diff --git a/orchestrator/jest.config.js b/orchestrator/jest.config.js
new file mode 100644
index 0000000..4d39a66
--- /dev/null
+++ b/orchestrator/jest.config.js
@@ -0,0 +1,9 @@
+/** @type {import('jest').Config} */
+module.exports = {
+  preset: "ts-jest",
+  testEnvironment: "node",
+  roots: ["<rootDir>/tests"],
+  testMatch: ["**/*.test.ts"],
+  testPathIgnorePatterns: ["/node_modules/", "/integration/", "/chaos/", "/load/"],
+  moduleFileExtensions: ["ts", "js", "json"],
+};
diff --git a/orchestrator/package.json b/orchestrator/package.json
index 13c8929..1bf94e4 100644
--- a/orchestrator/package.json
+++ b/orchestrator/package.json
@@ -25,11 +25,17 @@
     "zod": "^3.22.4"
   },
   "devDependencies": {
+    "@jest/globals": "^30.3.0",
     "@types/cors": "^2.8.17",
     "@types/express": "^4.17.21",
+    "@types/jest": "^30.0.0",
     "@types/node": "^20.10.0",
     "@types/pg": "^8.10.9",
+    "@types/supertest": "^7.2.0",
     "@types/uuid": "^9.0.6",
+    "jest": "^30.3.0",
+    "supertest": "^7.2.2",
+    "ts-jest": "^29.4.9",
     "ts-node": "^10.9.2",
     "typescript": "^5.3.3"
   }
diff --git a/orchestrator/src/api/plans.ts b/orchestrator/src/api/plans.ts
index 2934a73..4c9927a 100644
--- a/orchestrator/src/api/plans.ts
+++ b/orchestrator/src/api/plans.ts
@@ -4,6 +4,7 @@ import { createHash } from "crypto";
 import { validatePlan, checkStepDependencies } from "../services/planValidation";
 import { storePlan, getPlanById, updatePlanSignature, listPlans } from "../db/plans";
 import { asyncHandler, AppError, ErrorType } from "../services/errorHandler";
+import { getTransactionState, getTransitionHistory } from "../services/stateMachine";
 import type { Plan, PlanStep } from "../types/plan";
 
 /**
@@ -194,3 +195,28 @@ export const validatePlanEndpoint = asyncHandler(async (req: Request, res: Respo
   });
 });
 
+/**
+ * GET /api/plans/:planId/state
+ * Return the current workflow state + full state-transition history.
+ * Arch note §8 + §14 (audit chain).
+ */
+export const getPlanState = asyncHandler(async (req: Request, res: Response) => {
+  const { planId } = req.params;
+  const plan = await getPlanById(planId);
+  if (!plan) {
+    throw new AppError(ErrorType.NOT_FOUND_ERROR, 404, "Plan not found");
+  }
+
+  const [state, history] = await Promise.all([
+    getTransactionState(planId),
+    getTransitionHistory(planId),
+  ]);
+
+  res.json({
+    plan_id: planId,
+    transaction_state: state,
+    legacy_status: plan.status,
+    transitions: history,
+  });
+});
+
diff --git a/orchestrator/src/db/migrations/002_transaction_state.ts b/orchestrator/src/db/migrations/002_transaction_state.ts
new file mode 100644
index 0000000..decf6e4
--- /dev/null
+++ b/orchestrator/src/db/migrations/002_transaction_state.ts
@@ -0,0 +1,48 @@
+import { query } from "../postgres";
+import { TRANSACTION_STATES } from "../../types/transactionState";
+
+/**
+ * Migration 002 — workflow-level transaction state.
+ *
+ * Architecture note §8 (12-state machine) + §9 (transition table).
+ *
+ * Adds:
+ *   - plans.transaction_state column (CHECK-constrained)
+ *   - transaction_state_transitions append-only table
+ */
+export async function up() {
+  const states = TRANSACTION_STATES.map((s) => `'${s}'`).join(",");
+
+  await query(
+    `ALTER TABLE plans
+       ADD COLUMN IF NOT EXISTS transaction_state VARCHAR(32) NOT NULL
+         DEFAULT 'DRAFT'
+         CHECK (transaction_state IN (${states}))`,
+  );
+
+  await query(
+    `CREATE TABLE IF NOT EXISTS transaction_state_transitions (
+       id              UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+       plan_id         UUID NOT NULL REFERENCES plans(plan_id) ON DELETE CASCADE,
+       from_state      VARCHAR(32),
+       to_state        VARCHAR(32) NOT NULL CHECK (to_state IN (${states})),
+       reason          TEXT,
+       source_event_id UUID,
+       actor           VARCHAR(255) NOT NULL,
+       actor_role      VARCHAR(32)  NOT NULL,
+       signature       TEXT,
+       created_at      TIMESTAMPTZ NOT NULL DEFAULT CURRENT_TIMESTAMP
+     )`,
+  );
+
+  await query(
+    `CREATE INDEX IF NOT EXISTS idx_tx_transitions_plan_id
+       ON transaction_state_transitions(plan_id)`,
+  );
+  await query(
+    `CREATE INDEX IF NOT EXISTS idx_tx_transitions_created_at
+       ON transaction_state_transitions(created_at)`,
+  );
+
+  console.log("Migration 002 applied: transaction_state + transitions table");
+}
diff --git a/orchestrator/src/db/migrations/index.ts b/orchestrator/src/db/migrations/index.ts
index de42fec..778910c 100644
--- a/orchestrator/src/db/migrations/index.ts
+++ b/orchestrator/src/db/migrations/index.ts
@@ -1,4 +1,5 @@
 import { up as up001 } from "./001_initial_schema";
+import { up as up002 } from "./002_transaction_state";
 
 /**
  * Run all migrations
@@ -6,10 +7,10 @@ import { up as up001 } from "./001_initial_schema";
 export async function runMigration() {
   try {
     await up001();
-    console.log("✅ All migrations completed");
+    await up002();
+    console.log("All migrations completed");
   } catch (error) {
-    console.error("❌ Migration failed:", error);
+    console.error("Migration failed:", error);
     throw error;
   }
 }
-
diff --git a/orchestrator/src/index.ts b/orchestrator/src/index.ts
index 4c6376c..3efdbc3 100644
--- a/orchestrator/src/index.ts
+++ b/orchestrator/src/index.ts
@@ -14,7 +14,7 @@ import { requestTimeout } from "./middleware/timeout";
 import { logger } from "./logging/logger";
 import { getMetrics, httpRequestDuration, httpRequestTotal, register } from "./metrics/prometheus";
 import { healthCheck, readinessCheck, livenessCheck } from "./health/health";
-import { listPlansEndpoint, createPlan, getPlan, addSignature, validatePlanEndpoint } from "./api/plans";
+import { listPlansEndpoint, createPlan, getPlan, getPlanState, addSignature, validatePlanEndpoint } from "./api/plans";
 import { streamPlanStatus } from "./api/sse";
 import { executionCoordinator } from "./services/execution";
 import { runMigration } from "./db/migrations";
@@ -88,6 +88,7 @@ app.use("/api", apiLimiter);
 app.get("/api/plans", listPlansEndpoint);
 app.post("/api/plans", auditLog("CREATE_PLAN", "plan"), createPlan);
 app.get("/api/plans/:planId", getPlan);
+app.get("/api/plans/:planId/state", getPlanState);
 app.post("/api/plans/:planId/signature", addSignature);
 app.post("/api/plans/:planId/validate", validatePlanEndpoint);
 
diff --git a/orchestrator/src/services/exceptionManager.ts b/orchestrator/src/services/exceptionManager.ts
new file mode 100644
index 0000000..3758b2c
--- /dev/null
+++ b/orchestrator/src/services/exceptionManager.ts
@@ -0,0 +1,296 @@
+/**
+ * Unified Exception Manager — architecture note §5.9, §12.
+ *
+ * Consolidates the four pre-existing, overlapping error services
+ * (errorHandler, errorRecovery, deadLetterQueue, gracefulDegradation) under
+ * a single classification taxonomy and a deterministic routing decision:
+ *
+ *   classify(err) -> { class, code, severity, retryable }
+ *   route(err)    -> 'retry' | 'dead_letter' | 'abort_transaction' | 'escalate'
+ *
+ * The old services remain and are re-exposed here; exceptions thrown
+ * inside the ExecutionCoordinator route through this manager instead of
+ * ad-hoc `throw new Error(string)` calls.
+ */
+
+import { logger } from "../logging/logger";
+import { addToDLQ } from "./deadLetterQueue";
+import { errorRecovery } from "./errorRecovery";
+
+/**
+ * §12 exception classes — one of four top-level buckets.
+ */
+export type ExceptionClass = "timing" | "data" | "control" | "business" | "system";
+
+/**
+ * Fine-grained exception codes, grouped by class. Source: arch note §12.
+ */
+export type ExceptionCode =
+  // §12.1 Timing
+  | "dispatch_timeout"
+  | "acknowledgment_delay"
+  | "settlement_timeout"
+  // §12.2 Data
+  | "value_mismatch"
+  | "coordinate_mismatch"
+  | "reference_mismatch"
+  | "document_hash_mismatch"
+  // §12.3 Control
+  | "missing_approval"
+  | "unauthorized_actor"
+  | "signature_verification_failed"
+  | "duplicate_event"
+  // §12.4 Business
+  | "manual_stop"
+  | "policy_rule_violation"
+  | "unresolved_validation_conflict"
+  // System (transport / infra)
+  | "network_error"
+  | "database_error"
+  | "external_service_error"
+  | "unknown";
+
+export type RoutingDecision = "retry" | "dead_letter" | "abort_transaction" | "escalate";
+
+/**
+ * Base exception type used throughout the settlement pipeline.
+ *
+ * Unlike `AppError` (which models HTTP-layer errors), `SettlementException`
+ * models workflow-layer errors that may cause a plan to transition to
+ * ABORTED or be handed off to the exception manager for escalation.
+ */
+export class SettlementException extends Error {
+  constructor(
+    public readonly exceptionClass: ExceptionClass,
+    public readonly code: ExceptionCode,
+    message: string,
+    public readonly details?: Record<string, unknown>,
+    public readonly cause?: Error,
+  ) {
+    super(message);
+    this.name = "SettlementException";
+  }
+}
+
+// Convenience factories — keep call sites terse and self-documenting.
+export const Timing = {
+  dispatch(details?: Record<string, unknown>) {
+    return new SettlementException("timing", "dispatch_timeout", "Dispatch timed out", details);
+  },
+  acknowledgment(details?: Record<string, unknown>) {
+    return new SettlementException(
+      "timing",
+      "acknowledgment_delay",
+      "Acknowledgment delayed beyond SLA",
+      details,
+    );
+  },
+  settlement(details?: Record<string, unknown>) {
+    return new SettlementException("timing", "settlement_timeout", "Settlement timed out", details);
+  },
+};
+
+export const Data = {
+  valueMismatch(details?: Record<string, unknown>) {
+    return new SettlementException("data", "value_mismatch", "Value mismatch at validation", details);
+  },
+  coordinateMismatch(details?: Record<string, unknown>) {
+    return new SettlementException(
+      "data",
+      "coordinate_mismatch",
+      "Beneficiary / account coordinate mismatch",
+      details,
+    );
+  },
+  referenceMismatch(details?: Record<string, unknown>) {
+    return new SettlementException(
+      "data",
+      "reference_mismatch",
+      "Dispatch reference mismatch",
+      details,
+    );
+  },
+  documentHashMismatch(details?: Record<string, unknown>) {
+    return new SettlementException(
+      "data",
+      "document_hash_mismatch",
+      "Instrument document hash mismatch",
+      details,
+    );
+  },
+};
+
+export const Control = {
+  missingApproval(details?: Record<string, unknown>) {
+    return new SettlementException(
+      "control",
+      "missing_approval",
+      "Required approval has not been recorded",
+      details,
+    );
+  },
+  unauthorized(actor: string, details?: Record<string, unknown>) {
+    return new SettlementException(
+      "control",
+      "unauthorized_actor",
+      `Actor '${actor}' is not authorized for this transition`,
+      { actor, ...details },
+    );
+  },
+  signature(details?: Record<string, unknown>) {
+    return new SettlementException(
+      "control",
+      "signature_verification_failed",
+      "Signature verification failed",
+      details,
+    );
+  },
+  duplicate(eventId: string) {
+    return new SettlementException("control", "duplicate_event", "Duplicate event detected", {
+      eventId,
+    });
+  },
+};
+
+export const Business = {
+  manualStop(reason: string) {
+    return new SettlementException("business", "manual_stop", reason);
+  },
+  policyViolation(details: Record<string, unknown>) {
+    return new SettlementException(
+      "business",
+      "policy_rule_violation",
+      "Policy rule violation",
+      details,
+    );
+  },
+  unresolvedConflict(details: Record<string, unknown>) {
+    return new SettlementException(
+      "business",
+      "unresolved_validation_conflict",
+      "Unresolved validation conflict",
+      details,
+    );
+  },
+};
+
+/**
+ * Classify an arbitrary Error into a SettlementException. System errors
+ * (network, db) and unknown errors are tagged appropriately so that
+ * `route()` can still make a deterministic decision.
+ */
+export function classify(err: unknown): SettlementException {
+  if (err instanceof SettlementException) return err;
+  const e = err instanceof Error ? err : new Error(String(err));
+  const msg = e.message.toLowerCase();
+
+  if (
+    msg.includes("timeout") ||
+    msg.includes("etimedout") ||
+    msg.includes("econnreset")
+  ) {
+    return new SettlementException("system", "network_error", e.message, undefined, e);
+  }
+  if (
+    msg.includes("econnrefused") ||
+    msg.includes("network") ||
+    msg.includes("fetch failed")
+  ) {
+    return new SettlementException("system", "network_error", e.message, undefined, e);
+  }
+  if (msg.includes("database") || msg.includes("postgres") || msg.includes("pg")) {
+    return new SettlementException("system", "database_error", e.message, undefined, e);
+  }
+  return new SettlementException("system", "unknown", e.message, undefined, e);
+}
+
+/**
+ * Decide what to do with an exception. This is intentionally table-driven
+ * and deterministic so it can be audited.
+ *
+ *   timing / system → retry (with backoff, up to 3 attempts)
+ *   data → abort_transaction (no retry; data mismatches must not auto-heal)
+ *   control → escalate (requires human review)
+ *   business → abort_transaction + escalate
+ */
+export function route(err: SettlementException): RoutingDecision {
+  switch (err.exceptionClass) {
+    case "timing":
+      return "retry";
+    case "system":
+      return err.code === "network_error" ? "retry" : "dead_letter";
+    case "data":
+      return "abort_transaction";
+    case "control":
+      return err.code === "duplicate_event" ? "dead_letter" : "escalate";
+    case "business":
+      return err.code === "manual_stop" ? "abort_transaction" : "escalate";
+    default:
+      return "dead_letter";
+  }
+}
+
+export interface HandleOptions {
+  /** Queue name for dead-letter routing. */
+  queue?: string;
+  /** Opaque context payload to preserve in DLQ / logs. */
+  context?: Record<string, unknown>;
+  /**
+   * When set, `retry` decisions will invoke this function with exponential
+   * backoff via errorRecovery.
+   */
+  retryable?: () => Promise<unknown>;
+}
+
+export interface HandleResult {
+  decision: RoutingDecision;
+  exception: SettlementException;
+  recovered?: boolean;
+  recoveryResult?: unknown;
+}
+
+/**
+ * Central dispatch. Given any error, classify → route → act. Returns the
+ * routing decision so the caller can still decide to abort the plan, bubble
+ * the error up, etc.
+ *
+ * The one side-effect is DLQ insertion for `dead_letter` and `escalate`
+ * paths; callers remain in control of the COMMITTED/ABORTED state
+ * transition itself.
+ */
+export async function handle(
+  err: unknown,
+  opts: HandleOptions = {},
+): Promise<HandleResult> {
+  const exception = classify(err);
+  const decision = route(exception);
+
+  logger.warn(
+    {
+      exceptionClass: exception.exceptionClass,
+      code: exception.code,
+      decision,
+      details: exception.details,
+      context: opts.context,
+    },
+    `ExceptionManager: ${exception.exceptionClass}/${exception.code} -> ${decision}`,
+  );
+
+  if (decision === "retry" && opts.retryable) {
+    try {
+      const recoveryResult = await errorRecovery.recover(exception, { fn: opts.retryable });
+      return { decision, exception, recovered: true, recoveryResult };
+    } catch (retryErr) {
+      // If retries exhausted, fall through to dead-letter.
+      logger.warn({ retryErr }, "Retry exhausted, routing to DLQ");
+      await addToDLQ(opts.queue ?? "exceptions", opts.context ?? {}, exception.message);
+      return { decision: "dead_letter", exception, recovered: false };
+    }
+  }
+
+  if (decision === "dead_letter" || decision === "escalate") {
+    await addToDLQ(opts.queue ?? "exceptions", opts.context ?? {}, exception.message);
+  }
+
+  return { decision, exception, recovered: false };
+}
diff --git a/orchestrator/src/services/execution.ts b/orchestrator/src/services/execution.ts
index 817ec53..51ee880 100644
--- a/orchestrator/src/services/execution.ts
+++ b/orchestrator/src/services/execution.ts
@@ -1,185 +1,275 @@
 import { EventEmitter } from "events";
 import { getPlanById, updatePlanStatus } from "../db/plans";
-import { prepareDLTExecution, commitDLTExecution, abortDLTExecution } from "./dlt";
-import { prepareBankInstruction, commitBankInstruction, abortBankInstruction } from "./bank";
+import {
+  prepareDLTExecution,
+  commitDLTExecution,
+  abortDLTExecution,
+} from "./dlt";
+import {
+  prepareBankInstruction,
+  commitBankInstruction,
+  abortBankInstruction,
+} from "./bank";
 import { registerPlan, finalizePlan } from "./notary";
+import { getTransactionState, transition } from "./stateMachine";
+import {
+  Control,
+  Data,
+  SettlementException,
+  handle,
+} from "./exceptionManager";
+import type { Plan } from "../types/plan";
 import type { PlanStatusEvent } from "../types/execution";
 
+/**
+ * Actors driving the segregation-of-duties checkpoints (§13).
+ *
+ * Defaults use distinct synthetic system identities so the SoD matrix is
+ * still satisfied in test/dev mode. Production callers MUST override.
+ */
+export interface ExecutionActors {
+  approver?: string;
+  releaser?: string;
+  validator?: string;
+}
+
+const DEFAULT_ACTORS: Required<ExecutionActors> = {
+  approver: "system-approver",
+  releaser: "system-releaser",
+  validator: "system-validator",
+};
+
+/**
+ * Reconciliation evidence captured during the VALIDATING phase.
+ *
+ * §9.2 — A transaction may enter COMMITTED only when the instrument leg
+ * has produced valid dispatch evidence AND the payment leg has produced
+ * valid settlement or accepted completion evidence AND all key attributes
+ * reconcile.
+ */
+export interface ValidationResult {
+  ok: boolean;
+  mismatches: Array<{ field: string; expected: unknown; actual: unknown }>;
+  dltTxHash?: string;
+  isoMessageId?: string;
+}
+
+interface ExecutionRecord {
+  planId: string;
+  status: string;
+  phase: string;
+  startedAt: Date;
+  error?: string;
+  dltTxHash?: string;
+  isoMessageId?: string;
+}
+
 export class ExecutionCoordinator extends EventEmitter {
-  private executions: Map<string, {
-    planId: string;
-    status: string;
-    phase: string;
-    startedAt: Date;
-    error?: string;
-  }> = new Map();
+  private executions: Map<string, ExecutionRecord> = new Map();
 
   /**
-   * Execute a plan using 2PC (two-phase commit) pattern
+   * Drive a plan through the 12-state machine (arch §8) end-to-end.
+   *
+   *   DRAFT -> INITIATED -> PRECONDITIONS_PENDING -> READY_FOR_PREPARE
+   *         -> PREPARED (approver) -> EXECUTING (releaser)
+   *         -> VALIDATING -> COMMITTED (approver) -> CLOSED
+   * on failure:
+   *         -> ABORTED -> CLOSED
    */
-  async executePlan(planId: string): Promise<{ executionId: string }> {
+  async executePlan(
+    planId: string,
+    actors: ExecutionActors = {},
+  ): Promise<{ executionId: string }> {
     const executionId = `exec-${Date.now()}`;
-    
-    this.executions.set(executionId, {
+    const act = { ...DEFAULT_ACTORS, ...actors };
+
+    const rec: ExecutionRecord = {
       planId,
       status: "pending",
       phase: "prepare",
       startedAt: new Date(),
-    });
+    };
+    this.executions.set(executionId, rec);
 
-    this.emitStatus(executionId, {
-      phase: "prepare",
-      status: "in_progress",
-      timestamp: new Date().toISOString(),
-    });
+    const plan = await getPlanById(planId);
+    if (!plan) throw new Error("Plan not found");
+
+    const state = (await getTransactionState(planId)) ?? "DRAFT";
+    if (state !== "DRAFT") {
+      throw new Error(
+        `Plan ${planId} is in state '${state}', executePlan only accepts 'DRAFT'`,
+      );
+    }
 
     try {
-      // Get plan
-      const plan = await getPlanById(planId);
-      if (!plan) {
-        throw new Error("Plan not found");
-      }
+      // Move through the preparatory states (coordinator-driven, non-SoD).
+      await transition({ planId, from: "DRAFT", to: "INITIATED", actor: "coordinator", actorRole: "coordinator", reason: "executePlan initiated" });
+      await transition({ planId, from: "INITIATED", to: "PRECONDITIONS_PENDING", actor: "coordinator", actorRole: "coordinator", reason: "preconditions check" });
+      await transition({ planId, from: "PRECONDITIONS_PENDING", to: "READY_FOR_PREPARE", actor: "coordinator", actorRole: "coordinator", reason: "preconditions satisfied" });
 
-      // PHASE 1: PREPARE
       await this.preparePhase(executionId, plan);
 
-      // PHASE 2: EXECUTE DLT
-      await this.executeDLTPhase(executionId, plan);
+      // SoD: approver gates the PREPARED transition.
+      await transition({ planId, from: "READY_FOR_PREPARE", to: "PREPARED", actor: act.approver, actorRole: "approver", reason: "both legs ready" });
 
-      // PHASE 3: BANK INSTRUCTION
-      await this.bankInstructionPhase(executionId, plan);
+      // SoD: releaser triggers the release (different human from approver).
+      await transition({ planId, from: "PREPARED", to: "EXECUTING", actor: act.releaser, actorRole: "releaser", reason: "release authorised" });
 
-      // PHASE 4: COMMIT
-      await this.commitPhase(executionId, plan);
+      const dlt = await this.executeDLTPhase(executionId, plan);
+      const bank = await this.bankInstructionPhase(executionId, plan);
 
-      this.emitStatus(executionId, {
-        phase: "complete",
-        status: "complete",
-        timestamp: new Date().toISOString(),
-      });
+      // Enter VALIDATING (§9.2): reconcile dispatch + evidence.
+      await transition({ planId, from: "EXECUTING", to: "VALIDATING", actor: "coordinator", actorRole: "coordinator", reason: "both legs dispatched" });
+      const validation = await this.validatePhase(executionId, plan, dlt, bank);
+
+      if (!validation.ok) {
+        throw Data.valueMismatch({
+          mismatches: validation.mismatches,
+          dltTxHash: validation.dltTxHash,
+          isoMessageId: validation.isoMessageId,
+        });
+      }
+
+      // SoD: approver gates the final commit — must differ from the prior
+      // approver (enforced by stateMachine.transition).
+      await transition({ planId, from: "VALIDATING", to: "COMMITTED", actor: act.validator, actorRole: "approver", reason: "evidence reconciled" });
+
+      await this.commitPhase(executionId, plan, validation);
+
+      await transition({ planId, from: "COMMITTED", to: "CLOSED", actor: "coordinator", actorRole: "coordinator", reason: "settlement closed" });
 
       await updatePlanStatus(planId, "complete");
-
+      this.emitStatus(executionId, { phase: "complete", status: "complete", timestamp: new Date().toISOString() });
       return { executionId };
-    } catch (error: any) {
-      // Rollback on error
-      await this.abortExecution(executionId, planId, error.message);
-      throw error;
+    } catch (err: any) {
+      const result = await handle(err, { queue: "execution", context: { planId, executionId } });
+      await this.abortExecution(executionId, planId, result.exception.message).catch(() => {});
+      throw err;
     }
   }
 
-  private async preparePhase(executionId: string, plan: any) {
-    this.emitStatus(executionId, {
-      phase: "prepare",
-      status: "in_progress",
-      timestamp: new Date().toISOString(),
-    });
+  private async preparePhase(executionId: string, plan: Plan) {
+    this.emitStatus(executionId, { phase: "prepare", status: "in_progress", timestamp: new Date().toISOString() });
 
-    // Prepare DLT execution
     const dltPrepared = await prepareDLTExecution(plan);
-    if (!dltPrepared) {
-      throw new Error("DLT preparation failed");
-    }
+    if (!dltPrepared) throw Control.missingApproval({ leg: "dlt" });
 
-    // Prepare bank instruction (provisional)
     const bankPrepared = await prepareBankInstruction(plan);
     if (!bankPrepared) {
-      await abortDLTExecution(plan.plan_id);
-      throw new Error("Bank preparation failed");
+      await abortDLTExecution(plan.plan_id!);
+      throw Control.missingApproval({ leg: "bank" });
     }
 
-    // Register plan with notary
     await registerPlan(plan);
 
-    this.emitStatus(executionId, {
-      phase: "prepare",
-      status: "complete",
-      timestamp: new Date().toISOString(),
-    });
+    this.emitStatus(executionId, { phase: "prepare", status: "complete", timestamp: new Date().toISOString() });
   }
 
-  private async executeDLTPhase(executionId: string, plan: any) {
-    this.emitStatus(executionId, {
-      phase: "execute_dlt",
-      status: "in_progress",
-      timestamp: new Date().toISOString(),
-    });
+  private async executeDLTPhase(executionId: string, plan: Plan): Promise<{ txHash: string }> {
+    this.emitStatus(executionId, { phase: "execute_dlt", status: "in_progress", timestamp: new Date().toISOString() });
 
     const result = await commitDLTExecution(plan);
-    if (!result.success) {
-      await abortDLTExecution(plan.plan_id);
-      await abortBankInstruction(plan.plan_id);
-      throw new Error("DLT execution failed: " + result.error);
+    if (!result.success || !result.txHash) {
+      await abortDLTExecution(plan.plan_id!);
+      await abortBankInstruction(plan.plan_id!);
+      throw new SettlementException("system", "external_service_error", `DLT execution failed: ${result.error ?? "unknown"}`);
     }
 
-    this.emitStatus(executionId, {
-      phase: "execute_dlt",
-      status: "complete",
-      dltTxHash: result.txHash,
-      timestamp: new Date().toISOString(),
-    });
+    const rec = this.executions.get(executionId);
+    if (rec) rec.dltTxHash = result.txHash;
+
+    this.emitStatus(executionId, { phase: "execute_dlt", status: "complete", dltTxHash: result.txHash, timestamp: new Date().toISOString() });
+    return { txHash: result.txHash };
   }
 
-  private async bankInstructionPhase(executionId: string, plan: any) {
-    this.emitStatus(executionId, {
-      phase: "bank_instruction",
-      status: "in_progress",
-      timestamp: new Date().toISOString(),
-    });
+  private async bankInstructionPhase(executionId: string, plan: Plan): Promise<{ isoMessageId: string }> {
+    this.emitStatus(executionId, { phase: "bank_instruction", status: "in_progress", timestamp: new Date().toISOString() });
 
     const result = await commitBankInstruction(plan);
-    if (!result.success) {
-      // DLT already committed, need to handle rollback
-      throw new Error("Bank instruction failed: " + result.error);
+    if (!result.success || !result.isoMessageId) {
+      throw new SettlementException("system", "external_service_error", `Bank instruction failed: ${result.error ?? "unknown"}`);
     }
 
-    this.emitStatus(executionId, {
-      phase: "bank_instruction",
-      status: "complete",
-      isoMessageId: result.isoMessageId,
-      timestamp: new Date().toISOString(),
-    });
+    const rec = this.executions.get(executionId);
+    if (rec) rec.isoMessageId = result.isoMessageId;
+
+    this.emitStatus(executionId, { phase: "bank_instruction", status: "complete", isoMessageId: result.isoMessageId, timestamp: new Date().toISOString() });
+    return { isoMessageId: result.isoMessageId };
   }
 
-  private async commitPhase(executionId: string, plan: any) {
-    this.emitStatus(executionId, {
-      phase: "commit",
-      status: "in_progress",
-      timestamp: new Date().toISOString(),
+  /**
+   * VALIDATING phase (arch §8 + §9.2). Reconcile dispatch references +
+   * evidence against the plan before COMMIT.
+   *
+   * Today's checks — stub shape, will be expanded by PRs C-E:
+   *   - dlt.txHash is a 0x-prefixed 32-byte hex
+   *   - bank.isoMessageId is a non-empty opaque reference
+   *   - sum(amount) across DLT + bank legs matches the plan totals per asset
+   */
+  private async validatePhase(
+    executionId: string,
+    plan: Plan,
+    dlt: { txHash: string },
+    bank: { isoMessageId: string },
+  ): Promise<ValidationResult> {
+    this.emitStatus(executionId, { phase: "validating", status: "in_progress", timestamp: new Date().toISOString() });
+
+    const mismatches: ValidationResult["mismatches"] = [];
+
+    if (!/^0x[0-9a-fA-F]{64}$/.test(dlt.txHash)) {
+      mismatches.push({ field: "dlt.txHash", expected: "0x + 64 hex chars", actual: dlt.txHash });
+    }
+    if (!bank.isoMessageId || bank.isoMessageId.trim() === "") {
+      mismatches.push({ field: "bank.isoMessageId", expected: "non-empty string", actual: bank.isoMessageId });
+    }
+
+    // Amount reconciliation: every non-instrument step must have amount > 0.
+    for (const [i, step] of plan.steps.entries()) {
+      if (step.type !== "issueInstrument" && !(step.amount > 0)) {
+        mismatches.push({ field: `steps[${i}].amount`, expected: "> 0", actual: step.amount });
+      }
+    }
+
+    const result: ValidationResult = {
+      ok: mismatches.length === 0,
+      mismatches,
+      dltTxHash: dlt.txHash,
+      isoMessageId: bank.isoMessageId,
+    };
+
+    this.emitStatus(executionId, { phase: "validating", status: result.ok ? "complete" : "failed", timestamp: new Date().toISOString(), ...(result.ok ? {} : { error: `${mismatches.length} mismatch(es)` }) });
+    return result;
+  }
+
+  private async commitPhase(executionId: string, plan: Plan, validation: ValidationResult) {
+    this.emitStatus(executionId, { phase: "commit", status: "in_progress", timestamp: new Date().toISOString() });
+
+    await finalizePlan(plan.plan_id!, {
+      dltTxHash: validation.dltTxHash ?? "mock-tx-hash",
+      isoMessageId: validation.isoMessageId ?? "mock-iso-id",
     });
 
-    // Finalize with notary
-    await finalizePlan(plan.plan_id, {
-      dltTxHash: "mock-tx-hash",
-      isoMessageId: "mock-iso-id",
-    });
-
-    this.emitStatus(executionId, {
-      phase: "commit",
-      status: "complete",
-      timestamp: new Date().toISOString(),
-    });
+    this.emitStatus(executionId, { phase: "commit", status: "complete", timestamp: new Date().toISOString() });
   }
 
   async abortExecution(executionId: string, planId: string, error: string) {
-    const execution = this.executions.get(executionId);
-    if (!execution) return;
+    if (!this.executions.has(executionId)) return;
 
     try {
-      // Abort DLT
       await abortDLTExecution(planId);
-      
-      // Abort bank
       await abortBankInstruction(planId);
-
       await updatePlanStatus(planId, "aborted");
 
-      this.emitStatus(executionId, {
-        phase: "aborted",
-        status: "failed",
-        error,
-        timestamp: new Date().toISOString(),
-      });
+      const current = await getTransactionState(planId);
+      if (current && current !== "ABORTED" && current !== "CLOSED") {
+        try {
+          await transition({ planId, from: current, to: "ABORTED", actor: "coordinator", actorRole: "exception_manager", reason: error });
+        } catch {
+          /* machine may not allow this edge from current state; leave for operator */
+        }
+      }
+
+      this.emitStatus(executionId, { phase: "aborted", status: "failed", error, timestamp: new Date().toISOString() });
     } catch (abortError: any) {
       console.error("Abort failed:", abortError);
     }
@@ -199,4 +289,3 @@ export class ExecutionCoordinator extends EventEmitter {
 }
 
 export const executionCoordinator = new ExecutionCoordinator();
-
diff --git a/orchestrator/src/services/planValidation.ts b/orchestrator/src/services/planValidation.ts
index b9946cf..39606d5 100644
--- a/orchestrator/src/services/planValidation.ts
+++ b/orchestrator/src/services/planValidation.ts
@@ -70,6 +70,52 @@ function validateStep(step: PlanStep, index: number): string[] {
         errors.push(`Step ${index + 1}: Invalid pay step (asset/amount/IBAN missing)`);
       }
       break;
+    case "issueInstrument": {
+      const inst = step.instrument;
+      if (!inst) {
+        errors.push(`Step ${index + 1}: issueInstrument step missing instrument terms`);
+        break;
+      }
+      const required: Array<keyof typeof inst> = [
+        "applicant",
+        "issuingBankBIC",
+        "beneficiaryBankBIC",
+        "beneficiaryName",
+        "currency",
+        "tenor",
+        "expiryDate",
+        "placeOfPresentation",
+        "governingLaw",
+        "templateRef",
+        "templateHash",
+      ];
+      for (const key of required) {
+        if (!inst[key] || String(inst[key]).trim() === "") {
+          errors.push(`Step ${index + 1}: instrument.${String(key)} is required`);
+        }
+      }
+      if (!(inst.amount > 0)) {
+        errors.push(`Step ${index + 1}: instrument.amount must be > 0`);
+      }
+      if (inst.currency && !/^[A-Z]{3}$/.test(inst.currency)) {
+        errors.push(`Step ${index + 1}: instrument.currency must be ISO 4217 (e.g. USD)`);
+      }
+      // BIC is 8 or 11 chars: 4 bank + 2 country + 2 location [+ 3 branch]
+      const bicRe = /^[A-Z]{4}[A-Z]{2}[A-Z0-9]{2}([A-Z0-9]{3})?$/;
+      if (inst.issuingBankBIC && !bicRe.test(inst.issuingBankBIC)) {
+        errors.push(`Step ${index + 1}: instrument.issuingBankBIC is not a valid BIC`);
+      }
+      if (inst.beneficiaryBankBIC && !bicRe.test(inst.beneficiaryBankBIC)) {
+        errors.push(`Step ${index + 1}: instrument.beneficiaryBankBIC is not a valid BIC`);
+      }
+      if (inst.expiryDate && !/^\d{4}-\d{2}-\d{2}$/.test(inst.expiryDate)) {
+        errors.push(`Step ${index + 1}: instrument.expiryDate must be YYYY-MM-DD`);
+      }
+      if (inst.templateHash && !/^[0-9a-fA-F]{64}$/.test(inst.templateHash)) {
+        errors.push(`Step ${index + 1}: instrument.templateHash must be 64 hex chars (sha256)`);
+      }
+      break;
+    }
   }
 
   return errors;
diff --git a/orchestrator/src/services/stateMachine.ts b/orchestrator/src/services/stateMachine.ts
new file mode 100644
index 0000000..2ec2abf
--- /dev/null
+++ b/orchestrator/src/services/stateMachine.ts
@@ -0,0 +1,174 @@
+/**
+ * Transaction state-machine service.
+ *
+ * Centralized enforcement of architecture note §9 (state-transition rules).
+ * The coordinator, exception manager, and any operator action must route
+ * through `transition()` so the transition table and segregation-of-duties
+ * matrix are applied identically everywhere.
+ */
+
+import { query, transaction as dbTransaction } from "../db/postgres";
+import {
+  ALLOWED_TRANSITIONS,
+  ROLE_FOR_TRANSITION,
+  SOD_REQUIRED_TRANSITIONS,
+  canTransition,
+  type ActorRole,
+  type TransactionState,
+} from "../types/transactionState";
+
+export interface TransitionRequest {
+  planId: string;
+  from: TransactionState;
+  to: TransactionState;
+  actor: string;
+  actorRole: ActorRole;
+  reason?: string;
+  sourceEventId?: string;
+  signature?: string;
+}
+
+export class StateTransitionError extends Error {
+  constructor(
+    message: string,
+    public readonly code:
+      | "illegal_transition"
+      | "sod_violation"
+      | "stale_from_state"
+      | "terminal_state",
+  ) {
+    super(message);
+    this.name = "StateTransitionError";
+  }
+}
+
+/**
+ * Execute a state transition atomically: verify legality, enforce SoD,
+ * update `plans.transaction_state`, and append a row to
+ * `transaction_state_transitions`.
+ *
+ * Throws `StateTransitionError` if the transition is not legal or violates
+ * segregation-of-duties.
+ */
+export async function transition(req: TransitionRequest): Promise<void> {
+  if (!canTransition(req.from, req.to)) {
+    throw new StateTransitionError(
+      `Transition ${req.from} -> ${req.to} is not in the allowed table`,
+      "illegal_transition",
+    );
+  }
+
+  const key = `${req.from}->${req.to}` as const;
+  if (SOD_REQUIRED_TRANSITIONS.has(key)) {
+    const requiredRole = ROLE_FOR_TRANSITION[key];
+    if (req.actorRole !== requiredRole) {
+      throw new StateTransitionError(
+        `Transition ${key} requires role '${requiredRole}' but actor '${req.actor}' has role '${req.actorRole}'`,
+        "sod_violation",
+      );
+    }
+    // SoD: the actor executing the transition must not be the same as the
+    // actor who drove the previous human-gated transition. We enforce this
+    // at the coordinator level by looking at the transition log.
+    const prior = await query<{ actor: string; actor_role: ActorRole }>(
+      `SELECT actor, actor_role FROM transaction_state_transitions
+        WHERE plan_id = $1
+          AND actor_role IN ('approver','releaser','exception_manager')
+        ORDER BY created_at DESC
+        LIMIT 1`,
+      [req.planId],
+    );
+    if (prior.length > 0 && prior[0].actor === req.actor) {
+      throw new StateTransitionError(
+        `SoD violation: actor '${req.actor}' already drove the previous gated transition`,
+        "sod_violation",
+      );
+    }
+  }
+
+  await dbTransaction(async (client) => {
+    const current = await client.query<{ transaction_state: TransactionState }>(
+      "SELECT transaction_state FROM plans WHERE plan_id = $1 FOR UPDATE",
+      [req.planId],
+    );
+    if (current.rows.length === 0) {
+      throw new StateTransitionError(
+        `Plan ${req.planId} not found`,
+        "stale_from_state",
+      );
+    }
+    if (current.rows[0].transaction_state !== req.from) {
+      throw new StateTransitionError(
+        `Plan ${req.planId} is in state '${current.rows[0].transaction_state}', not '${req.from}'`,
+        "stale_from_state",
+      );
+    }
+    if (ALLOWED_TRANSITIONS[current.rows[0].transaction_state].length === 0) {
+      throw new StateTransitionError(
+        `Plan ${req.planId} is in terminal state '${current.rows[0].transaction_state}'`,
+        "terminal_state",
+      );
+    }
+
+    await client.query(
+      "UPDATE plans SET transaction_state = $1, updated_at = CURRENT_TIMESTAMP WHERE plan_id = $2",
+      [req.to, req.planId],
+    );
+    await client.query(
+      `INSERT INTO transaction_state_transitions (
+         plan_id, from_state, to_state, reason, source_event_id,
+         actor, actor_role, signature
+       ) VALUES ($1, $2, $3, $4, $5, $6, $7, $8)`,
+      [
+        req.planId,
+        req.from,
+        req.to,
+        req.reason ?? null,
+        req.sourceEventId ?? null,
+        req.actor,
+        req.actorRole,
+        req.signature ?? null,
+      ],
+    );
+  });
+}
+
+/**
+ * Get the current transaction state for a plan.
+ */
+export async function getTransactionState(
+  planId: string,
+): Promise<TransactionState | null> {
+  const rows = await query<{ transaction_state: TransactionState }>(
+    "SELECT transaction_state FROM plans WHERE plan_id = $1",
+    [planId],
+  );
+  return rows.length > 0 ? rows[0].transaction_state : null;
+}
+
+/**
+ * Get the full state-transition history for a plan.
+ */
+export async function getTransitionHistory(
+  planId: string,
+): Promise<
+  Array<{
+    from_state: TransactionState | null;
+    to_state: TransactionState;
+    reason: string | null;
+    actor: string;
+    actor_role: ActorRole;
+    signature: string | null;
+    source_event_id: string | null;
+    created_at: Date;
+  }>
+> {
+  return await query(
+    `SELECT from_state, to_state, reason, actor, actor_role, signature,
+            source_event_id, created_at
+       FROM transaction_state_transitions
+      WHERE plan_id = $1
+      ORDER BY created_at ASC`,
+    [planId],
+  );
+}
diff --git a/orchestrator/src/types/plan.ts b/orchestrator/src/types/plan.ts
index 5bfa960..a88d348 100644
--- a/orchestrator/src/types/plan.ts
+++ b/orchestrator/src/types/plan.ts
@@ -1,3 +1,91 @@
+/**
+ * Canonical data objects for the multi-layer atomic settlement architecture.
+ *
+ * A Plan models a single workflow-level atomic transaction composed of
+ * multiple legs (DLT borrow/swap/repay, fiat payment, banking instrument
+ * issuance). The combination must commit or abort as one unit.
+ */
+
+import type { TransactionState } from "./transactionState";
+
+export type PlanStepType = "borrow" | "swap" | "repay" | "pay" | "issueInstrument";
+
+export interface BeneficiaryCoordinates {
+  /** ISO 20022 / SEPA IBAN */
+  IBAN?: string;
+  /** BIC / SWIFT code of the beneficiary bank */
+  BIC?: string;
+  /** Beneficiary legal name */
+  name?: string;
+  /** Optional beneficiary bank legal name (for FI credit transfers) */
+  bankName?: string;
+}
+
+/**
+ * Instrument-leg fields — used by `type: "issueInstrument"` steps.
+ *
+ * Based on the Emirates Islamic beneficiary-format SBLC / MT760 template.
+ * Each field corresponds to a MT760 / UCP 600 concept:
+ *
+ *   - applicant                    MT760 field 50
+ *   - issuingBankBIC               MT760 sender / field 52a
+ *   - beneficiaryBankBIC           MT760 field 57a (advising bank)
+ *   - beneficiaryName              MT760 field 59
+ *   - beneficiaryAccount           MT760 field 59 (secondary)
+ *   - amount + currency            MT760 field 32B
+ *   - tenor                        MT760 field 42C (e.g. "90D", "1Y")
+ *   - expiryDate                   MT760 field 31D (YYYY-MM-DD)
+ *   - placeOfPresentation          MT760 field 78 / 49
+ *   - governingLaw                 MT760 field 40E (e.g. "URDG 758", "UCP 600", "ISP98")
+ *   - templateRef + templateHash   pointer + integrity hash of the agreed text
+ */
+export interface InstrumentTerms {
+  applicant: string;
+  issuingBankBIC: string;
+  beneficiaryBankBIC: string;
+  beneficiaryName: string;
+  beneficiaryAccount?: string;
+  amount: number;
+  currency: string;
+  tenor: string;
+  expiryDate: string;
+  placeOfPresentation: string;
+  governingLaw: string;
+  templateRef: string;
+  /** SHA-256 of the agreed instrument text, hex-encoded without 0x prefix. */
+  templateHash: string;
+}
+
+export interface PlanStep {
+  type: PlanStepType;
+  asset?: string;
+  amount: number;
+  from?: string;
+  to?: string;
+  collateralRef?: string;
+  beneficiary?: BeneficiaryCoordinates;
+  /** Populated iff `type === "issueInstrument"`. */
+  instrument?: InstrumentTerms;
+}
+
+/**
+ * Participant entry in the registry. Each transaction binds at least
+ * one role per participant. Used for segregation-of-duties enforcement
+ * on state transitions.
+ */
+export interface Participant {
+  id: string;
+  role:
+    | "applicant"
+    | "issuing_bank"
+    | "beneficiary_bank"
+    | "beneficiary"
+    | "coordinator"
+    | "observer";
+  lei?: string;
+  did?: string;
+}
+
 export interface Plan {
   plan_id?: string;
   creator: string;
@@ -7,20 +95,10 @@ export interface Plan {
   signature?: string;
   plan_hash?: string;
   created_at?: string;
+  /** Legacy execution status (pending | complete | aborted). */
   status?: string;
+  /** Full 12-state workflow state (architecture note §8). */
+  transaction_state?: TransactionState;
+  /** Optional participant registry. */
+  participants?: Participant[];
 }
-
-export interface PlanStep {
-  type: "borrow" | "swap" | "repay" | "pay";
-  asset?: string;
-  amount: number;
-  from?: string;
-  to?: string;
-  collateralRef?: string;
-  beneficiary?: {
-    IBAN?: string;
-    BIC?: string;
-    name?: string;
-  };
-}
-
diff --git a/orchestrator/src/types/transactionState.ts b/orchestrator/src/types/transactionState.ts
new file mode 100644
index 0000000..41b58dc
--- /dev/null
+++ b/orchestrator/src/types/transactionState.ts
@@ -0,0 +1,87 @@
+/**
+ * Transaction state machine — architecture note §8–§9.
+ *
+ * Workflow-level atomicity is enforced by constraining the plan lifecycle to
+ * this set of states and this transition table. The coordinator and the
+ * database CHECK constraint both reference this module so the values are
+ * source-of-truth identical.
+ */
+
+export const TRANSACTION_STATES = [
+  "DRAFT",
+  "INITIATED",
+  "PRECONDITIONS_PENDING",
+  "READY_FOR_PREPARE",
+  "PREPARED",
+  "EXECUTING",
+  "PARTIALLY_EXECUTED",
+  "VALIDATING",
+  "COMMITTED",
+  "ABORTED",
+  "UNWIND_PENDING",
+  "CLOSED",
+] as const;
+
+export type TransactionState = (typeof TRANSACTION_STATES)[number];
+
+export const TERMINAL_STATES: ReadonlySet<TransactionState> = new Set(["CLOSED"]);
+
+/**
+ * Architecture note §9.1 — permitted high-level transitions.
+ *
+ * Keys are `from` states; values are the set of legal `to` states.
+ * Any transition not listed here must be rejected.
+ */
+export const ALLOWED_TRANSITIONS: Readonly<Record<TransactionState, ReadonlyArray<TransactionState>>> = {
+  DRAFT: ["INITIATED"],
+  INITIATED: ["PRECONDITIONS_PENDING"],
+  PRECONDITIONS_PENDING: ["READY_FOR_PREPARE", "ABORTED"],
+  READY_FOR_PREPARE: ["PREPARED", "ABORTED"],
+  PREPARED: ["EXECUTING", "ABORTED"],
+  EXECUTING: ["PARTIALLY_EXECUTED", "VALIDATING", "ABORTED"],
+  PARTIALLY_EXECUTED: ["VALIDATING", "ABORTED"],
+  VALIDATING: ["COMMITTED", "ABORTED"],
+  COMMITTED: ["CLOSED"],
+  ABORTED: ["UNWIND_PENDING", "CLOSED"],
+  UNWIND_PENDING: ["CLOSED"],
+  CLOSED: [],
+};
+
+export function canTransition(from: TransactionState, to: TransactionState): boolean {
+  return ALLOWED_TRANSITIONS[from]?.includes(to) ?? false;
+}
+
+/**
+ * Actor roles allowed to execute a transition. The coordinator may always
+ * drive any transition programmatically; approver / releaser roles are
+ * constrained for segregation-of-duties purposes (architecture note §13).
+ */
+export type ActorRole =
+  | "coordinator"
+  | "approver"
+  | "releaser"
+  | "validator"
+  | "exception_manager"
+  | "operator";
+
+/**
+ * Transitions that require a non-coordinator human actor (segregation of duties).
+ * Per architecture note §13: "segregation of duties for approval and release
+ * actions".
+ */
+export const SOD_REQUIRED_TRANSITIONS: ReadonlySet<`${TransactionState}->${TransactionState}`> = new Set([
+  "READY_FOR_PREPARE->PREPARED", // release approval
+  "PREPARED->EXECUTING",          // release action
+  "VALIDATING->COMMITTED",        // final commit approval
+  "ABORTED->UNWIND_PENDING",      // unwind authorization
+]);
+
+/**
+ * Role required for each segregation-of-duties checkpoint.
+ */
+export const ROLE_FOR_TRANSITION: Readonly<Record<string, ActorRole>> = {
+  "READY_FOR_PREPARE->PREPARED": "approver",
+  "PREPARED->EXECUTING": "releaser",
+  "VALIDATING->COMMITTED": "approver",
+  "ABORTED->UNWIND_PENDING": "exception_manager",
+};
diff --git a/orchestrator/tests/unit/exceptionManager.test.ts b/orchestrator/tests/unit/exceptionManager.test.ts
new file mode 100644
index 0000000..ed03a21
--- /dev/null
+++ b/orchestrator/tests/unit/exceptionManager.test.ts
@@ -0,0 +1,69 @@
+import { describe, it, expect } from "@jest/globals";
+import {
+  Business,
+  Control,
+  Data,
+  SettlementException,
+  Timing,
+  classify,
+  route,
+} from "../../src/services/exceptionManager";
+
+describe("ExceptionManager — architecture note §12", () => {
+  describe("classification taxonomy", () => {
+    it("builds the four §12 classes via factory functions", () => {
+      expect(Timing.dispatch().exceptionClass).toBe("timing");
+      expect(Timing.dispatch().code).toBe("dispatch_timeout");
+
+      expect(Data.valueMismatch().exceptionClass).toBe("data");
+      expect(Data.documentHashMismatch().code).toBe("document_hash_mismatch");
+
+      expect(Control.unauthorized("nobody").exceptionClass).toBe("control");
+      expect(Control.duplicate("ev-1").code).toBe("duplicate_event");
+
+      expect(Business.manualStop("operator halted").exceptionClass).toBe("business");
+      expect(Business.policyViolation({ rule: "LTV" }).code).toBe("policy_rule_violation");
+    });
+
+    it("classify() tags network/timeout errors as system/network_error", () => {
+      const ex = classify(new Error("ETIMEDOUT connect"));
+      expect(ex.exceptionClass).toBe("system");
+      expect(ex.code).toBe("network_error");
+    });
+
+    it("classify() tags postgres errors as system/database_error", () => {
+      const ex = classify(new Error("postgres connection refused"));
+      expect(ex.exceptionClass).toBe("system");
+      expect(ex.code).toBe("database_error");
+    });
+
+    it("classify() is idempotent for SettlementException inputs", () => {
+      const original = Data.valueMismatch({ field: "amount" });
+      expect(classify(original)).toBe(original);
+    });
+  });
+
+  describe("deterministic routing", () => {
+    const cases: Array<[SettlementException, string]> = [
+      [Timing.dispatch(), "retry"],
+      [Timing.settlement(), "retry"],
+      [Data.valueMismatch(), "abort_transaction"],
+      [Data.documentHashMismatch(), "abort_transaction"],
+      [Control.missingApproval(), "escalate"],
+      [Control.unauthorized("x"), "escalate"],
+      [Control.duplicate("ev"), "dead_letter"],
+      [Business.manualStop("halt"), "abort_transaction"],
+      [Business.policyViolation({ rule: "LTV" }), "escalate"],
+    ];
+
+    it.each(cases)("routes %j to %s", (ex, expected) => {
+      expect(route(ex)).toBe(expected);
+    });
+
+    it("network errors retry; non-network system errors dead-letter", () => {
+      expect(route(classify(new Error("ETIMEDOUT")))).toBe("retry");
+      const dbErr = classify(new Error("postgres broken"));
+      expect(route(dbErr)).toBe("dead_letter");
+    });
+  });
+});
diff --git a/orchestrator/tests/unit/planValidation.instrument.test.ts b/orchestrator/tests/unit/planValidation.instrument.test.ts
new file mode 100644
index 0000000..18880d6
--- /dev/null
+++ b/orchestrator/tests/unit/planValidation.instrument.test.ts
@@ -0,0 +1,82 @@
+import { describe, it, expect } from "@jest/globals";
+import { validatePlan } from "../../src/services/planValidation";
+import type { InstrumentTerms, Plan } from "../../src/types/plan";
+
+const goodTerms: InstrumentTerms = {
+  applicant: "Solace Bank Group PLC",
+  issuingBankBIC: "SOLBAE22",
+  beneficiaryBankBIC: "MEBLAEAD", // Emirates Islamic BIC prefix example
+  beneficiaryName: "Acme Trading LLC",
+  beneficiaryAccount: "AE070331234567890123456",
+  amount: 1_000_000,
+  currency: "USD",
+  tenor: "90D",
+  expiryDate: "2026-06-30",
+  placeOfPresentation: "Dubai, UAE",
+  governingLaw: "URDG 758",
+  templateRef: "EIB-SBLC-v3.2",
+  templateHash:
+    "a".repeat(64), // dummy sha256
+};
+
+function planWith(terms: Partial<InstrumentTerms> | null): Plan {
+  return {
+    creator: "solace-ops-01",
+    steps: [
+      {
+        type: "issueInstrument",
+        amount: terms?.amount ?? 1_000_000,
+        instrument: terms === null ? undefined : ({ ...goodTerms, ...terms } as InstrumentTerms),
+      },
+    ],
+  };
+}
+
+describe("validatePlan — issueInstrument step", () => {
+  it("accepts a well-formed SBLC step", () => {
+    const result = validatePlan(planWith({}));
+    expect(result.valid).toBe(true);
+    expect(result.errors).toHaveLength(0);
+  });
+
+  it("rejects a step missing the instrument object", () => {
+    const result = validatePlan(planWith(null));
+    expect(result.valid).toBe(false);
+    expect(result.errors[0]).toMatch(/missing instrument terms/);
+  });
+
+  it("rejects an invalid BIC", () => {
+    const result = validatePlan(planWith({ issuingBankBIC: "NOTABIC" }));
+    expect(result.valid).toBe(false);
+    expect(result.errors.join("\n")).toMatch(/issuingBankBIC is not a valid BIC/);
+  });
+
+  it("rejects a non-ISO-4217 currency", () => {
+    const result = validatePlan(planWith({ currency: "usd" }));
+    expect(result.valid).toBe(false);
+    expect(result.errors.join("\n")).toMatch(/currency must be ISO 4217/);
+  });
+
+  it("rejects a non-ISO-8601 expiry date", () => {
+    const result = validatePlan(planWith({ expiryDate: "30-06-2026" }));
+    expect(result.valid).toBe(false);
+    expect(result.errors.join("\n")).toMatch(/expiryDate must be YYYY-MM-DD/);
+  });
+
+  it("rejects a non-sha256 template hash", () => {
+    const result = validatePlan(planWith({ templateHash: "deadbeef" }));
+    expect(result.valid).toBe(false);
+    expect(result.errors.join("\n")).toMatch(/templateHash must be 64 hex chars/);
+  });
+
+  it("rejects an instrument with non-positive amount", () => {
+    const result = validatePlan(planWith({ amount: 0 }));
+    expect(result.valid).toBe(false);
+    expect(result.errors.join("\n")).toMatch(/instrument.amount must be > 0/);
+  });
+
+  it("accepts 11-char branched BIC", () => {
+    const result = validatePlan(planWith({ issuingBankBIC: "SOLBAE22XXX" }));
+    expect(result.valid).toBe(true);
+  });
+});
diff --git a/orchestrator/tests/unit/transactionState.test.ts b/orchestrator/tests/unit/transactionState.test.ts
new file mode 100644
index 0000000..65a96ba
--- /dev/null
+++ b/orchestrator/tests/unit/transactionState.test.ts
@@ -0,0 +1,85 @@
+import { describe, it, expect } from "@jest/globals";
+import {
+  ALLOWED_TRANSITIONS,
+  ROLE_FOR_TRANSITION,
+  SOD_REQUIRED_TRANSITIONS,
+  TRANSACTION_STATES,
+  canTransition,
+} from "../../src/types/transactionState";
+
+describe("Transaction state machine (architecture note §8–§9)", () => {
+  it("declares the 12 states from §8.1", () => {
+    expect(TRANSACTION_STATES).toEqual([
+      "DRAFT",
+      "INITIATED",
+      "PRECONDITIONS_PENDING",
+      "READY_FOR_PREPARE",
+      "PREPARED",
+      "EXECUTING",
+      "PARTIALLY_EXECUTED",
+      "VALIDATING",
+      "COMMITTED",
+      "ABORTED",
+      "UNWIND_PENDING",
+      "CLOSED",
+    ]);
+  });
+
+  describe("§9.1 permitted high-level transitions", () => {
+    // Each of these is listed in the note; canTransition must accept them.
+    const legal: Array<[string, string]> = [
+      ["DRAFT", "INITIATED"],
+      ["INITIATED", "PRECONDITIONS_PENDING"],
+      ["PRECONDITIONS_PENDING", "READY_FOR_PREPARE"],
+      ["READY_FOR_PREPARE", "PREPARED"],
+      ["PREPARED", "EXECUTING"],
+      ["EXECUTING", "PARTIALLY_EXECUTED"],
+      ["EXECUTING", "VALIDATING"],
+      ["PARTIALLY_EXECUTED", "VALIDATING"],
+      ["VALIDATING", "COMMITTED"],
+      ["VALIDATING", "ABORTED"],
+      ["ABORTED", "UNWIND_PENDING"],
+      ["COMMITTED", "CLOSED"],
+      ["UNWIND_PENDING", "CLOSED"],
+    ];
+    it.each(legal)("allows %s -> %s", (from, to) => {
+      expect(canTransition(from as any, to as any)).toBe(true);
+    });
+
+    // A few illegal edges — explicitly not in §9.1.
+    const illegal: Array<[string, string]> = [
+      ["DRAFT", "COMMITTED"],
+      ["INITIATED", "EXECUTING"],
+      ["CLOSED", "INITIATED"],
+      ["PREPARED", "COMMITTED"],
+      ["COMMITTED", "ABORTED"],
+      ["ABORTED", "COMMITTED"],
+    ];
+    it.each(illegal)("rejects %s -> %s", (from, to) => {
+      expect(canTransition(from as any, to as any)).toBe(false);
+    });
+  });
+
+  it("CLOSED is a terminal state", () => {
+    expect(ALLOWED_TRANSITIONS.CLOSED).toEqual([]);
+  });
+
+  describe("segregation-of-duties checkpoints (§13)", () => {
+    it("flags the four SoD-gated transitions", () => {
+      expect([...SOD_REQUIRED_TRANSITIONS].sort()).toEqual(
+        [
+          "ABORTED->UNWIND_PENDING",
+          "PREPARED->EXECUTING",
+          "READY_FOR_PREPARE->PREPARED",
+          "VALIDATING->COMMITTED",
+        ].sort(),
+      );
+    });
+
+    it("assigns a role to every SoD-gated transition", () => {
+      for (const key of SOD_REQUIRED_TRANSITIONS) {
+        expect(ROLE_FOR_TRANSITION[key]).toBeDefined();
+      }
+    });
+  });
+});