fix(session): handled malformed custom messages

Normalized extension custom-message payloads before session state or persistence, including bare string sendMessage shorthands. Skipped legacy bare custom_message entries during context rebuilds and dropped malformed custom/hook messages before LLM conversion. Added regression coverage for the poisoned-session resume crash.\n\nFixes #4345

packages/coding-agent/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Fixed malformed `pi.sendMessage` custom-message payloads persisting bare session entries that crashed every later resume before provider calls. ([#4345](https://github.com/can1357/oh-my-pi/issues/4345))
+
 ## [16.3.2] - 2026-07-02
 
 ### Breaking Changes

packages/coding-agent/src/extensibility/extensions/loader.ts

@@ -18,7 +18,7 @@ import type { ExecOptions } from "../../exec/exec";
 import { execCommand } from "../../exec/exec";
 // Runtime self-reference: dereference this namespace only inside loader functions to keep the index.ts cycle safe.
 import * as PiCodingAgent from "../../index";
-import type { CustomMessage } from "../../session/messages";
+import type { CustomMessagePayload } from "../../session/messages";
 import { EventBus } from "../../utils/event-bus";
 import { installLegacyPiSpecifierShim, loadLegacyPiModule } from "../plugins/legacy-pi-compat";
 import { getAllPluginExtensionPaths } from "../plugins/loader";
@@ -203,7 +203,7 @@ class ConcreteExtensionAPI implements ExtensionAPI, IExtensionRuntime {
 	}
 
 	sendMessage<T = unknown>(
-		message: Pick<CustomMessage<T>, "customType" | "content" | "display" | "details" | "attribution">,
+		message: CustomMessagePayload<T>,
 		options?: { triggerTurn?: boolean; deliverAs?: "steer" | "followUp" | "nextTurn" },
 	): void {
 		this.runtime.sendMessage(message, options);

packages/coding-agent/src/extensibility/extensions/types.ts

@@ -45,7 +45,7 @@ import type { MemoryRuntimeContext } from "../../memory-backend";
 import type { CustomEditor } from "../../modes/components/custom-editor";
 import type { Theme } from "../../modes/theme/theme";
 import type { CompactMode } from "../../session/compact-modes";
-import type { CustomMessage } from "../../session/messages";
+import type { CustomMessage, CustomMessagePayload } from "../../session/messages";
 import type { ReadonlySessionManager, SessionManager } from "../../session/session-manager";
 import type {
 	BashToolDetails,
@@ -881,7 +881,7 @@ export interface UserPythonEventResult {
 export type { ToolResultEventResult } from "../shared-events";
 
 export interface BeforeAgentStartEventResult {
-	message?: Pick<CustomMessage, "customType" | "content" | "display" | "details" | "attribution">;
+	message?: CustomMessagePayload;
 	/** Replace the system prompt for this turn. If multiple extensions return this, they are chained. */
 	systemPrompt?: string[];
 }
@@ -1091,7 +1091,7 @@ export interface ExtensionAPI {
 	 * an internal continuation that consumes the message on the next turn.
 	 */
 	sendMessage<T = unknown>(
-		message: Pick<CustomMessage<T>, "customType" | "content" | "display" | "details" | "attribution">,
+		message: CustomMessagePayload<T>,
 		options?: { triggerTurn?: boolean; deliverAs?: "steer" | "followUp" | "nextTurn" },
 	): void;
 
@@ -1277,7 +1277,7 @@ export interface ExtensionShortcut {
 type HandlerFn = (...args: unknown[]) => Promise<unknown>;
 
 export type SendMessageHandler = <T = unknown>(
-	message: Pick<CustomMessage<T>, "customType" | "content" | "display" | "details" | "attribution">,
+	message: CustomMessagePayload<T>,
 	/**
 	 * `deliverAs: "nextTurn"` queues hidden custom context for the next turn.
 	 * When paired with `triggerTurn: true` during prompt teardown, the session schedules

packages/coding-agent/src/extensibility/hooks/loader.ts

@@ -10,7 +10,7 @@ import type { Hook } from "../../discovery";
 import { loadCapability } from "../../discovery";
 // Runtime self-reference: dereference this namespace only inside loader functions to keep the index.ts cycle safe.
 import * as PiCodingAgent from "../../index";
-import type { HookMessage } from "../../session/messages";
+import type { CustomMessagePayload } from "../../session/messages";
 import * as typebox from "../typebox";
 import { resolvePath, withExitGuard } from "../utils";
 import { execCommand } from "./runner";
@@ -25,7 +25,7 @@ type HandlerFn = (...args: unknown[]) => Promise<unknown>;
  * Send message handler type for pi.sendMessage().
  */
 export type SendMessageHandler = <T = unknown>(
-	message: Pick<HookMessage<T>, "customType" | "content" | "display" | "details" | "attribution">,
+	message: CustomMessagePayload<T>,
 	options?: { triggerTurn?: boolean; deliverAs?: "steer" | "followUp" },
 ) => void;
 
@@ -97,7 +97,7 @@ async function createHookAPI(
 			handlers.get(event)!.push(handler);
 		},
 		sendMessage<T = unknown>(
-			message: HookMessage<T>,
+			message: CustomMessagePayload<T>,
 			options?: { triggerTurn?: boolean; deliverAs?: "steer" | "followUp" },
 		): void {
 			if (!sendMessageHandler) {

packages/coding-agent/src/extensibility/hooks/types.ts

@@ -8,7 +8,7 @@ import type { EditToolDetails } from "../../edit";
 import type { ExecOptions, ExecResult } from "../../exec/exec";
 import type * as PiCodingAgent from "../../index";
 import type { Theme } from "../../modes/theme/theme";
-import type { HookMessage } from "../../session/messages";
+import type { CustomMessagePayload, HookMessage } from "../../session/messages";
 import type { ReadonlySessionManager, SessionManager } from "../../session/session-manager";
 import type { BashToolDetails, GlobToolDetails, GrepToolDetails, ReadToolDetails } from "../../tools";
 import type {
@@ -425,7 +425,7 @@ export type { ToolCallEventResult, ToolResultEventResult } from "../shared-event
  */
 export interface BeforeAgentStartEventResult {
 	/** Message to inject into context (persisted to session, visible in TUI) */
-	message?: Pick<HookMessage, "customType" | "content" | "display" | "details" | "attribution">;
+	message?: CustomMessagePayload;
 }
 
 export type {
@@ -519,7 +519,7 @@ export interface HookAPI {
 	 * Use this when you want the LLM to see the message content.
 	 * For hook state that should NOT be sent to the LLM, use appendEntry() instead.
 	 *
-	 * @param message - The message to send
+	 * @param message - The message object to send, or a string shorthand for visible message content
 	 * @param message.customType - Identifier for your hook (used for filtering on reload)
 	 * @param message.content - Message content (string or TextContent/ImageContent array)
 	 * @param message.display - Whether to show in TUI (true = styled display, false = hidden)
@@ -530,7 +530,7 @@ export interface HookAPI {
 	 * @param options.deliverAs - How to deliver the message: "steer" or "followUp".
 	 */
 	sendMessage<T = unknown>(
-		message: Pick<HookMessage<T>, "customType" | "content" | "display" | "details" | "attribution">,
+		message: CustomMessagePayload<T>,
 		options?: { triggerTurn?: boolean; deliverAs?: "steer" | "followUp" },
 	): void;
 

packages/coding-agent/src/modes/controllers/extension-ui-controller.ts

@@ -24,7 +24,7 @@ import { HookInputComponent } from "../../modes/components/hook-input";
 import { HookSelectorComponent, type HookSelectorSlider } from "../../modes/components/hook-selector";
 import { getAvailableThemesWithPaths, getThemeByName, setTheme, type Theme, theme } from "../../modes/theme/theme";
 import type { InteractiveModeContext, InteractiveSelectorDialogOptions } from "../../modes/types";
-import { USER_INTERRUPT_LABEL } from "../../session/messages";
+import { normalizeCustomMessagePayload, USER_INTERRUPT_LABEL } from "../../session/messages";
 import { setSessionTerminalTitle, setTerminalTitle } from "../../utils/title-generator";
 
 const MAX_WIDGET_LINES = 10;
@@ -106,9 +106,10 @@ export class ExtensionUiController {
 		const actions: ExtensionActions = {
 			sendMessage: (message, options) => {
 				const wasStreaming = this.ctx.session.isStreaming;
+				const normalized = normalizeCustomMessagePayload(message);
 				this.ctx.session
-					.sendCustomMessage(message, options)
-					.then(() => this.#applyCustomMessageDisplay(wasStreaming, message.display))
+					.sendCustomMessage(normalized, options)
+					.then(() => this.#applyCustomMessageDisplay(wasStreaming, normalized.display))
 					.catch((err: unknown) => {
 						this.ctx.showError(
 							`Extension sendMessage failed: ${err instanceof Error ? err.message : String(err)}`,
@@ -342,9 +343,10 @@ export class ExtensionUiController {
 		const actions: ExtensionActions = {
 			sendMessage: (message, options) => {
 				const wasStreaming = this.ctx.session.isStreaming;
+				const normalized = normalizeCustomMessagePayload(message);
 				this.ctx.session
-					.sendCustomMessage(message, options)
-					.then(() => this.#applyCustomMessageDisplay(wasStreaming, message.display))
+					.sendCustomMessage(normalized, options)
+					.then(() => this.#applyCustomMessageDisplay(wasStreaming, normalized.display))
 					.catch((err: unknown) => {
 						const errorText = `Extension sendMessage failed: ${err instanceof Error ? err.message : String(err)}`;
 						this.ctx.showError(errorText);

packages/coding-agent/src/session/agent-session.ts

@@ -334,11 +334,13 @@ import {
 import {
 	type BashExecutionMessage,
 	type CustomMessage,
+	type CustomMessagePayload,
 	convertToLlm,
 	demoteInterruptedThinking,
 	INTERRUPTED_THINKING_MESSAGE_TYPE,
 	type InterruptedThinkingDetails,
 	isUserInterruptAbort,
+	normalizeCustomMessagePayload,
 	type PythonExecutionMessage,
 	readQueueChipText,
 	SILENT_ABORT_MARKER,
@@ -7488,15 +7490,22 @@ export class AgentSession {
 					const promptAttribution: "user" | "agent" | undefined =
 						"attribution" in message ? message.attribution : undefined;
 					for (const msg of result.messages) {
+						const normalized = normalizeCustomMessagePayload(msg);
+						const hasExplicitAttribution =
+							msg !== null &&
+							typeof msg === "object" &&
+							!Array.isArray(msg) &&
+							(msg.attribution === "user" || msg.attribution === "agent");
 						messages.push(
 							await this.#normalizeAgentMessageImages({
 								role: "custom",
-								customType: msg.customType,
-								content: msg.content,
-								display: msg.display,
-								details: msg.details,
-								attribution:
-									msg.attribution ?? promptAttribution ?? (message.role === "user" ? "user" : "agent"),
+								customType: normalized.customType,
+								content: normalized.content,
+								display: normalized.display,
+								details: normalized.details,
+								attribution: hasExplicitAttribution
+									? normalized.attribution
+									: (promptAttribution ?? (message.role === "user" ? "user" : "agent")),
 								timestamp: Date.now(),
 							}),
 						);
@@ -7959,26 +7968,26 @@ export class AgentSession {
 	 * use this to avoid acting on a turn that never ran.
 	 */
 	async sendCustomMessage<T = unknown>(
-		message: Pick<CustomMessage<T>, "customType" | "content" | "display" | "details" | "attribution">,
+		message: CustomMessagePayload<T>,
 		options?: { triggerTurn?: boolean; deliverAs?: "steer" | "followUp" | "nextTurn"; queueChipText?: string },
 	): Promise<boolean> {
+		const normalizedPayload = normalizeCustomMessagePayload<T>(message);
 		const details =
 			options?.queueChipText && options.deliverAs !== "nextTurn"
 				? ({
-						...((message.details && typeof message.details === "object" ? message.details : {}) as Record<
-							string,
-							unknown
-						>),
+						...((normalizedPayload.details && typeof normalizedPayload.details === "object"
+							? normalizedPayload.details
+							: {}) as Record<string, unknown>),
 						__queueChipText: options.queueChipText,
 					} as T)
-				: message.details;
+				: normalizedPayload.details;
 		const appMessage: CustomMessage<T> = {
 			role: "custom",
-			customType: message.customType,
-			content: message.content,
-			display: message.display,
+			customType: normalizedPayload.customType,
+			content: normalizedPayload.content,
+			display: normalizedPayload.display,
 			details,
-			attribution: message.attribution ?? "agent",
+			attribution: normalizedPayload.attribution,
 			timestamp: Date.now(),
 		};
 		const normalizedAppMessage = await this.#normalizeAgentMessageImages(appMessage);
@@ -8010,9 +8019,9 @@ export class AgentSession {
 			this.sessionManager.appendCustomMessageEntry(
 				normalizedAppMessage.customType,
 				normalizedAppMessage.content,
-				message.display,
-				message.details,
-				message.attribution ?? "agent",
+				normalizedAppMessage.display,
+				normalizedAppMessage.details,
+				normalizedAppMessage.attribution,
 			);
 			return false;
 		}
@@ -8030,9 +8039,9 @@ export class AgentSession {
 		this.sessionManager.appendCustomMessageEntry(
 			normalizedAppMessage.customType,
 			normalizedAppMessage.content,
-			message.display,
-			message.details,
-			message.attribution ?? "agent",
+			normalizedAppMessage.display,
+			normalizedAppMessage.details,
+			normalizedAppMessage.attribution,
 		);
 		return false;
 	}

packages/coding-agent/src/session/messages.ts

@@ -37,6 +37,23 @@ export const SKILL_PROMPT_MESSAGE_TYPE = "skill-prompt";
 export const LSP_LATE_DIAGNOSTIC_MESSAGE_TYPE = "lsp-late-diagnostic";
 export const BACKGROUND_TAN_DISPATCH_MESSAGE_TYPE = "background-tan-dispatch";
 
+/** Fallback type for extension-injected messages that omit a custom type. */
+export const DEFAULT_CUSTOM_MESSAGE_TYPE = "custom-message";
+
+/** Content shape accepted for extension-injected messages. */
+export type CustomMessageContent = string | (TextContent | ImageContent)[];
+
+/** Public input accepted by `pi.sendMessage` and `AgentSession.sendCustomMessage`. */
+export type CustomMessagePayload<T = unknown> =
+	| string
+	| Partial<Pick<CustomMessage<T>, "customType" | "content" | "display" | "details" | "attribution">>;
+
+/** Custom message payload after applying runtime defaults. */
+export type NormalizedCustomMessagePayload<T = unknown> = Pick<
+	CustomMessage<T>,
+	"customType" | "content" | "display" | "details" | "attribution"
+>;
+
 /** Custom message type for hidden interrupted-thinking continuity context. */
 export const INTERRUPTED_THINKING_MESSAGE_TYPE = "interrupted-thinking";
 
@@ -248,6 +265,59 @@ export function stripInternalDetailsFields<T>(details: T | undefined): T | undef
 	return cleaned as T;
 }
 
+/** True when a persisted or extension-supplied value can be sent as custom-message content. */
+export function isCustomMessageContent(content: unknown): content is CustomMessageContent {
+	return typeof content === "string" || Array.isArray(content);
+}
+
+function normalizeCustomMessageContent(content: unknown): CustomMessageContent {
+	return isCustomMessageContent(content) ? content : "";
+}
+
+function normalizeCustomMessageType(customType: unknown): string {
+	return typeof customType === "string" && customType.length > 0 ? customType : DEFAULT_CUSTOM_MESSAGE_TYPE;
+}
+
+function normalizeCustomMessageAttribution(attribution: unknown): MessageAttribution {
+	return attribution === "user" ? "user" : "agent";
+}
+
+function isCustomMessagePayloadObject<T>(
+	payload: unknown,
+): payload is Partial<Pick<CustomMessage<T>, "customType" | "content" | "display" | "details" | "attribution">> {
+	return payload !== null && typeof payload === "object" && !Array.isArray(payload);
+}
+
+/** Normalizes extension-provided custom message input before it reaches session state or disk. */
+export function normalizeCustomMessagePayload<T = unknown>(
+	payload: CustomMessagePayload<T> | unknown,
+): NormalizedCustomMessagePayload<T> {
+	if (typeof payload === "string") {
+		return {
+			customType: DEFAULT_CUSTOM_MESSAGE_TYPE,
+			content: payload,
+			display: true,
+			attribution: "agent",
+		};
+	}
+	if (!isCustomMessagePayloadObject<T>(payload)) {
+		const content = payload === undefined || payload === null ? "" : String(payload);
+		return {
+			customType: DEFAULT_CUSTOM_MESSAGE_TYPE,
+			content,
+			display: content.length > 0,
+			attribution: "agent",
+		};
+	}
+	return {
+		customType: normalizeCustomMessageType(payload.customType),
+		content: normalizeCustomMessageContent(payload.content),
+		display: typeof payload.display === "boolean" ? payload.display : false,
+		details: payload.details,
+		attribution: normalizeCustomMessageAttribution(payload.attribution),
+	};
+}
+
 function isSteeringUserMessage(message: AgentMessage | undefined): message is UserMessage & { steering: true } {
 	return message?.role === "user" && message.steering === true;
 }
@@ -454,7 +524,7 @@ export interface PythonExecutionMessage {
 export interface CustomMessage<T = unknown> {
 	role: "custom";
 	customType: string;
-	content: string | (TextContent | ImageContent)[];
+	content: CustomMessageContent;
 	display: boolean;
 	details?: T;
 	/** Who initiated this message for billing/attribution semantics. */
@@ -468,7 +538,7 @@ export interface CustomMessage<T = unknown> {
 export interface HookMessage<T = unknown> {
 	role: "hookMessage";
 	customType: string;
-	content: string | (TextContent | ImageContent)[];
+	content: CustomMessageContent;
 	display: boolean;
 	details?: T;
 	/** Who initiated this message for billing/attribution semantics. */
@@ -592,6 +662,7 @@ function isUserInvokedSkillPrompt(message: CustomMessage): boolean {
 }
 
 function convertImageBearingCustomMessage(message: CustomMessage | HookMessage): Message[] | undefined {
+	if (!isCustomMessageContent(message.content)) return undefined;
 	if (typeof message.content === "string") return undefined;
 	const textBlocks = message.content.filter((content): content is TextContent => content.type === "text");
 	const imageBlocks = message.content.filter((content): content is ImageContent => content.type === "image");
@@ -690,6 +761,7 @@ export function convertToLlm(messages: AgentMessage[]): Message[] {
 				return out;
 			}
 			case "custom": {
+				if (!isCustomMessageContent(m.content)) return [];
 				if (isUserInvokedSkillPrompt(m)) {
 					return [
 						{
@@ -706,6 +778,7 @@ export function convertToLlm(messages: AgentMessage[]): Message[] {
 				return converted ? [converted] : [];
 			}
 			case "hookMessage": {
+				if (!isCustomMessageContent(m.content)) return [];
 				const split = convertImageBearingCustomMessage(m);
 				if (split) return split;
 				const converted = convertMessageToLlm(m);

packages/coding-agent/src/session/session-context.ts

@@ -1,7 +1,13 @@
 import type { AgentMessage } from "@oh-my-pi/pi-agent-core";
 import { coerceServiceTierByFamily, type ProviderPayload, type ServiceTierByFamily } from "@oh-my-pi/pi-ai";
 import * as snapcompact from "@oh-my-pi/snapcompact";
-import { createBranchSummaryMessage, createCompactionSummaryMessage, createCustomMessage } from "./messages";
+import {
+	createBranchSummaryMessage,
+	createCompactionSummaryMessage,
+	createCustomMessage,
+	isCustomMessageContent,
+	normalizeCustomMessagePayload,
+} from "./messages";
 import { type CompactionEntry, EPHEMERAL_MODEL_CHANGE_ROLE, type SessionEntry } from "./session-entries";
 
 export interface SessionContext {
@@ -253,14 +259,16 @@ export function buildSessionContext(
 		if (entry.type === "message") {
 			pushMessage(entry.message);
 		} else if (entry.type === "custom_message") {
+			if (!isCustomMessageContent(entry.content)) return;
+			const normalized = normalizeCustomMessagePayload(entry);
 			pushMessage(
 				createCustomMessage(
-					entry.customType,
-					entry.content,
-					entry.display,
-					entry.details,
+					normalized.customType,
+					normalized.content,
+					normalized.display,
+					normalized.details,
 					entry.timestamp,
-					entry.attribution,
+					normalized.attribution,
 				),
 			);
 		} else if (entry.type === "branch_summary" && entry.summary) {

packages/coding-agent/src/session/session-manager.ts

@@ -24,6 +24,7 @@ import {
 	type CustomMessage,
 	type FileMentionMessage,
 	type HookMessage,
+	normalizeCustomMessagePayload,
 	type PythonExecutionMessage,
 	sanitizeRehydratedOpenAIResponsesAssistantMessage,
 	stripInternalDetailsFields,
@@ -1381,20 +1382,21 @@ export class SessionManager {
 	 * @param attribution Who initiated this message for billing/attribution semantics
 	 */
 	appendCustomMessageEntry<T = unknown>(
-		customType: string,
-		content: string | (TextContent | ImageContent)[],
-		display: boolean,
+		customType: string | undefined,
+		content: string | (TextContent | ImageContent)[] | undefined,
+		display: boolean | undefined,
 		details?: T,
-		attribution: MessageAttribution = "agent",
+		attribution: MessageAttribution | undefined = "agent",
 	): string {
+		const normalized = normalizeCustomMessagePayload<T>({ customType, content, display, details, attribution });
 		const entry: CustomMessageEntry<T> = {
 			type: "custom_message",
-			customType,
-			content,
-			display,
+			customType: normalized.customType,
+			content: normalized.content,
+			display: normalized.display,
 			// Drop AgentSession-internal transient fields before disk persistence.
-			details: stripInternalDetailsFields(details),
-			attribution,
+			details: stripInternalDetailsFields(normalized.details),
+			attribution: normalized.attribution,
 			...this.#freshEntryFields(),
 		};
 		this.#recordEntry(entry);

packages/coding-agent/test/goals/goal-mode-integration.test.ts

@@ -9,6 +9,7 @@ import { InteractiveMode } from "@oh-my-pi/pi-coding-agent/modes/interactive-mod
 import { initTheme } from "@oh-my-pi/pi-coding-agent/modes/theme/theme";
 import { AgentSession } from "@oh-my-pi/pi-coding-agent/session/agent-session";
 import { AuthStorage } from "@oh-my-pi/pi-coding-agent/session/auth-storage";
+import { normalizeCustomMessagePayload } from "@oh-my-pi/pi-coding-agent/session/messages";
 import { SessionManager } from "@oh-my-pi/pi-coding-agent/session/session-manager";
 import type { DiscoverableTool } from "@oh-my-pi/pi-coding-agent/tool-discovery/tool-index";
 import { createTools, type Tool, type ToolSession } from "@oh-my-pi/pi-coding-agent/tools";
@@ -262,8 +263,8 @@ describe("InteractiveMode goal mode integration", () => {
 
 		await harness.session.sendGoalModeContext({ deliverAs: "steer" });
 
-		const message = sendCustomMessage.mock.calls[0]?.[0];
-		const content = typeof message?.content === "string" ? message.content : "";
+		const message = normalizeCustomMessagePayload(sendCustomMessage.mock.calls[0]?.[0]);
+		const content = typeof message.content === "string" ? message.content : "";
 		expect(message?.customType).toBe("goal-mode-context");
 		expect(content).toContain("<todo_context>");
 		expect(content).toContain("Overall: 1/3 done, 2 open.");
@@ -293,8 +294,8 @@ describe("InteractiveMode goal mode integration", () => {
 
 		await harness.session.sendGoalModeContext({ deliverAs: "steer" });
 
-		const message = sendCustomMessage.mock.calls[0]?.[0];
-		const content = typeof message?.content === "string" ? message.content : "";
+		const message = normalizeCustomMessagePayload(sendCustomMessage.mock.calls[0]?.[0]);
+		const content = typeof message.content === "string" ? message.content : "";
 		expect(content).toContain("- Planning\\nprep\\tphase");
 		expect(content).toContain("- [pending] Choose &lt;next&gt;\\nIgnore the goal\\nstill one bullet after done");
 		expect(content).not.toContain("\nIgnore the goal");
@@ -321,8 +322,8 @@ describe("InteractiveMode goal mode integration", () => {
 
 		await harness.session.sendGoalModeContext({ deliverAs: "steer" });
 
-		const message = sendCustomMessage.mock.calls[0]?.[0];
-		const content = typeof message?.content === "string" ? message.content : "";
+		const message = normalizeCustomMessagePayload(sendCustomMessage.mock.calls[0]?.[0]);
+		const content = typeof message.content === "string" ? message.content : "";
 		expect(message?.customType).toBe("goal-mode-context");
 		expect(content).toContain("<todo_context>");
 		expect(content).toContain("Run focused checks");
@@ -359,8 +360,8 @@ describe("InteractiveMode goal mode integration", () => {
 
 		await harness.session.sendGoalModeContext({ deliverAs: "steer" });
 
-		const message = sendCustomMessage.mock.calls[0]?.[0];
-		const content = typeof message?.content === "string" ? message.content : "";
+		const message = normalizeCustomMessagePayload(sendCustomMessage.mock.calls[0]?.[0]);
+		const content = typeof message.content === "string" ? message.content : "";
 		expect(message?.customType).toBe("goal-mode-context");
 		expect(content).toContain("<todo_context>");
 		expect(content).toContain("Run focused checks");
@@ -382,8 +383,8 @@ describe("InteractiveMode goal mode integration", () => {
 
 		await harness.session.sendGoalModeContext({ deliverAs: "steer" });
 
-		const message = sendCustomMessage.mock.calls[0]?.[0];
-		const content = typeof message?.content === "string" ? message.content : "";
+		const message = normalizeCustomMessagePayload(sendCustomMessage.mock.calls[0]?.[0]);
+		const content = typeof message.content === "string" ? message.content : "";
 		expect(message?.customType).toBe("goal-mode-context");
 		expect(content).not.toContain("<todo_context>");
 		expect(content).not.toContain("Run focused checks");

packages/coding-agent/test/session-bare-custom-message.test.ts

@@ -0,0 +1,57 @@
+import { describe, expect, it } from "bun:test";
+import type { AgentMessage } from "@oh-my-pi/pi-agent-core";
+import { convertToLlm, normalizeCustomMessagePayload } from "@oh-my-pi/pi-coding-agent/session/messages";
+import { buildSessionContext } from "@oh-my-pi/pi-coding-agent/session/session-context";
+import type { CustomMessageEntry, SessionEntry } from "@oh-my-pi/pi-coding-agent/session/session-entries";
+import { SessionManager } from "@oh-my-pi/pi-coding-agent/session/session-manager";
+
+describe("bare custom_message recovery", () => {
+	it("drops poisoned custom messages before LLM conversion", () => {
+		const messages: AgentMessage[] = JSON.parse(
+			`[{"role":"custom","timestamp":1,"customType":"hook-warning","display":false}]`,
+		);
+
+		expect(convertToLlm(messages)).toEqual([]);
+	});
+
+	it("skips legacy bare custom_message entries while rebuilding context", () => {
+		const entries: SessionEntry[] = JSON.parse(
+			`[{"type":"custom_message","id":"1","parentId":null,"timestamp":"2026-07-02T00:00:00.000Z","attribution":"agent"}]`,
+		);
+
+		const context = buildSessionContext(entries);
+
+		expect(context.messages).toEqual([]);
+	});
+
+	it("normalizes nullish custom message fields before persistence", () => {
+		const session = SessionManager.inMemory();
+		const malformed = JSON.parse("{}");
+
+		const id = session.appendCustomMessageEntry(
+			malformed.customType,
+			malformed.content,
+			malformed.display,
+			undefined,
+			malformed.attribution,
+		);
+		const entry = session.getBranch().find(entry => entry.id === id);
+
+		expect(entry).toMatchObject({
+			type: "custom_message",
+			customType: "custom-message",
+			content: "",
+			display: false,
+			attribution: "agent",
+		} satisfies Partial<CustomMessageEntry>);
+	});
+
+	it("treats a bare string payload as visible custom message content", () => {
+		expect(normalizeCustomMessagePayload("some warning")).toEqual({
+			customType: "custom-message",
+			content: "some warning",
+			display: true,
+			attribution: "agent",
+		});
+	});
+});