diff --git a/apps/server/src/orchestration/Errors.ts b/apps/server/src/orchestration/Errors.ts
index be7943f78a6..7abd567704f 100644
--- a/apps/server/src/orchestration/Errors.ts
+++ b/apps/server/src/orchestration/Errors.ts
@@ -53,6 +53,21 @@ export class OrchestrationCommandPreviouslyRejectedError extends Schema.TaggedEr
   }
 }
 
+export class OrchestrationCommandIdConflictError extends Schema.TaggedErrorClass<OrchestrationCommandIdConflictError>()(
+  "OrchestrationCommandIdConflictError",
+  {
+    commandId: Schema.String,
+    receiptAggregateKind: Schema.String,
+    receiptAggregateId: Schema.String,
+    commandAggregateKind: Schema.String,
+    commandAggregateId: Schema.String,
+  },
+) {
+  override get message(): string {
+    return `Command id '${this.commandId}' already used for ${this.receiptAggregateKind} '${this.receiptAggregateId}'; refusing to replay its receipt for ${this.commandAggregateKind} '${this.commandAggregateId}'.`;
+  }
+}
+
 export class OrchestrationProjectorDecodeError extends Schema.TaggedErrorClass<OrchestrationProjectorDecodeError>()(
   "OrchestrationProjectorDecodeError",
   {
@@ -82,6 +97,7 @@ export class OrchestrationListenerCallbackError extends Schema.TaggedErrorClass<
 export type OrchestrationDispatchError =
   | ProjectionRepositoryError
   | OrchestrationCommandInvariantError
+  | OrchestrationCommandIdConflictError
   | OrchestrationCommandPreviouslyRejectedError
   | OrchestrationProjectorDecodeError
   | OrchestrationListenerCallbackError;
diff --git a/apps/server/src/orchestration/Layers/OrchestrationEngine.test.ts b/apps/server/src/orchestration/Layers/OrchestrationEngine.test.ts
index 9ffe50d1341..41624a14e4c 100644
--- a/apps/server/src/orchestration/Layers/OrchestrationEngine.test.ts
+++ b/apps/server/src/orchestration/Layers/OrchestrationEngine.test.ts
@@ -1220,4 +1220,153 @@ describe("OrchestrationEngine", () => {
 
     await system.dispose();
   });
+
+  it("replays the accepted receipt for a genuine retry of the same command", async () => {
+    const createdAt = now();
+    const system = await createOrchestrationSystem();
+    const { engine } = system;
+
+    await system.run(
+      engine.dispatch({
+        type: "project.create",
+        commandId: CommandId.make("cmd-retry-project-create"),
+        projectId: asProjectId("project-retry"),
+        title: "Retry Project",
+        workspaceRoot: "/tmp/project-retry",
+        defaultModelSelection: {
+          instanceId: ProviderInstanceId.make("codex"),
+          model: "gpt-5-codex",
+        },
+        createdAt,
+      }),
+    );
+    await system.run(
+      engine.dispatch({
+        type: "thread.create",
+        commandId: CommandId.make("cmd-retry-thread-create"),
+        threadId: ThreadId.make("thread-retry"),
+        projectId: asProjectId("project-retry"),
+        title: "retry",
+        modelSelection: {
+          instanceId: ProviderInstanceId.make("codex"),
+          model: "gpt-5-codex",
+        },
+        interactionMode: DEFAULT_PROVIDER_INTERACTION_MODE,
+        runtimeMode: "approval-required",
+        branch: null,
+        worktreePath: null,
+        createdAt,
+      }),
+    );
+
+    const turnStart = {
+      type: "thread.turn.start",
+      commandId: CommandId.make("cmd-retry-turn-start"),
+      threadId: ThreadId.make("thread-retry"),
+      message: {
+        messageId: asMessageId("msg-retry"),
+        role: "user",
+        text: "hello",
+        attachments: [],
+      },
+      interactionMode: DEFAULT_PROVIDER_INTERACTION_MODE,
+      runtimeMode: "approval-required",
+      createdAt,
+    } as const;
+
+    const first = await system.run(engine.dispatch(turnStart));
+    const second = await system.run(engine.dispatch(turnStart));
+    expect(second.sequence).toBe(first.sequence);
+
+    const readModel = await system.readModel();
+    const thread = readModel.threads.find((candidate) => candidate.id === "thread-retry");
+    expect(thread?.messages.filter((message) => message.role === "user")).toHaveLength(1);
+
+    await system.dispose();
+  });
+
+  it("rejects reusing an accepted command id for a different aggregate", async () => {
+    const createdAt = now();
+    const system = await createOrchestrationSystem();
+    const { engine } = system;
+
+    await system.run(
+      engine.dispatch({
+        type: "project.create",
+        commandId: CommandId.make("cmd-conflict-project-create"),
+        projectId: asProjectId("project-conflict"),
+        title: "Conflict Project",
+        workspaceRoot: "/tmp/project-conflict",
+        defaultModelSelection: {
+          instanceId: ProviderInstanceId.make("codex"),
+          model: "gpt-5-codex",
+        },
+        createdAt,
+      }),
+    );
+    for (const threadId of ["thread-conflict-a", "thread-conflict-b"]) {
+      await system.run(
+        engine.dispatch({
+          type: "thread.create",
+          commandId: CommandId.make(`cmd-${threadId}-create`),
+          threadId: ThreadId.make(threadId),
+          projectId: asProjectId("project-conflict"),
+          title: threadId,
+          modelSelection: {
+            instanceId: ProviderInstanceId.make("codex"),
+            model: "gpt-5-codex",
+          },
+          interactionMode: DEFAULT_PROVIDER_INTERACTION_MODE,
+          runtimeMode: "approval-required",
+          branch: null,
+          worktreePath: null,
+          createdAt,
+        }),
+      );
+    }
+
+    await system.run(
+      engine.dispatch({
+        type: "thread.turn.start",
+        commandId: CommandId.make("cmd-conflict-turn-start"),
+        threadId: ThreadId.make("thread-conflict-a"),
+        message: {
+          messageId: asMessageId("msg-conflict-a"),
+          role: "user",
+          text: "hello",
+          attachments: [],
+        },
+        interactionMode: DEFAULT_PROVIDER_INTERACTION_MODE,
+        runtimeMode: "approval-required",
+        createdAt,
+      }),
+    );
+
+    await expect(
+      system.run(
+        engine.dispatch({
+          type: "thread.turn.start",
+          commandId: CommandId.make("cmd-conflict-turn-start"),
+          threadId: ThreadId.make("thread-conflict-b"),
+          message: {
+            messageId: asMessageId("msg-conflict-b"),
+            role: "user",
+            text: "hello again",
+            attachments: [],
+          },
+          interactionMode: DEFAULT_PROVIDER_INTERACTION_MODE,
+          runtimeMode: "approval-required",
+          createdAt,
+        }),
+      ),
+    ).rejects.toThrow("already used for thread 'thread-conflict-a'");
+
+    const readModel = await system.readModel();
+    const targetThread = readModel.threads.find(
+      (candidate) => candidate.id === "thread-conflict-b",
+    );
+    expect(targetThread?.messages.filter((message) => message.role === "user")).toHaveLength(0);
+
+    await system.dispose();
+  });
 });
diff --git a/apps/server/src/orchestration/Layers/OrchestrationEngine.ts b/apps/server/src/orchestration/Layers/OrchestrationEngine.ts
index 19184915ac7..da79b4395ac 100644
--- a/apps/server/src/orchestration/Layers/OrchestrationEngine.ts
+++ b/apps/server/src/orchestration/Layers/OrchestrationEngine.ts
@@ -32,6 +32,7 @@ import { toPersistenceSqlError } from "../../persistence/Errors.ts";
 import { OrchestrationEventStore } from "../../persistence/Services/OrchestrationEventStore.ts";
 import { OrchestrationCommandReceiptRepository } from "../../persistence/Services/OrchestrationCommandReceipts.ts";
 import {
+  OrchestrationCommandIdConflictError,
   OrchestrationCommandInvariantError,
   OrchestrationCommandPreviouslyRejectedError,
   type OrchestrationDispatchError,
@@ -48,6 +49,7 @@ import {
 const isOrchestrationCommandPreviouslyRejectedError = Schema.is(
   OrchestrationCommandPreviouslyRejectedError,
 );
+const isOrchestrationCommandIdConflictError = Schema.is(OrchestrationCommandIdConflictError);
 const isOrchestrationCommandInvariantError = Schema.is(OrchestrationCommandInvariantError);
 
 interface CommandEnvelope {
@@ -139,6 +141,21 @@ const makeOrchestrationEngine = Effect.gen(function* () {
           commandId: envelope.command.commandId,
         });
         if (Option.isSome(existingReceipt)) {
+          // A receipt only proves this exact command was handled. Replaying it
+          // for a command aimed at another aggregate would report success for
+          // work that never happened.
+          if (
+            existingReceipt.value.aggregateKind !== aggregateRef.aggregateKind ||
+            existingReceipt.value.aggregateId !== aggregateRef.aggregateId
+          ) {
+            return yield* new OrchestrationCommandIdConflictError({
+              commandId: envelope.command.commandId,
+              receiptAggregateKind: existingReceipt.value.aggregateKind,
+              receiptAggregateId: existingReceipt.value.aggregateId,
+              commandAggregateKind: aggregateRef.aggregateKind,
+              commandAggregateId: aggregateRef.aggregateId,
+            });
+          }
           if (existingReceipt.value.status === "accepted") {
             return {
               sequence: existingReceipt.value.resultSequence,
@@ -262,7 +279,10 @@ const makeOrchestrationEngine = Effect.gen(function* () {
           }
 
           const error = Cause.squash(exit.cause) as OrchestrationDispatchError;
-          if (!isOrchestrationCommandPreviouslyRejectedError(error)) {
+          if (
+            !isOrchestrationCommandPreviouslyRejectedError(error) &&
+            !isOrchestrationCommandIdConflictError(error)
+          ) {
             yield* reconcileReadModelAfterDispatchFailure.pipe(
               Effect.catch(() =>
                 Effect.logWarning(