[FiraSenax]

JavaScript resource failures currently escape inject_pywebview() on the native navigation callback's thread. In a contaminated application build, a stray customize 2.js retained %(text_select)s but received no template parameters, raising KeyError through Cocoa's webView_didFinishNavigation_ and aborting the process. Missing/unreadable resources reach the same unguarded call. Separately, the initial run_js(js_code) is outside the worker's exception handler and can leave loaded waiters blocked.

This change catches resource-loading failures at the shared injection boundary and includes the filename in template-format errors. It also moves the initial script execution inside the existing worker handler. Failure sets loaded, consistently with the existing API-injection failure path, but never sets _pywebviewready. Scripts are not silently skipped and resource loading/discovery rules stay unchanged.

Validation on macOS / Python 3.11:

• Added unit regressions for loader failures, initial/API injection failures, the successful path, and filename diagnostics. Four cases fail before the fix and pass afterward.
• Added a native window regression with a malformed JS resource: the Cocoa window can load and close without aborting, while the bridge remains unready.
• pytest tests/test_util.py tests/test_js_api.py tests/test_load_html.py -q: 45 passed, including the existing bridge and HTML-loading tests.
• All configured pre-commit hooks passed on the four changed files.

The fix is in the shared injection code; backend modules are unchanged. Native Windows/Linux/Android backends and the full integration suite have not been run locally.

[Copilot]

🟢 Approval recommended

The narrow exception-handling changes preserve successful initialization, with no unresolved findings.

0 open findings

What changed in this PR

Hardens pywebview’s shared JavaScript injection path so resource and execution failures are handled without escaping native callbacks or blocking load waiters.

Changes:

• Catches resource-loading and initial injection errors; template errors identify the failing file.
• Adds unit and native-window regressions for failure handling and bridge readiness.
• Documents the behavior in the changelog.

File	Description
webview/​util.py	Guards injection failures and improves template diagnostics.
tests/​test_util.py	Tests failure handling, successful injection, and diagnostics.
tests/​test_js_api.py	Adds a malformed-resource native-window regression.
docs/​CHANGELOG.md	Documents the shared injection fix.

🧠 Review effort: Balanced

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[r0x0r]

@copilot please fix the merge conflicts in this pull request.