Co-op companion kills its human team mate, by retaliation and by firing through them

[saworbit]

A co-op companion killed its human team mate twice in two sessions on e1m2, by two different mechanisms. Both are in the QC, and neither is stock Quake friendly fire being unlucky.

Mechanism one: it shoots back

Session 2026-09-05, killed 18 seconds in. Health went 100, 76, 64, 48, 24, 4 across five hits in five seconds.

The cause is in the tape. Both parties took exactly 24 damage within one second of each other:

Carmack  hp 100 -> 76 at t 13.3
player   hp 100 -> 76 at t 13.5

Shane shot Carmack. Argus_Pain then fights back against "any live player, human or bot" with no co-op test, so it made its own team mate the enemy and killed him.

In co-op that branch can only ever fire on a team mate, because monsters do not carry classname "player".

Mechanism two: it shoots through you

Session 2026-09-05 earlier, 157 s. Killed at 425 -469 320, obituary "chewed on Carmack's boomstick", two shotgun hits.

This one never targeted the player. Two engage events in the whole session, both engage monster, none against a human. The bot was in pursue, firing at a monster's last known position during the three second sight loss hold, and the human crossed the line. Immediately after the kill it pushed GOAL_REVIVE_SUPPORT and came to help.

What is already safe

Argus_CoopFindThreat requires FL_MONSTER, so it cannot return a player.

Argus_Perceive returns before its player scan whenever coop > 0, so a companion cannot acquire a team mate as a target through perception. Worth recording because it looks like a hole on a first read and is not one.

Fix

Two guards, both gated on coop > 0 so deathmatch is untouched.

1. Argus_Pain does not retaliate against a team mate.
2. The combat fire gate traces the shot it is about to take and holds fire if a team mate is what it reaches.

Splash is deliberately not covered: a rocket landing beside a team mate still hurts them. Worth a follow up if it shows up in a session.

Verification is the hard part

This cannot be tested headless. A co-op botmatch runs one bot, and adding more with impulse 101 does not help, because bots never target each other in co-op anyway thanks to the perception early return. The retaliation path needs a player to damage a bot, and the lab netclient can walk and send impulses but cannot fire. See the netclient issue.

So the ladder can only show absence of harm: dm4 and dm2 at parity, and the guards provably inert on a single bot tape where Argus_IsAlly can only return FALSE and the fire trace never runs. The real verification is a human session where the companion is shot and does not shoot back.

[saworbit]

Shipped in #260. Left open until a human session confirms it, because nothing headless can.

What to watch for in the next e1m2 co-op run:

• Shoot the companion. It should take the damage, flinch, and not shoot back. Before this it made you the enemy and killed you eighteen seconds in.
• Stand between the companion and a monster it is fighting. It should hold fire rather than shoot through you.

Two things this does not cover, both deliberate:

• Splash. A rocket landing beside you still hurts. If that shows up in a session it wants its own fix.
• Any other bot behaviour toward a team mate that begins with taking damage. Netclient cannot fire, so no player-damages-bot behaviour can be verified headless #259 is the blocker for testing that class at all.

[saworbit]

Verified in play and closing.

Session shane_e1m2_2026-09-05_v260, 102 s of co-op on e1m2 against the #260 build.

The test was the one this issue was left open for. Carmack was shot dead by the human, obituary "Carmack chewed on player's boomstick", and he did not retaliate. His four engage events across the whole session are all engage monster, none against a player, and he finished on zero frags. Before the fix he made the human his enemy and killed him eighteen seconds in.

The rest of the tape is the healthiest co-op session recorded: zero bot freezes, 88 cells with the busiest at 7.9 per cent, 14 stalls, swim rate down to 35.7 per minute from 124 and 98 in the two preceding sessions. The only frozen track is the human standing still for 12 s.

Not covered, and unchanged from the fix note above:

• Splash. A rocket landing beside a team mate still hurts. It has not shown up in a session yet.
• Everything else that begins with a player damaging a bot stays unverifiable headless. Netclient cannot fire, so no player-damages-bot behaviour can be verified headless #259 is the blocker.

Residuals from the same tape, none of them this issue:

• Escort separation runs median 546u with 53 per cent of samples past the 512u break bar, though it oscillates rather than drifting, so the companion ranges out and returns rather than abandoning.
• A new hazard and stall cluster at '960 -1152 448', 23 events, more than triple any other cell.
• Zero goals consumed in 102 s.