test: read static assets as utf-8 so locale/render tests run on Windows

34 test files read static/*.js via read_text()/open() without an encoding,
so Python's cp1252 default on Windows choked on non-Latin1 bytes and errored
at collection (Ubuntu CI defaults to utf-8, so it never saw this). Add
explicit encoding="utf-8" to those reads — purely mechanical, no assertion
changes.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/test_sprint42.py

@@ -19,7 +19,7 @@ import unittest
 from unittest import mock
 
 REPO_ROOT = pathlib.Path(__file__).parent.parent
-STREAMING_PY = (REPO_ROOT / "api" / "streaming.py").read_text()
+STREAMING_PY = (REPO_ROOT / "api" / "streaming.py").read_text(encoding="utf-8")
 
 
 # ── Shared helpers for sprint-42 additional tests ────────────────────────────
@@ -717,7 +717,7 @@ def test_cleanTitle_is_let_not_const():
 # ── Sprint 42 additional tests: thinking panel persistence (#427) ────────
 def test_streaming_persists_reasoning_in_session():
     """streaming.py must accumulate reasoning and patch assistant messages."""
-    src = (REPO / 'api' / 'streaming.py').read_text()
+    src = (REPO / 'api' / 'streaming.py').read_text(encoding="utf-8")
 
     # #3587: per-message reasoning segments replaced the flat _reasoning_text accumulator
     assert "_reasoning_segments" in src, \
@@ -752,7 +752,7 @@ def test_streaming_persists_reasoning_in_session():
 
 def test_done_handler_patches_reasoning_field():
     """messages.js done SSE handler must patch reasoningText onto the last assistant message."""
-    src = (REPO / 'static' / 'messages.js').read_text()
+    src = (REPO / 'static' / 'messages.js').read_text(encoding="utf-8")
 
     # The persistence comment must be present inside the done handler
     assert "Persist reasoning trace for Worklog Thinking Cards" in src, \
@@ -778,7 +778,7 @@ def test_done_handler_patches_reasoning_field():
 
 def test_rendermessages_keeps_reasoning_metadata_out_of_worklog_display():
     """ui.js renderMessages must not promote provider reasoning metadata into Worklog prose."""
-    src = (REPO / 'static' / 'ui.js').read_text()
+    src = (REPO / 'static' / 'ui.js').read_text(encoding="utf-8")
 
     sig_fn = src.split("function _messageHasReasoningPayload(m)", 1)[1].split("function", 1)[0]
     assert 'm.reasoning' in sig_fn, \
@@ -801,7 +801,7 @@ def test_streaming_restores_prior_reasoning_metadata_after_followup():
     history before saving the session, including reinserting dropped
     reasoning-only assistant segments.
     """
-    src = (REPO / 'api' / 'streaming.py').read_text()
+    src = (REPO / 'api' / 'streaming.py').read_text(encoding="utf-8")
     assert "def _restore_reasoning_metadata(" in src, \
         "streaming.py must define a helper to restore prior reasoning metadata"
     assert "_next_context_messages" in src and "s.context_messages" in src, \
@@ -814,7 +814,7 @@ def test_streaming_restores_prior_reasoning_metadata_after_followup():
 
 def test_routes_restores_prior_reasoning_metadata_after_followup():
     """The non-streaming route path must preserve prior reasoning metadata too."""
-    src = (REPO / 'api' / 'routes.py').read_text()
+    src = (REPO / 'api' / 'routes.py').read_text(encoding="utf-8")
     assert "_restore_reasoning_metadata" in src, \
         "routes.py must import reasoning metadata restoration helper"
     assert "_next_context_messages" in src and "s.context_messages" in src, \