fix(workspace): _profileDefaultWorkspace persists after newSession() (#823)

Closes #823.

Separates two conflated semantics in S._profileDefaultWorkspace:
- Persistent blank-page default (set by boot/settings, never nulled)
- Profile-switch one-shot (now S._profileSwitchWorkspace, consumed by newSession())

newSession() priority: switchWs → current session → _profileDefaultWorkspace.
switchToWorkspace() clears _profileSwitchWorkspace on explicit switch.

9 new tests. 1777/1777 suite. Browser-verified.

tests/test_profile_default_workspace_823.py

@@ -0,0 +1,134 @@
+"""Tests for #823 — _profileDefaultWorkspace persists after newSession() (#804 follow-up)
+
+Root cause: newSession() consumed S._profileDefaultWorkspace for the one-shot
+profile-switch semantic (setting it to null after the first new session). This
+caused the blank-page default workspace display to regress after any session
+was created and then deleted.
+
+Fix: introduce S._profileSwitchWorkspace as the dedicated one-shot flag for
+profile-switch semantics; S._profileDefaultWorkspace is now persistent.
+"""
+import pathlib
+import re
+
+REPO = pathlib.Path(__file__).parent.parent
+
+
+def read(rel):
+    return (REPO / rel).read_text(encoding='utf-8')
+
+
+class TestProfileDefaultWorkspacePersistence:
+    """_profileDefaultWorkspace must NOT be nulled by newSession()."""
+
+    def test_new_session_does_not_null_profile_default_workspace(self):
+        src = read('static/sessions.js')
+        m = re.search(r'async function newSession\(.*?\n\}', src, re.DOTALL)
+        assert m, "newSession not found"
+        fn = m.group(0)
+        # The old consume pattern must be gone
+        assert '_profileDefaultWorkspace=null' not in fn and \
+               '_profileDefaultWorkspace = null' not in fn, (
+            "newSession must NOT null S._profileDefaultWorkspace — it is the persistent "
+            "boot/settings default used for blank-page display after session delete (#823)"
+        )
+
+    def test_new_session_uses_dedicated_switch_workspace_flag(self):
+        src = read('static/sessions.js')
+        m = re.search(r'async function newSession\(.*?\n\}', src, re.DOTALL)
+        assert m
+        fn = m.group(0)
+        assert '_profileSwitchWorkspace' in fn, (
+            "newSession must read S._profileSwitchWorkspace for the one-shot "
+            "profile-switch inherit, not S._profileDefaultWorkspace"
+        )
+        # It should null the switch flag, not the default
+        assert '_profileSwitchWorkspace=null' in fn or '_profileSwitchWorkspace = null' in fn, (
+            "newSession must null S._profileSwitchWorkspace after consuming it"
+        )
+
+    def test_new_session_still_inherits_default_workspace(self):
+        """newSession must still pass a workspace to /api/session/new —
+        now via the _profileSwitchWorkspace → current session → _profileDefaultWorkspace chain."""
+        src = read('static/sessions.js')
+        m = re.search(r'async function newSession\(.*?\n\}', src, re.DOTALL)
+        assert m
+        fn = m.group(0)
+        # inheritWs must be computed and passed to /api/session/new
+        assert 'inheritWs' in fn or 'inherit' in fn.lower(), (
+            "newSession must compute an inheritWs from switch/current/default workspace"
+        )
+        assert '_profileDefaultWorkspace' in fn, (
+            "newSession must fall through to S._profileDefaultWorkspace as last resort"
+        )
+
+
+class TestProfileSwitchWorkspaceSetter:
+    """panels.js must set _profileSwitchWorkspace on profile switch."""
+
+    def test_panels_sets_profile_switch_workspace(self):
+        src = read('static/panels.js')
+        # Find the profile-switch workspace block
+        assert 'S._profileSwitchWorkspace' in src, (
+            "panels.js must set S._profileSwitchWorkspace during profile switch "
+            "so newSession() can apply it to the first new session"
+        )
+
+    def test_panels_still_sets_profile_default_workspace(self):
+        src = read('static/panels.js')
+        assert 'S._profileDefaultWorkspace = data.default_workspace' in src, (
+            "panels.js must still set S._profileDefaultWorkspace (persistent default) "
+            "alongside S._profileSwitchWorkspace"
+        )
+
+    def test_both_set_together_in_same_block(self):
+        src = read('static/panels.js')
+        default_pos = src.find('S._profileDefaultWorkspace = data.default_workspace')
+        switch_pos = src.find('S._profileSwitchWorkspace = data.default_workspace')
+        assert default_pos != -1, "S._profileDefaultWorkspace setter not found"
+        assert switch_pos != -1, "S._profileSwitchWorkspace setter not found"
+        # Both must be set within 200 chars of each other (same block)
+        assert abs(default_pos - switch_pos) < 300, (
+            "_profileDefaultWorkspace and _profileSwitchWorkspace must be set "
+            "together in the same profile-switch workspace block"
+        )
+
+
+    def test_switch_to_workspace_clears_profile_switch_workspace(self):
+        """Opus Q4: when the user manually changes workspace, the pending one-shot
+        switch flag should be cleared so a subsequent newSession() inherits the
+        user's explicit choice rather than the stale profile-switch default."""
+        src = read('static/panels.js')
+        m = re.search(r'async function switchToWorkspace\(.*?\n\}', src, re.DOTALL)
+        assert m, "switchToWorkspace not found"
+        fn = m.group(0)
+        assert '_profileSwitchWorkspace=null' in fn or '_profileSwitchWorkspace = null' in fn, (
+            "switchToWorkspace must null S._profileSwitchWorkspace after a manual switch "
+            "so the next newSession() inherits the user's explicit workspace choice"
+        )
+
+
+class TestBlankPageAfterSessionDelete:
+    """After all sessions are deleted, blank page must still show default workspace."""
+
+    def test_sync_workspace_displays_reads_profile_default(self):
+        """syncWorkspaceDisplays relies on S._profileDefaultWorkspace which must
+        still be set after a session is created and deleted."""
+        src = read('static/panels.js')
+        m = re.search(r'function syncWorkspaceDisplays\(\)\{.*?\n\}', src, re.DOTALL)
+        assert m, "syncWorkspaceDisplays not found"
+        fn = m.group(0)
+        assert '_profileDefaultWorkspace' in fn, (
+            "syncWorkspaceDisplays must read S._profileDefaultWorkspace as fallback"
+        )
+
+    def test_prompt_new_file_reads_profile_default(self):
+        """promptNewFile on blank page reads _profileDefaultWorkspace which must
+        be non-null even after a newSession() + deleteSession() cycle."""
+        src = read('static/ui.js')
+        m = re.search(r'async function promptNewFile\(\)\{.*?\n\}', src, re.DOTALL)
+        assert m, "promptNewFile not found"
+        fn = m.group(0)
+        assert '_profileDefaultWorkspace' in fn, (
+            "promptNewFile must read S._profileDefaultWorkspace (must persist after newSession)"
+        )