Single-session HTML exports of an un-named session render
`<title>None</title>` and `Model: None`. An untitled session (title
`None`) is the default state until async title generation completes, so
this is the common case, not an edge case.
The browser-tab `<title>` (page_title) and the `Model:` meta line use
`dict.get(key, default)`, whose default only fires when the key is
absent — not when it is present with value `None`. `_escape_html(None)`
then stringifies to the literal "None". The on-page `<h1>` in the same
function already uses the None-safe `... or "Hermes Session"` idiom, so
the tab title and header were inconsistent for the same session.
Use `... or "<default>"` at both sites so the tab title and model meta
fall back consistently with the header.
The HTML session export interpolated the tool-call name into the page
without escaping, while every sibling field went through _escape_html. A
tool-call name is attacker-influenced, so a prompt-injected model can emit
a name containing HTML that executes when the export is opened in a browser.
Escape the tool-call name like the other fields.
