feat: display reference book page numbers in song page footer (Closes #3)

Render a two-row footer at the bottom of each song page showing reference
book abbreviations as column headers with corresponding page numbers below.
A thin separator line is drawn above the footer. MeasurementEngine now
reserves vertical space for the reference footer when reference books are
configured and the song has references.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitignore

@@ -1,29 +1,22 @@
-# LaTeX build artifacts
+# Gradle
-*.aux
+.gradle/
-*.log
+build/
-*.out
+buildSrc/build/
-*.toc
-*.fls
-*.fdb_latexmk
-*.synctex.gz
-*.synctex(busy)
-*.sxd
-*.sxc
 
-# Output directory
+# IDE
-output/
-
-# OS files
-.DS_Store
-Thumbs.db
-
-# Editor files
 .idea/
 *.iml
 .vscode/
-*~
+
-*.swp
+# OS
+.DS_Store
+Thumbs.db
+
+# Output
+output/
+
+# Kotlin
+*.class
 
 # Claude
 .claude/
-__pycache__/

CLAUDE.md

@@ -2,83 +2,79 @@
 
 This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
 
-## Build Commands
+## Build & Test Commands
 
 ```bash
-# Build the songbook PDF (two-pass for TOC)
+# Build everything
-make
+gradle build
 
-# Remove auxiliary files
+# Run all tests
-make clean
+gradle test
 
-# Remove everything including PDF
+# Run tests for a specific module
-make distclean
+gradle :parser:test
+gradle :layout:test
+gradle :renderer-pdf:test
+gradle :app:test
+
+# Run a single test class
+gradle :parser:test --tests ChordProParserTest
+
+# Run a single test method
+gradle :parser:test --tests "ChordProParserTest.parse complete song"
+
+# Build and run CLI
+gradle :cli:run --args="build -d /path/to/project"
+gradle :cli:run --args="validate -d /path/to/project"
+
+# Launch GUI
+gradle :gui:run
 ```
 
-Requires LuaLaTeX (TeX Live) and the `leadsheets` package.
+Requires Java 21 (configured in `gradle.properties`). Kotlin 2.1.10, Gradle 9.3.1.
 
-## Project Structure
+## Architecture
 
+**Pipeline:** Parse → Measure → Paginate → Render
+
+`SongbookPipeline` (in `app`) orchestrates the full flow:
+1. `ConfigParser` reads `songbook.yaml` → `BookConfig`
+2. `ChordProParser` reads `.chopro` files → `Song` objects
+3. `Validator` checks config and songs
+4. `MeasurementEngine` calculates each song's height in mm using `FontMetrics`
+5. `TocGenerator` estimates TOC page count and creates entries
+6. `PaginationEngine` arranges songs into pages (greedy spread packing)
+7. `PdfBookRenderer` generates the PDF via OpenPDF
+
+**Module dependency graph:**
 ```
-songbook.tex          # Main document (title page, TOC, song inputs)
+model ← parser
-songbook-style.sty    # Style package (geometry, fonts, leadsheets config)
+model ← layout
-songs/                # One .tex file per song
+model ← renderer-pdf
-fonts/                # Font files (UnifrakturMaguntia for titles)
+parser, layout, renderer-pdf ← app
-images/               # Filler images (empty for now)
+app ← cli (Clikt)
-Makefile              # Build rules (lualatex, two passes)
+app, parser ← gui (Compose Desktop)
-output/               # Generated PDF (gitignored)
 ```
 
-## How It Works
+`model` is the foundation with no dependencies — all data classes, the `FontMetrics` interface, and the `BookRenderer` interface live here. The `FontMetrics` abstraction decouples layout from rendering: `PdfFontMetrics` is the real implementation (in renderer-pdf), `StubFontMetrics` is used in layout tests.
 
-Pure LaTeX songbook using the `leadsheets` package with LuaLaTeX. The style matches the Carmina Leonis songbook format:
+**Pagination constraint:** Songs spanning 2 pages must start on a left (even) page. The `PaginationEngine` inserts filler images or blank pages to enforce this.
-- Song titles in Fraktur/blackletter font (UnifrakturMaguntia)
+
-- Chords above lyrics in regular weight, black
+## Key Types
-- No verse labels (verses separated by blank lines)
+
-- Metadata (Worte/Weise) at bottom of each song page
+- `Song` → sections → `SongLine` → `LineSegment(chord?, text)` — chord is placed above the text segment
-- Reference book cross-references (MO, PfLB) in footer
+- `PageContent` — sealed class: `SongPage`, `FillerImage`, `BlankPage`
-- Each song starts on a new page
+- `SectionType` — enum: `VERSE`, `CHORUS`, `BRIDGE`, `REPEAT`
-- A5 twoside format with page numbers at bottom-outer
+- `BuildResult` — returned by `SongbookPipeline.build()` with success/errors/counts
 
 ## Song Format
 
-Each song uses the `leadsheets` `song` environment:
+ChordPro-compatible `.chopro` files: directives in `{braces}`, chords in `[brackets]` inline with lyrics, comments with `#`. See `songs/` for examples.
 
-```latex
+## Test Patterns
-\begin{song}{
-  title = Song Title,
-  lyrics = Lyricist,
-  composer = Composer,
-  key = G,
-  mundorgel = 42,
-  pfadfinderliederbuch = 118,
-  note = {Optional note text.},
-}
 
-\begin{verse}
+Tests use `kotlin.test` annotations with Kotest assertions (`shouldBe`, `shouldHaveSize`, etc.) on JUnit 5. Layout tests use `StubFontMetrics` to avoid PDF font dependencies. App integration tests create temp directories with song files and config.
-\chord{G}Lyrics with \chord{D}chords above. \\
-Next \chord{C}line here.
-\end{verse}
 
-\begin{verse}
+## Package
-Second verse without chords (or with).
-\end{verse}
 
-\end{song}
+All code under `de.pfadfinder.songbook.*` — subpackages match module names (`.model`, `.parser`, `.layout`, `.renderer.pdf`, `.app`, `.cli`, `.gui`).
-```
-
-**Important constraints:**
-- Use `\\` for line breaks within verses (not blank lines)
-- Never place two `\chord{}` commands without a space between them — split compound words with a hyphen: `\chord{D}Abend- \chord{A}zeit.`
-- Custom properties: `alias`, `note`, `mundorgel`, `pfadfinderliederbuch`
-- Verse types: `verse` (no label), `verse*` (for custom-labeled sections like Kanon, Ref.)
-- `musicsymbols` library skipped (requires `musix11` font not installed)
-
-## Style Details (songbook-style.sty)
-
-- Page geometry: A5, margins (top 15mm, bottom 20mm, inner 20mm, outer 12mm)
-- Body font: TeX Gyre Heros (Helvetica clone)
-- Title font: UnifrakturMaguntia (Fraktur/blackletter, from `fonts/` directory)
-- Chord format: small, regular weight, black
-- Song title template: Fraktur title only (metadata rendered at bottom via `after-song` hook)
-- Reference style based on Carmina Leonis (Pfadfinder scout songbook)

Makefile

@@ -1,36 +0,0 @@
-MAIN     = songbook
-ENGINE   = lualatex
-OUTDIR   = output
-TEXENV   = TEXINPUTS=.:$(shell pwd):$(shell pwd)/$(OUTDIR):
-FLAGS    = --output-directory=$(OUTDIR) --interaction=nonstopmode
-
-.PHONY: all clean distclean
-
-all: $(OUTDIR)/$(MAIN).pdf
-
-$(OUTDIR):
-	mkdir -p $(OUTDIR)
-
-# Run until page references stabilize (max 5 passes).
-# The .songtoc file needs: pass 1 to write, pass 2 to read into TOC,
-# pass 3+ to stabilize page numbers after TOC page count changes.
-$(OUTDIR)/$(MAIN).pdf: $(MAIN).tex songbook-style.sty songs/*.tex | $(OUTDIR)
-	@for i in 1 2 3 4 5; do \
-	  echo "=== LaTeX pass $$i ==="; \
-	  $(TEXENV) $(ENGINE) $(FLAGS) $(MAIN).tex || true; \
-	  if [ -f $(OUTDIR)/$(MAIN).songtoc ]; then \
-	    python3 -c "import re;lines=open('$(OUTDIR)/$(MAIN).songtoc').readlines();lines.sort(key=lambda l:re.sub(r'[^a-zäöüß ]','',re.search(r'\{(?:\\\\textit\s*\{)?([^}]+)',l).group(1).lower()) if re.search(r'\{(?:\\\\textit\s*\{)?([^}]+)',l) else '');open('$(OUTDIR)/$(MAIN).songtoc','w').writelines(lines)" ; \
-	  fi; \
-	  if [ $$i -ge 3 ] && ! grep -q "Rerun" $(OUTDIR)/$(MAIN).log 2>/dev/null; then \
-	    echo "=== Stable after $$i passes ==="; \
-	    break; \
-	  fi; \
-	done
-
-clean:
-	rm -f $(OUTDIR)/*.aux $(OUTDIR)/*.log $(OUTDIR)/*.out \
-	      $(OUTDIR)/*.toc $(OUTDIR)/*.fls $(OUTDIR)/*.fdb_latexmk \
-	      $(OUTDIR)/*.sxd $(OUTDIR)/*.sxc $(OUTDIR)/*.songtoc
-
-distclean: clean
-	rm -f $(OUTDIR)/$(MAIN).pdf

all-songs.tex

@@ -1,298 +0,0 @@
-% Auto-generated list of all songs (alphabetical order)
-% Generated by import-songs.py
-
-\input{songs/abends-gehn-die-liebespaare}
-\input{songs/abends-treten-elche}
-\input{songs/abends-wenn-das-tageslicht}
-\input{songs/ade-nun-zur-guten-nacht}
-\input{songs/alle-strassen}
-\input{songs/alle-die-mit-uns-auf-kaperfahrt}
-\input{songs/allzeit-bereit-bundeslied-der-cpd}
-\input{songs/almost-heaven}
-\input{songs/als-wir-nach-frankreich}
-\input{songs/als-wir-noch-knaben-waren}
-\input{songs/am-alten-hafen-piratenhafen}
-\input{songs/am-brunnen-vor-dem-tore}
-\input{songs/am-ural}
-\input{songs/am-westermanns-loenstief}
-\input{songs/an-de-eck}
-\input{songs/an-land}
-\input{songs/andre-die-das-land}
-\input{songs/auf-vielen-strassen}
-\input{songs/balkanlied}
-\input{songs/ballade-von-bergen}
-\input{songs/ballade-von-der-gemeinsamen-zeit-vorspiel-d-a-d-g}
-\input{songs/banner}
-\input{songs/bella-ciao}
-\input{songs/big-bomb-dolly-aus-dover}
-\input{songs/bin-ja-nur-ein-armer-zigeuner}
-\input{songs/birkenring}
-\input{songs/bis-in-die-roten-morgenstunden}
-\input{songs/brennt-die-sonne}
-\input{songs/bruder-nun-wird-es-abend}
-\input{songs/burschen-burschen}
-\input{songs/buendische-vaganten}
-\input{songs/buergerlied}
-\input{songs/come-by-the-hills}
-\input{songs/das-gotenlied}
-\input{songs/das-leben}
-\input{songs/das-lilienbanner}
-\input{songs/das-schiff-im-nebel}
-\input{songs/dat-du-min-leewsten-buest}
-\input{songs/dein-ist-dein-leben-vorspiel-e-c-g-d}
-\input{songs/der-da-vorn-so-laut}
-\input{songs/der-geist-der-fahrt}
-\input{songs/der-geist-ist-mued}
-\input{songs/der-holzschuhmann}
-\input{songs/der-kirchenmausrock}
-\input{songs/der-kleine-troll}
-\input{songs/der-lang-genug}
-\input{songs/der-mond-ist-aufgegangen}
-\input{songs/der-papagei-ein-vogel-ist}
-\input{songs/der-pfahl}
-\input{songs/der-rabe}
-\input{songs/der-tag-begann}
-\input{songs/der-tod-reit-auf}
-\input{songs/der-wagen}
-\input{songs/der-zug-faehrt-auf}
-\input{songs/die-affen-rasen}
-\input{songs/die-ballade-vom-roten-haar}
-\input{songs/die-blauen-dragoner}
-\input{songs/die-daemmerung-faellt}
-\input{songs/die-eisenfaust}
-\input{songs/die-freie-republik}
-\input{songs/die-gedanken}
-\input{songs/die-glocken}
-\input{songs/die-grauen-nebel}
-\input{songs/die-herren-waren-bei-laune}
-\input{songs/die-klampfen-erklingen}
-\input{songs/die-lappen-hoch}
-\input{songs/die-mazurka}
-\input{songs/die-nacht-ist-nicht-allein-zum-schlafen-da}
-\input{songs/die-roten-fahnen}
-\input{songs/die-sandbank}
-\input{songs/die-schluchten-des-balkan}
-\input{songs/die-sonne-geht}
-\input{songs/die-strasse-gleitet}
-\input{songs/die-trommel-her}
-\input{songs/die-weber}
-\input{songs/die-zunft-der-strassenbrueder}
-\input{songs/dort-an-dem-ueferchen}
-\input{songs/drei-rote-pfiffe}
-\input{songs/drei-tropfen-blut-chume-geselle}
-\input{songs/du-machst-kleinholz}
-\input{songs/durch-die-morgenroten-scheiben}
-\input{songs/daemmert-von-fern}
-\input{songs/edelweisspiraten}
-\input{songs/eh-die-sonne}
-\input{songs/ein-hase-sass-im-tiefen-tal}
-\input{songs/ein-hotdog-unten-am-hafen}
-\input{songs/ein-kleiner-matrose}
-\input{songs/ein-landsknecht}
-\input{songs/ein-neuer-tag-beginnt}
-\input{songs/ein-stolzes-schiff}
-\input{songs/eines-morgens-partisanenlied}
-\input{songs/eines-morgens-ging}
-\input{songs/einst-macht-ich}
-\input{songs/endlich-trocknet-der-landstrasse}
-\input{songs/endlos-lang}
-\input{songs/endlos-sind-jene-strassen}
-\input{songs/ensemble-on-est-mieux-intro-e-a-c-h7}
-\input{songs/erklingen-leise-lieder}
-\input{songs/es-dunkelt-schon}
-\input{songs/es-gibt-nur-wasser}
-\input{songs/es-ist-an-der-zeit}
-\input{songs/es-ist-ein-schnitter}
-\input{songs/es-liegen-drei-glaenzende-kugeln}
-\input{songs/es-liegt-etwas-auf-den-strassen}
-\input{songs/es-soll-sich-der-mensch}
-\input{songs/es-tropft-von-helm-und-saebel}
-\input{songs/es-war-an-einem-sommertag}
-\input{songs/es-war-ein-koenig}
-\input{songs/es-war-in-einer-regennacht}
-\input{songs/es-wollt-ein-maegdlein}
-\input{songs/falado}
-\input{songs/fields-of-athenry}
-\input{songs/finnlandlied}
-\input{songs/fordre-niemand}
-\input{songs/fresenhof}
-\input{songs/freunde-das-leben-seid-ihr}
-\input{songs/frueher-da-war-ich}
-\input{songs/fruehling-dringt-in-den-norden}
-\input{songs/geburtstagslied}
-\input{songs/gehe-nicht-o-gregor}
-\input{songs/gelbe-blaetter-fallen-im-wind}
-\input{songs/gestern-brueder}
-\input{songs/gospodar-dein-grossgut}
-\input{songs/griechischer-fruehling}
-\input{songs/grosser-gott-wir-loben-dich}
-\input{songs/graefin-anne}
-\input{songs/gut-wieder-hier-zu-sein}
-\input{songs/gute-nacht-kameraden}
-\input{songs/hans-spielmann}
-\input{songs/hell-strahlt-die-sonne}
-\input{songs/heulender-motor}
-\input{songs/heute-hier}
-\input{songs/hier-waechst-kein-ahorn}
-\input{songs/hoch-lebe-der-mann-mit-dem-hut}
-\input{songs/hochzeit}
-\input{songs/hohe-tannen}
-\input{songs/how-many-roads-blowin-in-the-wind}
-\input{songs/hymn-intro-e-esus4-e-esus4-e}
-\input{songs/hoerst-du-den-wind-bundeslied-der-esm}
-\input{songs/ich-kann-dich-sehen}
-\input{songs/ich-komme-schon}
-\input{songs/ich-komme-dir-zu-sagen-versprechenslied}
-\input{songs/ich-moecht-mit-einem-zirkus-ziehn}
-\input{songs/ich-reise-uebers-gruene-land}
-\input{songs/ich-und-ein-fass-voller-wein}
-\input{songs/ich-war-noch-so-jung-bettelvogt}
-\input{songs/ihr-huebschen-jungen-reiter}
-\input{songs/ihr-woelfe-kommt-und-schliesst-den-kreis}
-\input{songs/im-morgennebel}
-\input{songs/in-dem-dunklem-wald-von-paganovo}
-\input{songs/in-des-waldes-lola}
-\input{songs/in-die-sonne}
-\input{songs/in-junkers-kneipe}
-\input{songs/islandlied}
-\input{songs/jalava-lied}
-\input{songs/jasmin}
-\input{songs/jauchzende-jungen}
-\input{songs/jeden-abend-jerchenkow}
-\input{songs/jenseits-des-tales}
-\input{songs/jubilaeumslied-der-esm}
-\input{songs/joerg-von-frundsberg}
-\input{songs/kaffee-und-karin}
-\input{songs/kameraden-jagt-die-pferde}
-\input{songs/kameraden-wann-sehen-wir-uns-wieder}
-\input{songs/karl-der-kaefer}
-\input{songs/kein-schoener-land}
-\input{songs/klingt-ein-lied-durch-die-nacht-piratenlied}
-\input{songs/kommt-ihr-menschen}
-\input{songs/komodowaran-intro-ad7g-ad7g}
-\input{songs/land-der-dunklen-waelder}
-\input{songs/lasst-die-banner}
-\input{songs/leave-her-johnny}
-\input{songs/leut-die-leut}
-\input{songs/lord-of-the-dance}
-\input{songs/laender-fahrten-abenteuer}
-\input{songs/loewen-sind-jetzt-los}
-\input{songs/man-sagt}
-\input{songs/meersalz-seht}
-\input{songs/mein-ganzes-leben}
-\input{songs/mein-kleines-boot}
-\input{songs/meine-sonne-will-ich-fragen}
-\input{songs/michel-warum-weinest-du}
-\input{songs/miners-song}
-\input{songs/molly-malone}
-\input{songs/moorsoldaten}
-\input{songs/maedchen-maenner-meister}
-\input{songs/nacht-in-portugal}
-\input{songs/nachts-auf-dem-dorfplatz}
-\input{songs/nachts-steht-hunger}
-\input{songs/nehmt-abschied-brueder}
-\input{songs/nicht-nur-nebenbei}
-\input{songs/nichts-fuer-suesse-ziehharmonika}
-\input{songs/noch-lange-sassen-wir}
-\input{songs/nordwaerts}
-\input{songs/nun-greift-in-die-saiten}
-\input{songs/nun-lustig-lustig}
-\input{songs/oh-fischer}
-\input{songs/oh-bootsmann}
-\input{songs/originale-3-strophe}
-\input{songs/panama}
-\input{songs/papst-sultan}
-\input{songs/platoff}
-\input{songs/refrain-2x}
-\input{songs/rote-ritterscharen}
-\input{songs/roter-mond}
-\input{songs/roter-wein-im-becher}
-\input{songs/santiano}
-\input{songs/santiano-2}
-\input{songs/scarborough-fair}
-\input{songs/schilf-bleicht}
-\input{songs/schlaf-mein-bub}
-\input{songs/schliess-aug-und-ohr}
-\input{songs/sei-der-abend}
-\input{songs/she-hangs-her-head-sad-lisa}
-\input{songs/siehst-du-die-feuer}
-\input{songs/singt-freunde-lasst-die-klampfen}
-\input{songs/so-trolln-wir-uns}
-\input{songs/sonnenschein-und-wilde-feste}
-\input{songs/star-of-county-down}
-\input{songs/stiebt-vom-kasbek}
-\input{songs/stille-tage}
-\input{songs/strassen-auf-und-strassen-ab}
-\input{songs/sturm-bricht-los}
-\input{songs/sturm-und-drang}
-\input{songs/tief-im-busch}
-\input{songs/trinklied-vor-dem-abgang}
-\input{songs/trommeln-und-pfeifen}
-\input{songs/turm-um-uns}
-\input{songs/ty-morjak-deutscher-text}
-\input{songs/und-am-abend}
-\input{songs/und-der-herbst}
-\input{songs/und-die-morgenfruehe}
-\input{songs/unglueck-vor-mir}
-\input{songs/unser-stammesbus}
-\input{songs/unter-den-toren}
-\input{songs/vagabundenlied}
-\input{songs/verliebt-in-du-intro-c-g-a-a-2x}
-\input{songs/viva-la-feria}
-\input{songs/vom-barette}
-\input{songs/von-allen-blauen-huegeln}
-\input{songs/von-der-festung-droehnt}
-\input{songs/von-ueberall}
-\input{songs/wach-nun-auf}
-\input{songs/was-gehn-euch-meine}
-\input{songs/was-helfen-mir-tausend-dukaten}
-\input{songs/was-kann-ich-denn-dafuer}
-\input{songs/was-keiner-wagt}
-\input{songs/was-sollen-wir-trinken}
-\input{songs/weisser-sand}
-\input{songs/welle-wogte}
-\input{songs/wem-gott-will-rechte-gunst-erweisen}
-\input{songs/wenn-alle-bruennlein}
-\input{songs/wenn-der-abend-naht}
-\input{songs/wenn-der-fruehling-kommt}
-\input{songs/wenn-die-bunten-fahnen}
-\input{songs/wenn-die-zeit}
-\input{songs/wenn-hell-die-goldne-sonne}
-\input{songs/wenn-ich-des-morgens}
-\input{songs/weronika-mit-w}
-\input{songs/what-shall-we-do-drunken-sailor}
-\input{songs/whats-right-ye-jacobites}
-\input{songs/whiskey-in-the-jar}
-\input{songs/wie-ein-fest-nach-langer-trauer}
-\input{songs/wie-kommts-dass-du}
-\input{songs/wie-schoen-blueht}
-\input{songs/wild-rover}
-\input{songs/wilde-gesellen}
-\input{songs/wilde-reiter}
-\input{songs/wildgaense}
-\input{songs/wir-drei-wir-gehn-jetzt}
-\input{songs/wir-fahren-uebers-weite-meer}
-\input{songs/wir-haben-das-sehen}
-\input{songs/wir-kamen-einst}
-\input{songs/wir-lagen-vor-madagaskar}
-\input{songs/wir-lieben-die-stuerme}
-\input{songs/wir-rufen-zu-dir-michaelslied}
-\input{songs/wir-sassen-in-johnnys-spelunke}
-\input{songs/wir-sind-des-geyers}
-\input{songs/wir-sind-durch-deutschland-gefahren}
-\input{songs/wir-sind-eine-kleine}
-\input{songs/wir-sind-kameraden}
-\input{songs/wir-sind-wieder-da-st-goar-hymne}
-\input{songs/wir-sitzen-im-rostigen-haifsch}
-\input{songs/wir-sitzen-zu-pferde}
-\input{songs/wir-wollen-zu-land-ausfahren}
-\input{songs/wir-wolln-im-gruenen-wald}
-\input{songs/wo-schorle-der-apfelschorlen-blues}
-\input{songs/wohl-ueber-erde}
-\input{songs/wohlauf-die-luft}
-\input{songs/wollt-ihr-hoeren}
-\input{songs/wos-nur-felsen}
-\input{songs/zieh-meiner-strasse}
-\input{songs/zogen-einst}
-\input{songs/zogen-viele-strassen}
-\input{songs/ueber-meiner-heimat}

app/build.gradle.kts

@@ -0,0 +1,16 @@
+plugins {
+    id("songbook-conventions")
+}
+
+dependencies {
+    implementation(project(":model"))
+    implementation(project(":parser"))
+    implementation(project(":layout"))
+    implementation(project(":renderer-pdf"))
+
+    implementation("io.github.microutils:kotlin-logging-jvm:3.0.5")
+    implementation("ch.qos.logback:logback-classic:1.5.16")
+
+    testImplementation(kotlin("test"))
+    testImplementation("io.kotest:kotest-assertions-core:5.9.1")
+}

app/src/main/kotlin/de/pfadfinder/songbook/app/SongbookPipeline.kt

@@ -0,0 +1,158 @@
+package de.pfadfinder.songbook.app
+
+import de.pfadfinder.songbook.model.*
+import de.pfadfinder.songbook.parser.*
+import de.pfadfinder.songbook.layout.*
+import de.pfadfinder.songbook.renderer.pdf.*
+import mu.KotlinLogging
+import java.io.File
+import java.io.FileOutputStream
+
+private val logger = KotlinLogging.logger {}
+
+data class BuildResult(
+    val success: Boolean,
+    val outputFile: File? = null,
+    val errors: List<ValidationError> = emptyList(),
+    val songCount: Int = 0,
+    val pageCount: Int = 0
+)
+
+class SongbookPipeline(private val projectDir: File) {
+
+    fun build(): BuildResult {
+        // 1. Parse config
+        val configFile = File(projectDir, "songbook.yaml")
+        if (!configFile.exists()) {
+            return BuildResult(false, errors = listOf(ValidationError(configFile.name, null, "songbook.yaml not found")))
+        }
+        logger.info { "Parsing config: ${configFile.absolutePath}" }
+        val config = ConfigParser.parse(configFile)
+
+        // Validate config
+        val configErrors = Validator.validateConfig(config)
+        if (configErrors.isNotEmpty()) {
+            return BuildResult(false, errors = configErrors)
+        }
+
+        // 2. Parse songs
+        val songsDir = File(projectDir, config.songs.directory)
+        if (!songsDir.exists() || !songsDir.isDirectory) {
+            return BuildResult(false, errors = listOf(ValidationError(config.songs.directory, null, "Songs directory not found")))
+        }
+
+        val songFiles = songsDir.listFiles { f: File -> f.extension in listOf("chopro", "cho", "crd") }
+            ?.sortedBy { it.name }
+            ?: emptyList()
+
+        if (songFiles.isEmpty()) {
+            return BuildResult(false, errors = listOf(ValidationError(config.songs.directory, null, "No song files found")))
+        }
+
+        logger.info { "Found ${songFiles.size} song files" }
+
+        val songs = mutableListOf<Song>()
+        val allErrors = mutableListOf<ValidationError>()
+
+        for (file in songFiles) {
+            try {
+                val song = ChordProParser.parseFile(file)
+                val songErrors = Validator.validateSong(song, file.name)
+                if (songErrors.isNotEmpty()) {
+                    allErrors.addAll(songErrors)
+                } else {
+                    songs.add(song)
+                }
+            } catch (e: Exception) {
+                allErrors.add(ValidationError(file.name, null, "Parse error: ${e.message}"))
+            }
+        }
+
+        if (allErrors.isNotEmpty()) {
+            return BuildResult(false, errors = allErrors)
+        }
+
+        // Sort songs
+        val sortedSongs = when (config.songs.order) {
+            "alphabetical" -> songs.sortedBy { it.title.lowercase() }
+            else -> songs  // manual order = file order
+        }
+
+        logger.info { "Parsed ${sortedSongs.size} songs" }
+
+        // 3. Measure songs
+        val fontMetrics = PdfFontMetrics()
+        val measurementEngine = MeasurementEngine(fontMetrics, config)
+        val measuredSongs = sortedSongs.map { measurementEngine.measure(it) }
+
+        // 4. Generate TOC and paginate
+        val tocGenerator = TocGenerator(config)
+        val tocPages = tocGenerator.estimateTocPages(sortedSongs)
+
+        val paginationEngine = PaginationEngine(config)
+        val pages = paginationEngine.paginate(measuredSongs, tocPages)
+
+        val tocEntries = tocGenerator.generate(pages, tocPages)
+
+        val layoutResult = LayoutResult(
+            tocPages = tocPages,
+            pages = pages,
+            tocEntries = tocEntries
+        )
+
+        logger.info { "Layout: ${tocPages} TOC pages, ${pages.size} content pages" }
+
+        // 5. Render PDF
+        val outputDir = File(projectDir, config.output.directory)
+        outputDir.mkdirs()
+        val outputFile = File(outputDir, config.output.filename)
+
+        logger.info { "Rendering PDF: ${outputFile.absolutePath}" }
+
+        val renderer = PdfBookRenderer()
+        FileOutputStream(outputFile).use { fos ->
+            renderer.render(layoutResult, config, fos)
+        }
+
+        logger.info { "Build complete: ${sortedSongs.size} songs, ${pages.size + tocPages} pages" }
+
+        return BuildResult(
+            success = true,
+            outputFile = outputFile,
+            songCount = sortedSongs.size,
+            pageCount = pages.size + tocPages
+        )
+    }
+
+    fun validate(): List<ValidationError> {
+        val configFile = File(projectDir, "songbook.yaml")
+        if (!configFile.exists()) {
+            return listOf(ValidationError(configFile.name, null, "songbook.yaml not found"))
+        }
+
+        val config = ConfigParser.parse(configFile)
+        val errors = mutableListOf<ValidationError>()
+        errors.addAll(Validator.validateConfig(config))
+
+        val songsDir = File(projectDir, config.songs.directory)
+        if (!songsDir.exists()) {
+            errors.add(ValidationError(config.songs.directory, null, "Songs directory not found"))
+            return errors
+        }
+
+        val songFiles = songsDir.listFiles { f: File -> f.extension in listOf("chopro", "cho", "crd") }
+            ?.sortedBy { it.name }
+            ?: emptyList()
+
+        for (file in songFiles) {
+            try {
+                val song = ChordProParser.parseFile(file)
+                errors.addAll(Validator.validateSong(song, file.name))
+            } catch (e: Exception) {
+                errors.add(ValidationError(file.name, null, "Parse error: ${e.message}"))
+            }
+        }
+
+        return errors
+    }
+}

app/src/test/kotlin/de/pfadfinder/songbook/app/SongbookPipelineTest.kt

@@ -0,0 +1,534 @@
+package de.pfadfinder.songbook.app
+
+import io.kotest.matchers.booleans.shouldBeFalse
+import io.kotest.matchers.booleans.shouldBeTrue
+import io.kotest.matchers.collections.shouldBeEmpty
+import io.kotest.matchers.collections.shouldHaveSize
+import io.kotest.matchers.collections.shouldNotBeEmpty
+import io.kotest.matchers.ints.shouldBeGreaterThan
+import io.kotest.matchers.nulls.shouldBeNull
+import io.kotest.matchers.nulls.shouldNotBeNull
+import io.kotest.matchers.shouldBe
+import io.kotest.matchers.string.shouldContain
+import java.io.File
+import kotlin.test.Test
+
+class SongbookPipelineTest {
+
+    private fun createTempProject(): File {
+        val dir = kotlin.io.path.createTempDirectory("songbook-test").toFile()
+        dir.deleteOnExit()
+        return dir
+    }
+
+    private fun writeConfig(projectDir: File, config: String = defaultConfig()) {
+        File(projectDir, "songbook.yaml").writeText(config)
+    }
+
+    private fun defaultConfig(
+        songsDir: String = "./songs",
+        outputDir: String = "./output",
+        outputFilename: String = "liederbuch.pdf",
+        order: String = "alphabetical"
+    ): String = """
+        book:
+          title: "Test Liederbuch"
+          format: "A5"
+        songs:
+          directory: "$songsDir"
+          order: "$order"
+        fonts:
+          lyrics:
+            family: "Helvetica"
+            size: 10
+          chords:
+            family: "Helvetica"
+            size: 9
+          title:
+            family: "Helvetica"
+            size: 14
+          metadata:
+            family: "Helvetica"
+            size: 8
+          toc:
+            family: "Helvetica"
+            size: 9
+        layout:
+          margins:
+            top: 15
+            bottom: 15
+            inner: 20
+            outer: 12
+        images:
+          directory: "./images"
+        output:
+          directory: "$outputDir"
+          filename: "$outputFilename"
+    """.trimIndent()
+
+    private fun writeSongFile(songsDir: File, filename: String, content: String) {
+        songsDir.mkdirs()
+        File(songsDir, filename).writeText(content)
+    }
+
+    private fun sampleSong(title: String = "Test Song"): String = """
+        {title: $title}
+        {start_of_verse}
+        [Am]Hello [C]world
+        This is a test
+        {end_of_verse}
+    """.trimIndent()
+
+    // --- build() tests ---
+
+    @Test
+    fun `build returns error when songbook yaml is missing`() {
+        val projectDir = createTempProject()
+        try {
+            val pipeline = SongbookPipeline(projectDir)
+            val result = pipeline.build()
+
+            result.success.shouldBeFalse()
+            result.errors shouldHaveSize 1
+            result.errors[0].message shouldContain "songbook.yaml not found"
+            result.outputFile.shouldBeNull()
+        } finally {
+            projectDir.deleteRecursively()
+        }
+    }
+
+    @Test
+    fun `build returns error when songs directory does not exist`() {
+        val projectDir = createTempProject()
+        try {
+            writeConfig(projectDir, defaultConfig(songsDir = "./nonexistent"))
+            val pipeline = SongbookPipeline(projectDir)
+            val result = pipeline.build()
+
+            result.success.shouldBeFalse()
+            result.errors shouldHaveSize 1
+            result.errors[0].message shouldContain "Songs directory not found"
+        } finally {
+            projectDir.deleteRecursively()
+        }
+    }
+
+    @Test
+    fun `build returns error when songs directory is empty`() {
+        val projectDir = createTempProject()
+        try {
+            writeConfig(projectDir)
+            File(projectDir, "songs").mkdirs()
+
+            val pipeline = SongbookPipeline(projectDir)
+            val result = pipeline.build()
+
+            result.success.shouldBeFalse()
+            result.errors shouldHaveSize 1
+            result.errors[0].message shouldContain "No song files found"
+        } finally {
+            projectDir.deleteRecursively()
+        }
+    }
+
+    @Test
+    fun `build returns error for invalid config with zero margins`() {
+        val projectDir = createTempProject()
+        try {
+            val config = """
+                book:
+                  title: "Test"
+                layout:
+                  margins:
+                    top: 0
+                    bottom: 15
+                    inner: 20
+                    outer: 12
+            """.trimIndent()
+            writeConfig(projectDir, config)
+
+            val pipeline = SongbookPipeline(projectDir)
+            val result = pipeline.build()
+
+            result.success.shouldBeFalse()
+            result.errors.shouldNotBeEmpty()
+            result.errors.any { it.message.contains("margin", ignoreCase = true) }.shouldBeTrue()
+        } finally {
+            projectDir.deleteRecursively()
+        }
+    }
+
+    @Test
+    fun `build returns error for song with missing title`() {
+        val projectDir = createTempProject()
+        try {
+            writeConfig(projectDir)
+            val songsDir = File(projectDir, "songs")
+            writeSongFile(songsDir, "bad_song.chopro", """
+                {start_of_verse}
+                [Am]Hello world
+                {end_of_verse}
+            """.trimIndent())
+
+            val pipeline = SongbookPipeline(projectDir)
+            val result = pipeline.build()
+
+            result.success.shouldBeFalse()
+            result.errors.shouldNotBeEmpty()
+            result.errors.any { it.message.contains("title", ignoreCase = true) }.shouldBeTrue()
+        } finally {
+            projectDir.deleteRecursively()
+        }
+    }
+
+    @Test
+    fun `build returns error for song with no sections`() {
+        val projectDir = createTempProject()
+        try {
+            writeConfig(projectDir)
+            val songsDir = File(projectDir, "songs")
+            writeSongFile(songsDir, "empty_song.chopro", "{title: Empty Song}")
+
+            val pipeline = SongbookPipeline(projectDir)
+            val result = pipeline.build()
+
+            result.success.shouldBeFalse()
+            result.errors.shouldNotBeEmpty()
+            result.errors.any { it.message.contains("section", ignoreCase = true) }.shouldBeTrue()
+        } finally {
+            projectDir.deleteRecursively()
+        }
+    }
+
+    @Test
+    fun `build succeeds with valid project`() {
+        val projectDir = createTempProject()
+        try {
+            writeConfig(projectDir)
+            val songsDir = File(projectDir, "songs")
+            writeSongFile(songsDir, "song1.chopro", sampleSong("Alpha Song"))
+            writeSongFile(songsDir, "song2.chopro", sampleSong("Beta Song"))
+
+            val pipeline = SongbookPipeline(projectDir)
+            val result = pipeline.build()
+
+            result.success.shouldBeTrue()
+            result.errors.shouldBeEmpty()
+            result.outputFile.shouldNotBeNull()
+            result.outputFile!!.exists().shouldBeTrue()
+            result.songCount shouldBe 2
+            result.pageCount shouldBeGreaterThan 0
+        } finally {
+            projectDir.deleteRecursively()
+        }
+    }
+
+    @Test
+    fun `build creates output directory if it does not exist`() {
+        val projectDir = createTempProject()
+        try {
+            writeConfig(projectDir, defaultConfig(outputDir = "./out/build"))
+            val songsDir = File(projectDir, "songs")
+            writeSongFile(songsDir, "song1.chopro", sampleSong())
+
+            val pipeline = SongbookPipeline(projectDir)
+            val result = pipeline.build()
+
+            result.success.shouldBeTrue()
+            File(projectDir, "out/build").exists().shouldBeTrue()
+            result.outputFile!!.exists().shouldBeTrue()
+        } finally {
+            projectDir.deleteRecursively()
+        }
+    }
+
+    @Test
+    fun `build with alphabetical order sorts songs by title`() {
+        val projectDir = createTempProject()
+        try {
+            writeConfig(projectDir, defaultConfig(order = "alphabetical"))
+            val songsDir = File(projectDir, "songs")
+            writeSongFile(songsDir, "z_first.chopro", sampleSong("Zebra Song"))
+            writeSongFile(songsDir, "a_second.chopro", sampleSong("Alpha Song"))
+
+            val pipeline = SongbookPipeline(projectDir)
+            val result = pipeline.build()
+
+            result.success.shouldBeTrue()
+            result.songCount shouldBe 2
+        } finally {
+            projectDir.deleteRecursively()
+        }
+    }
+
+    @Test
+    fun `build with manual order preserves file order`() {
+        val projectDir = createTempProject()
+        try {
+            writeConfig(projectDir, defaultConfig(order = "manual"))
+            val songsDir = File(projectDir, "songs")
+            writeSongFile(songsDir, "02_second.chopro", sampleSong("Second Song"))
+            writeSongFile(songsDir, "01_first.chopro", sampleSong("First Song"))
+
+            val pipeline = SongbookPipeline(projectDir)
+            val result = pipeline.build()
+
+            result.success.shouldBeTrue()
+            result.songCount shouldBe 2
+        } finally {
+            projectDir.deleteRecursively()
+        }
+    }
+
+    @Test
+    fun `build recognizes cho extension`() {
+        val projectDir = createTempProject()
+        try {
+            writeConfig(projectDir)
+            val songsDir = File(projectDir, "songs")
+            writeSongFile(songsDir, "song1.cho", sampleSong("Cho Song"))
+
+            val pipeline = SongbookPipeline(projectDir)
+            val result = pipeline.build()
+
+            result.success.shouldBeTrue()
+            result.songCount shouldBe 1
+        } finally {
+            projectDir.deleteRecursively()
+        }
+    }
+
+    @Test
+    fun `build recognizes crd extension`() {
+        val projectDir = createTempProject()
+        try {
+            writeConfig(projectDir)
+            val songsDir = File(projectDir, "songs")
+            writeSongFile(songsDir, "song1.crd", sampleSong("Crd Song"))
+
+            val pipeline = SongbookPipeline(projectDir)
+            val result = pipeline.build()
+
+            result.success.shouldBeTrue()
+            result.songCount shouldBe 1
+        } finally {
+            projectDir.deleteRecursively()
+        }
+    }
+
+    @Test
+    fun `build ignores non-song files in songs directory`() {
+        val projectDir = createTempProject()
+        try {
+            writeConfig(projectDir)
+            val songsDir = File(projectDir, "songs")
+            writeSongFile(songsDir, "song1.chopro", sampleSong("Real Song"))
+            writeSongFile(songsDir, "readme.txt", "Not a song")
+            writeSongFile(songsDir, "notes.md", "# Notes")
+
+            val pipeline = SongbookPipeline(projectDir)
+            val result = pipeline.build()
+
+            result.success.shouldBeTrue()
+            result.songCount shouldBe 1
+        } finally {
+            projectDir.deleteRecursively()
+        }
+    }
+
+    @Test
+    fun `build output file has correct name`() {
+        val projectDir = createTempProject()
+        try {
+            writeConfig(projectDir, defaultConfig(outputFilename = "my-book.pdf"))
+            val songsDir = File(projectDir, "songs")
+            writeSongFile(songsDir, "song1.chopro", sampleSong())
+
+            val pipeline = SongbookPipeline(projectDir)
+            val result = pipeline.build()
+
+            result.success.shouldBeTrue()
+            result.outputFile!!.name shouldBe "my-book.pdf"
+        } finally {
+            projectDir.deleteRecursively()
+        }
+    }
+
+    @Test
+    fun `build pageCount includes toc pages`() {
+        val projectDir = createTempProject()
+        try {
+            writeConfig(projectDir)
+            val songsDir = File(projectDir, "songs")
+            writeSongFile(songsDir, "song1.chopro", sampleSong())
+
+            val pipeline = SongbookPipeline(projectDir)
+            val result = pipeline.build()
+
+            result.success.shouldBeTrue()
+            // At least 1 content page + TOC pages (minimum 2 for even count)
+            result.pageCount shouldBeGreaterThan 1
+        } finally {
+            projectDir.deleteRecursively()
+        }
+    }
+
+    // --- validate() tests ---
+
+    @Test
+    fun `validate returns error when songbook yaml is missing`() {
+        val projectDir = createTempProject()
+        try {
+            val pipeline = SongbookPipeline(projectDir)
+            val errors = pipeline.validate()
+
+            errors shouldHaveSize 1
+            errors[0].message shouldContain "songbook.yaml not found"
+        } finally {
+            projectDir.deleteRecursively()
+        }
+    }
+
+    @Test
+    fun `validate returns error when songs directory does not exist`() {
+        val projectDir = createTempProject()
+        try {
+            writeConfig(projectDir, defaultConfig(songsDir = "./nonexistent"))
+            val pipeline = SongbookPipeline(projectDir)
+            val errors = pipeline.validate()
+
+            errors.shouldNotBeEmpty()
+            errors.any { it.message.contains("Songs directory not found") }.shouldBeTrue()
+        } finally {
+            projectDir.deleteRecursively()
+        }
+    }
+
+    @Test
+    fun `validate returns empty list for valid project`() {
+        val projectDir = createTempProject()
+        try {
+            writeConfig(projectDir)
+            val songsDir = File(projectDir, "songs")
+            writeSongFile(songsDir, "song1.chopro", sampleSong())
+
+            val pipeline = SongbookPipeline(projectDir)
+            val errors = pipeline.validate()
+
+            errors.shouldBeEmpty()
+        } finally {
+            projectDir.deleteRecursively()
+        }
+    }
+
+    @Test
+    fun `validate reports config errors`() {
+        val projectDir = createTempProject()
+        try {
+            val config = """
+                layout:
+                  margins:
+                    top: 0
+                    bottom: 0
+                    inner: 0
+                    outer: 0
+            """.trimIndent()
+            writeConfig(projectDir, config)
+            // Still need songs dir to exist for full validate
+            File(projectDir, "./songs").mkdirs()
+
+            val pipeline = SongbookPipeline(projectDir)
+            val errors = pipeline.validate()
+
+            errors shouldHaveSize 4
+            errors.all { it.message.contains("margin", ignoreCase = true) }.shouldBeTrue()
+        } finally {
+            projectDir.deleteRecursively()
+        }
+    }
+
+    @Test
+    fun `validate reports song validation errors`() {
+        val projectDir = createTempProject()
+        try {
+            writeConfig(projectDir)
+            val songsDir = File(projectDir, "songs")
+            writeSongFile(songsDir, "bad_song.chopro", "{title: }")
+
+            val pipeline = SongbookPipeline(projectDir)
+            val errors = pipeline.validate()
+
+            errors.shouldNotBeEmpty()
+        } finally {
+            projectDir.deleteRecursively()
+        }
+    }
+
+    @Test
+    fun `validate reports errors for multiple invalid songs`() {
+        val projectDir = createTempProject()
+        try {
+            writeConfig(projectDir)
+            val songsDir = File(projectDir, "songs")
+            writeSongFile(songsDir, "bad1.chopro", "{title: Good Title}")  // no sections
+            writeSongFile(songsDir, "bad2.chopro", "{title: Another Title}")  // no sections
+
+            val pipeline = SongbookPipeline(projectDir)
+            val errors = pipeline.validate()
+
+            errors.shouldNotBeEmpty()
+            errors.size shouldBeGreaterThan 1
+        } finally {
+            projectDir.deleteRecursively()
+        }
+    }
+
+    @Test
+    fun `validate with empty songs directory returns no song errors`() {
+        val projectDir = createTempProject()
+        try {
+            writeConfig(projectDir)
+            File(projectDir, "songs").mkdirs()
+
+            val pipeline = SongbookPipeline(projectDir)
+            val errors = pipeline.validate()
+
+            // No errors because there are no song files to validate
+            errors.shouldBeEmpty()
+        } finally {
+            projectDir.deleteRecursively()
+        }
+    }
+
+    // --- BuildResult data class tests ---
+
+    @Test
+    fun `BuildResult defaults are correct`() {
+        val result = BuildResult(success = false)
+
+        result.success.shouldBeFalse()
+        result.outputFile.shouldBeNull()
+        result.errors.shouldBeEmpty()
+        result.songCount shouldBe 0
+        result.pageCount shouldBe 0
+    }
+
+    @Test
+    fun `BuildResult with all fields set`() {
+        val file = File("/tmp/test.pdf")
+        val errors = listOf(de.pfadfinder.songbook.parser.ValidationError("test", 1, "error"))
+        val result = BuildResult(
+            success = true,
+            outputFile = file,
+            errors = errors,
+            songCount = 5,
+            pageCount = 10
+        )
+
+        result.success.shouldBeTrue()
+        result.outputFile shouldBe file
+        result.errors shouldHaveSize 1
+        result.songCount shouldBe 5
+        result.pageCount shouldBe 10
+    }
+}

build.gradle.kts

@@ -0,0 +1,4 @@
+plugins {
+    id("org.jetbrains.compose") version "1.7.3" apply false
+    id("org.jetbrains.kotlin.plugin.compose") version "2.1.10" apply false
+}

buildSrc/build.gradle.kts

@@ -0,0 +1,12 @@
+plugins {
+    `kotlin-dsl`
+}
+
+repositories {
+    mavenCentral()
+    gradlePluginPortal()
+}
+
+dependencies {
+    implementation("org.jetbrains.kotlin:kotlin-gradle-plugin:2.1.10")
+}

buildSrc/src/main/kotlin/songbook-conventions.gradle.kts

@@ -0,0 +1,18 @@
+plugins {
+    kotlin("jvm")
+}
+
+java {
+    sourceCompatibility = JavaVersion.VERSION_21
+    targetCompatibility = JavaVersion.VERSION_21
+}
+
+kotlin {
+    compilerOptions {
+        jvmTarget.set(org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_21)
+    }
+}
+
+tasks.withType<Test> {
+    useJUnitPlatform()
+}

cli/build.gradle.kts

@@ -0,0 +1,17 @@
+plugins {
+    id("songbook-conventions")
+    application
+}
+
+application {
+    mainClass.set("de.pfadfinder.songbook.cli.MainKt")
+}
+
+dependencies {
+    implementation(project(":app"))
+    implementation(project(":model"))
+    implementation(project(":parser"))
+    implementation("com.github.ajalt.clikt:clikt:5.0.3")
+    implementation("io.github.microutils:kotlin-logging-jvm:3.0.5")
+    implementation("ch.qos.logback:logback-classic:1.5.16")
+}

cli/src/main/kotlin/de/pfadfinder/songbook/cli/BuildCommand.kt

@@ -0,0 +1,37 @@
+package de.pfadfinder.songbook.cli
+
+import com.github.ajalt.clikt.core.CliktCommand
+import com.github.ajalt.clikt.core.Context
+import com.github.ajalt.clikt.core.ProgramResult
+import com.github.ajalt.clikt.parameters.options.default
+import com.github.ajalt.clikt.parameters.options.option
+import de.pfadfinder.songbook.app.SongbookPipeline
+import java.io.File
+
+class BuildCommand : CliktCommand(name = "build") {
+    override fun help(context: Context) = "Build the songbook PDF"
+
+    private val projectDir by option("-d", "--dir", help = "Project directory").default(".")
+
+    override fun run() {
+        val dir = File(projectDir).absoluteFile
+        echo("Building songbook from: ${dir.path}")
+
+        val pipeline = SongbookPipeline(dir)
+        val result = pipeline.build()
+
+        if (result.success) {
+            echo("Build successful!")
+            echo("  Songs: ${result.songCount}")
+            echo("  Pages: ${result.pageCount}")
+            echo("  Output: ${result.outputFile?.absolutePath}")
+        } else {
+            echo("Build failed with ${result.errors.size} error(s):", err = true)
+            for (error in result.errors) {
+                val location = listOfNotNull(error.file, error.line?.toString()).joinToString(":")
+                echo("  [$location] ${error.message}", err = true)
+            }
+            throw ProgramResult(1)
+        }
+    }
+}

cli/src/main/kotlin/de/pfadfinder/songbook/cli/Main.kt

@@ -0,0 +1,15 @@
+package de.pfadfinder.songbook.cli
+
+import com.github.ajalt.clikt.core.CliktCommand
+import com.github.ajalt.clikt.core.main
+import com.github.ajalt.clikt.core.subcommands
+
+class SongbookCli : CliktCommand(name = "songbook") {
+    override fun run() = Unit
+}
+
+fun main(args: Array<String>) {
+    SongbookCli()
+        .subcommands(BuildCommand(), ValidateCommand())
+        .main(args)
+}

cli/src/main/kotlin/de/pfadfinder/songbook/cli/ValidateCommand.kt

@@ -0,0 +1,34 @@
+package de.pfadfinder.songbook.cli
+
+import com.github.ajalt.clikt.core.CliktCommand
+import com.github.ajalt.clikt.core.Context
+import com.github.ajalt.clikt.core.ProgramResult
+import com.github.ajalt.clikt.parameters.options.default
+import com.github.ajalt.clikt.parameters.options.option
+import de.pfadfinder.songbook.app.SongbookPipeline
+import java.io.File
+
+class ValidateCommand : CliktCommand(name = "validate") {
+    override fun help(context: Context) = "Validate all song files"
+
+    private val projectDir by option("-d", "--dir", help = "Project directory").default(".")
+
+    override fun run() {
+        val dir = File(projectDir).absoluteFile
+        echo("Validating songbook in: ${dir.path}")
+
+        val pipeline = SongbookPipeline(dir)
+        val errors = pipeline.validate()
+
+        if (errors.isEmpty()) {
+            echo("All songs are valid!")
+        } else {
+            echo("Found ${errors.size} error(s):", err = true)
+            for (error in errors) {
+                val location = listOfNotNull(error.file, error.line?.toString()).joinToString(":")
+                echo("  [$location] ${error.message}", err = true)
+            }
+            throw ProgramResult(1)
+        }
+    }
+}

gradle.properties

@@ -0,0 +1 @@
+org.gradle.java.home=/usr/lib/jvm/java-25-openjdk

gui/build.gradle.kts

@@ -0,0 +1,20 @@
+plugins {
+    id("songbook-conventions")
+    id("org.jetbrains.compose")
+    id("org.jetbrains.kotlin.plugin.compose")
+}
+
+dependencies {
+    implementation(project(":app"))
+    implementation(project(":model"))
+    implementation(project(":parser"))
+    implementation(compose.desktop.currentOs)
+    implementation("io.github.microutils:kotlin-logging-jvm:3.0.5")
+    implementation("ch.qos.logback:logback-classic:1.5.16")
+}
+
+compose.desktop {
+    application {
+        mainClass = "de.pfadfinder.songbook.gui.AppKt"
+    }
+}

gui/src/main/kotlin/de/pfadfinder/songbook/gui/App.kt

@@ -0,0 +1,347 @@
+package de.pfadfinder.songbook.gui
+
+import androidx.compose.desktop.ui.tooling.preview.Preview
+import androidx.compose.foundation.VerticalScrollbar
+import androidx.compose.foundation.layout.*
+import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.foundation.lazy.items
+import androidx.compose.foundation.lazy.rememberLazyListState
+import androidx.compose.foundation.rememberScrollbarAdapter
+import androidx.compose.material.*
+import androidx.compose.runtime.*
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.sp
+import androidx.compose.ui.window.Window
+import androidx.compose.ui.window.application
+import de.pfadfinder.songbook.app.BuildResult
+import de.pfadfinder.songbook.app.SongbookPipeline
+import de.pfadfinder.songbook.parser.ChordProParser
+import de.pfadfinder.songbook.parser.ValidationError
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.withContext
+import java.awt.Desktop
+import java.io.File
+import javax.swing.JFileChooser
+
+fun main() = application {
+    Window(
+        onCloseRequest = ::exitApplication,
+        title = "Songbook Builder"
+    ) {
+        App()
+    }
+}
+
+data class SongEntry(val fileName: String, val title: String)
+
+@Composable
+@Preview
+fun App() {
+    var projectPath by remember { mutableStateOf("") }
+    var songs by remember { mutableStateOf<List<SongEntry>>(emptyList()) }
+    var statusMessages by remember { mutableStateOf<List<StatusMessage>>(emptyList()) }
+    var isRunning by remember { mutableStateOf(false) }
+    var lastBuildResult by remember { mutableStateOf<BuildResult?>(null) }
+
+    val scope = rememberCoroutineScope()
+
+    fun loadSongs(path: String) {
+        val projectDir = File(path)
+        songs = emptyList()
+        if (!projectDir.isDirectory) return
+
+        val configFile = File(projectDir, "songbook.yaml")
+        val songsDir = if (configFile.exists()) {
+            try {
+                val config = de.pfadfinder.songbook.parser.ConfigParser.parse(configFile)
+                File(projectDir, config.songs.directory)
+            } catch (_: Exception) {
+                File(projectDir, "songs")
+            }
+        } else {
+            File(projectDir, "songs")
+        }
+
+        if (!songsDir.isDirectory) return
+
+        val songFiles = songsDir.listFiles { f: File -> f.extension in listOf("chopro", "cho", "crd") }
+            ?.sortedBy { it.name }
+            ?: emptyList()
+
+        songs = songFiles.mapNotNull { file ->
+            try {
+                val song = ChordProParser.parseFile(file)
+                SongEntry(fileName = file.name, title = song.title.ifBlank { file.nameWithoutExtension })
+            } catch (_: Exception) {
+                SongEntry(fileName = file.name, title = "${file.nameWithoutExtension} (Fehler beim Lesen)")
+            }
+        }
+    }
+
+    MaterialTheme {
+        Surface(modifier = Modifier.fillMaxSize()) {
+            Column(modifier = Modifier.padding(16.dp)) {
+                // Project directory selection
+                Text(
+                    text = "Songbook Builder",
+                    fontSize = 20.sp,
+                    fontWeight = FontWeight.Bold,
+                    modifier = Modifier.padding(bottom = 16.dp)
+                )
+
+                Text("Projektverzeichnis:", fontWeight = FontWeight.Medium)
+                Spacer(modifier = Modifier.height(4.dp))
+                Row(verticalAlignment = Alignment.CenterVertically) {
+                    OutlinedTextField(
+                        value = projectPath,
+                        onValueChange = {
+                            projectPath = it
+                            loadSongs(it)
+                        },
+                        modifier = Modifier.weight(1f),
+                        singleLine = true,
+                        placeholder = { Text("Pfad zum Projektverzeichnis...") }
+                    )
+                    Spacer(modifier = Modifier.width(8.dp))
+                    Button(
+                        onClick = {
+                            val chooser = JFileChooser().apply {
+                                fileSelectionMode = JFileChooser.DIRECTORIES_ONLY
+                                dialogTitle = "Projektverzeichnis auswählen"
+                                if (projectPath.isNotBlank()) {
+                                    currentDirectory = File(projectPath)
+                                }
+                            }
+                            if (chooser.showOpenDialog(null) == JFileChooser.APPROVE_OPTION) {
+                                projectPath = chooser.selectedFile.absolutePath
+                                loadSongs(projectPath)
+                            }
+                        },
+                        enabled = !isRunning
+                    ) {
+                        Text("Durchsuchen...")
+                    }
+                }
+
+                Spacer(modifier = Modifier.height(16.dp))
+
+                // Song list
+                Text(
+                    text = "Lieder (${songs.size}):",
+                    fontWeight = FontWeight.Medium
+                )
+                Spacer(modifier = Modifier.height(4.dp))
+
+                Box(modifier = Modifier.weight(1f).fillMaxWidth()) {
+                    val listState = rememberLazyListState()
+                    LazyColumn(
+                        state = listState,
+                        modifier = Modifier.fillMaxSize().padding(end = 12.dp)
+                    ) {
+                        if (songs.isEmpty() && projectPath.isNotBlank()) {
+                            item {
+                                Text(
+                                    "Keine Lieder gefunden. Bitte Projektverzeichnis prüfen.",
+                                    color = Color.Gray,
+                                    modifier = Modifier.padding(8.dp)
+                                )
+                            }
+                        } else if (projectPath.isBlank()) {
+                            item {
+                                Text(
+                                    "Bitte ein Projektverzeichnis auswählen.",
+                                    color = Color.Gray,
+                                    modifier = Modifier.padding(8.dp)
+                                )
+                            }
+                        }
+                        items(songs) { song ->
+                            Row(modifier = Modifier.fillMaxWidth().padding(vertical = 2.dp, horizontal = 8.dp)) {
+                                Text(song.title, modifier = Modifier.weight(1f))
+                                Text(song.fileName, color = Color.Gray, fontSize = 12.sp)
+                            }
+                            Divider()
+                        }
+                    }
+                    VerticalScrollbar(
+                        modifier = Modifier.align(Alignment.CenterEnd).fillMaxHeight(),
+                        adapter = rememberScrollbarAdapter(listState)
+                    )
+                }
+
+                Spacer(modifier = Modifier.height(16.dp))
+
+                // Action buttons
+                Row(horizontalArrangement = Arrangement.spacedBy(8.dp)) {
+                    Button(
+                        onClick = {
+                            if (projectPath.isBlank()) return@Button
+                            isRunning = true
+                            lastBuildResult = null
+                            statusMessages = listOf(StatusMessage("Buch wird erstellt...", MessageType.INFO))
+                            scope.launch {
+                                val result = withContext(Dispatchers.IO) {
+                                    try {
+                                        SongbookPipeline(File(projectPath)).build()
+                                    } catch (e: Exception) {
+                                        BuildResult(
+                                            success = false,
+                                            errors = listOf(
+                                                ValidationError(null, null, "Unerwarteter Fehler: ${e.message}")
+                                            )
+                                        )
+                                    }
+                                }
+                                lastBuildResult = result
+                                statusMessages = if (result.success) {
+                                    listOf(
+                                        StatusMessage(
+                                            "Buch erfolgreich erstellt! ${result.songCount} Lieder, ${result.pageCount} Seiten.",
+                                            MessageType.SUCCESS
+                                        ),
+                                        StatusMessage(
+                                            "Ausgabedatei: ${result.outputFile?.absolutePath ?: "unbekannt"}",
+                                            MessageType.INFO
+                                        )
+                                    )
+                                } else {
+                                    result.errors.map { error ->
+                                        val location = buildString {
+                                            if (error.file != null) append(error.file)
+                                            if (error.line != null) append(":${error.line}")
+                                        }
+                                        val prefix = if (location.isNotEmpty()) "[$location] " else ""
+                                        StatusMessage("$prefix${error.message}", MessageType.ERROR)
+                                    }
+                                }
+                                isRunning = false
+                            }
+                        },
+                        enabled = !isRunning && projectPath.isNotBlank()
+                    ) {
+                        Text("Buch erstellen")
+                    }
+
+                    Button(
+                        onClick = {
+                            if (projectPath.isBlank()) return@Button
+                            isRunning = true
+                            lastBuildResult = null
+                            statusMessages = listOf(StatusMessage("Validierung läuft...", MessageType.INFO))
+                            scope.launch {
+                                val errors = withContext(Dispatchers.IO) {
+                                    try {
+                                        SongbookPipeline(File(projectPath)).validate()
+                                    } catch (e: Exception) {
+                                        listOf(
+                                            ValidationError(null, null, "Unerwarteter Fehler: ${e.message}")
+                                        )
+                                    }
+                                }
+                                statusMessages = if (errors.isEmpty()) {
+                                    listOf(StatusMessage("Validierung erfolgreich! Keine Fehler gefunden.", MessageType.SUCCESS))
+                                } else {
+                                    errors.map { error ->
+                                        val location = buildString {
+                                            if (error.file != null) append(error.file)
+                                            if (error.line != null) append(":${error.line}")
+                                        }
+                                        val prefix = if (location.isNotEmpty()) "[$location] " else ""
+                                        StatusMessage("$prefix${error.message}", MessageType.ERROR)
+                                    }
+                                }
+                                isRunning = false
+                            }
+                        },
+                        enabled = !isRunning && projectPath.isNotBlank()
+                    ) {
+                        Text("Validieren")
+                    }
+
+                    if (lastBuildResult?.success == true && lastBuildResult?.outputFile != null) {
+                        Button(
+                            onClick = {
+                                lastBuildResult?.outputFile?.let { file ->
+                                    try {
+                                        Desktop.getDesktop().open(file)
+                                    } catch (e: Exception) {
+                                        statusMessages = statusMessages + StatusMessage(
+                                            "PDF konnte nicht geöffnet werden: ${e.message}",
+                                            MessageType.ERROR
+                                        )
+                                    }
+                                }
+                            },
+                            enabled = !isRunning
+                        ) {
+                            Text("PDF öffnen")
+                        }
+                    }
+
+                    if (isRunning) {
+                        Spacer(modifier = Modifier.width(8.dp))
+                        CircularProgressIndicator(
+                            modifier = Modifier.size(24.dp).align(Alignment.CenterVertically),
+                            strokeWidth = 2.dp
+                        )
+                    }
+                }
+
+                Spacer(modifier = Modifier.height(16.dp))
+
+                // Status/log area
+                Text("Status:", fontWeight = FontWeight.Medium)
+                Spacer(modifier = Modifier.height(4.dp))
+
+                Box(
+                    modifier = Modifier
+                        .fillMaxWidth()
+                        .height(150.dp)
+                ) {
+                    val logListState = rememberLazyListState()
+                    LazyColumn(
+                        state = logListState,
+                        modifier = Modifier.fillMaxSize().padding(end = 12.dp)
+                    ) {
+                        if (statusMessages.isEmpty()) {
+                            item {
+                                Text(
+                                    "Bereit.",
+                                    color = Color.Gray,
+                                    modifier = Modifier.padding(4.dp)
+                                )
+                            }
+                        }
+                        items(statusMessages) { msg ->
+                            Text(
+                                text = msg.text,
+                                color = when (msg.type) {
+                                    MessageType.ERROR -> MaterialTheme.colors.error
+                                    MessageType.SUCCESS -> Color(0xFF2E7D32)
+                                    MessageType.INFO -> Color.Unspecified
+                                },
+                                fontSize = 13.sp,
+                                modifier = Modifier.padding(vertical = 2.dp, horizontal = 4.dp)
+                            )
+                        }
+                    }
+                    VerticalScrollbar(
+                        modifier = Modifier.align(Alignment.CenterEnd).fillMaxHeight(),
+                        adapter = rememberScrollbarAdapter(logListState)
+                    )
+                }
+            }
+        }
+    }
+}
+
+enum class MessageType {
+    INFO, SUCCESS, ERROR
+}
+
+data class StatusMessage(val text: String, val type: MessageType)