diff --git a/CHANGELOG.md b/CHANGELOG.md
index d8760aa..45b2f7f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,7 @@ so entries say what changed, cite the issue, and stop.
 
 ## Unreleased
 
+- `lib/changelog.sh` + `bin/changelog-assemble` — read the `changelog.d/` fragments, assemble one release section (canonical group order, one shape per repo), and consume exactly what was published (#114).
 - BUILDER.md — the handed-off PR is the parked claim's fourth shape, its handoff is its declaration, and shape 2 covers the round awaiting its first verdicts (#109).
 - Changelog publication — count entries instead of bytes, refuse dangling grouped headings, and seed grouped re-arms with Added/Changed/Fixed (#98).
 - `labels-reconcile` — grant callers private-repo check reads and warn when an entire PR sweep is blind (#95).
diff --git a/test/changelog-assemble.test.sh b/test/changelog-assemble.test.sh
new file mode 100644
index 0000000..c21fc1a
--- /dev/null
+++ b/test/changelog-assemble.test.sh
@@ -0,0 +1,364 @@
+#!/usr/bin/env bash
+# Contract tests for bin/changelog-assemble (issue #114). Constructed
+# fixture trees, no git repos — the same discipline as
+# test/changelog-armed.test.sh. set -u, not -e: failing commands are
+# behavior for the harness to inspect.
+set -u
+
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+# shellcheck source=test/harness.sh
+. "$ROOT/test/harness.sh"
+# shellcheck source=lib/changelog.sh
+. "$ROOT/lib/changelog.sh"
+
+TOOL="$ROOT/bin/changelog-assemble"
+SECTION="$ROOT/bin/changelog-section"
+
+TMP="$(mktemp -d)"
+trap 'rm -rf "$TMP"' EXIT
+
+# tree <name> — a fixture tree with changelog.d/ and its README marker;
+# the changelog body arrives on stdin.
+tree() {
+  mkdir -p "$TMP/$1/changelog.d"
+  printf 'Machine-assembled; see heavy-duty/ceremony#112.\n' >"$TMP/$1/changelog.d/README.md"
+  cat >"$TMP/$1/CHANGELOG.md"
+}
+
+# frag <tree> <name> — a fragment; body on stdin.
+frag() {
+  cat >"$TMP/$1/changelog.d/$2"
+}
+
+# The tool reads the consumer's tree at its working directory, so every
+# case runs from inside a constructed fixture tree.
+in_tree() {
+  local dir="$1"
+  shift
+  (cd "$TMP/$dir" && "$TOOL" "$@")
+}
+
+assert_file() {
+  local file="$1" expected="$2" actual
+  actual="$(cat "$file")"
+  [ "$actual" = "$expected" ] || {
+    printf 'wanted:\n%s\ngot:\n%s\n' "$expected" "$actual"
+    return 1
+  }
+}
+
+BASE_CHANGELOG=$'# Changelog\n\nPreamble prose belongs to no section.\n\n## 0.1.0 — 2026-07-01\n\n- The shipped entry.'
+
+# --- flat write: exact bytes, exact deletions --------------------------------
+
+tree flat-one <<EOF
+$BASE_CHANGELOG
+EOF
+frag flat-one 12.md <<'EOF'
+- Twelve landed.
+EOF
+check "flat: one fragment assembles and stamps" 0 "consumed 1 fragment" \
+  in_tree flat-one 0.2.0 2026-07-24
+check "flat: preamble and shipped section stay byte-identical around the insert" 0 "" \
+  assert_file "$TMP/flat-one/CHANGELOG.md" \
+  $'# Changelog\n\nPreamble prose belongs to no section.\n\n## 0.2.0 — 2026-07-24\n\n- Twelve landed.\n\n## 0.1.0 — 2026-07-01\n\n- The shipped entry.'
+check "flat: the consumed fragment is deleted" 1 "" \
+  test -e "$TMP/flat-one/changelog.d/12.md"
+check "flat: README.md survives consumption" 0 "" \
+  test -e "$TMP/flat-one/changelog.d/README.md"
+
+# --- publication order: numeric, newest first, cross-repo beside local -------
+
+tree flat-many <<EOF
+$BASE_CHANGELOG
+EOF
+frag flat-many 2.md <<'EOF'
+- Two.
+EOF
+frag flat-many 9.md <<'EOF'
+- Nine.
+EOF
+frag flat-many 10.md <<'EOF'
+- Ten.
+EOF
+frag flat-many ceremony-14.md <<'EOF'
+- Fourteen crossed over — naïve reflows would mangle this café's
+  continuation line, so it must survive verbatim.
+EOF
+
+assert_check() {
+  local dir="$1" expected="$2" actual
+  actual="$(in_tree "$dir" 0.2.0 2026-07-24 --check)"
+  [ "$actual" = "$expected" ] || {
+    printf 'wanted:\n%s\ngot:\n%s\n' "$expected" "$actual"
+    return 1
+  }
+}
+check "flat: numeric-descending order (10.md before 9.md), cross-repo name beside local" 0 "" \
+  assert_check flat-many $'- Fourteen crossed over — naïve reflows would mangle this café'"'"$'s\n  continuation line, so it must survive verbatim.\n- Ten.\n- Nine.\n- Two.'
+
+# --- grouped write: canonical order, unnamed group appended ------------------
+
+tree grouped <<EOF
+$BASE_CHANGELOG
+EOF
+frag grouped 21.md <<'EOF'
+### Fixed
+
+- Fixed twenty-one.
+EOF
+frag grouped 20.md <<'EOF'
+### Added
+
+- Added twenty.
+- Added twenty, second bullet.
+
+### Docs
+
+- Docs twenty.
+EOF
+frag grouped 19.md <<'EOF'
+### Security
+
+- Security nineteen.
+
+### Added
+
+- Added nineteen.
+EOF
+GROUPED_BODY=$'### Added\n\n- Added twenty.\n- Added twenty, second bullet.\n- Added nineteen.\n\n### Fixed\n\n- Fixed twenty-one.\n\n### Security\n\n- Security nineteen.\n\n### Docs\n\n- Docs twenty.'
+check "grouped: --check shows canonical order, multi-bullet group, unnamed group last" 0 "" \
+  assert_check grouped "$GROUPED_BODY"
+check "grouped: write mode assembles the same section" 0 "consumed 3 fragment" \
+  in_tree grouped 0.2.0 2026-07-24
+check "grouped: the written file is exact" 0 "" \
+  assert_file "$TMP/grouped/CHANGELOG.md" \
+  $'# Changelog\n\nPreamble prose belongs to no section.\n\n## 0.2.0 — 2026-07-24\n\n'"$GROUPED_BODY"$'\n\n## 0.1.0 — 2026-07-01\n\n- The shipped entry.'
+
+# --- a changelog holding only its preamble -----------------------------------
+
+tree preamble-only <<'EOF'
+# Changelog
+
+Only preamble so far.
+EOF
+frag preamble-only 1.md <<'EOF'
+- The first entry ever.
+EOF
+check "a changelog with no section yet gets the section after the preamble" 0 "" \
+  in_tree preamble-only 0.1.0 2026-07-24
+check "preamble-only write is exact" 0 "" \
+  assert_file "$TMP/preamble-only/CHANGELOG.md" \
+  $'# Changelog\n\nOnly preamble so far.\n\n## 0.1.0 — 2026-07-24\n\n- The first entry ever.'
+
+# --- --check is provably read-only -------------------------------------------
+
+tree check-readonly <<EOF
+$BASE_CHANGELOG
+EOF
+frag check-readonly 5.md <<'EOF'
+- Five.
+EOF
+cp -R "$TMP/check-readonly" "$TMP/check-readonly.before"
+check "--check prints the assembled body" 0 "Five." \
+  in_tree check-readonly 0.2.0 2026-07-24 --check
+check "--check is read-only: the tree is byte-identical before and after" 0 "" \
+  diff -r "$TMP/check-readonly.before" "$TMP/check-readonly"
+
+# --- the date defaults to today (UTC) ----------------------------------------
+
+check "date defaults without an argument" 0 "consumed 1 fragment" \
+  in_tree check-readonly 0.2.0
+check "the defaulted stamp is a UTC date" 0 "" \
+  grep -qE '^## 0\.2\.0 — [0-9]{4}-[0-9]{2}-[0-9]{2}$' "$TMP/check-readonly/CHANGELOG.md"
+
+# --- --changelog and --dir override the defaults -----------------------------
+
+mkdir -p "$TMP/flagged/frags"
+printf '# Changelog\n\n## 0.1.0 — 2026-07-01\n\n- Shipped.\n' >"$TMP/flagged/NOTES.md"
+printf -- '- Flagged entry.\n' >"$TMP/flagged/frags/2.md"
+check "--changelog and --dir override the defaults" 0 "" \
+  "$TOOL" 0.2.0 2026-07-24 --changelog "$TMP/flagged/NOTES.md" --dir "$TMP/flagged/frags"
+check "the flag-driven write landed in the named changelog" 0 "" \
+  grep -qF -- "- Flagged entry." "$TMP/flagged/NOTES.md"
+
+# --- refusals: each names the file responsible -------------------------------
+
+tree empty-frags <<EOF
+$BASE_CHANGELOG
+EOF
+rm "$TMP/empty-frags/changelog.d/README.md"
+check "an empty directory refuses — a release publishes prose" 1 "zero fragments" \
+  in_tree empty-frags 0.2.0
+check "the empty-directory refusal names the directory" 1 "changelog.d" \
+  in_tree empty-frags 0.2.0
+
+tree only-readme <<EOF
+$BASE_CHANGELOG
+EOF
+check "a README-only directory refuses with zero fragments" 1 "zero fragments" \
+  in_tree only-readme 0.2.0
+
+tree no-bullet <<EOF
+$BASE_CHANGELOG
+EOF
+frag no-bullet 3.md <<'EOF'
+Prose without a bullet is a heading in spirit.
+EOF
+check "a fragment with no bullet refuses, file named" 1 \
+  "fragment 'changelog.d/3.md' has no entries" \
+  in_tree no-bullet 0.2.0
+
+tree dangling <<EOF
+$BASE_CHANGELOG
+EOF
+frag dangling 4.md <<'EOF'
+### Added
+
+### Fixed
+
+- Fixed entry.
+EOF
+check "a dangling grouped heading refuses, file and heading named" 1 \
+  "fragment 'changelog.d/4.md' has an empty heading: '### Added'" \
+  in_tree dangling 0.2.0
+
+tree smuggled <<EOF
+$BASE_CHANGELOG
+EOF
+frag smuggled 6.md <<'EOF'
+## 0.2.0 — 2026-07-24
+
+- An entry under a smuggled heading.
+EOF
+check "a fragment carrying a '## ' line refuses, file named" 1 \
+  "fragment 'changelog.d/6.md' carries a '## ' heading" \
+  in_tree smuggled 0.2.0
+
+tree stray-txt <<EOF
+$BASE_CHANGELOG
+EOF
+frag stray-txt 7.md <<'EOF'
+- Seven.
+EOF
+frag stray-txt notes.txt <<'EOF'
+A stray scratchpad.
+EOF
+check "a stray notes.txt refuses, file named" 1 "notes.txt" \
+  in_tree stray-txt 0.2.0
+
+tree stray-markdown <<EOF
+$BASE_CHANGELOG
+EOF
+frag stray-markdown 12.markdown <<'EOF'
+- Wrong extension.
+EOF
+check "12.markdown refuses on the name pattern" 1 "12.markdown" \
+  in_tree stray-markdown 0.2.0
+
+tree stray-case <<EOF
+$BASE_CHANGELOG
+EOF
+frag stray-case Fix-12.md <<'EOF'
+- Uppercase prefix.
+EOF
+check "Fix-12.md refuses on the name pattern" 1 "Fix-12.md" \
+  in_tree stray-case 0.2.0
+
+tree mixed <<EOF
+$BASE_CHANGELOG
+EOF
+frag mixed 5.md <<'EOF'
+- Flat five.
+EOF
+frag mixed 6.md <<'EOF'
+### Added
+
+- Grouped six.
+EOF
+check "grouped + flat mixed refuses, both files named" 1 "6.md" \
+  in_tree mixed 0.2.0
+check "the mixed refusal names the flat side too" 1 "5.md" \
+  in_tree mixed 0.2.0
+
+tree already <<'EOF'
+# Changelog
+
+## 0.2.0 — 2026-07-20
+
+- Already shipped.
+EOF
+frag already 4.md <<'EOF'
+- A late fragment.
+EOF
+check "an already-present section refuses — the ceremony was already run" 1 \
+  "already has a section for '0.2.0'" \
+  in_tree already 0.2.0
+
+# Whole-version matching, as everywhere in this family: an rc section never
+# blocks the bare version.
+tree rc-present <<'EOF'
+# Changelog
+
+## 0.2.0-rc1 — 2026-07-15
+
+- The candidate's entry.
+EOF
+frag rc-present 8.md <<'EOF'
+- The real release entry.
+EOF
+check "an rc section does not block assembling the bare version" 0 "" \
+  in_tree rc-present 0.2.0 2026-07-24
+
+mkdir -p "$TMP/no-changelog/changelog.d"
+printf -- '- Entry.\n' >"$TMP/no-changelog/changelog.d/2.md"
+check "a missing changelog refuses" 1 "no such file" \
+  in_tree no-changelog 0.2.0
+
+# --- usage errors exit 2 -----------------------------------------------------
+
+check "no arguments is a usage error" 2 "usage:" in_tree flat-one
+check "an unknown flag is a usage error" 2 "usage:" in_tree flat-one 0.2.0 --frobnicate
+check "a third positional is a usage error" 2 "usage:" in_tree flat-one 0.2.0 2026-07-24 extra
+check "--dir without a value is a usage error" 2 "usage:" in_tree flat-one 0.2.0 --dir
+
+# --- round trip: the publisher and the assembler agree by test ---------------
+
+tree round-trip <<EOF
+$BASE_CHANGELOG
+EOF
+frag round-trip 30.md <<'EOF'
+### Added
+
+- Thirty — wraps onto a
+  continuation line with a naïve café.
+EOF
+frag round-trip 29.md <<'EOF'
+### Fixed
+
+- Fixed twenty-nine.
+EOF
+CHECKED="$(in_tree round-trip 0.2.0 2026-07-24 --check)"
+check "round trip: write mode succeeds after --check" 0 "" \
+  in_tree round-trip 0.2.0 2026-07-24
+
+assert_round_trip() {
+  local published
+  published="$( (cd "$TMP/round-trip" && "$SECTION" 0.2.0) )"
+  [ "$published" = "$CHECKED" ] || {
+    printf -- '--check said:\n%s\nthe publisher said:\n%s\n' "$CHECKED" "$published"
+    return 1
+  }
+}
+check "round trip: bin/changelog-section returns exactly the body --check printed" 0 "" \
+  assert_round_trip
+check "round trip: the assembled section reports no problem" 0 "" \
+  changelog_section_problem "$TMP/round-trip/CHANGELOG.md" 0.2.0
+
+# --- idempotence: the ceremony cannot run twice ------------------------------
+
+check "a second write over the consumed directory refuses with zero fragments" 1 \
+  "zero fragments" \
+  in_tree round-trip 0.2.0 2026-07-24
+
+summary
diff --git a/test/changelog.test.sh b/test/changelog.test.sh
index 99ededb..f4fb5b5 100755
--- a/test/changelog.test.sh
+++ b/test/changelog.test.sh
@@ -168,4 +168,174 @@ check "realistic changelog keeps its production heading shape" 0 "A mint records
 check "realistic adjacent release remains independently extractable" 0 "Merging the release PR" \
   "$WRAPPER" 0.8.0 "$REALISTIC"
 
+# --- the fragment reader (#114) ----------------------------------------------
+
+FRAG="$TMP/frags"
+mkdir -p "$FRAG"
+
+check "fragments: absent directory is empty output, not an error" 0 "" \
+  changelog_fragments "$TMP/no-such-dir"
+check "fragments: fragment-free directory is empty output, not an error" 0 "" \
+  changelog_fragments "$FRAG"
+
+printf 'marker\n' >"$FRAG/README.md"
+check "fragments: README.md is the directory marker, never a fragment" 0 "" \
+  changelog_fragments "$FRAG"
+
+printf -- '- Two.\n' >"$FRAG/2.md"
+printf -- '- Nine.\n' >"$FRAG/9.md"
+printf -- '- Ten.\n' >"$FRAG/10.md"
+printf -- '- Cross.\n' >"$FRAG/ceremony-14.md"
+printf -- '- Local fourteen.\n' >"$FRAG/14.md"
+
+assert_fragments_order() {
+  local expected="$1" actual
+  actual="$(changelog_fragments "$FRAG" | awk -F/ '{ print $NF }' | tr '\n' ' ')"
+  actual="${actual% }"
+  [ "$actual" = "$expected" ] || {
+    printf 'wanted: %s\ngot: %s\n' "$expected" "$actual"
+    return 1
+  }
+}
+check "fragments: issue number descending (numeric, 10 before 9), filename tie-break" 0 "" \
+  assert_fragments_order "14.md ceremony-14.md 10.md 9.md 2.md"
+
+# --- the fragment predicate (#114) -------------------------------------------
+
+PF="$TMP/frag-problems"
+mkdir -p "$PF"
+
+printf -- '- Fine.\n' >"$PF/7.md"
+check "fragment predicate: a flat fragment passes" 0 "" \
+  changelog_fragment_problem "$PF/7.md"
+
+cat >"$PF/8.md" <<'EOF'
+### Added
+
+- Grouped fine.
+EOF
+check "fragment predicate: a grouped fragment passes" 0 "" \
+  changelog_fragment_problem "$PF/8.md"
+
+printf -- '- Cross-repo.\n' >"$PF/ceremony-14.md"
+check "fragment predicate: a cross-repo name passes" 0 "" \
+  changelog_fragment_problem "$PF/ceremony-14.md"
+
+printf -- '- Bad name.\n' >"$PF/Fix-12.md"
+check "fragment predicate: an uppercase prefix is refused, file named" 1 "Fix-12.md" \
+  changelog_fragment_problem "$PF/Fix-12.md"
+printf -- '- Bad name.\n' >"$PF/notes.txt"
+check "fragment predicate: a non-.md file is refused, file named" 1 "notes.txt" \
+  changelog_fragment_problem "$PF/notes.txt"
+printf -- '- Bad name.\n' >"$PF/12.markdown"
+check "fragment predicate: .markdown is refused, file named" 1 "12.markdown" \
+  changelog_fragment_problem "$PF/12.markdown"
+printf -- '- No number.\n' >"$PF/notes.md"
+check "fragment predicate: a name with no trailing issue number is refused" 1 "notes.md" \
+  changelog_fragment_problem "$PF/notes.md"
+
+cat >"$PF/20.md" <<'EOF'
+## 1.0.0 — 2026-07-24
+
+- Smuggled heading.
+EOF
+check "fragment predicate: a '## ' line is refused — the heading is the assembler's" 1 \
+  "the section heading is the assembler's to write" \
+  changelog_fragment_problem "$PF/20.md"
+
+printf '### Added\n' >"$PF/21.md"
+check "fragment predicate: no bullet anywhere is refused" 1 \
+  "has no entries — a heading is not an entry" \
+  changelog_fragment_problem "$PF/21.md"
+
+cat >"$PF/22.md" <<'EOF'
+### Added
+
+### Fixed
+
+- Fixed entry.
+EOF
+check "fragment predicate: a dangling grouped heading is refused, heading named" 1 \
+  "has an empty heading: '### Added'" \
+  changelog_fragment_problem "$PF/22.md"
+
+# --- the assembler (#114) ----------------------------------------------------
+
+assert_assemble() {
+  local dir="$1" expected="$2" actual
+  actual="$(changelog_assemble "$dir")"
+  [ "$actual" = "$expected" ] || {
+    printf 'wanted:\n%s\ngot:\n%s\n' "$expected" "$actual"
+    return 1
+  }
+}
+
+AF="$TMP/assemble-flat"
+mkdir -p "$AF"
+printf 'marker\n' >"$AF/README.md"
+cat >"$AF/3.md" <<'EOF'
+- Three — an em dash, and prose that
+  wraps onto a continuation line.
+EOF
+printf -- '- Ten.\n- Ten again.\n' >"$AF/10.md"
+check "assemble: flat fragments, newest issue first, prose verbatim" 0 "" \
+  assert_assemble "$AF" $'- Ten.\n- Ten again.\n- Three — an em dash, and prose that\n  wraps onto a continuation line.'
+
+check "assemble: an empty directory is empty output — refusing is the caller's stance" 0 "" \
+  changelog_assemble "$TMP/no-such-dir"
+
+AG="$TMP/assemble-grouped"
+mkdir -p "$AG"
+cat >"$AG/21.md" <<'EOF'
+### Fixed
+
+- Fixed twenty-one.
+EOF
+cat >"$AG/20.md" <<'EOF'
+### Added
+
+- Added twenty.
+
+### Docs
+
+- Docs twenty.
+EOF
+cat >"$AG/19.md" <<'EOF'
+### Security
+
+- Security nineteen.
+
+### Added
+
+- Added nineteen.
+EOF
+check "assemble: canonical group order, unnamed group appended, fragment order inside a group" 0 "" \
+  assert_assemble "$AG" $'### Added\n\n- Added twenty.\n- Added nineteen.\n\n### Fixed\n\n- Fixed twenty-one.\n\n### Security\n\n- Security nineteen.\n\n### Docs\n\n- Docs twenty.'
+
+AM="$TMP/assemble-mixed"
+mkdir -p "$AM"
+printf -- '- Flat five.\n' >"$AM/5.md"
+cat >"$AM/6.md" <<'EOF'
+### Added
+
+- Grouped six.
+EOF
+check "assemble: mixed shapes refused, grouped side named" 1 "6.md" \
+  changelog_assemble "$AM"
+check "assemble: mixed shapes refused, flat side named too" 1 "5.md" \
+  changelog_assemble "$AM"
+
+AX="$TMP/assemble-selfmixed"
+mkdir -p "$AX"
+cat >"$AX/7.md" <<'EOF'
+- Ungrouped lead.
+
+### Added
+
+- Grouped follow.
+EOF
+check "assemble: one fragment mixing both shapes is refused, file named" 1 \
+  "'$AX/7.md' mixes grouped headings and ungrouped bullets" \
+  changelog_assemble "$AX"
+
 summary