diff --git a/packages/coding-agent/src/core/session-manager.ts b/packages/coding-agent/src/core/session-manager.ts
index 115740d1..25c0bddf 100644
--- a/packages/coding-agent/src/core/session-manager.ts
+++ b/packages/coding-agent/src/core/session-manager.ts
@@ -212,6 +212,7 @@ export class SessionManager {
 	private sessionDir: string;
 	private cwd: string;
 	private persist: boolean;
+	private flushed: boolean = false;
 	private inMemoryEntries: SessionEntry[] = [];
 
 	private constructor(cwd: string, agentDir: string, sessionFile: string | null, persist: boolean) {
@@ -236,9 +237,11 @@ export class SessionManager {
 			this.inMemoryEntries = loadEntriesFromFile(this.sessionFile);
 			const header = this.inMemoryEntries.find((e) => e.type === "session");
 			this.sessionId = header ? (header as SessionHeader).id : uuidv4();
+			this.flushed = true;
 		} else {
 			this.sessionId = uuidv4();
 			this.inMemoryEntries = [];
+			this.flushed = false;
 			const entry: SessionHeader = {
 				type: "session",
 				id: this.sessionId,
@@ -266,14 +269,32 @@ export class SessionManager {
 	}
 
 	reset(): void {
-		this.inMemoryEntries = [];
 		this.sessionId = uuidv4();
+		this.flushed = false;
 		const timestamp = new Date().toISOString().replace(/[:.]/g, "-");
 		this.sessionFile = join(this.sessionDir, `${timestamp}_${this.sessionId}.jsonl`);
+		this.inMemoryEntries = [
+			{
+				type: "session",
+				id: this.sessionId,
+				timestamp: new Date().toISOString(),
+				cwd: this.cwd,
+			},
+		];
 	}
 
 	_persist(entry: SessionEntry): void {
-		if (this.persist && this.inMemoryEntries.some((e) => e.type === "message" && e.message.role === "assistant")) {
+		if (!this.persist) return;
+
+		const hasAssistant = this.inMemoryEntries.some((e) => e.type === "message" && e.message.role === "assistant");
+		if (!hasAssistant) return;
+
+		if (!this.flushed) {
+			for (const e of this.inMemoryEntries) {
+				appendFileSync(this.sessionFile, `${JSON.stringify(e)}\n`);
+			}
+			this.flushed = true;
+		} else {
 			appendFileSync(this.sessionFile, `${JSON.stringify(entry)}\n`);
 		}
 	}
diff --git a/packages/mom/src/agent.ts b/packages/mom/src/agent.ts
index 87152924..86124b24 100644
--- a/packages/mom/src/agent.ts
+++ b/packages/mom/src/agent.ts
@@ -411,12 +411,7 @@ function createRunner(sandboxConfig: SandboxConfig, channelId: string, channelDi
 	const systemPrompt = buildSystemPrompt(workspacePath, channelId, memory, sandboxConfig, [], [], skills);
 
 	// Create session manager and settings manager
-	// Pass model info so new sessions get a header written immediately
-	const sessionManager = new MomSessionManager(channelDir, {
-		provider: model.provider,
-		id: model.id,
-		thinkingLevel: "off",
-	});
+	const sessionManager = new MomSessionManager(channelDir);
 	const settingsManager = new MomSettingsManager(join(channelDir, ".."));
 
 	// Create agent
diff --git a/packages/mom/src/context.ts b/packages/mom/src/context.ts
index 16eb8e35..4dc0fbd0 100644
--- a/packages/mom/src/context.ts
+++ b/packages/mom/src/context.ts
@@ -48,11 +48,10 @@ export class MomSessionManager {
 	private contextFile: string;
 	private logFile: string;
 	private channelDir: string;
-	private sessionInitialized: boolean = false;
+	private flushed: boolean = false;
 	private inMemoryEntries: SessionEntry[] = [];
-	private pendingEntries: SessionEntry[] = [];
 
-	constructor(channelDir: string, initialModel?: { provider: string; id: string; thinkingLevel?: string }) {
+	constructor(channelDir: string) {
 		this.channelDir = channelDir;
 		this.contextFile = join(channelDir, "context.jsonl");
 		this.logFile = join(channelDir, "log.jsonl");
@@ -66,30 +65,33 @@ export class MomSessionManager {
 		if (existsSync(this.contextFile)) {
 			this.inMemoryEntries = this.loadEntriesFromFile();
 			this.sessionId = this.extractSessionId() || uuidv4();
-			this.sessionInitialized = this.inMemoryEntries.length > 0;
+			this.flushed = true;
 		} else {
-			// New session - write header immediately
 			this.sessionId = uuidv4();
-			if (initialModel) {
-				this.writeSessionHeader();
-			}
+			this.inMemoryEntries = [
+				{
+					type: "session",
+					id: this.sessionId,
+					timestamp: new Date().toISOString(),
+					cwd: this.channelDir,
+				},
+			];
 		}
 		// Note: syncFromLog() is called explicitly from agent.ts with excludeTimestamp
 	}
 
-	/** Write session header to file (called on new session creation) */
-	private writeSessionHeader(): void {
-		this.sessionInitialized = true;
+	private _persist(entry: SessionEntry): void {
+		const hasAssistant = this.inMemoryEntries.some((e) => e.type === "message" && e.message.role === "assistant");
+		if (!hasAssistant) return;
 
-		const entry: SessionHeader = {
-			type: "session",
-			id: this.sessionId,
-			timestamp: new Date().toISOString(),
-			cwd: this.channelDir,
-		};
-
-		this.inMemoryEntries.push(entry);
-		appendFileSync(this.contextFile, `${JSON.stringify(entry)}\n`);
+		if (!this.flushed) {
+			for (const e of this.inMemoryEntries) {
+				appendFileSync(this.contextFile, `${JSON.stringify(e)}\n`);
+			}
+			this.flushed = true;
+		} else {
+			appendFileSync(this.contextFile, `${JSON.stringify(entry)}\n`);
+		}
 	}
 
 	/**
@@ -245,44 +247,14 @@ export class MomSessionManager {
 		return entries;
 	}
 
-	/** Initialize session with header if not already done */
-	startSession(): void {
-		if (this.sessionInitialized) return;
-		this.sessionInitialized = true;
-
-		const entry: SessionHeader = {
-			type: "session",
-			id: this.sessionId,
-			timestamp: new Date().toISOString(),
-			cwd: this.channelDir,
-		};
-
-		this.inMemoryEntries.push(entry);
-		for (const pending of this.pendingEntries) {
-			this.inMemoryEntries.push(pending);
-		}
-		this.pendingEntries = [];
-
-		// Write to file
-		appendFileSync(this.contextFile, `${JSON.stringify(entry)}\n`);
-		for (const memEntry of this.inMemoryEntries.slice(1)) {
-			appendFileSync(this.contextFile, `${JSON.stringify(memEntry)}\n`);
-		}
-	}
-
 	saveMessage(message: AppMessage): void {
 		const entry: SessionMessageEntry = {
 			type: "message",
 			timestamp: new Date().toISOString(),
 			message,
 		};
-
-		if (!this.sessionInitialized) {
-			this.pendingEntries.push(entry);
-		} else {
-			this.inMemoryEntries.push(entry);
-			appendFileSync(this.contextFile, `${JSON.stringify(entry)}\n`);
-		}
+		this.inMemoryEntries.push(entry);
+		this._persist(entry);
 	}
 
 	saveThinkingLevelChange(thinkingLevel: string): void {
@@ -291,13 +263,8 @@ export class MomSessionManager {
 			timestamp: new Date().toISOString(),
 			thinkingLevel,
 		};
-
-		if (!this.sessionInitialized) {
-			this.pendingEntries.push(entry);
-		} else {
-			this.inMemoryEntries.push(entry);
-			appendFileSync(this.contextFile, `${JSON.stringify(entry)}\n`);
-		}
+		this.inMemoryEntries.push(entry);
+		this._persist(entry);
 	}
 
 	saveModelChange(provider: string, modelId: string): void {
@@ -307,18 +274,13 @@ export class MomSessionManager {
 			provider,
 			modelId,
 		};
-
-		if (!this.sessionInitialized) {
-			this.pendingEntries.push(entry);
-		} else {
-			this.inMemoryEntries.push(entry);
-			appendFileSync(this.contextFile, `${JSON.stringify(entry)}\n`);
-		}
+		this.inMemoryEntries.push(entry);
+		this._persist(entry);
 	}
 
 	saveCompaction(entry: CompactionEntry): void {
 		this.inMemoryEntries.push(entry);
-		appendFileSync(this.contextFile, `${JSON.stringify(entry)}\n`);
+		this._persist(entry);
 	}
 
 	/** Load session with compaction support */
@@ -343,20 +305,18 @@ export class MomSessionManager {
 		return this.contextFile;
 	}
 
-	/** Check if session should be initialized */
-	shouldInitializeSession(messages: AppMessage[]): boolean {
-		if (this.sessionInitialized) return false;
-		const userMessages = messages.filter((m) => m.role === "user");
-		const assistantMessages = messages.filter((m) => m.role === "assistant");
-		return userMessages.length >= 1 && assistantMessages.length >= 1;
-	}
-
 	/** Reset session (clears context.jsonl) */
 	reset(): void {
-		this.pendingEntries = [];
-		this.inMemoryEntries = [];
-		this.sessionInitialized = false;
 		this.sessionId = uuidv4();
+		this.flushed = false;
+		this.inMemoryEntries = [
+			{
+				type: "session",
+				id: this.sessionId,
+				timestamp: new Date().toISOString(),
+				cwd: this.channelDir,
+			},
+		];
 		// Truncate the context file
 		if (existsSync(this.contextFile)) {
 			writeFileSync(this.contextFile, "");