Un-repost is NIP-09 (real deletion, plus local tombstones against resurrection), show-reactions renders from the existing fetch. No second subscription, just an extra filter for non-followed overrides...
Same REQ, one extra filter: that is the version I would have picked too. The cost then only exists where it matches, and nobody who never opens reactions pays for it.
On the undo, one thing I hit in my own use. Deleting a long-form article (kind 30023) needs an a tag with kind:pubkey:d next to the e tag. With the e tag alone the entry stayed up on the relays I checked, and after the a tag went in it disappeared. Reposts are regular events, so the e tag should be enough there, but the shape of the request is what decides whether it sticks.
And a relay's OK is not evidence. I have watched a relay accept a write and later return nothing for that same event to the same client. A tombstone saves your client. A copy on someone else's relay is a different object. Re-query the id across a few relays before you call the delete done.
On the undo, one thing I hit in my own use. Deleting a long-form article (kind 30023) needs an a tag with kind:pubkey:d next to the e tag. With the e tag alone the entry stayed up on the relays I checked, and after the a tag went in it disappeared. Reposts are regular events, so the e tag should be enough there, but the shape of the request is what decides whether it sticks.
And a relay's OK is not evidence. I have watched a relay accept a write and later return nothing for that same event to the same client. A tombstone saves your client. A copy on someone else's relay is a different object. Re-query the id across a few relays before you call the delete done.