diff --git a/docs/re/structures/isl-builtins.md b/docs/re/structures/isl-builtins.md
index cbede08..9ec1190 100644
--- a/docs/re/structures/isl-builtins.md
+++ b/docs/re/structures/isl-builtins.md
@@ -140,6 +140,39 @@ and spread checks but its maximum *exceeds* the table — flag indices run 0..31
 against symbol tables as small as 40 — so it is excluded, and the disassembler
 now declines to resolve it rather than printing an invented name.
 
+### ✅ Four built-ins are TUTORIAL-ONLY — 85 sites, every one in S18–S23
+
+`96`, `97`, `98` and `104` were unnamed. Measured over all 28 stages, they form a
+family that appears **nowhere outside the six tutorials**:
+
+| id | sites | stages | shape |
+|---|---|---|---|
+| **96** | 8 | S18–S23 only | one call per tutorial *section* |
+| **97** | 38 | S18–S23 only | followed by `start_coroutine` (27/38) |
+| **98** | **0** | — | never called anywhere |
+| **104** | 39 | S18–S23 only | **followed by `wait_s` 39/39**, preceded by `end_coroutine` 37/39 |
+
+`104`'s adjacency is a textbook poll loop: a coroutine starts, tests the
+predicate, waits, and goes round again — 39 sites, no exceptions.
+
+`96`'s operand is the giveaway. Its eight payloads are, in stage order:
+
+```
+Stage18 → 101, 102, 103     Stage19 → 201     Stage20 → 301
+Stage21 → 401               Stage22 → 501     Stage23 → 601
+```
+
+That is `(stage − 17) * 100 + section`: tutorial 1 has three sections, the other
+five have one each. The tutorial index is encoded in the argument.
+
+🟡 **Names are NOT applied.** `tutorial_begin` / `tutorial_end` /
+`tutorial_message_pending` fit the shape, and `sub_82260710` reportedly suspends
+while `[phase+340] == 2` with the payload latched at `[phase+344]` — but I have
+not read that myself, and this file has already had to withdraw five names
+guessed from shape. What is established here is the **distribution and the
+argument encoding**, which is what a port actually needs; the labels can wait for
+someone to read the handler.
+
 ### ✅ Five built-ins are the mission banners — named from usage, not from a guess
 
 `77`, `78`, `81`, `82` and `135` were unnamed. The engine has five contiguous