fix(blueprint): add error handling for JSON.parse in state, config, and migration loaders

[pjt222]

Summary

• Add try-catch error handling around bare JSON.parse calls in loadState(), loadOnboardConfig(), and readSnapshotManifest()
• Follows the existing pattern established by loadConfigDocument() in migration-state.ts (lines 143-153)
• loadState() recovers silently (returns blank state) — state is machine-written ephemeral data, and the next saveState() call self-heals the file
• loadOnboardConfig() recovers silently (returns null) — allows re-onboarding
• readSnapshotManifest() throws a descriptive error with structural validation (matching loadConfigDocument pattern) — migration cannot proceed safely with corrupt data

Related to #553

Test plan

• cd nemoclaw && npx vitest run — 79 tests pass (4 new)
• npx tsc --noEmit — no type errors
• Added test for malformed JSON in state.test.ts
• Added test for malformed JSON in config.test.ts
• Added tests for malformed JSON and array input in migration-state.test.ts

Co-Authored-By: Claude Opus 4.6 (1M context) noreply@anthropic.com

[coderabbitai]

📝 Walkthrough

Walkthrough

The PR adds error-handling safeguards for JSON file operations across three modules (state, migration-state, and config). Each loader function now gracefully handles malformed or invalid JSON by returning fallback values instead of throwing exceptions, and validation logic ensures parsed data matches expected types.

Changes

Cohort / File(s)	Summary
State Module nemoclaw/src/blueprint/state.ts, nemoclaw/src/blueprint/state.test.ts	Added try/catch wrapper to loadState() to return blank state on JSON parse failures; new test validates malformed JSON handling.
Migration State Module nemoclaw/src/commands/migration-state.ts, nemoclaw/src/commands/migration-state.test.ts	Added runtime validation to readSnapshotManifest() ensuring parsed JSON is an object (not array); two new tests cover malformed JSON and non-object parsing scenarios.
Config Module nemoclaw/src/onboard/config.ts, nemoclaw/src/onboard/config.test.ts	Added try/catch wrapper to loadOnboardConfig() to return null on JSON parse failures; new test validates invalid JSON handling.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 When JSON stumbles, graceful we stand,
With try/catch shields across the land,
No parse shall crash our precious flow,
We bounce back gently, steady and slow! 🌿

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately and concisely describes the main change: adding error handling for JSON.parse operations across three loaders (state, config, and migration), which is the primary focus of the changeset.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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