Does the emission of pre-seminal fluid (madhy) – or something resembling semen – during a normal conversation with a female colleague, without intention or lust, break one's fast?

You must repent from speaking with a non-mahram girl due to the temptation involved. As for madhy (pre-seminal fluid), its emission does not invalidate the fast at all, according to the preponderant opinion. Similarly, semen resulting from repeated looking does not invalidate the fast, according to many scholars.