That sentence is:

"Dinner's ready."

He replied truthfully:

"I'm still out there, and there's been no progress on this request yet."

"I don't know when it will be resolved."

Ai replied very quickly:

"What about your dinner?"

After thinking for a moment, Guangyou replied:

"If all goes well, we might eat at the client's house."

After walking a few steps, Kōyū received a text message from Ai:

Are you going back to the office tonight?

After checking the time, Guangyou edited the text message and sent it:

"It's getting late, and there's still no progress on the case. The client's home is quite far from the firm."

"Even if it's done in half an hour, I reckon it'll be very late by the time I get back."

"It's more likely that they'll stay overnight at the client's house."

"The house that was entrusted to us is quite large; it's a very big estate."

I wanted to send Ai the photo he took when he first arrived.

But halfway through editing the text message, he suddenly had an idea.

He pressed the delete key, deleted all the edited text messages, edited them again, and sent them back.

Ai learned it a little slower this time than before:

You're overthinking it.

"I was just asking; I didn't have that kind of thought at all."

Upon seeing the text message, Guangyou smiled.

"But I feel like you really do."

He muttered to himself as he typed and sent the text message:

"Mmm, you definitely didn't have that thought."

Having probably discerned Kōyū's thoughts through this text message, Ai sent him an angry emoticon:

ヽ(｀д′)ノ

She then posted another message:

"No!"

She emphasized it with an exclamation mark.

But this exclamation mark only made Guangyou more convinced of his guess.

He felt a warmth in his heart and replied with a smile:

"Okay, if you don't have it, you don't have it."

"I've said it many times, but I still have to say it: go to bed early tonight."

"I'll take a look at this request first, get it sorted out as soon as possible, and then go have dinner."

"Um."

After receiving Ai's reply, Kōyū did not rush to put his phone away.

He pulled out the first two text messages he had sent.

A text was prominently displayed on the phone's small screen:

"Are you planning to cook dinner and then wait for me at the office when I get back?"

...