hooks: branch guard, 300-line cap, task ref, auto PR (V-445)

Four git hooks, tracked in .githooks and wired with core.hooksPath so a
fresh clone gets them with one config line.

pre-commit refuses master and refuses more than 300 changed lines in
non-markdown files. Markdown is exempt because docs land as one batch.
commit-msg requires (V-<id>), not (#<id>), because Gitea autolinks # to
its own issues and that is the wrong tracker. post-checkout records the
parent branch, since git does not track where a branch was cut from and
the PR needs the base. pre-push opens the PR with tea and never blocks.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.githooks/commit-msg

@@ -0,0 +1,30 @@
+#!/bin/sh
+# Every commit names the Vikunja task it belongs to.
+#
+#   router: narrow the single-token rule (V-359)
+#
+# V- and not #, because Gitea autolinks #359 to a Gitea issue, which is a
+# different tracker and a wrong link.
+#
+# Exempt: merges, reverts, fixup/squash, and the initial commit.
+
+msg_file=$1
+subject=$(sed -n '1p' "$msg_file")
+
+case "$subject" in
+	Merge\ *|Revert\ *|fixup!\ *|squash!\ *|amend!\ *) exit 0 ;;
+esac
+
+if [ -f "$(git rev-parse --git-dir)/MERGE_HEAD" ]; then
+	exit 0
+fi
+
+if printf '%s' "$subject" | grep -qE '\(V-[0-9]+\)$'; then
+	exit 0
+fi
+
+echo "commit-msg: subject must end with a Vikunja task ref." >&2
+echo "  got:  $subject" >&2
+echo "  want: router: narrow the single-token rule (V-359)" >&2
+echo "  No task yet? Create one. Work without a task is work nobody can resume." >&2
+exit 1

.githooks/post-checkout

@@ -0,0 +1,34 @@
+#!/bin/sh
+# Git does not remember which branch a branch was cut from, and the PR needs it.
+# Record it once, at creation, best effort.
+#
+# Args: <prev-head> <new-head> <branch-flag>. branch-flag is 1 for a branch
+# switch, 0 for a file checkout.
+
+prev=$1
+flag=$3
+
+[ "$flag" = "1" ] || exit 0
+
+branch=$(git symbolic-ref --short HEAD 2>/dev/null) || exit 0
+[ -n "$branch" ] || exit 0
+
+dir="$(git rev-parse --git-dir)/maven-parent"
+key=$(printf '%s' "$branch" | tr '/' '_')
+
+# Already recorded, or we are on a long-lived branch. Leave it alone.
+[ -f "$dir/$key" ] && exit 0
+case "$branch" in master|main) exit 0 ;; esac
+
+# name-rev resolves the sha we came from back to a branch name. It picks the
+# closest ref, which is right often enough to beat guessing master.
+parent=$(git name-rev --name-only --refs='refs/heads/*' "$prev" 2>/dev/null |
+	sed 's/[~^].*//')
+
+case "$parent" in
+	""|undefined|"$branch") parent=master ;;
+esac
+
+mkdir -p "$dir"
+printf '%s\n' "$parent" > "$dir/$key"
+exit 0

.githooks/pre-commit

@@ -0,0 +1,30 @@
+#!/bin/sh
+# Two guards, both bypassable with --no-verify when you mean it.
+#   1. master is not a working branch.
+#   2. a code commit stays under 300 changed lines.
+# Markdown is exempt from the size cap on purpose: docs land as one batch.
+
+branch=$(git symbolic-ref --short HEAD 2>/dev/null)
+
+case "$branch" in
+	master|main)
+		echo "pre-commit: refusing to commit on $branch." >&2
+		echo "  scripts/task-branch.sh <vikunja-id> <slug>   # branch, and record the parent" >&2
+		exit 1
+		;;
+esac
+
+# Added + deleted lines across staged files that are not markdown.
+# numstat prints "-\t-\t<path>" for binaries; those count 0 and that is fine,
+# a binary blob is not the kind of diff this cap exists to stop.
+loc=$(git diff --cached --numstat -- . ':(exclude)*.md' |
+	awk '$1 ~ /^[0-9]+$/ { a += $1 } $2 ~ /^[0-9]+$/ { d += $2 } END { print a + d + 0 }')
+
+if [ "$loc" -gt 300 ]; then
+	echo "pre-commit: $loc changed lines in non-markdown files, cap is 300." >&2
+	echo "  Split it. Each commit should be one reviewable idea." >&2
+	echo "  git reset <path> to unstage, or --no-verify if this genuinely cannot split." >&2
+	exit 1
+fi
+
+exit 0

.githooks/pre-push

@@ -0,0 +1,33 @@
+#!/bin/sh
+# Open the PR on first push of a task branch, against the branch it was cut
+# from. A commit is too early for this. A push means the work is shareable.
+#
+# Never fatal: a missing tea login or an unreachable Gitea must not block a
+# push. It prints the command instead.
+
+branch=$(git symbolic-ref --short HEAD 2>/dev/null) || exit 0
+case "$branch" in ""|master|main) exit 0 ;; esac
+
+command -v tea >/dev/null 2>&1 || exit 0
+
+dir="$(git rev-parse --git-dir)/maven-parent"
+key=$(printf '%s' "$branch" | tr '/' '_')
+parent=$(cat "$dir/$key" 2>/dev/null)
+[ -n "$parent" ] || parent=master
+
+if tea pr list --output simple 2>/dev/null | grep -q "[[:space:]]$branch\$"; then
+	exit 0
+fi
+
+title=$(git log -1 --format=%s)
+body=$(git log "$parent..$branch" --format='- %s' 2>/dev/null)
+
+if tea pr create --head "$branch" --base "$parent" \
+	--title "$title" --description "$body" >/dev/null 2>&1; then
+	echo "pre-push: opened PR $branch -> $parent"
+else
+	echo "pre-push: could not open the PR. Run it yourself:" >&2
+	echo "  tea pr create --head $branch --base $parent --title \"$title\"" >&2
+fi
+
+exit 0

scripts/task-branch.sh

@@ -0,0 +1,29 @@
+#!/bin/sh
+# Cut a task branch and record the branch it came from, so pre-push can open
+# the PR against the right base.
+#
+#   scripts/task-branch.sh 359 narrow-single-token
+#   -> task/359-narrow-single-token, parent recorded as the current branch
+
+set -eu
+
+if [ $# -lt 2 ]; then
+	echo "usage: $0 <vikunja-id> <slug>" >&2
+	exit 2
+fi
+
+id=$1
+shift
+slug=$(printf '%s' "$*" | tr '[:upper:] ' '[:lower:]-' | tr -cd 'a-z0-9-')
+
+parent=$(git symbolic-ref --short HEAD)
+branch="task/$id-$slug"
+
+git checkout -b "$branch"
+
+dir="$(git rev-parse --git-dir)/maven-parent"
+mkdir -p "$dir"
+printf '%s\n' "$parent" > "$dir/$(printf '%s' "$branch" | tr '/' '_')"
+
+echo "$branch, cut from $parent"
+echo "Commits on it must end with (V-$id)."