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-directory-adoption.test.ts

@@ -0,0 +1,82 @@
+import { beforeEach, describe, expect, test } from "bun:test"
+
+import { ChildStoreManager } from "./child-store"
+import { setSyncRefs } from "./sync-refs"
+import { useSessionUIStore } from "./session-ui-store"
+
+/**
+ * Selecting a session whose directory this client has not indexed yet routes it
+ * through the active directory as a deliberate guess. Nothing used to settle
+ * that guess once the owning directory finished bootstrapping, so every fetch
+ * stayed addressed to a directory that does not own the session and the session
+ * never rendered.
+ *
+ * These tests pin both directions: a guess is promoted once the authoritative
+ * directory becomes readable, and a confirmed selection is never rewritten.
+ */
+
+const PARENT = "/repo"
+const WORKTREE = "/repo/.worktrees/feature"
+const SESSION_ID = "ses_directory_adoption"
+
+const indexSessionIn = (manager: ChildStoreManager, directory: string): void => {
+  const store = manager.ensureChild(directory, { bootstrap: false })
+  store.setState({
+    session: [{ id: SESSION_ID, directory, title: "test" } as never],
+  })
+}
+
+let manager: ChildStoreManager
+
+beforeEach(() => {
+  manager = new ChildStoreManager()
+  setSyncRefs({} as never, manager, PARENT)
+  useSessionUIStore.getState().setCurrentSession(null)
+})
+
+describe("adoptAuthoritativeSessionDirectory", () => {
+  test("promotes a guessed selection once the owning directory is indexed", () => {
+    useSessionUIStore.getState().setCurrentSession(SESSION_ID)
+    expect(useSessionUIStore.getState().currentSessionDirectory).not.toBe(WORKTREE)
+
+    indexSessionIn(manager, WORKTREE)
+    useSessionUIStore.getState().adoptAuthoritativeSessionDirectory()
+
+    expect(useSessionUIStore.getState().currentSessionDirectory).toBe(WORKTREE)
+  })
+
+  test("does nothing while the owning directory is still unknown", () => {
+    useSessionUIStore.getState().setCurrentSession(SESSION_ID)
+    const before = useSessionUIStore.getState().currentSessionDirectory
+
+    useSessionUIStore.getState().adoptAuthoritativeSessionDirectory()
+
+    expect(useSessionUIStore.getState().currentSessionDirectory).toBe(before)
+  })
+
+  test("never rewrites a selection that was confirmed at selection time", () => {
+    useSessionUIStore.getState().setCurrentSession(SESSION_ID, WORKTREE)
+    expect(useSessionUIStore.getState().currentSessionDirectory).toBe(WORKTREE)
+
+    // A different directory claiming the session must not move a confirmed
+    // selection: the confirmed value outranks anything sync learns later.
+    indexSessionIn(manager, PARENT)
+    useSessionUIStore.getState().adoptAuthoritativeSessionDirectory()
+
+    expect(useSessionUIStore.getState().currentSessionDirectory).toBe(WORKTREE)
+  })
+
+  test("is a no-op for a session that is no longer selected", () => {
+    useSessionUIStore.getState().setCurrentSession(SESSION_ID)
+    indexSessionIn(manager, WORKTREE)
+    useSessionUIStore.getState().setCurrentSession("ses_other")
+
+    // Whatever the new selection resolved to, a late adoption for the previous
+    // session must not touch it.
+    const before = useSessionUIStore.getState().currentSessionDirectory
+    useSessionUIStore.getState().adoptAuthoritativeSessionDirectory(SESSION_ID)
+
+    expect(useSessionUIStore.getState().currentSessionId).toBe("ses_other")
+    expect(useSessionUIStore.getState().currentSessionDirectory).toBe(before)
+  })
+})