Indentation falls through to Emacs Lisp inside a binding vector

DISCUSS.md

@@ -269,3 +269,21 @@ Questions it opens:
   different feature — closer to a HUD than a debugger — and worth not conflating.
 - **Whether it belongs in the break buffer at all**, or in its own window that is useful while the program is *running*,
   which is arguably where a game developer wants it.
+
+## 9. Indentation is wrong inside a binding vector
+
+Reported against the `let` in `sand.flan`'s `settle`: the second and later bindings indent one column too far.
+
+**Cause, found by reading `flan-mode.el`.** `flan-indent-function` looks at the head of the *enclosing* form and, when
+it is one of Flan's body forms (`defn`, `let`, `if`, `while`, `until`, `dotimes`, `match`, `do`, `loop`, `defer`),
+indents one past the open paren. Inside a `let`'s binding *vector* the enclosing open is the `[`, and the symbol after
+it is the first binding's **name** — never a body form — so the check fails and it falls through to Emacs's generic
+`lisp-indent-function`, which treats the vector as a function call and aligns continuation lines under the first
+*argument* rather than under the first *binding*.
+
+**What it is built on:** Emacs's built-in `lisp-indent-function`, with that one override. Not `clojure-mode`, which is
+where the missing piece lives — `clojure-mode` special-cases binding vectors and aligns them as pairs.
+
+The fix is a binding-vector case in `flan-indent-function`: when the enclosing open is `[` and the form containing it is
+a binding form, align to the column of the first binding. Worth checking the other bracket users at the same time —
+`defn` parameter lists and `restart-case` clause parameters have the same shape.