized = true;
+        }
+        catch (Exception exception) when (exception is not LogWriteException)
+        {
+            try { onWriteFailure(); } catch { }
+            throw new LogWriteException(exception);
+        }
+    }
+
+    private void Initialize()
+    {
+        if (!initialized) Maintain();
+    }
+
+    private void Rotate()
+    {
+        File.Delete(Path.Combine(directory, $"{component}.{fileLimit - 1}.jsonl"));
+        for (var index = fileLimit - 2; index >= 1; index--)
+        {
+            var source = Path.Combine(directory, $"{component}.{index}.jsonl");
+            if (File.Exists(source)) File.Move(source, Path.Combine(directory, $"{component}.{index + 1}.jsonl"));
+        }
+        if (File.Exists(ActivePath())) File.Move(ActivePath(), Path.Combine(directory, $"{component}.1.jsonl"));
+        currentSize = 0;
+    }
+
+    private IReadOnlyList<(int Index, FileInfo Info)> Files()
+    {
+        if (!Directory.Exists(directory)) return [];
+        var prefix = component + ".";
+        return Directory.EnumerateFiles(directory, $"{component}*.jsonl")
+            .Select(path =>
+            {
+                var name = Path.GetFileName(path);
+                var index = name == $"{component}.jsonl"
+                    ? 0
+                    : int.TryParse(name[prefix.Length..^".jsonl".Length], out var parsed) ? parsed : int.MaxValue;
+                return (Index: index, Info: new FileInfo(path));
+            })
+            .OrderBy(file => file.Index)
+            .ToArray();
+    }
+
+    private string ActivePath() => Path.Combine(directory, $"{component}.jsonl");
+}
+
+internal sealed class LogWriteException(Exception innerException) : IOException("log_write_failed", innerException);
diff --git a/supervisor/Dada.Supervisor/SupervisorForm.cs b/supervisor/Dada.Supervisor/SupervisorForm.cs
index b552212..bac43fd 100644
--- a/supervisor/Dada.Supervisor/SupervisorForm.cs
+++ b/supervisor/Dada.Supervisor/SupervisorForm.cs
@@ -268,6 +268,8 @@ internal sealed class SupervisorForm : Form
 
 internal sealed class DiagnosticsForm : Form
 {
+    internal string CopyPayload { get; }
+
     internal DiagnosticsForm(SupervisorState state)
     {
         BackColor = Color.White;
@@ -281,11 +283,22 @@ internal sealed class DiagnosticsForm : Form
         checks.Columns.Add("组件", 170);
         checks.Columns.Add("状态", 110);
         checks.Columns.Add("检查结果", 390);
+        var report = DiagnosticReport.Create(
+            state,
+            [
+                state == SupervisorState.StorageUnavailable
+                    ? DiagnosticCheck.Fail("log_writable", "log_write_failed")
+                    : DiagnosticCheck.Pass("log_writable", "log_ready"),
+                DiagnosticCheck.Pass("fixed_port", "loopback_only"),
+            ],
+            new DiagnosticStorageSummary(0, 0, 0),
+            []);
+        CopyPayload = System.Text.Json.JsonSerializer.Serialize(report, new System.Text.Json.JsonSerializerOptions { WriteIndented = true });
         checks.Items.Add(new ListViewItem(["Supervisor", "正常", StateLabel(state)]));
         checks.Items.Add(new ListViewItem(["固定端口", "43121", "仅绑定 127.0.0.1"]));
         checks.Items.Add(new ListViewItem(["凭据", "已脱敏", "仅显示是否已配置"]));
         var copy = new Button { Location = new Point(592, 382), Size = new Size(138, 36), Text = "复制脱敏结果" };
-        copy.Click += (_, _) => Clipboard.SetText("Dada diagnostics: redacted");
+        copy.Click += (_, _) => Clipboard.SetText(CopyPayload);
         Controls.AddRange([title, detail, checks, copy]);
     }
 
diff --git a/supervisor/Dada.Supervisor/SupervisorRuntime.cs b/supervisor/Dada.Supervisor/SupervisorRuntime.cs
index 17f35c2..dae1956 100644
--- a/supervisor/Dada.Supervisor/SupervisorRuntime.cs
+++ b/supervisor/Dada.Supervisor/SupervisorRuntime.cs
@@ -7,6 +7,7 @@ internal sealed class SupervisorRuntime : IAsyncDisposable
     private readonly ICredentialStore credentials;
     private ManagedComponentSupervisor? api;
     private ManagedComponentSupervisor? worker;
+    private StructuredJsonlLogger? logger;
 
     internal SupervisorRuntime(ICredentialStore credentials)
     {
@@ -24,6 +25,15 @@ internal sealed class SupervisorRuntime : IAsyncDisposable
         {
             return SupervisorState.StartupFailed;
         }
+        try
+        {
+            logger = new StructuredJsonlLogger(Path.Combine(configuration.LocalDataRoot, "logs", "supervisor"), "supervisor");
+            logger.Write(new StructuredLogEvent("starting", ErrorCategory: "none"));
+        }
+        catch (LogWriteException)
+        {
+            return SupervisorState.StorageUnavailable;
+        }
         if (CredentialCatalog.RequiredFor(ChildRole.Api).Concat(CredentialCatalog.RequiredFor(ChildRole.Worker)).Any(target => !credentials.IsConfigured(target)))
         {
             return SupervisorState.StartupFailed;
@@ -35,22 +45,50 @@ internal sealed class SupervisorRuntime : IAsyncDisposable
         if (!File.Exists(node) || !File.Exists(apiEntry) || !File.Exists(workerEntry)) return SupervisorState.StartupFailed;
 
         api = CreateComponent(node, apiEntry, ChildRole.Api, SupervisorState.ApiDegraded);
-        api.StateChanged += state => StateChanged?.Invoke(state);
         await api.StartAsync(cancellationToken);
 
         worker = CreateComponent(node, workerEntry, ChildRole.Worker, SupervisorState.WorkerDegraded);
-        worker.StateChanged += state => StateChanged?.Invoke(state);
         await worker.StartAsync(cancellationToken);
-        return SupervisorState.Ready;
+        return TryLog(new StructuredLogEvent("ready", ErrorCategory: "none")) ? SupervisorState.Ready : SupervisorState.StorageUnavailable;
     }
 
-    private ManagedComponentSupervisor CreateComponent(string node, string entry, ChildRole role, SupervisorState degradedState) =>
-        new(async cancellationToken =>
+    private ManagedComponentSupervisor CreateComponent(string node, string entry, ChildRole role, SupervisorState degradedState)
+    {
+        var component = new ManagedComponentSupervisor(async cancellationToken =>
         {
             var startInfo = new ProcessStartInfo(node);
             startInfo.ArgumentList.Add(entry);
-            return await ManagedChildProcess.StartAsync(startInfo, role, credentials, cancellationToken);
+            var child = await ManagedChildProcess.StartAsync(startInfo, role, credentials, cancellationToken);
+            child.StatusReceived += status =>
+            {
+                if (status == "storage_unavailable")
+                {
+                    TryLog(new StructuredLogEvent("unavailable", ErrorCategory: "log_write_failed"));
+                    StateChanged?.Invoke(SupervisorState.StorageUnavailable);
+                }
+            };
+            return child;
         }, degradedState);
+        component.StateChanged += state =>
+        {
+            if (TryLog(new StructuredLogEvent("degraded", ErrorCategory: "service_unavailable"))) StateChanged?.Invoke(state);
+        };
+        return component;
+    }
+
+    private bool TryLog(StructuredLogEvent entry)
+    {
+        try
+        {
+            logger?.Write(entry);
+            return true;
+        }
+        catch (LogWriteException)
+        {
+            StateChanged?.Invoke(SupervisorState.StorageUnavailable);
+            return false;
+        }
+    }
 
     public async ValueTask DisposeAsync()
     {
diff --git a/tests/integration/wp0-08-structured-log.test.ts b/tests/integration/wp0-08-structured-log.test.ts
new file mode 100644
index 0000000..ae400af
--- /dev/null
+++ b/tests/integration/wp0-08-structured-log.test.ts
@@ -0,0 +1,137 @@
+import { randomUUID } from "node:crypto";
+import { mkdirSync, readFileSync, readdirSync, statSync, utimesSync, writeFileSync } from "node:fs";
+import { join } from "node:path";
+import { tmpdir } from "node:os";
+
+import { afterEach, describe, expect, it } from "vitest";
+
+import { ManagedStorage } from "../../apps/api/src/managed-storage.js";
+import {
+  LOG_FILE_LIMIT,
+  LOG_RETENTION_DAYS,
+  LOG_SIZE_LIMIT_BYTES,
+  StructuredJsonlLogger,
+  sanitizeDiagnosticRecord,
+} from "../../apps/api/src/structured-log.js";
+
+const temporaryRoots: string[] = [];
+
+function fixtureRoot() {
+  const root = join(tmpdir(), `dada-wp0-08-${randomUUID()}`);
+  mkdirSync(root, { recursive: true });
+  temporaryRoots.push(root);
+  return root;
+}
+
+function evidence(name: string, value: unknown) {
+  const directory = process.env.DADA_EVIDENCE_DIR_LOG;
+  if (!directory) return;
+  mkdirSync(directory, { recursive: true });
+  writeFileSync(join(directory, name), `${JSON.stringify(value, null, 2)}\n`);
+}
+
+afterEach(async () => {
+  const { rm } = await import("node:fs/promises");
+  await Promise.all(temporaryRoots.splice(0).map((root) => rm(root, { force: true, recursive: true })));
+});
+
+describe("TDD-WP0-LOG-001 rotation and redaction", () => {
+  it("enforces 10 MiB, 10 files, 30 days and emits only allowlisted JSONL fields", () => {
+    const root = fixtureRoot();
+    const logDirectory = join(root, "logs", "api");
+    mkdirSync(logDirectory, { recursive: true });
+    const activePath = join(logDirectory, "api.jsonl");
+    const seedLine = `${JSON.stringify({
+      component: "api",
+      correlation_id: "corr_fixture",
+      schema_version: "1.0",
+      status_category: "ready",
+      timestamp: "2026-01-01T00:00:00.000Z",
+    })}\n`;
+    const repeats = Math.floor(LOG_SIZE_LIMIT_BYTES / Buffer.byteLength(seedLine));
+    writeFileSync(activePath, seedLine.repeat(repeats));
+    const bytesBeforeBoundaryWrite = statSync(activePath).size;
+
+    const marker = `trap-${randomUUID()}`;
+    const logger = new StructuredJsonlLogger({ component: "api", directory: logDirectory });
+    logger.write({
+      absolute_path: join(root, marker),
+      api_key: `${marker}-key`,
+      correlation_id: "corr_boundary",
+      duration_ms: 12,
+      email: `${marker}@example.invalid`,
+      error_category: "none",
+      image: Buffer.from(marker),
+      object_id: "obj_boundary",
+      prompt: `${marker} private prompt`,
+      provider_error: `${marker} upstream body`,
+      status_category: "completed",
+    });
+    expect(statSync(join(logDirectory, "api.1.jsonl")).size).toBeLessThanOrEqual(LOG_SIZE_LIMIT_BYTES);
+    expect(statSync(activePath).size).toBeLessThanOrEqual(LOG_SIZE_LIMIT_BYTES);
+
+    for (let index = 2; index <= 14; index += 1) writeFileSync(join(logDirectory, `api.${index}.jsonl`), seedLine);
+    const stalePath = join(logDirectory, "api.4.jsonl");
+    const stale = new Date(Date.now() - (LOG_RETENTION_DAYS + 1) * 24 * 60 * 60 * 1000);
+    utimesSync(stalePath, stale, stale);
+    new StructuredJsonlLogger({ component: "api", directory: logDirectory }).maintain();
+
+    const files = readdirSync(logDirectory).sort();
+    const scanned = files.map((name) => readFileSync(join(logDirectory, name), "utf8")).join("");
+    expect(files.length).toBeLessThanOrEqual(LOG_FILE_LIMIT);
+    expect(files).not.toContain("api.4.jsonl");
+    expect(scanned).not.toContain(marker);
+    const activeEntry = JSON.parse(readFileSync(activePath, "utf8").trim()) as Record<string, unknown>;
+    expect(Object.keys(activeEntry).sort()).toEqual([
+      "component", "correlation_id", "duration_ms", "error_category", "object_id", "schema_version", "status_category", "timestamp",
+    ]);
+
+    const diagnostic = sanitizeDiagnosticRecord({
+      app_version: "0.0.0",
+      checked_at: "2026-01-01T00:00:00.000Z",
+      component: "api",
+      message_key: "log_write_failed",
+      private_content: marker,
+      result: "fail",
+      stable_check_code: "log_writable",
+      user_path: join(root, marker),
+    });
+    expect(JSON.stringify(diagnostic)).not.toContain(marker);
+    evidence("log-manifest.json", {
+      bytes_before_boundary_write: bytesBeforeBoundaryWrite,
+      file_limit: LOG_FILE_LIMIT,
+      files: files.map((name) => ({ name, size: statSync(join(logDirectory, name)).size })),
+      retention_days: LOG_RETENTION_DAYS,
+      size_limit_bytes: LOG_SIZE_LIMIT_BYTES,
+      status: "passed",
+      total_generated_bytes: bytesBeforeBoundaryWrite + statSync(activePath).size,
+    });
+    evidence("redaction.json", { diagnostic, marker_absent: true, status: "passed" });
+  });
+
+  it("marks storage unavailable when the log directory cannot be written", () => {
+    const root = fixtureRoot();
+    const storage = new ManagedStorage({ dataRoot: root, databasePath: join(root, "db", "dada.sqlite3") });
+    const blockedDirectory = join(root, "logs-blocked");
+    writeFileSync(blockedDirectory, "not-a-directory");
+    const logger = new StructuredJsonlLogger({
+      component: "api",
+      directory: blockedDirectory,
+      onWriteFailure: () => storage.setLogAvailability(false),
+    });
+    expect(() => logger.write({ correlation_id: "corr_log_failure", error_category: "log_write_failed", status_category: "failed" })).toThrow("log_write_failed");
+    expect(storage.getState().storage_status).toBe("unavailable");
+    expect(storage.inspectAction("ai_call")).toBe("reject_unavailable");
+    evidence("response.json", {
+      ai_call: storage.inspectAction("ai_call"),
+      business_objects_changed: 0,
+      storage_status: storage.getState().storage_status,
+      status: "passed",
+    });
+    storage.setLogAvailability(true);
+    expect(storage.getState().storage_status).toBe("unavailable");
+    storage.applyControlledMeasurement(0);
+    expect(storage.getState().storage_status).toBe("active");
+    storage.close();
+  });
+});
diff --git a/tests/worker/wp0-08-log-availability.test.ts b/tests/worker/wp0-08-log-availability.test.ts
new file mode 100644
index 0000000..ea51e67
--- /dev/null
+++ b/tests/worker/wp0-08-log-availability.test.ts
@@ -0,0 +1,52 @@
+import { randomUUID } from "node:crypto";
+import { mkdirSync, writeFileSync } from "node:fs";
+import { join } from "node:path";
+import { tmpdir } from "node:os";
+
+import { expect, it, vi } from "vitest";
+
+import { ManagedStorage } from "../../apps/api/src/managed-storage.js";
+import { WorkerAiCallGate } from "../../apps/worker/src/ai-call-gate.js";
+import { WorkerStorageStatus } from "../../apps/worker/src/storage-status.js";
+import { StructuredJsonlLogger } from "../../apps/worker/src/structured-log.js";
+
+it("TDD-WP0-LOG-001 blocks AI before an upstream call when logging becomes unavailable", async () => {
+  const root = join(tmpdir(), `dada-wp0-08-worker-${randomUUID()}`);
+  mkdirSync(root, { recursive: true });
+  const blockedDirectory = join(root, "blocked-log-directory");
+  writeFileSync(blockedDirectory, "not-a-directory");
+  const databasePath = join(root, "db", "dada.sqlite3");
+  const managedStorage = new ManagedStorage({ dataRoot: root, databasePath });
+  const workerStorage = new WorkerStorageStatus(databasePath);
+  let storageStatus: "active" | "unavailable" = "active";
+  const logger = new StructuredJsonlLogger({
+    component: "worker",
+    directory: blockedDirectory,
+    onWriteFailure: () => {
+      storageStatus = "unavailable";
+      workerStorage.markLogUnavailable();
+    },
+  });
+  const externalCall = vi.fn(async () => ({ provider_request_id: "must-not-exist" }));
+  const gate = new WorkerAiCallGate({ getStorageStatus: () => storageStatus, logger });
+
+  await expect(gate.execute("corr_worker_log_failure", "job_internal", externalCall)).resolves.toEqual({
+    reason: "storage_unavailable",
+    status: "blocked",
+  });
+  expect(storageStatus).toBe("unavailable");
+  expect(workerStorage.getStatus()).toBe("unavailable");
+  expect(managedStorage.getState().storage_status).toBe("unavailable");
+  expect(externalCall).not.toHaveBeenCalled();
+
+  const directory = process.env.DADA_EVIDENCE_DIR_LOG;
+  if (directory) {
+    mkdirSync(directory, { recursive: true });
+    writeFileSync(join(directory, "external-calls.json"), `${JSON.stringify({ calls: 0, reason: "storage_unavailable", status: "passed" }, null, 2)}\n`);
+  }
+
+  const { rm } = await import("node:fs/promises");
+  workerStorage.close();
+  managedStorage.close();
+  await rm(root, { force: true, recursive: true });
+});