SSH connections, kept by the people who own them

An agent chat will act on a machine you choose, so this is the screen where
you choose it. User-owned like a note, not admin-owned like a connection:
these are somebody's own machines and somebody's own keys, and "anyone in
this group may log in to my server" is a different feature with a different
blast radius. services/sharing.py is deliberately not involved either --
sharing grants reading, and a host somebody else can read is a host they
can log in to.

Trust on first use, made explicit rather than assumed. Adding a host does
not connect to it. Check looks at its key and shows you the fingerprint;
nothing is sent until you accept, because get_server_host_key completes the
key exchange and stops -- no username, no credential. Accepting pins it,
and a host that later presents a different key is refused with the reason
rather than quietly trusted. Moving a profile to another host or port
forgets the pin, since a key belongs to the machine it came from.

Four asyncssh defaults are actively wrong here and all four are passed
explicitly: every LLeMbas user shares one unix account, so `known_hosts`
would be a shared trust store, `client_keys` would authenticate one person
with another's key, `config` would let a ProxyCommand redirect the
connection, and `agent_path` would silently use $SSH_AUTH_SOCK. There is a
test for exactly that, and it needs no server.

Files go over SFTP rather than through a shell. The SSH exec protocol
carries one command *string* that the far side parses, with no argv form at
all, so a model-supplied path in a command line is unavoidably a quoting
problem. Over SFTP a path is a path.

Chat gains its kind, connection, project directory and mode; the first
three are fixed once a chat has a message, because a transcript whose
earlier turns ran somewhere else is not one conversation.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/lembas/web/templates/agents/index.html

@@ -0,0 +1,94 @@
+{% extends "agents/_layout.html" %}
+{% from "_macros.html" import icon %}
+
+{% block title %}Connections - LLeMbas{% endblock %}
+{% block heading %}Connections{% endblock %}
+{% block actions %}
+<a class="btn btn--primary btn--sm" href="/agents/new">
+  {{ icon("plus", "icon--sm") }} Add a connection
+</a>
+{% endblock %}
+
+{% block agents_content %}
+<p class="admin-lede">
+  Machines an <strong>Agent</strong> chat can work on. A model with one of these
+  can read files, write files and run commands <em>there</em> — never here.
+  Which of those it may do without asking you first is the chat's mode.
+</p>
+
+<div class="alert">
+  {{ icon("shield", "icon--sm") }}
+  <span>
+    Whatever this connection can reach, a model in an agent chat can reach. A
+    container built for the job, with one project mounted into it, is a very
+    different thing from a key to a machine you care about — and LLeMbas cannot
+    tell them apart.
+  </span>
+</div>
+
+{% if problem %}
+<div class="alert alert--error">
+  {{ icon("warning", "icon--sm") }} <span>{{ problem }}</span>
+</div>
+{% elif not enabled %}
+<div class="alert alert--error">
+  {{ icon("warning", "icon--sm") }}
+  <span>
+    Agent chats are switched off for this instance. You can still add
+    connections here, but nothing will use them until an administrator turns
+    them on.
+  </span>
+</div>
+{% endif %}
+
+{% if saved %}
+<div class="alert alert--success">{{ icon("check", "icon--sm") }} <span>{{ saved }}</span></div>
+{% endif %}
+
+{% if not profiles %}
+<div class="empty">
+  {{ icon("server", "empty__mark") }}
+  <h2 class="empty__title">No connections yet</h2>
+  <p class="empty__text">
+    Add the host, the user to log in as, and a key or password. Then press
+    <strong>Check</strong> — you will be shown its fingerprint to confirm before
+    anything is sent to it.
+  </p>
+  <a class="btn btn--primary" href="/agents/new">
+    {{ icon("plus", "icon--sm") }} Add a connection
+  </a>
+</div>
+{% else %}
+
+<div class="model-rows">
+  {% for profile in profiles %}
+  <div class="model-row {{ 'is-off' if not profile.enabled }}">
+    <div class="model-row__main">
+      <div class="model-row__title">
+        <a class="model-row__name" href="/agents/{{ profile.id }}">{{ profile.name }}</a>
+        {% if profile.verified %}
+        <span class="badge badge--leaf">key confirmed</span>
+        {% else %}
+        <span class="badge badge--danger">not checked</span>
+        {% endif %}
+        {% if not profile.enabled %}<span class="badge">disabled</span>{% endif %}
+        {% if profile.auth == "password" %}<span class="badge">password</span>{% endif %}
+      </div>
+      <code class="model-row__id">
+        {{ profile.address }}{% if profile.default_dir %} · {{ profile.default_dir }}{% endif %}
+      </code>
+      {% if profile.last_error %}
+      <p class="text-xs danger">{{ profile.last_error }}</p>
+      {% elif profile.server_info.system %}
+      <p class="text-xs faint">{{ profile.server_info.system }}</p>
+      {% endif %}
+    </div>
+
+    <div class="model-row__actions">
+      <a class="btn btn--sm" href="/agents/{{ profile.id }}">Open</a>
+    </div>
+  </div>
+  {% endfor %}
+</div>
+{% endif %}
+{% endblock %}