fix(shared): preserve empty legacy image payloads

[Flow-Fly]

Summary

• normalize empty and whitespace-only legacy image strings to empty byte arrays
• preserve empty payloads from syntactically valid exact-base64 data URLs
• add public decodeProjectFile coverage for representative legacy layer and cel payloads
• keep malformed and unsupported non-empty legacy payloads rejected

Linked task issues

Closes #425

Regression evidence

Before the production change, npx vitest run tests/shared/project-contract.test.ts failed both new cases with TypeError: Legacy project image data is empty at shared/src/project-data.ts:71; the other 11 contract tests passed.

After the fix, npm run shared:build && npx vitest run tests/shared/project-contract.test.ts tests/serialization/project-data.test.ts passes all 30 tests.

Verification

• npm run shared:check (21 tests, including Node ESM import)
• npx tsc --noEmit
• npm run lint (passes with 5 pre-existing warnings, 0 errors)
• npm run test:run (112 files, 707 tests, plus Node ESM import)
• npm run build
• npm run fallow:audit
• git diff --check

No project format version, migration, or persisted schema changes.

Summary by CodeRabbit

• Bug Fixes
  • Improved handling of empty or whitespace-only project image data.
  • Empty image payloads now decode safely as empty image data instead of producing an error.
  • Supports empty payloads across legacy project layers and cels, including empty base64 image data URLs.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 9ef4759b-5de7-4167-ab4b-f5e00383ab80

📥 Commits

Reviewing files that changed from the base of the PR and between 230611d and e1aa218.

📒 Files selected for processing (3)

• shared/src/project-data.ts
• tests/serialization/project-data.test.ts
• tests/shared/project-contract.test.ts

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📝 Walkthrough

Walkthrough

Legacy image decoding now normalizes empty and whitespace-only payloads, including exact empty Base64 data URLs, to empty byte arrays. Tests cover normalization and decoding of empty layer and cel image data.

Changes

Legacy image compatibility

Layer / File(s)	Summary
Empty payload decoding and regression coverage shared/src/project-data.ts, tests/serialization/project-data.test.ts, tests/shared/project-contract.test.ts	decodeLegacyBase64ImageData trims inputs and returns empty byte arrays for empty payloads; normalization and legacy project decoding tests cover plain, whitespace-only, and empty Base64 data URL inputs.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: preserving empty legacy image payloads.
Linked Issues check	✅ Passed	The fix and tests satisfy #425 by restoring empty payload support while keeping malformed non-empty inputs rejected.
Out of Scope Changes check	✅ Passed	The PR stays within the compatibility fix and test coverage scope, with no unrelated feature or schema changes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch dev-425-empty-legacy-image-payloads

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_{Comment @coderabbitai help to get the list of available commands.}

[Flow-Fly]

Hotfix ready for owner merge at exact head e1aa2185abc1ef2494c74838d30ce11b844eefcc.

• Regression test failed on parent 230611d and passes on this head.
• Full local gate and required GitHub checks are green.
• CodeRabbit reported no findings.
• Automatic Codex Review completed clean with 👍.
• Independent Terra exact-head review: APPROVE, no findings.

After merge, draft reconciliation PR #424 will be regenerated from corrected main. No merge was performed here.