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/detail.html

@@ -0,0 +1,183 @@
+{% extends "agents/_layout.html" %}
+{% from "_macros.html" import icon %}
+
+{% block title %}{{ "New connection" if is_new else profile.name }} - LLeMbas{% endblock %}
+{% block heading %}{{ "New connection" if is_new else profile.name }}{% endblock %}
+
+{% block agents_content %}
+<nav class="crumbs">
+  <a class="crumbs__back" href="/agents">
+    {{ icon("chevron-right", "icon--sm crumbs__icon") }} All connections
+  </a>
+</nav>
+
+{% if error %}
+<div class="alert alert--error">{{ icon("warning", "icon--sm") }} <span>{{ error }}</span></div>
+{% endif %}
+{% if problem %}
+<div class="alert alert--error">{{ icon("warning", "icon--sm") }} <span>{{ problem }}</span></div>
+{% endif %}
+{% if saved %}
+<div class="alert alert--success">{{ icon("check", "icon--sm") }} <span>{{ saved }}</span></div>
+{% endif %}
+
+{% if not is_new %}
+<section class="card">
+  <h2 class="card__title">Check it</h2>
+  <p class="field__hint">
+    {% if profile.verified %}
+      Confirms the host is still the one you accepted, then logs in and runs
+      something harmless to see that it works.
+    {% else %}
+      Looks at this host's key and shows you its fingerprint. Nothing is sent to
+      it — not your username, not your credential — until you accept.
+    {% endif %}
+  </p>
+
+  <div class="btn-row">
+    <button class="btn" type="button"
+            hx-post="/api/agents/{{ profile.id }}/check"
+            hx-target="#check-result">
+      {{ icon("refresh", "icon--sm") }} Check
+    </button>
+  </div>
+
+  <div id="check-result">
+    {% if profile.verified %}
+    <p class="field__hint">
+      Accepted fingerprint: <code>{{ profile.host_fingerprint }}</code>
+    </p>
+    {% endif %}
+  </div>
+</section>
+{% endif %}
+
+<form method="post" class="form-grid"
+      action="{{ '/api/agents' if is_new else '/api/agents/' ~ profile.id }}">
+
+  <section class="card">
+    <h2 class="card__title">The machine</h2>
+
+    <div class="field">
+      <label class="field__label" for="name">Name</label>
+      <input class="input" id="name" name="name" value="{{ profile.name }}" required
+             maxlength="120" placeholder="Project container">
+      <p class="field__hint">What you will pick from when starting an agent chat.</p>
+    </div>
+
+    <div class="field">
+      <label class="field__label" for="host">Host</label>
+      <input class="input input--mono" id="host" name="host" value="{{ profile.host }}" required
+             maxlength="255" placeholder="127.0.0.1">
+    </div>
+
+    <div class="field">
+      <label class="field__label" for="port">Port</label>
+      <input class="input" id="port" name="port" value="{{ profile.port }}" inputmode="numeric">
+    </div>
+
+    <div class="field">
+      <label class="field__label" for="username">Log in as</label>
+      <input class="input input--mono" id="username" name="username" required
+             value="{{ profile.username }}" maxlength="120" placeholder="root">
+    </div>
+
+    <div class="field">
+      <label class="field__label" for="default_dir">Project directory</label>
+      <input class="input input--mono" id="default_dir" name="default_dir"
+             value="{{ profile.default_dir }}" maxlength="500" placeholder="/project">
+      <p class="field__hint">
+        Where a chat starts by default. Each chat records its own when it is
+        created, so changing this later does not move a conversation already
+        under way.
+      </p>
+    </div>
+
+    <div class="field">
+      <label class="field__label" for="connect_timeout">Connect timeout (seconds)</label>
+      <input class="input" id="connect_timeout" name="connect_timeout"
+             value="{{ profile.connect_timeout }}" inputmode="numeric">
+    </div>
+  </section>
+
+  <section class="card">
+    <h2 class="card__title">How it logs in</h2>
+
+    <div class="field">
+      <div class="checkbox-row">
+        <label class="checkbox">
+          <input type="radio" name="auth" value="key"
+                 {{ 'checked' if profile.auth != 'password' }}>
+          <span>A private key</span>
+        </label>
+        <label class="checkbox">
+          <input type="radio" name="auth" value="password"
+                 {{ 'checked' if profile.auth == 'password' }}>
+          <span>A password</span>
+        </label>
+      </div>
+    </div>
+
+    <div class="field">
+      <label class="field__label" for="private_key">Private key</label>
+      <textarea class="textarea input--mono" id="private_key" name="private_key" rows="5"
+                spellcheck="false"
+                placeholder="-----BEGIN OPENSSH PRIVATE KEY-----"
+                >{{ unchanged if has_key else '' }}</textarea>
+      <p class="field__hint">
+        {% if has_key %}
+          A key is saved. Leave the dots alone to keep it, or clear the box to
+          remove it.
+        {% else %}
+          Pasted whole, encrypted at rest, and never shown again.
+        {% endif %}
+      </p>
+    </div>
+
+    <div class="field">
+      <label class="field__label" for="key_passphrase">Key passphrase</label>
+      <input class="input input--mono" id="key_passphrase" name="key_passphrase"
+             type="password" autocomplete="off" placeholder="If the key has one">
+    </div>
+
+    <div class="field">
+      <label class="field__label" for="password">Password</label>
+      <input class="input input--mono" id="password" name="password" type="password"
+             autocomplete="off" placeholder="No password set"
+             value="{{ unchanged if profile.password_encrypted else '' }}">
+      <p class="field__hint">
+        {% if profile.password_encrypted %}
+          Currently <code>{{ masked_password }}</code>. Leave the dots alone to
+          keep it, or clear the field to remove it.
+        {% else %}
+          Only used when this connection logs in with a password.
+        {% endif %}
+      </p>
+    </div>
+  </section>
+
+  <section class="card">
+    <h2 class="card__title">Availability</h2>
+    <div class="field">
+      <label class="checkbox">
+        <input type="checkbox" name="enabled" value="true" {{ 'checked' if profile.enabled }}>
+        <span>Enabled — can be picked when starting an agent chat</span>
+      </label>
+    </div>
+  </section>
+
+  <div class="btn-row">
+    <button class="btn btn--primary" type="submit">
+      {{ "Add connection" if is_new else "Save changes" }}
+    </button>
+    <a class="btn btn--ghost" href="/agents">Back to all connections</a>
+    {% if not is_new %}
+    <button class="btn btn--danger" type="submit" formnovalidate
+            formaction="/api/agents/{{ profile.id }}/delete"
+            data-confirm-button="Delete the connection “{{ profile.name }}”? Chats that used it keep their transcripts.">
+      Delete
+    </button>
+    {% endif %}
+  </div>
+</form>
+{% endblock %}