diff --git a/tests/test_batch_fixes.py b/tests/test_batch_fixes.py
index 907e08d3..625f9dea 100644
--- a/tests/test_batch_fixes.py
+++ b/tests/test_batch_fixes.py
@@ -15,7 +15,7 @@ REPO = pathlib.Path(__file__).parent.parent
 
 
 def read(rel):
-    return (REPO / rel).read_text()
+    return (REPO / rel).read_text(encoding="utf-8")
 
 
 # ── Group A: /root workspace ──────────────────────────────────────────────────
@@ -80,7 +80,7 @@ class TestCronSkillCacheInvalidation:
     def _panels_src(self):
         return read("static/panels.js")
 
-    def test_cache_busted_on_form_open(self):
+    def test_cache_busted_on_form_open(self, encoding="utf-8"):
         src = self._panels_src()
         # toggleCronForm should set cache to null unconditionally
         # openCronCreate() opens the task create form (renamed from toggleCronForm
@@ -94,7 +94,7 @@ class TestCronSkillCacheInvalidation:
             "before fetching skills"
         )
 
-    def test_cache_not_guarded_by_if_on_open(self):
+    def test_cache_not_guarded_by_if_on_open(self, encoding="utf-8"):
         src = self._panels_src()
         # openCronCreate must not gate the fetch behind an if(!_cronSkillsCache) guard.
         m = re.search(
diff --git a/tests/test_cron_no_agent_edit.py b/tests/test_cron_no_agent_edit.py
index 00ac092e..d6dba655 100644
--- a/tests/test_cron_no_agent_edit.py
+++ b/tests/test_cron_no_agent_edit.py
@@ -5,7 +5,7 @@ from __future__ import annotations
 from pathlib import Path
 
 ROOT = Path(__file__).resolve().parents[1]
-PANELS_JS = (ROOT / "static" / "panels.js").read_text()
+PANELS_JS = (ROOT / "static" / "panels.js").read_text(encoding="utf-8")
 
 
 def _function_body(name: str) -> str:
diff --git a/tests/test_csv_table_rendering.py b/tests/test_csv_table_rendering.py
index 02c1eb52..2069a0cb 100644
--- a/tests/test_csv_table_rendering.py
+++ b/tests/test_csv_table_rendering.py
@@ -7,7 +7,7 @@ WORKSPACE_JS = Path("static/workspace.js").read_text(encoding="utf-8")
 
 def test_csv_extension_regex():
     """Verify _CSV_EXTS regex is defined."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     assert '_CSV_EXTS' in src, "Missing _CSV_EXTS regex"
     assert '.csv' in src, "CSV regex should match .csv extension"
@@ -15,7 +15,7 @@ def test_csv_extension_regex():
 
 def test_csv_fence_block_handler():
     """Verify fenced ```csv blocks are handled."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     assert "lang==='csv'" in src, "Missing csv language detection in fence handler"
     assert 'csv-table' in src, "Missing csv-table class for fenced CSV rendering"
@@ -24,7 +24,7 @@ def test_csv_fence_block_handler():
 
 def test_csv_fence_renders_table_structure():
     """Verify fenced CSV blocks produce proper table HTML."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     # Should have thead, tbody, th, td
     assert '<thead>' in src, "CSV table should have <thead>"
@@ -37,7 +37,7 @@ def test_csv_fence_renders_table_structure():
 
 def test_csv_fence_fallback_for_insufficient_rows():
     """Verify CSV with < 2 rows falls back to code block."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     fence_section = src[src.find("lang==='csv'"):src.find("lang==='csv'") + 800]
     assert 'rows.length>=2' in fence_section, "Should check for at least 2 rows"
@@ -48,7 +48,7 @@ def test_csv_fence_fallback_for_insufficient_rows():
 
 def test_csv_media_file_handler():
     """Verify MEDIA: CSV files trigger inline loading."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     assert 'csv-inline-load' in src, "Missing csv-inline-load class for MEDIA: CSV"
     assert 'csv_loading' in src, "Missing csv_loading i18n key usage"
@@ -62,7 +62,7 @@ def test_csv_media_file_handler():
 
 def test_loadCsvInline_function():
     """Verify loadCsvInline lazy-load function exists."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     assert 'function loadCsvInline' in src, "Missing loadCsvInline function"
     assert 'function buildCsvTablePreview(path, text)' in src, "Missing shared CSV preview helper"
@@ -70,7 +70,7 @@ def test_loadCsvInline_function():
 
 def test_csv_inline_max_size():
     """Verify CSV inline rendering has a size cap."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     assert 'const CSV_MAX_SIZE=256*1024' in src, "Should have CSV_MAX_SIZE constant"
     helper_section = src[src.find('function buildCsvTablePreview'):src.find('function buildCsvTablePreview') + 2000]
@@ -79,7 +79,7 @@ def test_csv_inline_max_size():
 
 def test_csv_auto_detect_separator():
     """Verify CSV handler auto-detects separator."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     csv_section = src[src.find('function buildCsvTablePreview'):src.find('function buildCsvTablePreview') + 2000]
     assert 'separators' in csv_section, "Should have separator detection"
@@ -89,14 +89,14 @@ def test_csv_auto_detect_separator():
 
 def test_csv_quote_stripping():
     """Verify CSV handler strips surrounding quotes from fields."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     assert "replace(/^[\"']|[\"']$/g,'')" in src, "Should strip quotes from CSV fields"
 
 
 def test_csv_error_handling():
     """Verify CSV error and empty data handling."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     csv_section = src[src.find('function buildCsvTablePreview'):src.find('function loadCsvInline') + 1000]
     assert 'csv_error' in csv_section, "Should use csv_error i18n on fetch failure"
@@ -110,7 +110,7 @@ def test_csv_error_handling():
 
 def test_csv_loadCsvInline_called_after_render():
     """Verify loadCsvInline is called by the consolidated post-render pass."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     # Behavior assertion (not a brittle rAF-literal match): the post-render pass
     # is scheduled a frame later, now routed through _postProcessWithAnchorSuppression
@@ -144,7 +144,7 @@ def test_csv_loadCsvInline_called_after_render():
 
 def test_csv_line_ending_normalization():
     """Verify CSV handler normalizes line endings."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     csv_section = src[src.find('function buildCsvTablePreview'):src.find('function buildCsvTablePreview') + 2000]
     assert '\\r\\n' in csv_section, "Should handle \\r\\n line endings"
@@ -153,7 +153,7 @@ def test_csv_line_ending_normalization():
 
 def test_csv_i18n_keys():
     """Verify CSV i18n keys exist in all 7 locales."""
-    with open('static/i18n.js') as f:
+    with open('static/i18n.js', encoding="utf-8") as f:
         src = f.read()
     required_keys = ['csv_loading', 'csv_too_large', 'csv_no_data', 'csv_error']
     for key in required_keys:
@@ -163,7 +163,7 @@ def test_csv_i18n_keys():
 
 def test_csv_css_classes():
     """Verify CSV table CSS classes are defined."""
-    with open('static/style.css') as f:
+    with open('static/style.css', encoding="utf-8") as f:
         src = f.read()
     required_classes = ['csv-table-wrap', 'csv-table', 'csv-table th', 'csv-table td']
     for cls in required_classes:
@@ -174,7 +174,7 @@ def test_csv_css_classes():
 
 def test_csv_not_matched_by_image_exts():
     """Verify .csv is NOT in _IMAGE_EXTS."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     match = re.search(r"const _IMAGE_EXTS=/([^/]+)/i", src)
     assert match
@@ -187,7 +187,7 @@ def test_csv_preview_preserves_edit_flow():
     workspace Edit affordance that .csv had when it fell through to the code
     preview. csv mode must be editable, the preview must cache raw content for
     the textarea, and a save must re-render the table (not markdown)."""
-    with open('static/workspace.js') as f:
+    with open('static/workspace.js', encoding="utf-8") as f:
         src = f.read()
     # csv mode is editable
     assert "_previewCurrentMode==='csv'" in src, "csv mode should be editable / handled in workspace edit flow"
diff --git a/tests/test_excalidraw_inline_embed.py b/tests/test_excalidraw_inline_embed.py
index 73c83f87..f65c4aac 100644
--- a/tests/test_excalidraw_inline_embed.py
+++ b/tests/test_excalidraw_inline_embed.py
@@ -4,7 +4,7 @@ import re
 
 def test_excalidraw_extension_regex():
     """Verify _EXCALIDRAW_EXTS regex is defined."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     assert '_EXCALIDRAW_EXTS' in src, "Missing _EXCALIDRAW_EXTS regex"
     assert '.excalidraw' in src, "Excalidraw regex should match .excalidraw"
@@ -12,7 +12,7 @@ def test_excalidraw_extension_regex():
 
 def test_excalidraw_media_handler():
     """Verify MEDIA: .excalidraw files trigger inline loading."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     assert 'excalidraw-inline-load' in src, "Missing excalidraw-inline-load class"
     assert 'excalidraw_loading' in src, "Missing excalidraw_loading i18n key usage"
@@ -20,14 +20,14 @@ def test_excalidraw_media_handler():
 
 def test_loadExcalidrawInline_function():
     """Verify loadExcalidrawInline lazy-load function exists."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     assert 'function loadExcalidrawInline' in src, "Missing loadExcalidrawInline function"
 
 
 def test_excalidraw_json_validation():
     """Verify Excalidraw handler validates JSON format."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     func = src[src.find('function loadExcalidrawInline'):src.find('function loadExcalidrawInline') + 2000]
     assert 'JSON.parse' in func, "Should parse JSON"
@@ -37,7 +37,7 @@ def test_excalidraw_json_validation():
 
 def test_excalidraw_size_cap():
     """Verify Excalidraw inline rendering has a size cap."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     func = src[src.find('function loadExcalidrawInline'):src.find('function loadExcalidrawInline') + 2000]
     assert 'EXCALIDRAW_MAX_SIZE' in func, "Should have EXCALIDRAW_MAX_SIZE constant"
@@ -46,7 +46,7 @@ def test_excalidraw_size_cap():
 
 def test_excalidraw_error_handling():
     """Verify Excalidraw error handling."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     func = src[src.find('function loadExcalidrawInline'):src.find('function loadExcalidrawInline') + 3500]
     assert 'excalidraw_error' in func, "Should use excalidraw_error i18n on fetch failure"
@@ -54,7 +54,7 @@ def test_excalidraw_error_handling():
 
 def test_excalidraw_svg_renderer_exists():
     """Verify SVG renderer for Excalidraw elements exists."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     assert 'function _renderExcalidrawCanvases()' in src, "Missing _renderExcalidrawCanvases function"
     start = src.find('function _renderExcalidrawCanvases()')
@@ -66,7 +66,7 @@ def test_excalidraw_svg_renderer_exists():
 
 def test_excalidraw_renders_element_types():
     """Verify SVG renderer handles common Excalidraw element types."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     start = src.find('function _renderExcalidrawCanvases()')
     end = src.find('// ── PDF inline preview', start)
@@ -78,7 +78,7 @@ def test_excalidraw_renders_element_types():
 
 def test_excalidraw_arrow_marker():
     """Verify SVG renderer includes arrow marker definition."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     start = src.find('function _renderExcalidrawCanvases()')
     end = src.find('// ── PDF inline preview', start)
@@ -89,7 +89,7 @@ def test_excalidraw_arrow_marker():
 
 def test_excalidraw_bounds_calculation():
     """Verify SVG renderer calculates viewBox from element bounds."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     start = src.find('function _renderExcalidrawCanvases()')
     end = src.find('// ── PDF inline preview', start)
@@ -101,7 +101,7 @@ def test_excalidraw_bounds_calculation():
 
 def test_excalidraw_empty_elements():
     """Verify empty diagrams show a message."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     start = src.find('function _renderExcalidrawCanvases()')
     end = src.find('// ── PDF inline preview', start)
@@ -112,7 +112,7 @@ def test_excalidraw_empty_elements():
 
 def test_excalidraw_download_link():
     """Verify Excalidraw embed includes download link."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     func = src[src.find('function loadExcalidrawInline'):src.find('function loadExcalidrawInline') + 2000]
     assert 'excalidraw-open-link' in func, "Should include open/download link"
@@ -121,7 +121,7 @@ def test_excalidraw_download_link():
 
 def test_excalidraw_called_after_render():
     """Verify loadExcalidrawInline is called by the consolidated post-render pass."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     # Behavior assertion (#5338): post-render is now scheduled through
     # _postProcessWithAnchorSuppression (which still calls postProcessRenderedMessages).
@@ -139,7 +139,7 @@ def test_excalidraw_called_after_render():
 
 def test_excalidraw_embed_wrap_structure():
     """Verify Excalidraw embed uses proper container structure."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     assert 'excalidraw-embed-wrap' in src, "Missing excalidraw-embed-wrap container"
     assert 'excalidraw-canvas' in src, "Missing excalidraw-canvas div"
@@ -148,7 +148,7 @@ def test_excalidraw_embed_wrap_structure():
 
 def test_excalidraw_i18n_keys():
     """Verify Excalidraw i18n keys exist in all 7 locales."""
-    with open('static/i18n.js') as f:
+    with open('static/i18n.js', encoding="utf-8") as f:
         src = f.read()
     required_keys = [
         'excalidraw_loading', 'excalidraw_too_large', 'excalidraw_invalid',
@@ -162,7 +162,7 @@ def test_excalidraw_i18n_keys():
 
 def test_excalidraw_css_classes():
     """Verify Excalidraw CSS classes are defined."""
-    with open('static/style.css') as f:
+    with open('static/style.css', encoding="utf-8") as f:
         src = f.read()
     required_classes = [
         'excalidraw-embed-wrap', 'excalidraw-canvas', 'excalidraw-svg',
@@ -189,7 +189,7 @@ def test_excalidraw_css_classes():
 # be coerced via Number()/isFinite gates so they cannot carry strings.
 
 def _excalidraw_render_block():
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     start = src.find('function _renderExcalidrawCanvases')
     assert start != -1, '_renderExcalidrawCanvases not found'
diff --git a/tests/test_issue1096_copy_buttons.py b/tests/test_issue1096_copy_buttons.py
index a504ef89..8d70d8ce 100644
--- a/tests/test_issue1096_copy_buttons.py
+++ b/tests/test_issue1096_copy_buttons.py
@@ -3,12 +3,12 @@ import re
 
 
 def _src(name: str) -> str:
-    with open(f"static/{name}") as f:
+    with open(f"static/{name}", encoding="utf-8") as f:
         return f.read()
 
 
 def _py_src() -> str:
-    with open("api/helpers.py") as f:
+    with open("api/helpers.py", encoding="utf-8") as f:
         return f.read()
 
 
diff --git a/tests/test_issue1438_fence_anchoring.py b/tests/test_issue1438_fence_anchoring.py
index 530a9707..f6b9aacd 100644
--- a/tests/test_issue1438_fence_anchoring.py
+++ b/tests/test_issue1438_fence_anchoring.py
@@ -36,7 +36,7 @@ import pytest
 from tests.test_sprint16 import render_md  # Python mirror of renderMd()
 
 
-UI_JS = (Path(__file__).resolve().parent.parent / "static" / "ui.js").read_text()
+UI_JS = (Path(__file__).resolve().parent.parent / "static" / "ui.js").read_text(encoding="utf-8")
 
 
 def _strip_pre_blocks(out: str) -> str:
diff --git a/tests/test_issue1488_composer_voice_buttons.py b/tests/test_issue1488_composer_voice_buttons.py
index 134b0990..5e1dc335 100644
--- a/tests/test_issue1488_composer_voice_buttons.py
+++ b/tests/test_issue1488_composer_voice_buttons.py
@@ -20,7 +20,7 @@ import re
 
 
 def _src(name: str) -> str:
-    with open(f"static/{name}") as f:
+    with open(f"static/{name}", encoding="utf-8") as f:
         return f.read()
 
 
diff --git a/tests/test_issue1743_model_picker_race.py b/tests/test_issue1743_model_picker_race.py
index 33413902..51d48124 100644
--- a/tests/test_issue1743_model_picker_race.py
+++ b/tests/test_issue1743_model_picker_race.py
@@ -3,7 +3,7 @@
 from pathlib import Path
 
 ROOT = Path(__file__).resolve().parents[1]
-UI_JS = (ROOT / "static" / "ui.js").read_text()
+UI_JS = (ROOT / "static" / "ui.js").read_text(encoding="utf-8")
 
 
 def _body_between(src: str, start: str, end: str) -> str:
diff --git a/tests/test_issue1796_error_toasts.py b/tests/test_issue1796_error_toasts.py
index d8ed25cc..7fd9194a 100644
--- a/tests/test_issue1796_error_toasts.py
+++ b/tests/test_issue1796_error_toasts.py
@@ -1,8 +1,8 @@
 from pathlib import Path
 
 ROOT = Path(__file__).resolve().parents[1]
-UI_JS = (ROOT / "static" / "ui.js").read_text()
-STYLE_CSS = (ROOT / "static" / "style.css").read_text()
+UI_JS = (ROOT / "static" / "ui.js").read_text(encoding="utf-8")
+STYLE_CSS = (ROOT / "static" / "style.css").read_text(encoding="utf-8")
 
 
 def test_error_toast_default_duration_is_substantially_longer_than_info_toasts():
diff --git a/tests/test_issue2508_session_pin_cap.py b/tests/test_issue2508_session_pin_cap.py
index 385da1f4..04c14b60 100644
--- a/tests/test_issue2508_session_pin_cap.py
+++ b/tests/test_issue2508_session_pin_cap.py
@@ -11,9 +11,9 @@ from tests._pytest_port import BASE, TEST_STATE_DIR
 
 
 ROOT = pathlib.Path(__file__).resolve().parent.parent
-ROUTES_PY = (ROOT / "api" / "routes.py").read_text()
-SESSIONS_JS = (ROOT / "static" / "sessions.js").read_text()
-STYLE_CSS = (ROOT / "static" / "style.css").read_text()
+ROUTES_PY = (ROOT / "api" / "routes.py").read_text(encoding="utf-8")
+SESSIONS_JS = (ROOT / "static" / "sessions.js").read_text(encoding="utf-8")
+STYLE_CSS = (ROOT / "static" / "style.css").read_text(encoding="utf-8")
 
 
 def post(path, body=None):
diff --git a/tests/test_issue2569_model_provider_picker.py b/tests/test_issue2569_model_provider_picker.py
index f46ebce5..53c95342 100644
--- a/tests/test_issue2569_model_provider_picker.py
+++ b/tests/test_issue2569_model_provider_picker.py
@@ -2,7 +2,7 @@ from pathlib import Path
 
 
 ROOT = Path(__file__).resolve().parents[1]
-UI_JS = (ROOT / "static" / "ui.js").read_text()
+UI_JS = (ROOT / "static" / "ui.js").read_text(encoding="utf-8")
 
 
 def test_temporary_configured_model_option_carries_provider_badge():
diff --git a/tests/test_issue3402_workspace_os_import.py b/tests/test_issue3402_workspace_os_import.py
index d39a7f0e..7fa472ea 100644
--- a/tests/test_issue3402_workspace_os_import.py
+++ b/tests/test_issue3402_workspace_os_import.py
@@ -5,7 +5,7 @@ import subprocess
 
 
 def _src(name: str) -> str:
-    with open(f"static/{name}") as f:
+    with open(f"static/{name}", encoding="utf-8") as f:
         return f.read()
 
 
diff --git a/tests/test_issue3869_thinking_dots.py b/tests/test_issue3869_thinking_dots.py
index 4dfd4599..2f685648 100644
--- a/tests/test_issue3869_thinking_dots.py
+++ b/tests/test_issue3869_thinking_dots.py
@@ -2,7 +2,7 @@ from pathlib import Path
 
 
 REPO_ROOT = Path(__file__).resolve().parents[1]
-UI_JS = (REPO_ROOT / "static" / "ui.js").read_text()
+UI_JS = (REPO_ROOT / "static" / "ui.js").read_text(encoding="utf-8")
 
 
 def _function_body(src: str, name: str) -> str:
diff --git a/tests/test_issue4356_no_git_update_check.py b/tests/test_issue4356_no_git_update_check.py
index 92e93d20..be823d07 100644
--- a/tests/test_issue4356_no_git_update_check.py
+++ b/tests/test_issue4356_no_git_update_check.py
@@ -52,7 +52,7 @@ def test_check_repo_still_returns_dict_when_dot_git_exists(tmp_path):
 def test_format_update_target_status_excludes_no_git():
     """_formatUpdateTargetStatus returns null for no_git so it doesn't show as update available."""
     ui_path = Path(__file__).resolve().parent.parent / 'static' / 'ui.js'
-    content = ui_path.read_text()
+    content = ui_path.read_text(encoding="utf-8")
 
     assert '_formatUpdateTargetStatus' in content
     assert 'info.no_git' in content
@@ -67,7 +67,7 @@ def test_panels_has_no_git_branch():
     target is no_git (which hid the indicator in mixed installs).
     """
     panels_path = Path(__file__).resolve().parent.parent / 'static' / 'panels.js'
-    content = panels_path.read_text()
+    content = panels_path.read_text(encoding="utf-8")
 
     # Check for the no_git conditional in the update consumer
     assert 'no_git' in content
@@ -82,7 +82,7 @@ def test_panels_has_no_git_branch():
 def test_i18n_no_git_key_all_locales():
     """settings_update_no_git key appears in all 14 locale blocks in static/i18n.js."""
     i18n_path = Path(__file__).resolve().parent.parent / 'static' / 'i18n.js'
-    content = i18n_path.read_text()
+    content = i18n_path.read_text(encoding="utf-8")
 
     # Count occurrences of the new key (should be exactly 13, one per locale)
     count = content.count("settings_update_no_git")
diff --git a/tests/test_issue470.py b/tests/test_issue470.py
index 78893075..1fe50175 100644
--- a/tests/test_issue470.py
+++ b/tests/test_issue470.py
@@ -19,7 +19,7 @@ import re
 import html as _html
 
 REPO_ROOT = pathlib.Path(__file__).parent.parent
-UI_JS = (REPO_ROOT / "static" / "ui.js").read_text()
+UI_JS = (REPO_ROOT / "static" / "ui.js").read_text(encoding="utf-8")
 
 
 # ── Helpers ──────────────────────────────────────────────────────────────────
diff --git a/tests/test_issue486_487.py b/tests/test_issue486_487.py
index 822c7269..4b4b07d5 100644
--- a/tests/test_issue486_487.py
+++ b/tests/test_issue486_487.py
@@ -21,8 +21,8 @@ import re
 import html as _html
 
 REPO_ROOT = pathlib.Path(__file__).parent.parent
-UI_JS = (REPO_ROOT / "static" / "ui.js").read_text()
-STYLE_CSS = (REPO_ROOT / "static" / "style.css").read_text()
+UI_JS = (REPO_ROOT / "static" / "ui.js").read_text(encoding="utf-8")
+STYLE_CSS = (REPO_ROOT / "static" / "style.css").read_text(encoding="utf-8")
 
 
 # ── Helpers ───────────────────────────────────────────────────────────────────
diff --git a/tests/test_issue487b.py b/tests/test_issue487b.py
index 18e43749..fa1b4222 100644
--- a/tests/test_issue487b.py
+++ b/tests/test_issue487b.py
@@ -14,7 +14,7 @@ import pathlib
 import re
 
 REPO_ROOT = pathlib.Path(__file__).parent.parent
-UI_JS = (REPO_ROOT / "static" / "ui.js").read_text()
+UI_JS = (REPO_ROOT / "static" / "ui.js").read_text(encoding="utf-8")
 
 
 # ── Source-level check ────────────────────────────────────────────────────────
diff --git a/tests/test_issue856_active_session_read_state.py b/tests/test_issue856_active_session_read_state.py
index a3dc8f0c..93755716 100644
--- a/tests/test_issue856_active_session_read_state.py
+++ b/tests/test_issue856_active_session_read_state.py
@@ -3,7 +3,7 @@
 from pathlib import Path
 
 
-MESSAGES_JS = (Path(__file__).resolve().parent.parent / "static" / "messages.js").read_text()
+MESSAGES_JS = (Path(__file__).resolve().parent.parent / "static" / "messages.js").read_text(encoding="utf-8")
 
 
 def test_messages_js_defines_active_session_viewed_helper():
diff --git a/tests/test_issue856_pinned_indicator_layout.py b/tests/test_issue856_pinned_indicator_layout.py
index 2130441e..5dfaa500 100644
--- a/tests/test_issue856_pinned_indicator_layout.py
+++ b/tests/test_issue856_pinned_indicator_layout.py
@@ -3,8 +3,8 @@
 from pathlib import Path
 
 
-SESSIONS_JS = (Path(__file__).resolve().parent.parent / "static" / "sessions.js").read_text()
-STYLE_CSS = (Path(__file__).resolve().parent.parent / "static" / "style.css").read_text()
+SESSIONS_JS = (Path(__file__).resolve().parent.parent / "static" / "sessions.js").read_text(encoding="utf-8")
+STYLE_CSS = (Path(__file__).resolve().parent.parent / "static" / "style.css").read_text(encoding="utf-8")
 
 
 def test_pinned_indicator_renders_inside_title_row():
@@ -133,7 +133,7 @@ def test_plain_mouse_hover_does_not_mark_session_row_dragging():
 
 
 def test_sidebar_uses_local_inflight_state_for_immediate_spinner():
-    messages_js = (Path(__file__).resolve().parent.parent / "static" / "messages.js").read_text()
+    messages_js = (Path(__file__).resolve().parent.parent / "static" / "messages.js").read_text(encoding="utf-8")
 
     assert "function _isSessionLocallyStreaming(s)" in SESSIONS_JS
     assert "isActive && Boolean(S.busy)" in SESSIONS_JS
@@ -158,7 +158,7 @@ def test_date_group_caret_expanded_down_collapsed_right():
 def test_apperror_path_calls_render_session_list():
     """apperror handler must call renderSessionList() to clear the streaming indicator
     immediately rather than waiting for the 5s streaming poll interval."""
-    messages_js = (Path(__file__).resolve().parent.parent / "static" / "messages.js").read_text()
+    messages_js = (Path(__file__).resolve().parent.parent / "static" / "messages.js").read_text(encoding="utf-8")
     apperror_idx = messages_js.find("source.addEventListener('apperror'")
     assert apperror_idx != -1, "apperror handler not found in messages.js"
     warning_idx = messages_js.find("source.addEventListener('warning'", apperror_idx)
diff --git a/tests/test_kanban_view_toggle.py b/tests/test_kanban_view_toggle.py
index e169daef..37a7aaf4 100644
--- a/tests/test_kanban_view_toggle.py
+++ b/tests/test_kanban_view_toggle.py
@@ -14,10 +14,10 @@ import pytest
 
 ROOT = Path(__file__).resolve().parents[1]
 
-INDEX_HTML = (ROOT / "static" / "index.html").read_text()
-PANELS_JS = (ROOT / "static" / "panels.js").read_text()
-STYLE_CSS = (ROOT / "static" / "style.css").read_text()
-I18N_JS = (ROOT / "static" / "i18n.js").read_text()
+INDEX_HTML = (ROOT / "static" / "index.html").read_text(encoding="utf-8")
+PANELS_JS = (ROOT / "static" / "panels.js").read_text(encoding="utf-8")
+STYLE_CSS = (ROOT / "static" / "style.css").read_text(encoding="utf-8")
+I18N_JS = (ROOT / "static" / "i18n.js").read_text(encoding="utf-8")
 
 
 def test_kanban_header_exposes_accessible_view_toggle():
diff --git a/tests/test_model_selection_refresh_persistence.py b/tests/test_model_selection_refresh_persistence.py
index 361cea94..09f12e3a 100644
--- a/tests/test_model_selection_refresh_persistence.py
+++ b/tests/test_model_selection_refresh_persistence.py
@@ -9,9 +9,9 @@ next ``loadSession()`` before ``syncTopbar()`` projects server metadata.
 from pathlib import Path
 
 ROOT = Path(__file__).resolve().parents[1]
-BOOT_JS = (ROOT / "static" / "boot.js").read_text()
-SESSIONS_JS = (ROOT / "static" / "sessions.js").read_text()
-UI_JS = (ROOT / "static" / "ui.js").read_text()
+BOOT_JS = (ROOT / "static" / "boot.js").read_text(encoding="utf-8")
+SESSIONS_JS = (ROOT / "static" / "sessions.js").read_text(encoding="utf-8")
+UI_JS = (ROOT / "static" / "ui.js").read_text(encoding="utf-8")
 
 
 def _body_between(src: str, start: str, end: str) -> str:
diff --git a/tests/test_pdf_html_preview.py b/tests/test_pdf_html_preview.py
index c0a3c8ca..3343b901 100644
--- a/tests/test_pdf_html_preview.py
+++ b/tests/test_pdf_html_preview.py
@@ -10,12 +10,12 @@ import pytest
 
 
 def _read_js(name):
-    with open(os.path.join('static', name)) as f:
+    with open(os.path.join('static', name), encoding="utf-8") as f:
         return f.read()
 
 
 def _read_css():
-    with open(os.path.join('static', 'style.css')) as f:
+    with open(os.path.join('static', 'style.css'), encoding="utf-8") as f:
         return f.read()
 
 
@@ -316,7 +316,7 @@ class TestI18nKeys:
     HTML_KEYS = ['html_loading', 'html_too_large', 'html_error', 'html_open_full', 'html_sandbox_label']
 
     def _find_locale_block(self, locale):
-        with open('static/i18n.js') as f:
+        with open('static/i18n.js', encoding="utf-8") as f:
             content = f.read()
         start = content.find(f"'{locale}':")
         if start < 0:
diff --git a/tests/test_run_journal_frontend_static.py b/tests/test_run_journal_frontend_static.py
index ed94f720..e63b084a 100644
--- a/tests/test_run_journal_frontend_static.py
+++ b/tests/test_run_journal_frontend_static.py
@@ -4,9 +4,9 @@ from pathlib import Path
 
 
 ROOT = Path(__file__).resolve().parents[1]
-MESSAGES_SRC = (ROOT / "static" / "messages.js").read_text()
-SESSIONS_SRC = (ROOT / "static" / "sessions.js").read_text()
-UI_SRC = (ROOT / "static" / "ui.js").read_text()
+MESSAGES_SRC = (ROOT / "static" / "messages.js").read_text(encoding="utf-8")
+SESSIONS_SRC = (ROOT / "static" / "sessions.js").read_text(encoding="utf-8")
+UI_SRC = (ROOT / "static" / "ui.js").read_text(encoding="utf-8")
 
 
 def _function_body(src: str, signature: str) -> str:
diff --git a/tests/test_run_journal_routes.py b/tests/test_run_journal_routes.py
index efc4324b..d5a40626 100644
--- a/tests/test_run_journal_routes.py
+++ b/tests/test_run_journal_routes.py
@@ -6,7 +6,7 @@ import queue
 
 
 ROOT = Path(__file__).resolve().parents[1]
-ROUTES_SRC = (ROOT / "api" / "routes.py").read_text()
+ROUTES_SRC = (ROOT / "api" / "routes.py").read_text(encoding="utf-8")
 
 
 def test_stream_status_exposes_replay_summary():
diff --git a/tests/test_session_batch_select.py b/tests/test_session_batch_select.py
index 7794a45a..e82cc3d5 100644
--- a/tests/test_session_batch_select.py
+++ b/tests/test_session_batch_select.py
@@ -4,7 +4,7 @@ import re
 
 def test_batch_select_state_variables():
     """Verify batch select state variables are declared."""
-    with open('static/sessions.js') as f:
+    with open('static/sessions.js', encoding="utf-8") as f:
         src = f.read()
     assert '_sessionSelectMode' in src, "Missing _sessionSelectMode variable"
     assert '_selectedSessions' in src, "Missing _selectedSessions variable"
@@ -13,7 +13,7 @@ def test_batch_select_state_variables():
 
 def test_batch_select_functions_exist():
     """Verify all batch select functions are defined."""
-    with open('static/sessions.js') as f:
+    with open('static/sessions.js', encoding="utf-8") as f:
         src = f.read()
     required_funcs = [
         'toggleSessionSelectMode',
@@ -31,7 +31,7 @@ def test_batch_select_functions_exist():
 
 def test_batch_select_checkbox_rendering():
     """Verify checkbox is rendered when in select mode."""
-    with open('static/sessions.js') as f:
+    with open('static/sessions.js', encoding="utf-8") as f:
         src = f.read()
     assert 'session-select-cb' in src, "Missing session-select-cb class"
     assert 'session-select-cb-wrapper' in src, "Missing session-select-cb-wrapper class"
@@ -40,7 +40,7 @@ def test_batch_select_checkbox_rendering():
 
 def test_batch_select_intercepts_navigation():
     """Verify select mode intercepts session navigation."""
-    with open('static/sessions.js') as f:
+    with open('static/sessions.js', encoding="utf-8") as f:
         src = f.read()
     assert "_sessionSelectMode" in src
     # Should have early return when in select mode
@@ -50,7 +50,7 @@ def test_batch_select_intercepts_navigation():
 
 def test_batch_checkbox_sets_selection_without_row_double_toggle():
     """Clicking the checkbox itself must not also trigger row-level toggling."""
-    with open('static/sessions.js') as f:
+    with open('static/sessions.js', encoding="utf-8") as f:
         src = f.read()
     assert 'function setSessionSelected(sid, selected)' in src, \
         "Checkbox changes should set explicit state instead of toggling blindly"
@@ -64,7 +64,7 @@ def test_batch_checkbox_sets_selection_without_row_double_toggle():
 
 def test_batch_select_escape_handler():
     """Verify Escape key exits select mode."""
-    with open('static/sessions.js') as f:
+    with open('static/sessions.js', encoding="utf-8") as f:
         src = f.read()
     assert "e.key==='Escape'&&_sessionSelectMode" in src, \
         "Should have Escape key handler for select mode"
@@ -72,7 +72,7 @@ def test_batch_select_escape_handler():
 
 def test_batch_select_toggle_button():
     """Verify select mode toggle button is rendered."""
-    with open('static/sessions.js') as f:
+    with open('static/sessions.js', encoding="utf-8") as f:
         src = f.read()
     assert 'session-select-toggle' in src, "Missing session-select-toggle class"
     assert 'toggleSessionSelectMode' in src, "Missing toggleSessionSelectMode call"
@@ -80,7 +80,7 @@ def test_batch_select_toggle_button():
 
 def test_batch_select_bar_element():
     """Verify batch action bar DOM element is created."""
-    with open('static/sessions.js') as f:
+    with open('static/sessions.js', encoding="utf-8") as f:
         src = f.read()
     assert 'batchActionBar' in src, "Missing batchActionBar element"
     assert 'batch-action-bar' in src, "Missing batch-action-bar CSS class"
@@ -89,7 +89,7 @@ def test_batch_select_bar_element():
 
 def test_batch_action_bar_overrides_css_hidden_state():
     """Selected sessions must make the fixed action bar visible."""
-    with open('static/sessions.js') as f:
+    with open('static/sessions.js', encoding="utf-8") as f:
         src = f.read()
     assert "if(count>0){_renderBatchActionBar();}" in src, \
         "Updating selected count must render action buttons, not just reveal an empty bar"
@@ -107,9 +107,9 @@ def test_batch_action_bar_overrides_css_hidden_state():
 
 def test_batch_action_bar_is_sidebar_inline_not_global_footer():
     """Batch actions should appear in the session list, not over the composer."""
-    with open('static/sessions.js') as f:
+    with open('static/sessions.js', encoding="utf-8") as f:
         js = f.read()
-    with open('static/style.css') as f:
+    with open('static/style.css', encoding="utf-8") as f:
         css = f.read()
     assert "list.appendChild(batchBar)" in js, \
         "Batch action bar should be rendered inside the session list"
@@ -123,9 +123,9 @@ def test_batch_action_bar_is_sidebar_inline_not_global_footer():
 
 def test_batch_project_picker_is_anchored_to_batch_actions():
     """Batch move project picker should open inside the sidebar action bar."""
-    with open('static/sessions.js') as f:
+    with open('static/sessions.js', encoding="utf-8") as f:
         js = f.read()
-    with open('static/style.css') as f:
+    with open('static/style.css', encoding="utf-8") as f:
         css = f.read()
     assert "const bar=$('batchActionBar');if(!bar)return;" in js, \
         "Batch project picker should anchor to the batch action bar"
@@ -143,7 +143,7 @@ def test_batch_project_picker_is_anchored_to_batch_actions():
 
 def test_streaming_zero_message_sessions_stay_visible_after_reload():
     """In-flight sessions may have zero saved messages during reload recovery."""
-    with open('static/sessions.js') as f:
+    with open('static/sessions.js', encoding="utf-8") as f:
         src = f.read()
     assert "_isSessionEffectivelyStreaming(s)" in src, \
         "Streaming sessions must bypass the zero-message sidebar filter"
@@ -155,7 +155,7 @@ def test_streaming_zero_message_sessions_stay_visible_after_reload():
 
 def test_boot_does_not_drop_zero_message_inflight_session():
     """Reloading /session/<id> during a running turn must keep the session open."""
-    with open('static/boot.js') as f:
+    with open('static/boot.js', encoding="utf-8") as f:
         src = f.read()
     assert "const _restoredInFlight = S.session && (" in src, \
         "Boot must detect restored in-flight sessions before ephemeral cleanup"
@@ -169,7 +169,7 @@ def test_boot_does_not_drop_zero_message_inflight_session():
 
 def test_batch_select_i18n_keys():
     """Verify all batch select i18n keys exist in all locales."""
-    with open('static/i18n.js') as f:
+    with open('static/i18n.js', encoding="utf-8") as f:
         src = f.read()
     required_keys = [
         'session_select_mode',
@@ -202,7 +202,7 @@ def test_batch_select_i18n_keys():
 
 def test_i18n_string_placeholder_interpolation_supported():
     """String-valued translations with {0} placeholders should interpolate args."""
-    with open('static/i18n.js') as f:
+    with open('static/i18n.js', encoding="utf-8") as f:
         src = f.read()
     assert "String(val).replace(/\\{(\\d+)\\}/g" in src, \
         "t() must interpolate {0}-style placeholders for string-valued translations"
@@ -212,7 +212,7 @@ def test_i18n_string_placeholder_interpolation_supported():
 
 def test_batch_select_css_exists():
     """Verify batch select CSS classes are defined."""
-    with open('static/style.css') as f:
+    with open('static/style.css', encoding="utf-8") as f:
         src = f.read()
     required_classes = [
         'session-select-toggle',
@@ -233,7 +233,7 @@ def test_batch_select_css_exists():
 
 def test_batch_select_mode_flags():
     """Verify select mode properly toggles state."""
-    with open('static/sessions.js') as f:
+    with open('static/sessions.js', encoding="utf-8") as f:
         src = f.read()
     # toggleSessionSelectMode should flip the flag
     assert '_sessionSelectMode=!_sessionSelectMode' in src, \
@@ -247,7 +247,7 @@ def test_batch_select_mode_flags():
 
 def test_batch_delete_uses_confirm_dialog():
     """Verify batch delete shows confirmation dialog."""
-    with open('static/sessions.js') as f:
+    with open('static/sessions.js', encoding="utf-8") as f:
         src = f.read()
     # The delete handler should call showConfirmDialog with batch message
     assert "session_batch_delete_confirm" in src, \
diff --git a/tests/test_sprint38.py b/tests/test_sprint38.py
index 8cb2ce89..427252a0 100644
--- a/tests/test_sprint38.py
+++ b/tests/test_sprint38.py
@@ -7,8 +7,8 @@ and the streaming render path (messages.js _streamDisplay logic).
 import pathlib
 
 REPO_ROOT = pathlib.Path(__file__).parent.parent
-UI_JS     = (REPO_ROOT / "static" / "ui.js").read_text()
-MSG_JS    = (REPO_ROOT / "static" / "messages.js").read_text()
+UI_JS     = (REPO_ROOT / "static" / "ui.js").read_text(encoding="utf-8")
+MSG_JS    = (REPO_ROOT / "static" / "messages.js").read_text(encoding="utf-8")
 
 
 # ── ui.js: static render path ────────────────────────────────────────────────
diff --git a/tests/test_sprint40.py b/tests/test_sprint40.py
index 6a39bc16..a39b003d 100644
--- a/tests/test_sprint40.py
+++ b/tests/test_sprint40.py
@@ -16,8 +16,8 @@ from unittest.mock import patch
 import api.onboarding as mod
 
 REPO_ROOT = pathlib.Path(__file__).parent.parent
-I18N_JS = (REPO_ROOT / "static" / "i18n.js").read_text()
-ONBOARDING_JS = (REPO_ROOT / "static" / "onboarding.js").read_text()
+I18N_JS = (REPO_ROOT / "static" / "i18n.js").read_text(encoding="utf-8")
+ONBOARDING_JS = (REPO_ROOT / "static" / "onboarding.js").read_text(encoding="utf-8")
 
 
 # ── Backend: _build_setup_catalog ──────────────────────────────────────────
@@ -152,7 +152,7 @@ class TestOAuthOnboardingJs(unittest.TestCase):
 
     def test_style_css_has_oauth_card_rules(self):
         """style.css must contain the .onboarding-oauth-card rules."""
-        css = (REPO_ROOT / "static" / "style.css").read_text()
+        css = (REPO_ROOT / "static" / "style.css").read_text(encoding="utf-8")
         self.assertIn("onboarding-oauth-card", css)
         self.assertIn("onboarding-oauth-ready", css)
         self.assertIn("onboarding-oauth-pending", css)
diff --git a/tests/test_sprint40_ui_polish.py b/tests/test_sprint40_ui_polish.py
index 6f26aad7..5743ceba 100644
--- a/tests/test_sprint40_ui_polish.py
+++ b/tests/test_sprint40_ui_polish.py
@@ -18,9 +18,9 @@ if str(_REPO_ROOT) not in sys.path:
     sys.path.insert(0, str(_REPO_ROOT))
 
 REPO_ROOT  = _REPO_ROOT
-STYLE_CSS  = (REPO_ROOT / "static" / "style.css").read_text()
-SESSIONS_JS = (REPO_ROOT / "static" / "sessions.js").read_text()
-PANELS_JS   = (REPO_ROOT / "static" / "panels.js").read_text()
+STYLE_CSS  = (REPO_ROOT / "static" / "style.css").read_text(encoding="utf-8")
+SESSIONS_JS = (REPO_ROOT / "static" / "sessions.js").read_text(encoding="utf-8")
+PANELS_JS   = (REPO_ROOT / "static" / "panels.js").read_text(encoding="utf-8")
 
 try:
     from api import config as _api_config
@@ -101,7 +101,7 @@ class TestGatewaySessionNullModel(unittest.TestCase):
         """api/models.py must not use `or 'unknown'` for the model field
         so that a NULL model in state.db is returned as None (falsy) to
         the frontend rather than the truthy string 'unknown'."""
-        models_src = (REPO_ROOT / "api" / "models.py").read_text()
+        models_src = (REPO_ROOT / "api" / "models.py").read_text(encoding="utf-8")
         # Ensure the old fallback pattern is gone
         self.assertNotIn(
             "'model': row['model'] or 'unknown'",
@@ -113,7 +113,7 @@ class TestGatewaySessionNullModel(unittest.TestCase):
     def test_gateway_watcher_null_model_returns_none_not_unknown(self):
         """api/gateway_watcher.py must not use `or 'unknown'` for the model
         field so that a NULL model in state.db is returned as None (falsy)."""
-        gw_src = (REPO_ROOT / "api" / "gateway_watcher.py").read_text()
+        gw_src = (REPO_ROOT / "api" / "gateway_watcher.py").read_text(encoding="utf-8")
         self.assertNotIn(
             "'model': row['model'] or 'unknown'",
             gw_src,
@@ -124,8 +124,8 @@ class TestGatewaySessionNullModel(unittest.TestCase):
     def test_gateway_session_model_uses_none_fallback(self):
         """Both source files must use `row['model'] or None` (explicit None
         fallback) for the model field assignment."""
-        models_src = (REPO_ROOT / "api" / "models.py").read_text()
-        gw_src = (REPO_ROOT / "api" / "gateway_watcher.py").read_text()
+        models_src = (REPO_ROOT / "api" / "models.py").read_text(encoding="utf-8")
+        gw_src = (REPO_ROOT / "api" / "gateway_watcher.py").read_text(encoding="utf-8")
         self.assertIn(
             "'model': row['model'] or None,",
             models_src,
diff --git a/tests/test_sprint41.py b/tests/test_sprint41.py
index eee0898c..a4ca9672 100644
--- a/tests/test_sprint41.py
+++ b/tests/test_sprint41.py
@@ -12,10 +12,10 @@ import re
 import unittest
 
 REPO_ROOT = pathlib.Path(__file__).parent.parent
-CSS = (REPO_ROOT / "static" / "style.css").read_text()
-HTML = (REPO_ROOT / "static" / "index.html").read_text()
-MESSAGES_JS = (REPO_ROOT / "static" / "messages.js").read_text()
-STREAMING_PY = (REPO_ROOT / "api" / "streaming.py").read_text()
+CSS = (REPO_ROOT / "static" / "style.css").read_text(encoding="utf-8")
+HTML = (REPO_ROOT / "static" / "index.html").read_text(encoding="utf-8")
+MESSAGES_JS = (REPO_ROOT / "static" / "messages.js").read_text(encoding="utf-8")
+STREAMING_PY = (REPO_ROOT / "api" / "streaming.py").read_text(encoding="utf-8")
 
 
 # ── streaming.py: title auto-generation condition ─────────────────────────
diff --git a/tests/test_sprint42.py b/tests/test_sprint42.py
index 9c027fac..17a28ddc 100644
--- a/tests/test_sprint42.py
+++ b/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, \
diff --git a/tests/test_sprint43.py b/tests/test_sprint43.py
index 7a379325..627dfc4f 100644
--- a/tests/test_sprint43.py
+++ b/tests/test_sprint43.py
@@ -18,16 +18,16 @@ import sys
 import unittest
 
 REPO_ROOT = pathlib.Path(__file__).parent.parent
-GATEWAY_WATCHER_PY = (REPO_ROOT / "api" / "gateway_watcher.py").read_text()
-CONFIG_PY = (REPO_ROOT / "api" / "config.py").read_text()
-BOOTSTRAP_PY = (REPO_ROOT / "bootstrap.py").read_text()
-SERVER_PY = (REPO_ROOT / "server.py").read_text()
-ROUTES_PY = (REPO_ROOT / "api" / "routes.py").read_text()
-AUTH_PY = (REPO_ROOT / "api" / "auth.py").read_text()
-PROFILES_PY = (REPO_ROOT / "api" / "profiles.py").read_text()
-STREAMING_PY = (REPO_ROOT / "api" / "streaming.py").read_text()
-WORKSPACE_PY = (REPO_ROOT / "api" / "workspace.py").read_text()
-STATE_SYNC_PY = (REPO_ROOT / "api" / "state_sync.py").read_text()
+GATEWAY_WATCHER_PY = (REPO_ROOT / "api" / "gateway_watcher.py").read_text(encoding="utf-8")
+CONFIG_PY = (REPO_ROOT / "api" / "config.py").read_text(encoding="utf-8")
+BOOTSTRAP_PY = (REPO_ROOT / "bootstrap.py").read_text(encoding="utf-8")
+SERVER_PY = (REPO_ROOT / "server.py").read_text(encoding="utf-8")
+ROUTES_PY = (REPO_ROOT / "api" / "routes.py").read_text(encoding="utf-8")
+AUTH_PY = (REPO_ROOT / "api" / "auth.py").read_text(encoding="utf-8")
+PROFILES_PY = (REPO_ROOT / "api" / "profiles.py").read_text(encoding="utf-8")
+STREAMING_PY = (REPO_ROOT / "api" / "streaming.py").read_text(encoding="utf-8")
+WORKSPACE_PY = (REPO_ROOT / "api" / "workspace.py").read_text(encoding="utf-8")
+STATE_SYNC_PY = (REPO_ROOT / "api" / "state_sync.py").read_text(encoding="utf-8")
 
 
 # ── B324: MD5 usedforsecurity=False ─────────────────────────────────────────
diff --git a/tests/test_sprint48.py b/tests/test_sprint48.py
index 2de27e23..5aa403cf 100644
--- a/tests/test_sprint48.py
+++ b/tests/test_sprint48.py
@@ -15,7 +15,7 @@ REPO = pathlib.Path(__file__).parent.parent
 
 
 def read(rel):
-    return (REPO / rel).read_text()
+    return (REPO / rel).read_text(encoding="utf-8")
 
 
 # ── Bug #702 — XML tool-call leak on DeepSeek ────────────────────────────────
diff --git a/tests/test_svg_audio_video_rendering.py b/tests/test_svg_audio_video_rendering.py
index 40475917..d5e7309d 100644
--- a/tests/test_svg_audio_video_rendering.py
+++ b/tests/test_svg_audio_video_rendering.py
@@ -4,7 +4,7 @@ import re
 
 def test_media_extension_regexes_exist():
     """Verify SVG/audio/video extension regexes are defined."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     assert '_SVG_EXTS' in src, "Missing _SVG_EXTS regex"
     assert '_AUDIO_EXTS' in src, "Missing _AUDIO_EXTS regex"
@@ -19,7 +19,7 @@ def test_media_extension_regexes_exist():
 
 def test_svg_rendered_before_image_catch_all():
     """Verify SVG handler for URLs runs before the catch-all image handler."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     # Find positions of SVG vs image catch-all in the URL section
     svg_url_match = src.find("SVG URLs")
@@ -33,7 +33,7 @@ def test_svg_rendered_before_image_catch_all():
 
 def test_local_svg_inline_rendering():
     """Verify local SVG files render as inline image."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     assert "msg-media-svg" in src, "Missing msg-media-svg CSS class for SVG rendering"
     # Should have at least 2 SVG handlers (URL + local)
@@ -43,7 +43,7 @@ def test_local_svg_inline_rendering():
 
 def test_local_audio_inline_rendering():
     """Verify local audio files render as inline player."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     assert "msg-media-audio" in src, "Missing msg-media-audio CSS class"
     assert "<audio controls" in src, "Should render <audio> element with controls"
@@ -53,7 +53,7 @@ def test_local_audio_inline_rendering():
 
 def test_local_video_inline_rendering():
     """Verify local video files render as inline player."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     assert "msg-media-video" in src, "Missing msg-media-video CSS class"
     assert "<video controls" in src, "Should render <video> element with controls"
@@ -63,7 +63,7 @@ def test_local_video_inline_rendering():
 
 def test_url_svg_audio_video_handlers():
     """Verify HTTPS URLs for SVG/audio/video get inline rendering."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     # SVG URLs should be handled via _SVG_EXTS test on urlPath
     url_svg = "_SVG_EXTS.test(urlPath)" in src or ("_SVG_EXTS.test" in src and "urlPath" in src)
@@ -77,7 +77,7 @@ def test_url_svg_audio_video_handlers():
 
 def test_attachment_svg_audio_video():
     """Verify file attachments for SVG/audio/video get inline previews."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     assert "attach-thumb--svg" in src, "Missing attach-thumb--svg for SVG thumbnails"
     assert "attach-chip--audio" in src, "Missing attach-chip--audio"
@@ -87,7 +87,7 @@ def test_attachment_svg_audio_video():
 
 def test_attachment_blob_url_cleanup():
     """Verify audio/video attachment chips create blob URLs."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     # SVG and media attachments should use createObjectURL
     assert "URL.createObjectURL(f)" in src, "Should create blob URLs for attachments"
@@ -95,21 +95,21 @@ def test_attachment_blob_url_cleanup():
 
 def test_preload_metadata():
     """Verify audio/video elements use preload='metadata' for performance."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     assert 'preload="metadata"' in src, "Audio/video should use preload='metadata'"
 
 
 def test_media_label_class():
     """Verify media label class exists for type identification."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     assert "msg-media-label" in src, "Missing msg-media-label class"
 
 
 def test_i18n_keys():
     """Verify media rendering i18n keys exist in all locales."""
-    with open('static/i18n.js') as f:
+    with open('static/i18n.js', encoding="utf-8") as f:
         src = f.read()
     required_keys = [
         'media_audio_label',
@@ -123,7 +123,7 @@ def test_i18n_keys():
 
 def test_css_classes_exist():
     """Verify all media CSS classes are defined."""
-    with open('static/style.css') as f:
+    with open('static/style.css', encoding="utf-8") as f:
         src = f.read()
     required_classes = [
         'msg-media-svg',
@@ -141,7 +141,7 @@ def test_css_classes_exist():
 
 def test_svg_not_matched_by_image_exts():
     """Verify .svg is NOT in _IMAGE_EXTS (SVG has its own handler)."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     # Extract the _IMAGE_EXTS regex
     match = re.search(r"const _IMAGE_EXTS=/([^/]+)/i", src)
@@ -152,7 +152,7 @@ def test_svg_not_matched_by_image_exts():
 
 def test_audio_video_not_matched_by_image_exts():
     """Verify audio/video extensions are NOT in _IMAGE_EXTS."""
-    with open('static/ui.js') as f:
+    with open('static/ui.js', encoding="utf-8") as f:
         src = f.read()
     match = re.search(r"const _IMAGE_EXTS=/([^/]+)/i", src)
     assert match
diff --git a/tests/test_topbar_lazy_message_count.py b/tests/test_topbar_lazy_message_count.py
index ff37c2e9..b33990bf 100644
--- a/tests/test_topbar_lazy_message_count.py
+++ b/tests/test_topbar_lazy_message_count.py
@@ -1,7 +1,7 @@
 from pathlib import Path
 
 ROOT = Path(__file__).resolve().parents[1]
-UI_JS = (ROOT / "static" / "ui.js").read_text()
+UI_JS = (ROOT / "static" / "ui.js").read_text(encoding="utf-8")
 
 
 def test_topbar_uses_session_total_for_lazy_loaded_transcripts():
@@ -28,7 +28,7 @@ def test_sync_topbar_does_not_count_only_loaded_tail_messages():
     assert "document.title='● '+document.title;" in block
     assert "const pendingPrefix=(typeof activeSessionHasPendingPromptAttention==='function'&&activeSessionHasPendingPromptAttention())?'● ':'';" not in block
 
-    sessions_js = (ROOT / "static" / "sessions.js").read_text()
+    sessions_js = (ROOT / "static" / "sessions.js").read_text(encoding="utf-8")
     fn = sessions_js[
         sessions_js.index("async function _ensureMessagesLoaded") :
         sessions_js.index("function _messageComparableText", sessions_js.index("async function _ensureMessagesLoaded"))