[codex] Structure web diff worker failures

[juliusmarminge]

Summary

• add a structured diff worker error with operation, theme, and exact cause
• distinguish worker construction, render-option reads, and theme updates
• preserve the existing UI behavior while making rejected theme synchronization observable

Adjacent diff parsing and syntax-language fallbacks remain unchanged because they are intentional rendering fallbacks rather than discarded worker failures.

Verification

• vp check
• vp run typecheck

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Note

Low Risk
Small observability change in diff rendering setup; no auth, data, or user-facing behavior changes beyond richer error logging.

Overview
Introduces DiffWorkerError (Effect Schema.TaggedErrorClass) so Pierre diff worker problems carry operation, themeName, and the underlying cause.

Worker creation in workerFactory now wraps new DiffsWorker() and rethrows failures as create-worker errors instead of a bare exception.

Theme sync in DiffWorkerThemeSync tracks whether failure happened during get-render-options or set-render-options, runs the update in an async IIFE with try/catch, and console.errors a DiffWorkerError instead of swallowing rejections via .catch(() => undefined)—user-visible behavior stays the same, but failed theme updates are observable in the console.

^{Reviewed by Cursor Bugbot for commit b8a09ab. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Structure diff worker failures with a typed DiffWorkerError class

• Adds DiffWorkerError (via effect/Schema) with fields for operation, themeName, and cause to give worker failures a consistent shape.
• DiffWorkerPoolProvider now throws DiffWorkerError (operation: create-worker) when new DiffsWorker() fails, replacing an untyped error.
• DiffWorkerThemeSync now awaits setRenderOptions and logs a DiffWorkerError on failure instead of silently swallowing errors.
• Behavioral Change: errors during setRenderOptions are now logged to console.error rather than discarded.

^{Macroscope summarized b8a09ab.}

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✨ Finishing Touches

🧪 Generate unit tests (beta)

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• Commit unit tests in branch codex/web-diff-worker-errors

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[macroscopeapp]

Approvability

Verdict: Approved

This PR adds structured error handling for diff worker operations, replacing silent error swallowing with properly typed error classes and console logging. The changes are self-contained, don't alter runtime behavior beyond improved error observability, and carry minimal risk.

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