fix(stories): preserve Unicode code points in spelling markup

[rudycelekli]

Summary

The renderer spelling helper uses split(''), which spaces UTF-16 code units. A supplementary letter or emoji is split into isolated surrogate halves and can become replacement characters during transport. Spelling markup should space Unicode code points, matching the Python parser.

Closes #2650.

Changes

• Space Unicode code points and extend the shared JS/Python parser corpus.
• Synchronize relevant documentation and add a quiet credited Unreleased changelog entry.
• No new UI strings or locale keys; maintained version files are unchanged.

Type

• 🐛 Bug fix
• ✨ New feature
• ♻️ Refactor
• 📝 Documentation
• 🧪 Tests
• 🔧 CI / Build
• 🚀 Release prep

Testing

• Hosted CI audit at 2026-10-06T12:35:20.584679+00:00: no failing latest checks; required CLA passes. All latest reported checks completed successfully. No upstream merge performed.

• JS parser regressions: 2 failed and 96 passed before; 98 pass after. Python 3.13 parser corpus: 86 pass with offline HF settings and an empty cache; no speech inference.

• git diff --check and the repository changelog style gate pass.

• Focused JavaScript tests used Node 24.19.0 and a reused Vitest 5.0.1 runtime; this repository pins Vitest 4.1.11. No full build qualification is claimed.

• Full backend suites and bun run check:electron were not run locally. The human CLA signature is registered and the required CLA status passes; hosted results are reported separately below.

Checklist

• I've tested this locally
• Every commit author has signed the CLA (the CLA check tells you how)
• I've updated relevant documentation (if applicable)
• No local machine paths, logs, or personal env details in this PR
• Maintained version files are in sync (if an owner-requested bump): root package.json, pyproject.toml, backend/core/version.py, and lockfiles
• If this PR changes runtime behavior, the regression fixture at tests/fixtures/omnivoice_data/ still loads green on the smoke-matrix CI job (macOS + Windows + Linux)

Release cadence

VoiceStudio ships continuous-to-main — no release candidates, no soak windows.
Every merged PR is immediately part of rolling source (main) and Docker
:latest. Electron artifact rehearsals validate desktop packages without publishing.
Version bumps require owner approval; validated releases are tagged from main
and published explicitly under the release checklist.
Users who want stability install an Electron release or pin Docker :stable.

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📥 Commits

Reviewing files that changed from the base of the PR and between 286f46b and dd6714d.

⛔ Files ignored due to path filters (1)

• tests/fixtures/longform_parser_cases.json is excluded by !tests/fixtures/**

📒 Files selected for processing (4)

• CHANGELOG.md
• docs/expressive-speech.md
• electron/src/shared/test/ssmlLite.test.js
• electron/src/shared/utils/ssmlLite.js

• Autopilot · Keep fixing CodeRabbit findings and required CI, and resolving merge conflicts

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[greptile-apps]

[Medium risk] Fixes Unicode handling in the spelling markup feature.

The PR appears safe to merge based on the reviewed changes.

Summary

The PR changes Stories spelling markup to preserve supplementary Unicode characters and adds regression coverage and documentation.

_{Reviews (1) · Last reviewed commit: "fix(stories): preserve Unicode code poin..."}

[github-actions]

All contributors on this pull request have signed the VoiceStudio CLA. Thank you!

[rudycelekli]

recheck