feat(app): embed isolated Hermes profile sessions

apps/MTPLXApp/Sources/MTPLXAppCore/Models/AppConfiguration.swift

@@ -306,6 +306,26 @@ public struct MTPLXAppConfiguration: Codable, Equatable, Sendable {
         self.hfEndpoint = hfEndpoint
     }
 
+    /// Records the app-owned embedded Hermes session to offer on the next
+    /// overlay visit. This deliberately leaves the generic daemon launch
+    /// target alone: embedded Hermes is not a `mtplx start hermes` handoff.
+    public mutating func rememberEmbeddedHermesSession(_ reference: HermesSessionReference) {
+        lastHermesProfile = reference.profileName
+        lastHermesSessionID = reference.sessionID
+        lastHermesSessionTitle = reference.title
+    }
+
+    /// Persists profile-only navigation independently from the generic launch
+    /// target. A session belongs to its profile, so crossing that boundary
+    /// must discard the old resume identity while reselecting the same profile
+    /// keeps its remembered session intact.
+    public mutating func rememberHermesProfileSelection(_ profileName: String) {
+        guard lastHermesProfile != profileName else { return }
+        lastHermesProfile = profileName
+        lastHermesSessionID = nil
+        lastHermesSessionTitle = nil
+    }
+
     /// Fresh installs must be portable. Installed local copies are discovered
     /// by the model catalog; the default configuration should never point at
     /// a developer machine path.

apps/MTPLXApp/Sources/MTPLXAppCore/Services/HermesComposerPolicy.swift

@@ -0,0 +1,15 @@
+public enum HermesComposerPolicy {
+    /// The composer may accept text for an existing writable session or for a
+    /// selected profile that can create a fresh session on first send.
+    public static func acceptsInput(
+        gatewayReady: Bool,
+        hasPendingRequest: Bool,
+        activeSessionWritable: Bool,
+        hasActiveSession: Bool,
+        hasAvailableProfile: Bool
+    ) -> Bool {
+        guard gatewayReady, !hasPendingRequest else { return false }
+        if activeSessionWritable { return true }
+        return !hasActiveSession && hasAvailableProfile
+    }
+}