build: the book compiles on this Ubuntu — tectonic + dual-engine preamble

No root available here, so the toolchain is tectonic (single user-space
binary, packages fetched on demand). The preamble unicode block is now
dual-engine: pdfTeX keeps its DeclareUnicodeCharacter list, XeTeX gets a
newunicodechar twin generated from the same 37 mappings — both branches
must stay green (Mac pdflatex, Ubuntu tectonic). build.sh is the one
command. The committed PDF is current for the first time since July 6:
116 pages, ch13 + the live-log section finally in print.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

build.sh

@@ -0,0 +1,16 @@
+#!/usr/bin/env bash
+# Build the book. No root, no TeX Live install: tectonic is a single
+# user-space binary that fetches packages on demand (first run is slow,
+# after that it's seconds). pdflatex also works (the preamble carries a
+# dual-engine unicode block); tectonic is what the repo's button uses.
+set -euo pipefail
+cd "$(dirname "$0")"
+TECTONIC="${TECTONIC:-$HOME/.local/bin/tectonic}"
+if [ ! -x "$TECTONIC" ] && command -v tectonic >/dev/null; then TECTONIC=tectonic; fi
+[ -x "$TECTONIC" ] || command -v "$TECTONIC" >/dev/null || {
+  echo "no tectonic. Install (no root):"
+  echo "  curl -sL https://github.com/tectonic-typesetting/tectonic/releases/download/tectonic%400.15.0/tectonic-0.15.0-x86_64-unknown-linux-musl.tar.gz | tar xz -C ~/.local/bin"
+  exit 1
+}
+"$TECTONIC" -X compile main.tex
+pdfinfo main.pdf 2>/dev/null | grep Pages || true

preamble.tex

@@ -109,6 +109,51 @@
 \newcommand{\lean}[1]{\inlinecode{#1}}
 \newcommand{\rust}[1]{\inlinecode{#1}}
 \newcommand{\code}[1]{\inlinecode{#1}}
+% Unicode in Lean listings, both engines. pdfTeX maps code points via
+% inputenc; XeTeX/Tectonic is natively Unicode but the tt font lacks the
+% glyphs, so newunicodechar substitutes the same math forms. BOTH branches
+% derive from one list — edit both or the engines diverge (the build button
+% compiles under tectonic, the Mac under pdflatex; both must stay green).
+\ifdefined\XeTeXversion
+  \usepackage{newunicodechar}
+  \newunicodechar{→}{\ensuremath{\to}} % →
+  \newunicodechar{←}{\ensuremath{\leftarrow}} % ←
+  \newunicodechar{↔}{\ensuremath{\leftrightarrow}} % ↔
+  \newunicodechar{∀}{\ensuremath{\forall}} % ∀
+  \newunicodechar{∃}{\ensuremath{\exists}} % ∃
+  \newunicodechar{∧}{\ensuremath{\wedge}} % ∧
+  \newunicodechar{∨}{\ensuremath{\vee}} % ∨
+  \newunicodechar{¬}{\ensuremath{\neg}} % ¬
+  \newunicodechar{≠}{\ensuremath{\neq}} % ≠
+  \newunicodechar{≤}{\ensuremath{\leq}} % ≤
+  \newunicodechar{≥}{\ensuremath{\geq}} % ≥
+  \newunicodechar{⊢}{\ensuremath{\vdash}} % ⊢
+  \newunicodechar{·}{\ensuremath{\cdot}} % ·
+  \newunicodechar{ℕ}{\ensuremath{\mathbb{N}}} % ℕ
+  \newunicodechar{ℤ}{\ensuremath{\mathbb{Z}}} % ℤ
+  \newunicodechar{ℓ}{\ensuremath{\ell}} % ℓ
+  \newunicodechar{×}{\ensuremath{\times}} % ×
+  \newunicodechar{∈}{\ensuremath{\in}} % ∈
+  \newunicodechar{∑}{\ensuremath{\Sigma}} % ∑
+  \newunicodechar{≡}{\ensuremath{\equiv}} % ≡
+  \newunicodechar{∣}{\ensuremath{\mid}} % ∣
+  \newunicodechar{⟨}{\ensuremath{\langle}} % ⟨
+  \newunicodechar{⟩}{\ensuremath{\rangle}} % ⟩
+  \newunicodechar{𝔽}{\ensuremath{\mathbb{F}}} % 𝔽
+  \newunicodechar{₀}{\ensuremath{{}_0}} % ₀
+  \newunicodechar{₁}{\ensuremath{{}_1}} % ₁
+  \newunicodechar{₂}{\ensuremath{{}_2}} % ₂
+  \newunicodechar{²}{\ensuremath{{}^2}} % ²
+  \newunicodechar{⁵}{\ensuremath{{}^5}} % ⁵
+  \newunicodechar{✓}{\ensuremath{\checkmark}} % ✓
+  \newunicodechar{✗}{\ensuremath{\times}} % ✗
+  \newunicodechar{⁻}{\ensuremath{{}^{-}}} % ⁻
+  \newunicodechar{¹}{\ensuremath{{}^{1}}} % ¹
+  \newunicodechar{³}{\ensuremath{{}^{3}}} % ³
+  \newunicodechar{⁰}{\ensuremath{{}^{0}}} % ⁰
+  \newunicodechar{⁴}{\ensuremath{{}^{4}}} % ⁴
+  \newunicodechar{⁶}{\ensuremath{{}^{6}}} % ⁶
+\else
   \DeclareUnicodeCharacter{2192}{\ensuremath{\to}}          % →
   \DeclareUnicodeCharacter{2190}{\ensuremath{\leftarrow}}   % ←
   \DeclareUnicodeCharacter{2194}{\ensuremath{\leftrightarrow}} % ↔
@@ -146,6 +191,7 @@
   \DeclareUnicodeCharacter{2070}{\ensuremath{{}^{0}}}       % ⁰
   \DeclareUnicodeCharacter{2074}{\ensuremath{{}^{4}}}       % ⁴
   \DeclareUnicodeCharacter{2076}{\ensuremath{{}^{6}}}       % ⁶
+\fi
 
 % ---- pedagogical boxes: each means ONE thing ----------------------------
 % BIG IDEA — the load-bearing concept of a section.