* fix(skills): escape untrusted skill metadata before it enters the model prompt
Skill name/description/allowed-tools come from the frontmatter of a
user-installable .skill archive (POST /api/skills/install or a drop into
skills/custom/); the parser only strips them. The slash-activation and
durable-context siblings already html.escape these exact fields before
rendering them into a model-visible block -- but five other render sites emit
them raw. The sharpest is the default path, <available_skills> in the system
prompt (skills.deferred_discovery: false): a community skill whose description
closes the block can forge a framework-trusted <system-reminder> into the
lead-agent system prompt. Driven through the real apply_prompt_template(), the
forged tag reaches the system prompt raw on main and is neutralized here.
Escape at every render site that emits untrusted skill metadata/content:
- <available_skills> (name/description/location) and <disabled_skills> (name)
in lead_agent/prompt.py;
- describe_skill output (name/description/allowed-tools/location) and
<skill_index> (name) in skills/describe.py;
- the subagent <skill name=...> attribute plus the raw SKILL.md body in
subagents/executor.py::_load_skill_messages -- its direct sibling
skill_activation escapes both, this escaped neither.
quote=False in element-text positions (matching skill_context and the #4097
correction), quote=True in the one attribute position (matching
skill_activation). category is a controlled enum and is left as-is; escaping is
render-time only, so stored skills are unchanged and re-rendering never
double-escapes.
* fix(skills): escape skill name in the slash-activation prose line
The slash-activation reminder emitted `activation.skill_name` raw in its
prose line while escaping the same value in the adjacent
<skill name="..."> attribute. skill_name is grammar-gated to [a-z0-9-] by
resolve_slash_skill before it reaches the renderer, so this is a
defense-in-depth / consistency fix rather than a reachable injection: the
two positions can never drift if a future caller builds an activation from
an unconstrained name. Reuse the already-computed escaped_skill_name.
