diff --git a/.githooks/commit-msg b/.githooks/commit-msg
new file mode 100755
index 0000000..93d9b70
--- /dev/null
+++ b/.githooks/commit-msg
@@ -0,0 +1,5 @@
+#!/bin/sh
+set -eu
+
+repo_root=$(git rev-parse --show-toplevel)
+exec "$repo_root/scripts/normalize-commit-message.sh" "$@"
diff --git a/.githooks/pre-commit b/.githooks/pre-commit
new file mode 100755
index 0000000..a02f0f3
--- /dev/null
+++ b/.githooks/pre-commit
@@ -0,0 +1,5 @@
+#!/bin/sh
+set -eu
+
+repo_root=$(git rev-parse --show-toplevel)
+exec "$repo_root/scripts/pre-commit.sh" "$@"
diff --git a/Makefile b/Makefile
index 088be01..10e4ec9 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,4 @@
-.PHONY: build test test-verbose test-race coverage coverage-html lint clean deps check install calibrate-providers install-hooks help
+.PHONY: build test test-commit-message test-verbose test-race coverage coverage-html lint clean deps check install calibrate-providers install-hooks help
 
 # Binary name
 BINARY=nightshift
@@ -18,9 +18,13 @@ calibrate-providers:
 	go run ./cmd/provider-calibration --repo "$$(pwd)" --codex-originator codex_cli_rs --min-user-turns 2
 
 # Run all tests
-test:
+test: test-commit-message
 	go test ./...
 
+# Run commit-message hook regression tests
+test-commit-message:
+	./tests/commit-message-normalizer.sh
+
 # Run tests with verbose output
 test-verbose:
 	go test -v ./...
@@ -65,6 +69,7 @@ help:
 	@echo "Available targets:"
 	@echo "  build         - Build the binary"
 	@echo "  test          - Run all tests"
+	@echo "  test-commit-message - Run commit-message hook regression tests"
 	@echo "  test-verbose  - Run tests with verbose output"
 	@echo "  test-race     - Run tests with race detection"
 	@echo "  coverage      - Run tests with coverage report"
@@ -75,10 +80,10 @@ help:
 	@echo "  check         - Run tests and lint"
 	@echo "  install       - Build and install to Go bin directory"
 	@echo "  calibrate-providers - Compare local Claude/Codex session usage for calibration"
-	@echo "  install-hooks  - Install git pre-commit hook"
+	@echo "  install-hooks  - Enable repository-managed git hooks"
 	@echo "  help          - Show this help"
 
-# Install git pre-commit hook
+# Enable repository-managed git hooks
 install-hooks:
-	@ln -sf ../../scripts/pre-commit.sh .git/hooks/pre-commit
-	@echo "✓ pre-commit hook installed (.git/hooks/pre-commit → scripts/pre-commit.sh)"
+	@git config core.hooksPath .githooks
+	@echo "✓ repository hooks enabled (.githooks)"
diff --git a/README.md b/README.md
index b7c2b5d..3935b29 100644
--- a/README.md
+++ b/README.md
@@ -301,19 +301,52 @@ Each task has a default cooldown interval to prevent the same task from running
 
 ## Development
 
-### Pre-commit hooks
+### Git hooks and commit messages
 
-Install the git pre-commit hook to catch formatting and vet issues before pushing:
+Enable the repository-managed hooks before committing:
 
 ```bash
 make install-hooks
+# Equivalent command:
+git config core.hooksPath .githooks
 ```
 
-This symlinks `scripts/pre-commit.sh` into `.git/hooks/pre-commit`. The hook runs:
+The `pre-commit` hook runs:
 - **gofmt** - flags any staged `.go` files that need formatting
 - **go vet** - catches common correctness issues
 - **go build** - ensures the project compiles
 
+The `commit-msg` hook normalizes and validates Conventional Commit subjects in
+the `type(scope)!: summary` format. The scope and `!` marker are optional. The
+supported types are `build`, `chore`, `ci`, `docs`, `feat`, `fix`, `perf`,
+`refactor`, `style`, and `test`.
+
+The normalizer lowercases supported types, removes spacing around the optional
+scope and breaking-change marker, collapses repeated subject whitespace, trims
+leading and trailing blank lines, and removes trailing whitespace. Message body
+paragraphs and Git trailers otherwise keep their original content.
+
+Examples:
+
+```text
+feat(run): add pause command
+fix(config)!: reject unknown provider keys
+docs: explain hook installation
+```
+
+Merge and revert messages, `fixup!`, `squash!`, and `amend!` commits, stash
+subjects, and comment-led messages generated by Git are preserved byte for byte.
+Comment-led messages honor Git's configured `core.commentChar` or
+`core.commentString` prefix, falling back to Git's default `#` prefix.
+An empty message, unsupported type, missing summary, or malformed scope is
+rejected without changing the message file.
+
+Run the shell regression suite directly with:
+
+```bash
+make test-commit-message
+```
+
 To bypass in a pinch: `git commit --no-verify`
 
 ## Uninstalling
diff --git a/scripts/normalize-commit-message.sh b/scripts/normalize-commit-message.sh
new file mode 100755
index 0000000..8cdfe19
--- /dev/null
+++ b/scripts/normalize-commit-message.sh
@@ -0,0 +1,170 @@
+#!/bin/sh
+
+# Normalize and validate a Conventional Commit message in place.
+set -eu
+
+usage() {
+  echo "usage: $0 <commit-message-file>" >&2
+}
+
+if [ "$#" -ne 1 ]; then
+  usage
+  exit 2
+fi
+
+message_file=$1
+if [ ! -f "$message_file" ] || [ ! -r "$message_file" ] || [ ! -w "$message_file" ]; then
+  echo "commit message is not a readable, writable file: $message_file" >&2
+  exit 2
+fi
+
+# Git creates these subjects itself. Rewriting them can break merges, reverts,
+# autosquash, stashes, and interactive rebases, so preserve the entire file.
+first_line=$(awk '
+  {
+    line = $0
+    sub(/\r$/, "", line)
+    if (line !~ /^[[:space:]]*$/) {
+      sub(/^[[:space:]]+/, "", line)
+      print line
+      exit
+    }
+  }
+' "$message_file")
+
+comment_prefix=$(
+  git config --get-regexp '^core\.comment(char|string)$' 2>/dev/null |
+    awk '
+      {
+        sub(/^[^[:space:]]+[[:space:]]+/, "")
+        prefix = $0
+      }
+      END { print prefix }
+    '
+)
+case "$comment_prefix" in
+  ""|auto)
+    comment_prefix="#"
+    ;;
+esac
+
+case "$first_line" in
+  "$comment_prefix"*)
+    exit 0
+    ;;
+esac
+
+case "$first_line" in
+  Merge\ *|Revert\ *|fixup\!\ *|squash\!\ *|amend\!\ *|WIP\ on\ *|index\ on\ *)
+    exit 0
+    ;;
+esac
+
+tmp_file=$(mktemp "${TMPDIR:-/tmp}/nightshift-commit-msg.XXXXXX") || exit 2
+cleanup() {
+  rm -f "$tmp_file"
+}
+trap cleanup 0
+trap 'exit 1' 1 2 15
+
+if ! awk '
+  function trim(value) {
+    sub(/^[[:space:]]+/, "", value)
+    sub(/[[:space:]]+$/, "", value)
+    return value
+  }
+
+  function collapse(value) {
+    value = trim(value)
+    gsub(/[[:space:]]+/, " ", value)
+    return value
+  }
+
+  function supported(value) {
+    return value == "build" || value == "chore" || value == "ci" ||
+      value == "docs" || value == "feat" || value == "fix" ||
+      value == "perf" || value == "refactor" || value == "style" ||
+      value == "test"
+  }
+
+  {
+    line = $0
+    sub(/[[:space:]]+$/, "", line)
+    lines[++count] = line
+  }
+
+  END {
+    first = 1
+    while (first <= count && lines[first] == "") {
+      first++
+    }
+
+    last = count
+    while (last >= first && lines[last] == "") {
+      last--
+    }
+
+    if (first > last) {
+      exit 1
+    }
+
+    subject = collapse(lines[first])
+    colon = index(subject, ":")
+    if (colon == 0) {
+      exit 1
+    }
+
+    header = trim(substr(subject, 1, colon - 1))
+    summary = collapse(substr(subject, colon + 1))
+    if (summary == "") {
+      exit 1
+    }
+
+    breaking = ""
+    if (header ~ /![[:space:]]*$/) {
+      sub(/![[:space:]]*$/, "", header)
+      header = trim(header)
+      breaking = "!"
+    }
+
+    open = index(header, "(")
+    scope = ""
+    if (open > 0) {
+      if (substr(header, length(header), 1) != ")") {
+        exit 1
+      }
+      type = tolower(trim(substr(header, 1, open - 1)))
+      scope = collapse(substr(header, open + 1, length(header) - open - 1))
+      if (scope == "" || scope !~ /^[[:alnum:]_.\/#-]+$/) {
+        exit 1
+      }
+    } else {
+      type = tolower(trim(header))
+      if (type ~ /[()]/) {
+        exit 1
+      }
+    }
+
+    if (!supported(type)) {
+      exit 1
+    }
+
+    normalized = type
+    if (scope != "") {
+      normalized = normalized "(" scope ")"
+    }
+    print normalized breaking ": " summary
+
+    for (i = first + 1; i <= last; i++) {
+      print lines[i]
+    }
+  }
+' "$message_file" > "$tmp_file"; then
+  cat >&2 <<'EOF'
+invalid commit subject; expected type(scope)!: summary
+supported types: build, chore, ci, docs, feat, fix, perf, refactor, style, test
+EOF
+  exit 1
+fi
+
+cat "$tmp_file" > "$message_file"
diff --git a/tests/commit-message-normalizer.sh b/tests/commit-message-normalizer.sh
new file mode 100755
index 0000000..b08a14c
--- /dev/null
+++ b/tests/commit-message-normalizer.sh
@@ -0,0 +1,182 @@
+#!/bin/sh
+set -eu
+
+repo_root=$(CDPATH= cd "$(dirname "$0")/.." && pwd)
+normalizer="$repo_root/scripts/normalize-commit-message.sh"
+hook="$repo_root/.githooks/commit-msg"
+test_dir=$(mktemp -d "${TMPDIR:-/tmp}/nightshift-commit-msg-test.XXXXXX")
+cleanup() {
+  rm -rf "$test_dir"
+}
+trap cleanup 0
+trap 'exit 1' 1 2 15
+
+tests_run=0
+
+fail() {
+  echo "not ok - $1" >&2
+  exit 1
+}
+
+assert_normalizes() {
+  name=$1
+  input=$2
+  expected=$3
+  message="$test_dir/message"
+  expected_file="$test_dir/expected"
+
+  printf '%b' "$input" > "$message"
+  printf '%b' "$expected" > "$expected_file"
+  "$normalizer" "$message" || fail "$name (normalizer failed)"
+  cmp -s "$expected_file" "$message" || {
+    diff -u "$expected_file" "$message" >&2 || true
+    fail "$name"
+  }
+  tests_run=$((tests_run + 1))
+  echo "ok - $name"
+}
+
+assert_preserved() {
+  name=$1
+  input=$2
+  assert_normalizes "$name" "$input" "$input"
+}
+
+assert_preserved_with_comment_prefix() {
+  name=$1
+  comment_key=$2
+  comment_prefix=$3
+  input=$4
+  message="$test_dir/message"
+  expected_file="$test_dir/expected"
+
+  printf '%b' "$input" > "$message"
+  printf '%b' "$input" > "$expected_file"
+  GIT_CONFIG_COUNT=1 \
+    GIT_CONFIG_KEY_0="core.$comment_key" \
+    GIT_CONFIG_VALUE_0="$comment_prefix" \
+    "$normalizer" "$message" || fail "$name (normalizer failed)"
+  cmp -s "$expected_file" "$message" || {
+    diff -u "$expected_file" "$message" >&2 || true
+    fail "$name"
+  }
+  tests_run=$((tests_run + 1))
+  echo "ok - $name"
+}
+
+assert_rejected() {
+  name=$1
+  input=$2
+  message="$test_dir/message"
+  original="$test_dir/original"
+
+  printf '%b' "$input" > "$message"
+  cp "$message" "$original"
+  if "$normalizer" "$message" >/dev/null 2>&1; then
+    fail "$name (unexpected success)"
+  fi
+  cmp -s "$original" "$message" || fail "$name (message changed)"
+  tests_run=$((tests_run + 1))
+  echo "ok - $name"
+}
+
+assert_normalizes \
+  "already-valid subject" \
+  'feat(cli): add status output
+' \
+  'feat(cli): add status output
+'
+
+assert_normalizes \
+  "capitalization and spacing" \
+  '
+  FEAT  ( cli ) ! :   add   status output\040\040\040
+
+' \
+  'feat(cli)!: add status output
+'
+
+assert_normalizes \
+  "scoped breaking change" \
+  'FIX (config)!:   reject unknown keys
+' \
+  'fix(config)!: reject unknown keys
+'
+
+assert_normalizes \
+  "body paragraphs and trailers" \
+  'DOCS :   explain   provider setup\040\040\040
+
+Keep  repeated  body spacing.\040\040\040
+
+Nightshift-Task: commit-normalize\040\040\040
+Nightshift-Ref: https://github.com/marcus/nightshift
+
+' \
+  'docs: explain provider setup
+
+Keep  repeated  body spacing.
+
+Nightshift-Task: commit-normalize
+Nightshift-Ref: https://github.com/marcus/nightshift
+'
+
+assert_rejected "blank input" '
+\040\040\040
+'
+assert_rejected "unsupported type" 'release: prepare 1.0
+'
+
+assert_preserved "merge message" 'Merge branch '\''main'\'' into feature\040\040\040
+
+Generated merge body.\040\040\040
+'
+assert_preserved "revert message" 'Revert "feat: remove legacy API"
+
+This reverts commit abc123.\040\040\040
+'
+assert_preserved "fixup commit" 'fixup! feat(cli): add status output\040\040\040
+'
+assert_preserved "squash commit" 'squash! fix(config): reject unknown keys\040\040\040
+'
+assert_preserved "generated rebase message" '# This is a combination of 2 commits.
+# This is the 1st commit message:
+
+feat: first message\040\040\040
+'
+assert_preserved_with_comment_prefix \
+  "generated message with configured comment character" \
+  "commentChar" \
+  ";" \
+  '; Please enter the commit message for your changes.\040\040\040
+; Lines starting with '\'';'\'' will be ignored.
+'
+assert_preserved_with_comment_prefix \
+  "generated message with configured comment string" \
+  "commentString" \
+  "//" \
+  '// Please enter the commit message for your changes.\040\040\040
+// Lines starting with '\''//'\'' will be ignored.
+'
+
+message="$test_dir/message"
+printf '%b' ' CHORE :   normalize messages\040
+' > "$message"
+"$hook" "$message" || fail "commit-msg hook"
+printf '%s' 'chore: normalize messages
+' > "$test_dir/expected"
+cmp -s "$test_dir/expected" "$message" || fail "commit-msg hook"
+if "$hook" "$test_dir/missing" >/dev/null 2>&1; then
+  fail "commit-msg hook propagates failures"
+fi
+tests_run=$((tests_run + 2))
+echo "ok - commit-msg hook"
+echo "ok - commit-msg hook propagates failures"
+
+cp "$message" "$test_dir/once"
+"$normalizer" "$message" || fail "idempotence (second run failed)"
+cmp -s "$test_dir/once" "$message" || fail "idempotence"
+tests_run=$((tests_run + 1))
+echo "ok - idempotence"
+
+echo "$tests_run tests passed"