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.

testing/projections/src/test/kotlin/DefaultSessionReducerTest.kt

@@ -1,5 +1,6 @@
 import com.correx.core.events.events.OrchestrationPausedEvent
 import com.correx.core.events.events.OrchestrationResumedEvent
+import com.correx.core.events.events.SessionWorkspaceBoundEvent
 import com.correx.core.events.events.StageCompletedEvent
 import com.correx.core.events.events.StageFailedEvent
 import com.correx.core.events.events.TransitionExecutedEvent
@@ -9,6 +10,7 @@ import com.correx.core.events.events.WorkflowStartedEvent
 import com.correx.core.events.types.SessionId
 import com.correx.core.events.types.StageId
 import com.correx.core.events.types.TransitionId
+import com.correx.core.sessions.BoundWorkspace
 import com.correx.core.sessions.DefaultSessionReducer
 import com.correx.core.sessions.SessionState
 import com.correx.core.sessions.SessionStatus
@@ -227,6 +229,55 @@ class DefaultSessionReducerTest {
         assertEquals(timestamp, result.updatedAt)
     }
 
+    @Test
+    fun `SessionWorkspaceBoundEvent sets boundWorkspace in state`() {
+        val result = reducer.reduce(
+            state = initialState(),
+            event = stored(
+                sessionId = sessionId,
+                payload = SessionWorkspaceBoundEvent(
+                    sessionId = sessionId,
+                    workspaceRoot = "/home/user/project",
+                    allowedPaths = listOf("/home/user/project"),
+                )
+            )
+        )
+
+        assertEquals(
+            BoundWorkspace(
+                workspaceRoot = "/home/user/project",
+                allowedPaths = listOf("/home/user/project"),
+            ),
+            result.boundWorkspace,
+        )
+    }
+
+    @Test
+    fun `boundWorkspace is preserved by subsequent unrelated events`() {
+        val withWorkspace = initialState().copy(
+            boundWorkspace = BoundWorkspace(
+                workspaceRoot = "/home/user/project",
+                allowedPaths = listOf("/home/user/project"),
+            )
+        )
+
+        val result = reducer.reduce(
+            state = withWorkspace,
+            event = stored(
+                sessionId = sessionId,
+                payload = WorkflowStartedEvent(sessionId, workflowId = "wf", startStageId = StageId("s1"))
+            )
+        )
+
+        assertEquals(
+            BoundWorkspace(
+                workspaceRoot = "/home/user/project",
+                allowedPaths = listOf("/home/user/project"),
+            ),
+            result.boundWorkspace,
+        )
+    }
+
     private fun initialState() =
         SessionState(
             status = SessionStatus.CREATED