diff --git a/packages/chat/src/channel.ts b/packages/chat/src/channel.ts
index 3a29a233..88941016 100644
--- a/packages/chat/src/channel.ts
+++ b/packages/chat/src/channel.ts
@@ -10,7 +10,7 @@ import {
   toPlainText,
 } from "./markdown";
 import { Message } from "./message";
-import { isPostableObject } from "./plan";
+import { isPostableObject } from "./postable-object";
 import type {
   Adapter,
   AdapterPostableMessage,
@@ -297,10 +297,15 @@ export class ChannelImpl<TState = Record<string, unknown>>
         threadId: raw.threadId ?? this.id,
       });
     } else {
+      // Adapter doesn't support this object type - post fallback text
+      const fallbackText = obj.getFallbackText();
+      const raw = this.adapter.postChannelMessage
+        ? await this.adapter.postChannelMessage(this.id, fallbackText)
+        : await this.adapter.postMessage(this.id, fallbackText);
       obj.onPosted({
         adapter,
-        messageId: `${obj.kind}_${crypto.randomUUID()}`,
-        threadId: this.id,
+        messageId: raw.id,
+        threadId: raw.threadId ?? this.id,
       });
     }
   }
diff --git a/packages/chat/src/index.ts b/packages/chat/src/index.ts
index 0f3d88b8..76a4ad43 100644
--- a/packages/chat/src/index.ts
+++ b/packages/chat/src/index.ts
@@ -11,7 +11,23 @@ export {
   type MessageData,
   type SerializedMessage,
 } from "./message";
-export { isPostableObject, Plan } from "./plan";
+export type {
+  AddTaskOptions,
+  CompletePlanOptions,
+  PlanContent,
+  PlanModel,
+  PlanModelTask,
+  PlanTask,
+  PlanTaskStatus,
+  StartPlanOptions,
+  UpdateTaskInput,
+} from "./plan";
+export { Plan } from "./plan";
+export type {
+  PostableObject,
+  PostableObjectContext,
+} from "./postable-object";
+export { isPostableObject } from "./postable-object";
 export { StreamingMarkdownRenderer } from "./streaming-markdown";
 export { type SerializedThread, ThreadImpl } from "./thread";
 
@@ -199,13 +215,12 @@ export type {
   TextInputElement,
   TextInputOptions,
 } from "./modals";
-// Types
+// Types (Plan types are exported from ./plan, PostableObject types from ./postable-object)
 export type {
   ActionEvent,
   ActionHandler,
   Adapter,
   AdapterPostableMessage,
-  AddTaskOptions,
   AppHomeOpenedEvent,
   AppHomeOpenedHandler,
   AssistantContextChangedEvent,
@@ -218,7 +233,6 @@ export type {
   ChannelInfo,
   ChatConfig,
   ChatInstance,
-  CompletePlanOptions,
   CustomEmojiMap,
   Emoji,
   EmojiFormats,
@@ -246,18 +260,11 @@ export type {
   ModalSubmitEvent,
   ModalSubmitHandler,
   ModalUpdateResponse,
-  PlanContent,
-  PlanModel,
-  PlanModelTask,
-  PlanTask,
-  PlanTaskStatus,
   Postable,
   PostableAst,
   PostableCard,
   PostableMarkdown,
   PostableMessage,
-  PostableObject,
-  PostableObjectContext,
   PostableRaw,
   PostEphemeralOptions,
   RawMessage,
@@ -266,14 +273,12 @@ export type {
   SentMessage,
   SlashCommandEvent,
   SlashCommandHandler,
-  StartPlanOptions,
   StateAdapter,
   StreamOptions,
   SubscribedMessageHandler,
   Thread,
   ThreadInfo,
   ThreadSummary,
-  UpdateTaskInput,
   WebhookOptions,
   WellKnownEmoji,
 } from "./types";
diff --git a/packages/chat/src/plan.ts b/packages/chat/src/plan.ts
index 30507937..7a5895a3 100644
--- a/packages/chat/src/plan.ts
+++ b/packages/chat/src/plan.ts
@@ -1,17 +1,71 @@
+import type { Root } from "mdast";
 import { parseMarkdown, toPlainText } from "./markdown";
-import type {
-  Adapter,
-  AddTaskOptions,
-  CompletePlanOptions,
-  PlanContent,
-  PlanModel,
-  PlanModelTask,
-  PlanTask,
-  PostableObject,
-  PostableObjectContext,
-  StartPlanOptions,
-  UpdateTaskInput,
-} from "./types";
+import {
+  POSTABLE_OBJECT,
+  type PostableObject,
+  type PostableObjectContext,
+} from "./postable-object";
+import type { Adapter } from "./types";
+
+// =============================================================================
+// Plan Types (moved from types.ts per review feedback)
+// =============================================================================
+
+export type PlanTaskStatus = "pending" | "in_progress" | "complete" | "error";
+
+export interface PlanTask {
+  id: string;
+  status: PlanTaskStatus;
+  title: string;
+}
+
+export interface PlanModel {
+  tasks: PlanModelTask[];
+  title: string;
+}
+
+export interface PlanModelTask {
+  details?: PlanContent;
+  id: string;
+  output?: PlanContent;
+  status: PlanTaskStatus;
+  title: string;
+}
+
+export type PlanContent =
+  | string
+  | string[]
+  | { markdown: string }
+  | { ast: Root };
+
+export interface StartPlanOptions {
+  /** Initial plan title and first task title */
+  initialMessage: PlanContent;
+}
+
+export interface AddTaskOptions {
+  /** Task details/substeps. */
+  children?: PlanContent;
+  title: PlanContent;
+}
+
+export type UpdateTaskInput =
+  | PlanContent
+  | {
+      /** Task output/results. */
+      output?: PlanContent;
+      /** Optional status override. */
+      status?: PlanTaskStatus;
+    };
+
+export interface CompletePlanOptions {
+  /** Final plan title shown when completed */
+  completeMessage: PlanContent;
+}
+
+// =============================================================================
+// Plan Implementation
+// =============================================================================
 
 /**
  * Convert PlanContent to plain text for titles/labels.
@@ -35,22 +89,9 @@ function contentToPlainText(content: PlanContent | undefined): string {
   return "";
 }
 
-/** Symbol identifying Plan objects */
-const POSTABLE_OBJECT = Symbol.for("chat.postable");
-
-/**
- * Type guard to check if a value is a PostableObject.
- */
-export function isPostableObject(value: unknown): value is PostableObject {
-  return (
-    typeof value === "object" &&
-    value !== null &&
-    (value as PostableObject).$$typeof === POSTABLE_OBJECT
-  );
-}
-
 interface BoundState {
   adapter: Adapter;
+  fallback: boolean;
   messageId: string;
   threadId: string;
   updateChain: Promise<void>;
@@ -71,7 +112,7 @@ interface BoundState {
  * await plan.complete({ completeMessage: "Done!" });
  * ```
  */
-export class Plan implements PostableObject {
+export class Plan implements PostableObject<PlanModel> {
   readonly $$typeof = POSTABLE_OBJECT;
   readonly kind = "plan";
 
@@ -91,13 +132,30 @@ export class Plan implements PostableObject {
   isSupported(adapter: Adapter): boolean {
     return !!adapter.postObject && !!adapter.editObject;
   }
+
   getPostData(): PlanModel {
     return this._model;
   }
 
+  getFallbackText(): string {
+    const lines: string[] = [];
+    lines.push(`📋 ${this._model.title || "Plan"}`);
+    for (const task of this._model.tasks) {
+      const statusIcons: Record<string, string> = {
+        complete: "✅",
+        in_progress: "🔄",
+        error: "❌",
+      };
+      const statusIcon = statusIcons[task.status] ?? "⬜";
+      lines.push(`${statusIcon} ${task.title}`);
+    }
+    return lines.join("\n");
+  }
+
   onPosted(context: PostableObjectContext): void {
     this._bound = {
       adapter: context.adapter,
+      fallback: !this.isSupported(context.adapter),
       messageId: context.messageId,
       threadId: context.threadId,
       updateChain: Promise.resolve(),
@@ -218,26 +276,34 @@ export class Plan implements PostableObject {
   }
 
   private canMutate(): boolean {
-    return !!(this._bound && this.isSupported(this._bound.adapter));
+    return !!this._bound;
   }
 
   private enqueueEdit(): Promise<void> {
     if (!this._bound) {
       return Promise.resolve();
     }
-    const editObject = this._bound.adapter.editObject;
-    if (!editObject) {
-      return Promise.resolve();
-    }
     const bound = this._bound;
     const doEdit = async (): Promise<void> => {
-      await editObject.call(
-        bound.adapter,
-        bound.threadId,
-        bound.messageId,
-        this.kind,
-        this._model
-      );
+      if (bound.fallback) {
+        await bound.adapter.editMessage(
+          bound.threadId,
+          bound.messageId,
+          this.getFallbackText()
+        );
+      } else {
+        const editObject = bound.adapter.editObject;
+        if (!editObject) {
+          return;
+        }
+        await editObject.call(
+          bound.adapter,
+          bound.threadId,
+          bound.messageId,
+          this.kind,
+          this._model
+        );
+      }
     };
     const chained = bound.updateChain.then(doEdit, doEdit);
     bound.updateChain = chained.then(
diff --git a/packages/chat/src/postable-object.ts b/packages/chat/src/postable-object.ts
new file mode 100644
index 00000000..e59dfbcd
--- /dev/null
+++ b/packages/chat/src/postable-object.ts
@@ -0,0 +1,56 @@
+import type { Adapter } from "./types";
+
+/**
+ * Symbol identifying PostableObject instances.
+ * Used by type guards to detect postable objects.
+ */
+export const POSTABLE_OBJECT = Symbol.for("chat.postable");
+
+/**
+ * Context provided to a PostableObject after it has been posted.
+ */
+export interface PostableObjectContext {
+  adapter: Adapter;
+  messageId: string;
+  threadId: string;
+}
+
+/**
+ * Base interface for objects that can be posted to threads/channels.
+ * Examples: Plan, Poll, etc.
+ *
+ * @template TData - The data type returned by getPostData()
+ */
+export interface PostableObject<TData = unknown> {
+  /** Symbol identifying this as a postable object */
+  readonly $$typeof: symbol;
+
+  /**
+   * Get a fallback text representation for adapters that don't support this object type.
+   * This should return a human-readable string representation.
+   */
+  getFallbackText(): string;
+
+  /** Get the data to send to the adapter */
+  getPostData(): TData;
+
+  /** Check if the adapter supports this object type */
+  isSupported(adapter: Adapter): boolean;
+
+  /** The kind of object - used by adapters to dispatch */
+  readonly kind: string;
+
+  /** Called after successful posting to bind the object to the thread */
+  onPosted(context: PostableObjectContext): void;
+}
+
+/**
+ * Type guard to check if a value is a PostableObject.
+ */
+export function isPostableObject(value: unknown): value is PostableObject {
+  return (
+    typeof value === "object" &&
+    value !== null &&
+    (value as PostableObject).$$typeof === POSTABLE_OBJECT
+  );
+}
diff --git a/packages/chat/src/thread.test.ts b/packages/chat/src/thread.test.ts
index ad114030..62e792e7 100644
--- a/packages/chat/src/thread.test.ts
+++ b/packages/chat/src/thread.test.ts
@@ -1131,26 +1131,55 @@ describe("ThreadImpl", () => {
       });
     });
 
-    it("should silently no-op when adapter does not support plans", async () => {
+    it("should post fallback text when adapter does not support plans", async () => {
       const plan = new Plan({ initialMessage: "Starting..." });
       await thread.post(plan);
 
+      // Should have posted fallback text via postMessage
+      expect(mockAdapter.postMessage).toHaveBeenCalledWith(
+        "slack:C123:1234.5678",
+        expect.stringContaining("Starting...")
+      );
+
       expect(plan.title).toBe("Starting...");
       expect(plan.tasks).toHaveLength(1);
       expect(plan.tasks[0].status).toBe("in_progress");
+      expect(plan.id).toBe("msg-1");
+    });
+
+    it("should update via editMessage in fallback mode", async () => {
+      const plan = new Plan({ initialMessage: "Starting..." });
+      await thread.post(plan);
 
-      // Methods should return null (no-op)
       const task = await plan.addTask({ title: "Task 1" });
-      expect(task).toBeNull();
+      expect(task).not.toBeNull();
+      expect(task?.title).toBe("Task 1");
 
-      const updated = await plan.updateTask("progress");
-      expect(updated).toBeNull();
+      // Should edit the message with updated fallback text
+      expect(mockAdapter.editMessage).toHaveBeenCalledWith(
+        "slack:C123:1234.5678",
+        "msg-1",
+        expect.stringContaining("Task 1")
+      );
+    });
 
-      const reset = await plan.reset({ initialMessage: "Reset" });
-      expect(reset).toBeNull();
+    it("should complete plan via editMessage in fallback mode", async () => {
+      const plan = new Plan({ initialMessage: "Starting..." });
+      await thread.post(plan);
 
-      // complete should not throw
-      await plan.complete({ completeMessage: "Done" });
+      await plan.addTask({ title: "Step 1" });
+      await plan.complete({ completeMessage: "All done!" });
+
+      expect(plan.title).toBe("All done!");
+      for (const task of plan.tasks) {
+        expect(task.status).toBe("complete");
+      }
+
+      // Last editMessage call should contain completed status icons
+      const lastCall = (
+        mockAdapter.editMessage as ReturnType<typeof vi.fn>
+      ).mock.calls.at(-1);
+      expect(lastCall?.[2]).toContain("✅");
     });
 
     it("should call adapter postObject when supported", async () => {
diff --git a/packages/chat/src/thread.ts b/packages/chat/src/thread.ts
index e7b9051b..7f0a1721 100644
--- a/packages/chat/src/thread.ts
+++ b/packages/chat/src/thread.ts
@@ -12,7 +12,7 @@ import {
   toPlainText,
 } from "./markdown";
 import { Message, type SerializedMessage } from "./message";
-import { isPostableObject } from "./plan";
+import { isPostableObject } from "./postable-object";
 import { StreamingMarkdownRenderer } from "./streaming-markdown";
 import type {
   Adapter,
@@ -389,10 +389,13 @@ export class ThreadImpl<TState = Record<string, unknown>>
         threadId: raw.threadId ?? this.id,
       });
     } else {
+      // Adapter doesn't support this object type - post fallback text
+      const fallbackText = obj.getFallbackText();
+      const raw = await this.adapter.postMessage(this.id, fallbackText);
       obj.onPosted({
         adapter,
-        messageId: `${obj.kind}_${crypto.randomUUID()}`,
-        threadId: this.id,
+        messageId: raw.id,
+        threadId: raw.threadId ?? this.id,
       });
     }
   }
diff --git a/packages/chat/src/types.ts b/packages/chat/src/types.ts
index 015d21b4..52dfdb26 100644
--- a/packages/chat/src/types.ts
+++ b/packages/chat/src/types.ts
@@ -8,6 +8,7 @@ import type { CardJSXElement } from "./jsx-runtime";
 import type { Logger, LogLevel } from "./logger";
 import type { Message } from "./message";
 import type { ModalElement } from "./modals";
+import type { PostableObject } from "./postable-object";
 
 // =============================================================================
 // Re-exports from extracted modules
@@ -855,83 +856,23 @@ export interface Thread<TState = Record<string, unknown>, TRawMessage = unknown>
 // Postable Objects
 // =============================================================================
 
-/**
- * Context provided to a PostableObject after it has been posted.
- */
-export interface PostableObjectContext {
-  adapter: Adapter;
-  messageId: string;
-  threadId: string;
-}
-
-export interface PostableObject {
-  /** Symbol identifying this as a postable object */
-  readonly $$typeof: symbol;
-
-  /** Get the data to send to the adapter */
-  getPostData(): unknown;
-
-  /** Check if the adapter supports this object type */
-  isSupported(adapter: Adapter): boolean;
-
-  /** The kind of object - used by adapters to dispatch */
-  readonly kind: string;
-
-  /** Called after successful posting to bind the object to the thread */
-  onPosted(context: PostableObjectContext): void;
-}
-
-export type PlanTaskStatus = "pending" | "in_progress" | "complete" | "error";
-
-export interface PlanTask {
-  id: string;
-  status: PlanTaskStatus;
-  title: string;
-}
-
-export interface PlanModel {
-  tasks: PlanModelTask[];
-  title: string;
-}
-
-export interface PlanModelTask {
-  details?: PlanContent;
-  id: string;
-  output?: PlanContent;
-  status: PlanTaskStatus;
-  title: string;
-}
-
-export type PlanContent =
-  | string
-  | string[]
-  | { markdown: string }
-  | { ast: Root };
-
-export interface StartPlanOptions {
-  /** Initial plan title and first task title */
-  initialMessage: PlanContent;
-}
-
-export interface AddTaskOptions {
-  /** Task details/substeps. */
-  children?: PlanContent;
-  title: PlanContent;
-}
-
-export type UpdateTaskInput =
-  | PlanContent
-  | {
-      /** Task output/results. */
-      output?: PlanContent;
-      /** Optional status override. */
-      status?: PlanTaskStatus;
-    };
-
-export interface CompletePlanOptions {
-  /** Final plan title shown when completed */
-  completeMessage: PlanContent;
-}
+// Re-export Plan types from plan.ts for backwards compatibility
+export type {
+  AddTaskOptions,
+  CompletePlanOptions,
+  PlanContent,
+  PlanModel,
+  PlanModelTask,
+  PlanTask,
+  PlanTaskStatus,
+  StartPlanOptions,
+  UpdateTaskInput,
+} from "./plan";
+// Re-export PostableObject types from plan.ts for backwards compatibility
+export type {
+  PostableObject,
+  PostableObjectContext,
+} from "./postable-object";
 
 export interface ThreadInfo {
   channelId: string;