fix(hooks): close the five escapes the skills#52 review found

- Fail-closed path no longer needs jq: the ask JSON is a printf literal,
  and a host without jq asks instead of staying silent.
- A tool_name that is not a non-empty string asks (was: no opinion).
- Gate workflow_run_trigger, tag_create, release_create, and
  file_write_branch when it lands on main/master, has no branch, or
  empties a file (same effect as pr_merge / file_delete).
- Header claim narrowed: gitea-mcp spellings on any server name, not
  other servers' spellings of the same operation.
- Tests run the hook as hooks.json does (bash <path>), assert exit 0 on
  every case, and cover null/missing/wrong-type tool_name, last-segment
  verb parsing and a PATH without jq. 13 new cases were red first.

Refs mathias/infra#508

Bump-Type: minor

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

hooks/mcp-destructive-guard.sh

@@ -6,41 +6,67 @@
 # so an agent holds the full scope of the caller's PAT. repo_delete's own guard
 # (confirm == repo) is filled in by the model on both sides: it stops typos,
 # not an injected or mistaken agent. The infra-mcp README claimed client-side
-# deny lists covered this; on 2026-10-01 none existed on any settings file.
+# deny lists covered this; on 2026-10-01 none existed in any settings file.
 #
-# Policy: match the VERB, not the server. The same tool is reachable as
-# mcp__plugin_skills_gitea__*, mcp__claude_ai_gitea__* (connector) or under
-# any name a host registers it with, so keying on the server name would let a
-# rename bypass the gate.
+# Policy: match gitea-mcp's verb spellings on ANY server name. The same tool is
+# reachable as mcp__plugin_skills_gitea__*, mcp__claude_ai_gitea__* or under
+# whatever name a host registers it with, so keying on the server name would
+# let a rename bypass the gate. It does NOT recognise other servers' spellings
+# of the same operation (e.g. a third-party `delete_repo`).
 #
-# Emits "ask" or nothing. Never "allow": a hook allow would override the
-# user's own deny/ask rules. Malformed input fails closed (ask).
+# file_write_branch is gated when it would land on main/master (on infra that
+# is a Flux deploy within ~60s — the same effect as pr_merge) or empty a file
+# (the same effect as file_delete). Writes to other branches pass.
 #
-# Scope limit, recorded in the ADR: this gates MCP calls only. A session with
-# the PAT in its environment can still reach the Gitea REST API via Bash.
+# Emits "ask" or nothing; never "allow" (a hook allow would override the
+# user's own deny/ask rules). Always exits 0: Claude Code ignores a hook's
+# JSON on a non-zero exit. Anything it cannot parse — including a host
+# without jq — fails closed to "ask". The ask JSON is a literal, so the
+# fail-closed path needs no tool that might be missing.
+#
+# Scope limit, recorded in infra ADR-0027: this gates MCP calls only. A
+# session with the PAT in its environment can still reach the Gitea REST API
+# through a shell.
 
-set -uo pipefail
+set -u
 
-DESTRUCTIVE='repo_delete|file_delete|branch_delete|pr_merge|tbd_ship|repo_update|repo_mirror_push'
+DESTRUCTIVE='repo_delete|file_delete|branch_delete|pr_merge|tbd_ship|repo_update|repo_mirror_push|workflow_run_trigger|tag_create|release_create'
 
 ask() {
-  jq -n --arg reason "$1" \
-    '{hookSpecificOutput: {hookEventName: "PreToolUse", permissionDecision: "ask", permissionDecisionReason: $reason}}'
+  # $1 must contain only [A-Za-z0-9 _.:()'/-] — it is spliced into JSON verbatim.
+  printf '{"hookSpecificOutput":{"hookEventName":"PreToolUse","permissionDecision":"ask","permissionDecisionReason":"%s"}}\n' "$1"
   exit 0
 }
 
 INPUT="$(cat)"
-if ! TOOL_NAME="$(printf '%s' "$INPUT" | jq -er '.tool_name' 2>/dev/null)"; then
-  ask "mcp-destructive-guard: could not parse the tool call, so it cannot be shown safe. Approve only if you expected it."
+
+command -v jq >/dev/null 2>&1 \
+  || ask "mcp-destructive-guard: jq is not installed, so this MCP call cannot be checked. Approve only if you expected it."
+
+if ! TOOL_NAME="$(printf '%s' "$INPUT" | jq -er '.tool_name | strings | select(length > 0)' 2>/dev/null)"; then
+  ask "mcp-destructive-guard: could not read a tool name from this call, so it cannot be shown safe. Approve only if you expected it."
 fi
 
-verb="${TOOL_NAME##*__}"
 case "$TOOL_NAME" in
   mcp__*__*) ;;
   *) exit 0 ;;
 esac
 
+verb="${TOOL_NAME##*__}"
+safe_verb="$(printf '%s' "$verb" | tr -cd 'A-Za-z0-9_-')"
+
 if printf '%s' "$verb" | grep -Eqix "($DESTRUCTIVE)"; then
-  ask "Irreversible MCP verb '$verb' (infra ADR-0027): needs your approval. The model filled in every argument, including any confirm field."
+  ask "Irreversible MCP verb '$safe_verb' (infra ADR-0027): needs your approval. The model filled in every argument, including any confirm field."
+fi
+
+if printf '%s' "$verb" | grep -Eqix 'file_write_branch'; then
+  verdict="$(printf '%s' "$INPUT" | jq -r '
+      .tool_input as $i
+      | if ($i | type) != "object" then "ask"
+        elif (($i.branch // "") | ascii_downcase) as $b | ($b == "" or $b == "main" or $b == "master") then "ask"
+        elif (($i.content // "") == "") then "ask"
+        else "pass" end' 2>/dev/null || echo ask)"
+  [ "$verdict" = "pass" ] \
+    || ask "file_write_branch to main/master, with no branch, or emptying a file (infra ADR-0027): needs your approval."
 fi
 exit 0