session: make session/new get-or-create

CreateEmpty now returns (session, created, error): if a session with the
given name already exists it is returned untouched instead of erroring,
and only a freshly created session receives the provided cwd/workflow/
variant. The o script no longer suppresses errors from session/new, so
real failures surface while re-creating an existing session stays a
no-op success.

cmd/olliesrv/internal/fs/spec.go

@@ -332,16 +332,21 @@ func buildTreeSpec(cfg *Config) virtfs.FsNodeDecl {
 					if cwd == "" {
 						return nil, fmt.Errorf("cwd is required")
 					}
-					sess, err := session.CreateEmpty(name, remote, yolo)
+					sess, created, err := session.CreateEmpty(name, remote, yolo)
 					if err != nil {
 						return nil, err
 					}
-					sess.SetCwd(cwd)
-					if workflow != "" {
-						sess.SetWorkflow(workflow)
-					}
-					if variant != "" {
-						sess.SetVariant(variant)
+					// Get-or-create: only a freshly created session takes the
+					// provided configuration. An existing session is returned
+					// untouched.
+					if created {
+						sess.SetCwd(cwd)
+						if workflow != "" {
+							sess.SetWorkflow(workflow)
+						}
+						if variant != "" {
+							sess.SetVariant(variant)
+						}
 					}
 					return []byte(sess.Name() + "\n"), nil
 				}),

cmd/olliesrv/internal/session/registry.go

@@ -284,7 +284,11 @@ func BuildAgentIndex(sess *Session) []byte {
 }
 
 // CreateEmpty creates an empty session (no agent) and registers it.
-func CreateEmpty(name, remote string, yolo ...bool) (*Session, error) {
+// CreateEmpty returns the session named `name`, creating it if it does not yet
+// exist (get-or-create). created reports whether a new session was made; when
+// false the returned session already existed and its configuration is left
+// untouched — creation never mutates an existing session.
+func CreateEmpty(name, remote string, yolo ...bool) (sess *Session, created bool, err error) {
 	sessID := util.NewUUID()
 	if name == "" {
 		name = sessID
@@ -293,16 +297,16 @@ func CreateEmpty(name, remote string, yolo ...bool) (*Session, error) {
 		}
 	}
 
-	// Early check (non-atomic, avoids expensive setup in the common case).
+	// Early path: return the existing session without building a tool server.
 	mu.RLock()
-	_, exists := sessions[name]
+	existing := sessions[name]
 	mu.RUnlock()
-	if exists {
-		return nil, fmt.Errorf("session already exists: %s", name)
+	if existing != nil {
+		return existing, false, nil
 	}
 
 	ctx, cancel := context.WithCancel(serverCtx)
-	sess := NewEmpty(sessID, ctx, cancel)
+	sess = NewEmpty(sessID, ctx, cancel)
 	sess.SetName(name)
 	sess.Remote = remote
 	sess.Yolo = len(yolo) > 0 && yolo[0]
@@ -317,7 +321,7 @@ func CreateEmpty(name, remote string, yolo ...bool) (*Session, error) {
 	})
 	if err != nil {
 		cancel()
-		return nil, fmt.Errorf("setup tool server: %w", err)
+		return nil, false, fmt.Errorf("setup tool server: %w", err)
 	}
 	sess.Proc = infra.Proc
 	sess.Keeper = infra.Keeper
@@ -328,19 +332,20 @@ func CreateEmpty(name, remote string, yolo ...bool) (*Session, error) {
 		sess.StartBypassLoop(pkgBypassNotify)
 	}
 
-	// Atomic check-and-insert to prevent races.
+	// Atomic check-and-insert. If another caller won the race, discard our
+	// freshly-built session and return theirs — still get-or-create.
 	mu.Lock()
-	if _, exists := sessions[name]; exists {
+	if won := sessions[name]; won != nil {
 		mu.Unlock()
 		cancel()
-		return nil, fmt.Errorf("session already exists: %s", name)
+		return won, false, nil
 	}
 	sessions[name] = sess
 	mu.Unlock()
 
 	pkgLog.Info("created empty session %s (id=%s)", name, sessID)
 	PublishEvent("session."+sessID+".new", name)
-	return sess, nil
+	return sess, true, nil
 }
 
 // NextUname generates a unique agent name (12 hex chars).

data/scripts/o

@@ -281,8 +281,9 @@ cmd_new() {
         exit 1
     fi
     local agent_cwd="${1:-$PWD}"
-    # Create session if it doesn't exist
-    printf 'name=%s\ncwd=%s\n' "$CTX_SESSION" "$agent_cwd" | ollie-9p write "session/new" 2>/dev/null || true
+    # session/new is get-or-create: creating an existing session is a no-op
+    # success, so real failures now surface instead of being suppressed.
+    printf 'name=%s\ncwd=%s\n' "$CTX_SESSION" "$agent_cwd" | ollie-9p write "session/new"
     # Create the agent
     printf 'name=%s\ncwd=%s\n' "$CTX_AGENT" "$agent_cwd" | ollie-9p write "session/$CTX_SESSION/agent/new"
     echo "created: $CTX_SESSION/$CTX_AGENT"