diff --git a/docs/re/BACKLOG.md b/docs/re/BACKLOG.md
index ca5bcc9a..74135f91 100644
--- a/docs/re/BACKLOG.md
+++ b/docs/re/BACKLOG.md
@@ -188,6 +188,22 @@ unknown, what evidence exists, and what the first step would be. Move an item in
   `payload+8` (a computed value passed to both testers — waypoint-index shaped,
   which is why it is not being called one).
 
+* ✅ **(2026-08-27) THE KIND-0 TRIGGER CONDITION IS A POINT-TO-SEGMENT PROXIMITY
+  TEST. [structures/isl-trigger-node](structures/isl-trigger-node.md).**
+  `sub_8226DAF8` resolves the route name (`sub_823012D8`), requires the unit record's
+  `rec+100 != 0`, extracts **two 3-double vectors** — `rec+32/+40/+48` and
+  `rec+64/+72/+80` — and makes a VIRTUAL call to **ScriptPhase vtable slot 60 =
+  `sub_82268068`** (used by no built-in, so engine-internal) with those two vectors,
+  the route point, and the node's double. Slot 60's arithmetic is unambiguous:
+  per-axis `fsub`, `fmul` + two `fmadd`, `fsqrt` → `|B−A|`; **reject if `|B−A| < 0.1`**
+  (degenerate); **reject if `|P−A| > f1` or `|P−B| > f1`**; then
+  **`t = (P−A)·(B−A) / |B−A|²`, reject if `t < 0`**. So it is a point-to-segment
+  distance test and **the node's double (`local[24]`) is a RADIUS**. 🟡 **What A and
+  B are is NOT established** — a previous/current position pair would make this the
+  standard frame-rate-robust waypoint test, which is exactly the tidy reading this
+  corpus insists on proving. 🟡 Still unread: `sub_8226DC80` (kind 1) entirely, and
+  slot 60 past the `t < 0` rejection.
+
 ## ✅✅ SOLVED — the mission freeze was a modal sign-in dialog (2026-08-26)
 
 `XamShowSigninUI` opens a modal dialog and `xeXamDispatchDialog` blocks the
diff --git a/docs/re/structures/isl-trigger-node.md b/docs/re/structures/isl-trigger-node.md
index 9606cd44..f0bd5f4c 100644
--- a/docs/re/structures/isl-trigger-node.md
+++ b/docs/re/structures/isl-trigger-node.md
@@ -207,14 +207,57 @@ measured to rise **at a squadron's route arrival time**. Route triggers are the
 mechanism that would do that. 🟡 Stated as a connection, not a demonstration —
 nothing here traces a trigger to that counter.
 
+## ✅ What the kind-0 condition TESTS — a point-to-segment proximity check
+
+`sub_8226DAF8` past the route-name lookup:
+
+```
+8226DB84  bl   0x823012D8        ; look the route name up -> a route object; bail if absent
+8226DBB8  lwz  r11, 324(r30)     ; the unit array
+8226DBBC  rlwinm r10, r26, 2,0,29; r26 = payload+0, the unit index
+8226DBC8  lwz  r10, 100(r11)     ; require rec+100 != 0, else return 0
+8226DBD4  lfd  f0, 32(r11) …     ; THREE doubles: rec+32, +40, +48   -> out vector B
+8226DBF8  lfd  f0, 64(r11) …     ; THREE doubles: rec+64, +72, +80   -> out vector A
+8226DBFC  fmr  f1, f31           ; the node's double (payload+16)
+8226DC1C  lwz  r11, 0(r30)       ; the ScriptPhase vptr
+8226DC28  lwz  r11, 60(r11)      ; VTABLE SLOT 60
+8226DC30  bcctrl                 ; test(phase, A, B, P=the route, f1)
+```
+
+**Slot 60 → `sub_82268068`**, which no built-in uses — it is engine-internal — and
+its arithmetic is unambiguous:
+
+```
+f29 = |B - A|                     ; fsub per axis, fmul + 2x fmadd, fsqrt
+if |B - A| <  0.1        -> 0     ; degenerate segment (the constant is 0.1)
+f28 = |P - A| ; if > f1  -> 0
+      |P - B| ; if > f1  -> 0
+t   = (P-A)·(B-A) / |B-A|²        ; the projection parameter
+if t < 0.0               -> 0
+```
+
+Per-axis `fsub`, a sum of three squares, `fsqrt`, and a dot product divided by
+the squared length: this is a **point-to-segment distance test**, and the node's
+double is therefore a **RADIUS**.
+
+So a kind-0 trigger fires when a route point lies within `local[24]` of the
+segment between two vectors taken from the unit's record.
+
+🟡 **What A and B are is not established.** `rec+64/72/80` and `rec+32/40/48` are
+two positions; a previous/current pair would make this the standard
+frame-rate-robust waypoint test, and that is exactly the kind of tidy reading
+this corpus makes itself prove. Not proven here.
+
 ## 🟡 Not settled
 
 * ~~What the drain actually spawns.~~ ✅ Resolved above: built-in 19's nodes carry
   a real routine offset at `+28`.
 * ~~Whether `+24` selects between the two node kinds~~ ✅ It does — see above.
-* **What the conditions actually TEST.** Only `sub_8226DAF8`'s first ~34
-  instructions are read — up to the route-name lookup. What it compares the route
-  against, and the whole of `sub_8226DC80` (kind 1), are unread.
+* ~~What the kind-0 condition tests~~ ✅ Read above. **`sub_8226DC80` (kind 1) is
+  still unread entirely.**
+* **Which unit-record fields A and B are** — `rec+64/72/80` vs `rec+32/40/48`.
+* **The rest of slot 60** past the `t < 0` rejection (a second constant at
+  `0x820B0000+25192` is loaded next).
 * **`payload+8`** is a computed value in both appenders (`r29-1` in built-in 19)
   and is passed to both testers; a waypoint index would fit, which is exactly why
   it is not being called one.