remove vm session feature

Cuts the daemon-managed guest-session machinery (start/list/show/
logs/stop/kill/attach/send). The feature shipped aimed at agent-
orchestration workflows (programmatic stdin piping into a long-lived
guest process) that aren't driving any concrete user today, and the
~2.3K LOC of daemon surface area — attach bridge, FIFO keepalive,
controller registry, sessionstream framing, SQLite persistence — was
locking in an API we'd have to keep through v0.1.0.

Anything session-flavoured that people actually need today can be
done with `vm ssh + tmux` or `vm run -- cmd`.

Deleted:
- internal/cli/commands_vm_session.go
- internal/daemon/{guest_sessions,session_lifecycle,session_attach,session_stream,session_controller}.go
- internal/daemon/session/ (guest-session helpers package)
- internal/sessionstream/ (framing package)
- internal/daemon/guest_sessions_test.go
- internal/store/guest_session_test.go
- GuestSession* types from internal/{api,model}
- Store UpsertGuestSession/GetGuestSession/ListGuestSessionsByVM/DeleteGuestSession + scanner helpers
- guest.session.* RPC dispatch entries
- 5 CLI session tests, 2 completion tests, 2 printer tests

Extracted:
- ShellQuote + FormatStepError lifted to internal/daemon/workspace/util.go
  (only non-session consumer); workspace package now self-contained
- internal/daemon/guest_ssh.go keeps guestSSHClient + dialGuest +
  waitForGuestSSH — still used by workspace prepare/export
- internal/daemon/fake_firecracker_test.go preserves the test helper
  that used to live in guest_sessions_test.go

Store schema: CREATE TABLE guest_sessions and its column migrations
removed. Existing dev DBs keep an orphan table (harmless, pre-v0.1.0).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/cli/cli_test.go

@@ -1918,34 +1918,9 @@ func (c *testVMRunGuestClient) StreamTarEntries(ctx context.Context, sourceDir s
 	return nil
 }
 
-func TestVMSessionSendCommandExists(t *testing.T) {
-	root := NewBangerCommand()
-	vm, _, err := root.Find([]string{"vm"})
-	if err != nil {
-		t.Fatalf("find vm: %v", err)
-	}
-	session, _, err := vm.Find([]string{"session"})
-	if err != nil {
-		t.Fatalf("find session: %v", err)
-	}
-	if _, _, err := session.Find([]string{"send"}); err != nil {
-		t.Fatalf("find session send: %v", err)
-	}
-}
-
-func TestVMSessionSendRejectsWrongArgCount(t *testing.T) {
-	cmd := NewBangerCommand()
-	cmd.SetArgs([]string{"vm", "session", "send", "only-one-arg"})
-	err := cmd.Execute()
-	if err == nil || !strings.Contains(err.Error(), "usage: banger vm session send") {
-		t.Fatalf("Execute() error = %v, want send usage error", err)
-	}
-}
-
 // stubEnsureDaemonForSend isolates XDG dirs and installs a daemon-ping
 // fake onto the caller's *deps so `ensureDaemon` short-circuits without
-// trying to spawn bangerd. `vm session send` uses this to avoid needing
-// a built binary on disk.
+// trying to spawn bangerd.
 func stubEnsureDaemonForSend(t *testing.T, d *deps) {
 	t.Helper()
 	t.Setenv("XDG_CONFIG_HOME", filepath.Join(t.TempDir(), "config"))
@@ -1956,98 +1931,6 @@ func stubEnsureDaemonForSend(t *testing.T, d *deps) {
 	}
 }
 
-func TestVMSessionSendWithMessageFlag(t *testing.T) {
-	d := defaultDeps()
-	stubEnsureDaemonForSend(t, d)
-
-	var capturedParams api.GuestSessionSendParams
-	d.guestSessionSend = func(_ context.Context, _ string, params api.GuestSessionSendParams) (api.GuestSessionSendResult, error) {
-		capturedParams = params
-		return api.GuestSessionSendResult{
-			Session:      model.GuestSession{ID: "sess-id", Name: "planner"},
-			BytesWritten: len(params.Payload),
-		}, nil
-	}
-
-	cmd := d.newRootCommand()
-	var out bytes.Buffer
-	cmd.SetOut(&out)
-	cmd.SetArgs([]string{"vm", "session", "send", "devbox", "planner", "--message", `{"type":"abort"}`})
-	if err := cmd.Execute(); err != nil {
-		t.Fatalf("Execute: %v", err)
-	}
-
-	wantPayload := []byte(`{"type":"abort"}` + "\n")
-	if string(capturedParams.Payload) != string(wantPayload) {
-		t.Fatalf("payload = %q, want %q", capturedParams.Payload, wantPayload)
-	}
-	if capturedParams.VMIDOrName != "devbox" {
-		t.Fatalf("VMIDOrName = %q, want %q", capturedParams.VMIDOrName, "devbox")
-	}
-	if capturedParams.SessionIDOrName != "planner" {
-		t.Fatalf("SessionIDOrName = %q, want %q", capturedParams.SessionIDOrName, "planner")
-	}
-	if !strings.Contains(out.String(), "17") {
-		t.Fatalf("output = %q, want bytes_written in output", out.String())
-	}
-}
-
-func TestVMSessionSendMessageAlreadyHasNewline(t *testing.T) {
-	d := defaultDeps()
-	stubEnsureDaemonForSend(t, d)
-
-	var capturedPayload []byte
-	d.guestSessionSend = func(_ context.Context, _ string, params api.GuestSessionSendParams) (api.GuestSessionSendResult, error) {
-		capturedPayload = params.Payload
-		return api.GuestSessionSendResult{
-			Session:      model.GuestSession{Name: "s"},
-			BytesWritten: len(params.Payload),
-		}, nil
-	}
-
-	cmd := d.newRootCommand()
-	cmd.SetOut(io.Discard)
-	cmd.SetArgs([]string{"vm", "session", "send", "devbox", "s", "--message", "{\"type\":\"abort\"}\n"})
-	if err := cmd.Execute(); err != nil {
-		t.Fatalf("Execute: %v", err)
-	}
-
-	// Must not double-append newline.
-	if capturedPayload[len(capturedPayload)-1] != '\n' {
-		t.Fatalf("payload missing trailing newline: %q", capturedPayload)
-	}
-	if len(capturedPayload) > 0 && capturedPayload[len(capturedPayload)-2] == '\n' {
-		t.Fatalf("payload has double trailing newline: %q", capturedPayload)
-	}
-}
-
-func TestVMSessionSendFromStdin(t *testing.T) {
-	d := defaultDeps()
-	stubEnsureDaemonForSend(t, d)
-
-	var capturedPayload []byte
-	d.guestSessionSend = func(_ context.Context, _ string, params api.GuestSessionSendParams) (api.GuestSessionSendResult, error) {
-		capturedPayload = params.Payload
-		return api.GuestSessionSendResult{
-			Session:      model.GuestSession{Name: "planner"},
-			BytesWritten: len(params.Payload),
-		}, nil
-	}
-
-	stdinPayload := `{"type":"steer","message":"Focus on src/"}` + "\n"
-	cmd := d.newRootCommand()
-	cmd.SetOut(io.Discard)
-	cmd.SetIn(strings.NewReader(stdinPayload))
-	cmd.SetArgs([]string{"vm", "session", "send", "devbox", "planner"})
-	if err := cmd.Execute(); err != nil {
-		t.Fatalf("Execute: %v", err)
-	}
-
-	if string(capturedPayload) != stdinPayload {
-		t.Fatalf("payload = %q, want %q", capturedPayload, stdinPayload)
-	}
-}
-
 func TestVMWorkspaceExportCommandExists(t *testing.T) {
 	root := NewBangerCommand()
 	vm, _, err := root.Find([]string{"vm"})