[debug/export] 语法错误和构建失败未可靠显示在诊断界面

[jamiesun]

Context Boundary

• Repo/module: talkincode/GameKit, runtime diagnostics, preview status, and export feedback
• Version/commit: main, 9eb811e7bc3db3193b57609425723c478e438d32
• Runtime: browser preview plus ZIP export
• OS/browser: not recorded; one parser case was verified against standard SyntaxError text, but no browser E2E was run
• Dependencies/config: pygbag 0.9.3; no feature flag involved

Expectation vs. Reality

Expected: Runtime and build failures appear as stable, actionable Problems/Console feedback, and an error state is not reset by stale startup messages.

Actual: problemsFromConsole returns no problem unless it finds the literal Traceback (most recent call last):; standard SyntaxError text without that header is therefore missed. The preview poller reports ready every 400 ms while the terminal still contains default.tmpl: done, and noteReady unconditionally sets the run state to running, which can overwrite a later error. Exporting after deleting main.py throws from buildWebBundle without being converted into a user notice.

Reproduction Path

1. Call problemsFromConsole with standard SyntaxError output that has a File ... line ... frame but no Traceback header; it returns [].
2. Start a preview, leave default.tmpl: done in the terminal, then trigger a runtime exception; observe whether the repeated ready poll changes the state back to running.
3. Delete main.py and choose an export format; observe the unhandled build error instead of an in-app message.

Minimal reproduction: problemsFromConsole(' File "main.py", line 1\nSyntaxError: invalid syntax') returns an empty list.

Blast Radius

• Affected users/paths: users relying on the Problems panel for syntax/runtime failures or exporting an invalid project.
• Frequency: SyntaxError format, persistent startup terminal text after a runtime failure, or missing main.py during export.
• Severity rationale: failures are harder to diagnose and can be reported with the wrong run state; recommend P2.
• Workaround: inspect the Console and restore main.py before exporting.

Evidence

• Console parser requires a traceback marker: diagnostics.ts
• Repeated ready polling: PreviewPane.tsx
• Ready replaces the run state unconditionally: noteReady
• Build throws on missing entry point and export handler has no catch: buildWebBundle, exportKind
• Existing export tests cover archive contents and source round-tripping, not running an exported game: export.test.ts