Hi

just played against eldar as tau and an interesting situation came up

at my HQ i had my warlord and a experimental devilfish

both my opponent and I committed to the same planet

so after committing to the planet

my warlord gives a unit at the planet an attachment

my devilfish readies

their warlord exhausts one of my units

all of this is done as a reaction to committing to the planet but in what order do they resolve?

Can my opponent exhaust my devilfish after I ready it?

Can they chose to exhause whichever unit I give an attachment?

The order is thus:

Something happens

The player with Initiative resolves one (if any) of his triggered Interrupts

The player without Initiative resolves one (if any) of his triggered Interrupts

Alternate until both players have passed.

The player with Initiative resolves one (if any) of his triggered Reactions

The player without Initiative resolves one (if any) of his triggered Reactions

Alternate until both players have passed.

So the answer to your question depends on who has initiative.

Some further points:

Forced Interrupts or Forced Reactions must resolve before any optional ones.

If an Interrupt or Reaction being resolved meets the requirement to trigger a new Interrupt or Reaction, resolve the new trigger before continuing to resolve effects that were triggered by the first trigger.

See Rules Reference entries for Interrupts, Reactions, Nested Effect Sequences and Priority of Simultaneous Resolution.

thanks