feat(workspace): Axis 2 Phase B — client→server workspace handshake

Wires the workspace handshake end to end so a session's workspace is bound
from the client's cwd at connect time and is event-sourced for replay.

- Go TUI sends Hello{workingDir=os.Getwd()} as the first WS frame on connect
  (protocol.go encoder + client.go connect path; golden test pins the wire
  format against the Kotlin discriminator).
- Server adds ClientMessage.Hello, stashes the per-connection workingDir, and
  on session start resolves it through WorkspaceResolver's trust pipeline,
  emits SessionWorkspaceBoundEvent (invariant #9), and threads the resolved
  workspace into OrchestrationConfig for the live run. A Hello after the first
  StartSession is ignored (warn); a rejected path binds the resolver fallback.
- Replay derives the workspace from the recorded event: SessionState gains
  boundWorkspace, DefaultSessionReducer fills it from SessionWorkspaceBoundEvent,
  and ReplayOrchestrator uses it (Path.of only, no filesystem re-query —
  invariant #8) with graceful fallback to config for pre-Phase-B logs.

Absent Hello / null resolver degrades to the prior config-workspace behavior.

apps/tui-go/internal/protocol/golden_test.go

@@ -1,6 +1,9 @@
 package protocol
 
-import "testing"
+import (
+	"encoding/json"
+	"testing"
+)
 
 // Golden wire frames as emitted by the Kotlin server (kotlinx.serialization). These
 // strings are the cross-language contract: the Kotlin side pins the encode in
@@ -111,3 +114,44 @@ func TestDecodeGoldenServerFrames(t *testing.T) {
 		})
 	}
 }
+
+// TestEncodeGoldenClientFrames pins the Go→Kotlin wire format for client messages.
+// The discriminator is the fully-qualified Kotlin class name (kotlinx default for
+// sealed classes without @SerialName), keyed under "type". These bytes must be
+// accepted verbatim by the Kotlin server's ProtocolSerializer / Json decoder.
+func TestEncodeGoldenClientFrames(t *testing.T) {
+	cases := []struct {
+		name     string
+		frame    []byte
+		wantType string
+		check    func(t *testing.T, raw map[string]any)
+	}{
+		{
+			// Hello is the first frame on every (re)connect — carries the client cwd so
+			// the server can bind a workspace before any session starts.
+			name:     "Hello carries workingDir",
+			frame:    Hello("/home/kami/Projects/correx"),
+			wantType: clientPrefix + "Hello",
+			check: func(t *testing.T, raw map[string]any) {
+				if raw["workingDir"] != "/home/kami/Projects/correx" {
+					t.Fatalf("Hello workingDir = %v", raw["workingDir"])
+				}
+			},
+		},
+	}
+
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			var raw map[string]any
+			if err := json.Unmarshal(c.frame, &raw); err != nil {
+				t.Fatalf("unmarshal failed: %v", err)
+			}
+			if raw["type"] != c.wantType {
+				t.Fatalf("type = %q, want %q", raw["type"], c.wantType)
+			}
+			if c.check != nil {
+				c.check(t, raw)
+			}
+		})
+	}
+}

apps/tui-go/internal/protocol/protocol.go

@@ -254,3 +254,9 @@ func CreateGrant(sessionID, scope string, permittedTiers []string, reason, toolN
 		"toolName":       toolName,
 	})
 }
+
+// Hello is the first frame sent on every (re)connect. It carries the client's
+// working directory so the server can bind a workspace before any session starts.
+func Hello(workingDir string) []byte {
+	return encode("Hello", map[string]any{"workingDir": workingDir})
+}