test(forge): hermetic cases for the two forgejo edit asymmetries

The coverage owed with the call-site port (@grok-reviewer-andresmgsl #4741
note 2, #4751 item 2). Live scratch-repo evidence proved these work; these
pin the request SHAPE so they keep working.

  - a removal resolves name -> numeric id, and never sends the name as the
    path segment (measured: DELETE .../labels/probe:one -> 422,
    DELETE .../labels/149 -> 204);
  - a removal of a label the repo does not have writes nothing, matching gh:
    the reconcilers call --remove-label unconditionally to converge state;
  - adds take names directly, one request, comma-separated values split as
    gh splits them;
  - an assignee removal PATCHes the SURVIVING list, because Forgejo sets
    assignees rather than adding and removing them — a naive translation
    would have cleared every other assignee as a side effect of removing
    one, which is what the mutation test proves is caught.

Payloads are now compact JSON. They were pretty-printed, which spread a
single write across several lines — harder to read in a log, and it hid the
shape from any assertion matching a line.

Refs #188

lib/forge-forgejo.sh

@@ -276,7 +276,7 @@ forge_issue_edit() {
 
   if [ "${#add_labels[@]}" -gt 0 ]; then
     local payload
-    payload="$(printf '%s\n' "${add_labels[@]}" | jq -R . | jq -s '{labels: .}')"
+    payload="$(printf '%s\n' "${add_labels[@]}" | jq -R . | jq -sc '{labels: .}')"
     forgejo_write POST "repos/$REPO/issues/$n/labels" "$payload" >/dev/null || return 1
   fi
 
@@ -305,14 +305,14 @@ forge_issue_edit() {
     if [ "${#rm_assignees[@]}" -gt 0 ]; then
       want="$(grep -vxF -f <(printf '%s\n' "${rm_assignees[@]}") <<<"$want" || true)"
     fi
-    payload="$(printf '%s' "$want" | jq -R . | jq -s '{assignees: [.[] | select(. != "")]}')"
+    payload="$(printf '%s' "$want" | jq -R . | jq -sc '{assignees: [.[] | select(. != "")]}')"
     forgejo_write PATCH "repos/$REPO/issues/$n" "$payload" >/dev/null || return 1
   fi
 }
 
 forge_issue_comment() {
   local n="${1:?forge_issue_comment: number required}" body="${2?forge_issue_comment: body required}"
-  forgejo_write POST "repos/$REPO/issues/$n/comments" "$(jq -n --arg b "$body" '{body: $b}')" >/dev/null
+  forgejo_write POST "repos/$REPO/issues/$n/comments" "$(jq -nc --arg b "$body" '{body: $b}')" >/dev/null
 }
 
 forge_pr_list() {
@@ -359,7 +359,7 @@ forge_label_list() { forge_api --paginate "repos/$REPO/labels" --jq '.[].name';
 # existing name aborts the bootstrap under set -e.
 forge_label_create() {
   local name="${1:?}" color="${2:?}" desc="${3:-}" ids id payload
-  payload="$(jq -n --arg n "$name" --arg c "$color" --arg d "$desc" '{name:$n,color:$c,description:$d}')"
+  payload="$(jq -nc --arg n "$name" --arg c "$color" --arg d "$desc" '{name:$n,color:$c,description:$d}')"
   ids="$(forgejo_label_ids)" || return 1
   id="$(awk -F '\t' -v want="$name" '$1 == want { print $2; exit }' <<<"$ids")"
   if [ -n "$id" ]; then
@@ -417,7 +417,7 @@ forge_labels_add() {
   shift
   [ "$#" -gt 0 ] || return 0
   forgejo_write POST "repos/$REPO/issues/$n/labels" \
-    "$(printf '%s\n' "$@" | jq -R . | jq -s '{labels: .}')" >/dev/null
+    "$(printf '%s\n' "$@" | jq -R . | jq -sc '{labels: .}')" >/dev/null
 }
 
 # forge_request_reviewer <n> <user> — ask <user> for a verdict.
@@ -436,5 +436,5 @@ forge_labels_add() {
 forge_request_reviewer() {
   local n="${1:?}" user="${2:?}"
   forgejo_write POST "repos/$REPO/pulls/$n/requested_reviewers" \
-    "$(jq -n --arg u "$user" '{reviewers: [$u]}')" >/dev/null
+    "$(jq -nc --arg u "$user" '{reviewers: [$u]}')" >/dev/null
 }

test/forge-backends.test.sh

@@ -274,6 +274,62 @@ check "recreating an existing label PATCHes it" 0 "" \
 check "...and does not POST a duplicate" 1 "" grep -q '^POST repos/o/r/labels ' "$WRITES"
 check "...carrying the updated description" 0 "" grep -q 'new text' "$WRITES"
 
+# --- forge_issue_edit on forgejo: the two asymmetries, hermetically ------
+# Promised with the call-site port (@grok-reviewer-andresmgsl #4741 note 2,
+# #4751 item 2). Live scratch-repo evidence proved these work; these prove
+# they keep working, and pin the SHAPE of the requests.
+
+# Removal resolves name -> id, because Forgejo takes names on add and only a
+# numeric id on remove. Measured: DELETE .../labels/probe:one -> 422,
+# DELETE .../labels/149 -> 204.
+FAKE_LABELS='[{"name":"stale","id":11},{"name":"ready","id":12}]' FAKE_LABEL_N=2 stub_writes
+FAKE_LABELS='[{"name":"stale","id":11},{"name":"ready","id":12}]' FAKE_LABEL_N=2   REPO=o/r forge_issue_edit 5 --remove-label stale
+check "removing a label resolves its numeric id" 0 ""   grep -q '^DELETE repos/o/r/issues/5/labels/11 ' "$WRITES"
+check "...and never sends the name as the path segment" 1 ""   grep -q 'labels/stale' "$WRITES"
+
+# A label the repo does not have is a no-op, matching gh: the reconcilers
+# call --remove-label unconditionally to converge state.
+FAKE_LABELS='[{"name":"ready","id":12}]' FAKE_LABEL_N=1 stub_writes
+FAKE_LABELS='[{"name":"ready","id":12}]' FAKE_LABEL_N=1   REPO=o/r forge_issue_edit 5 --remove-label nonexistent
+check "removing an absent label writes nothing" 0 "" test ! -s "$WRITES"
+
+# Adding takes names directly — no lookup, one request.
+FAKE_LABELS='[]' FAKE_LABEL_N=0 stub_writes
+FAKE_LABELS='[]' FAKE_LABEL_N=0 REPO=o/r forge_issue_edit 5 --add-label "ready,stale"
+check "adding labels posts them by name" 0 ""   grep -q '^POST repos/o/r/issues/5/labels .*"ready"' "$WRITES"
+check "...comma-separated values are split, as gh splits them" 0 ""   grep -q '"stale"' "$WRITES"
+
+# Assignees are SET, not added/removed: PATCH takes the whole list. So a
+# removal is a read-modify-write, and a naive translation would have cleared
+# every OTHER assignee as a side effect of removing one.
+assignee_stub() {
+  : >"$WRITES"
+  # shellcheck disable=SC2317 # invoked indirectly, by forge_issue_edit
+  curl() {
+    local hdr="" out="" method=GET url="" payload=""
+    while [ $# -gt 0 ]; do
+      case "$1" in
+        -D) hdr="$2"; shift ;; -o) out="$2"; shift ;;
+        -X) method="$2"; shift ;; -d) payload="$2"; shift ;;
+        -H) shift ;; -*) ;; *) url="$1" ;;
+      esac
+      shift
+    done
+    printf 'HTTP/1.1 200 OK\r\nX-Total-Count: 0\r\n\r\n' >"$hdr"
+    printf '{"assignees":[{"login":"alice"},{"login":"bob"}]}' >"$out"
+    [ "$method" = GET ] || printf '%s %s %s\n' "$method" "${url##*/api/v1/}" "$payload" >>"$WRITES"
+    return 0
+  }
+}
+assignee_stub
+REPO=o/r forge_issue_edit 5 --remove-assignee alice
+check "removing one assignee PATCHes the surviving list" 0 ""   grep -q '^PATCH repos/o/r/issues/5 .*"bob"' "$WRITES"
+check "...and the removed one is gone from it" 1 "" grep -q '"alice"' "$WRITES"
+
+assignee_stub
+REPO=o/r forge_issue_edit 5 --add-assignee carol
+check "adding an assignee keeps the existing ones" 0 ""   grep -qE '^PATCH repos/o/r/issues/5 .*"alice".*"bob".*"carol"|^PATCH repos/o/r/issues/5 .*"alice".*"carol".*"bob"' "$WRITES"
+
 # --- forge_pr_view: newest verdict per context must win ------------------
 # checks_state groups repeated contexts and selects the newest by
 # [.startedAt, .createdAt, .completedAt]. Mapping only {context,state} left