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/db/models/agent.py

@@ -0,0 +1,103 @@
+"""SSH connections an agent chat can act through.
+
+User-owned, like a `Note` and unlike a `Connection`. That is the opposite of
+the rule custom tools and MCP servers follow, and the difference is the point:
+those are instance configuration an administrator could grant themselves in one
+click anyway, while this is somebody's own machine and somebody's own key.
+"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.
+
+**Nothing an agent does runs on the LLeMbas machine.** A local sandbox was
+designed and dropped: every hard problem in it came from executing on the host
+that holds the database and the encryption key. Over SSH, isolation is whatever
+host somebody points this at -- which means the security of an agent chat is the
+security of that host, and nothing here can tell a throwaway container from a
+production server. The admin copy says so out loud.
+"""
+
+from __future__ import annotations
+
+from datetime import datetime
+from typing import TYPE_CHECKING, Any
+
+from sqlalchemy import Boolean, DateTime, ForeignKey, Integer, String, Text, UniqueConstraint
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from lembas.db.base import Base, Timestamps, UUIDPrimaryKey
+from lembas.db.types import JSONDict
+
+if TYPE_CHECKING:  # pragma: no cover - annotation only
+    from lembas.db.models.user import User
+
+# How the connection authenticates.
+AUTH_KEY = "key"
+AUTH_PASSWORD = "password"
+AUTH_METHODS = (AUTH_KEY, AUTH_PASSWORD)
+
+
+class SshProfile(UUIDPrimaryKey, Timestamps, Base):
+    """One host somebody can point an agent chat at."""
+
+    __tablename__ = "ssh_profiles"
+    __table_args__ = (UniqueConstraint("owner_id", "name", name="uq_ssh_profile_name"),)
+
+    owner_id: Mapped[str] = mapped_column(
+        String(32), ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    name: Mapped[str] = mapped_column(String(120), nullable=False)
+
+    host: Mapped[str] = mapped_column(String(255), nullable=False)
+    port: Mapped[int] = mapped_column(Integer, default=22, nullable=False)
+    username: Mapped[str] = mapped_column(String(120), nullable=False)
+
+    auth: Mapped[str] = mapped_column(String(16), default=AUTH_KEY, nullable=False)
+    password_encrypted: Mapped[str] = mapped_column(Text, default="")
+    private_key_encrypted: Mapped[str] = mapped_column(Text, default="")
+    key_passphrase_encrypted: Mapped[str] = mapped_column(Text, default="")
+
+    # One OpenSSH known_hosts line, captured the first time this host answered
+    # and shown as a fingerprint to be confirmed, then pinned. Empty means
+    # "never seen". Handed to asyncssh as `known_hosts=<these bytes>` and never
+    # as None, which turns host key checking off altogether.
+    host_key: Mapped[str] = mapped_column(Text, default="")
+    # The SHA256 fingerprint of the above, so the profile page can show what was
+    # accepted without parsing the line again on every render.
+    host_fingerprint: Mapped[str] = mapped_column(String(120), default="")
+
+    # Where a chat starts by default. A chat records its own, chosen when it is
+    # created and fixed thereafter; this is only the suggestion in the picker.
+    default_dir: Mapped[str] = mapped_column(String(500), default="")
+
+    connect_timeout: Mapped[int] = mapped_column(Integer, default=15, nullable=False)
+    enabled: Mapped[bool] = mapped_column(Boolean, default=True, nullable=False)
+
+    # What the last connection attempt found, for the list. `server_banner` is
+    # whatever the host said about itself -- useful for telling two containers
+    # apart.
+    last_checked_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True))
+    last_error: Mapped[str] = mapped_column(Text, default="")
+    server_info: Mapped[dict[str, Any]] = mapped_column(JSONDict, default=dict)
+
+    owner: Mapped[User] = relationship()
+
+    @property
+    def label(self) -> str:
+        return self.name or f"{self.username}@{self.host}"
+
+    @property
+    def address(self) -> str:
+        return f"{self.username}@{self.host}" + (f":{self.port}" if self.port != 22 else "")
+
+    @property
+    def verified(self) -> bool:
+        """Whether this host's key has been seen and pinned."""
+        return bool(self.host_key)
+
+    def __repr__(self) -> str:
+        return f"<SshProfile {self.name} {self.address}>"
+
+
+__all__ = ["AUTH_KEY", "AUTH_METHODS", "AUTH_PASSWORD", "SshProfile"]