fix(sync): settle a guessed session directory once its owner is known

Selecting a session whose directory this client has not indexed yet routes it
through the active directory. That is a deliberate, documented guess: it keeps
routing usable while the owning store bootstraps, and it is excluded from both
the resolver and persistence.

Nothing settled the guess afterwards. `setSessionDirectory` performs exactly
that promotion, but only confirmed destinations call it — a completed move or a
worktree this client created. A session whose directory the client learned about
later, such as one in a worktree created outside this client, kept the guess
forever: every message fetch was addressed to the parent repository, which does
not own the session.

Captured for such a session before this change, with the session already
indexed and its owning store known:

  routedDirectory          .../worktree/feature
  currentSessionDirectory  /repo            <- guess, never settled
  opencodeClientDirectory  /repo
  conflict                 selected -> /repo

and after:

  routedDirectory          .../worktree/feature
  currentSessionDirectory  .../worktree/feature
  opencodeClientDirectory  .../worktree/feature
  conflict                 null

Directory bootstrap completion is the moment the authoritative directory first
becomes readable, so the promotion runs there. It only ever promotes a guess:
a confirmed selection and a selection that has since moved on are both left
alone, and tests cover both directions.

This removes a real routing split-brain. It does not by itself fix the reported
symptom of a session created mid-session never rendering; that remains open.

packages/ui/src/sync/session-ui-store.ts

@@ -352,6 +352,12 @@ export type SessionUIState = {
   debugSessionMessages: (sessionId: string) => Promise<void>
   pollForTokenUpdates: () => void
   setSessionDirectory: (sessionId: string, directory: string | null) => void
+  /**
+   * Replace a guessed selection directory with the authoritative one once sync
+   * has indexed the session. Safe to call at any time: it only ever promotes a
+   * guess, never overrides a confirmed selection.
+   */
+  adoptAuthoritativeSessionDirectory: (sessionId?: string) => void
 }
 
 // ---------------------------------------------------------------------------
@@ -1739,6 +1745,26 @@ export const useSessionUIStore = create<SessionUIState>()((set, get) => ({
     // Handled by sync system's SSE stream
   },
 
+  adoptAuthoritativeSessionDirectory: (sessionId) => {
+    const target = sessionId ?? get().currentSessionId
+    // Only a guess is promoted. A confirmed selection outranks anything sync
+    // learns later, and a selection that has since moved on must not be
+    // rewritten by a directory that finished bootstrapping in the background.
+    if (!target || target !== guessedSelectionSessionId) return
+    if (target !== get().currentSessionId) return
+
+    const authoritative = getAuthoritativeSessionDirectory(target)
+    if (!authoritative) return
+
+    // The selection stops being a guess even when the directory is unchanged:
+    // the value has now been confirmed by the store that owns the session.
+    guessedSelectionSessionId = null
+    if (authoritative !== get().currentSessionDirectory) {
+      set({ currentSessionDirectory: authoritative })
+    }
+    writeRuntimeSessionMemory(runtimeMemoryKey(), { sessionId: target, directory: authoritative })
+  },
+
   setSessionDirectory: (sessionId, directory) => {
     const normalized = normalizePath(directory)
     // Callers set this from a confirmed destination (a completed move, a