Problem

Fixes #33. Task files written before the blocking feature have no blockedBy / blocks / metadata. TaskStore.load() deserialized them as-is, and consumers read those fields unguarded (e.g. task.blockedBy.length in the widget). The first widget render on such a task threw TypeError: Cannot read properties of undefined (reading 'length'). Because the widget renders on a pi-tui timer, the throw was uncaught and killed the whole pi process — not just the extension — on the first render after upgrade. Unrecoverable without hand-editing the file.

Fix

Two layers:

1. Normalize at the load boundary (TaskStore.load → normalizeTask). Defaults metadata: {}, blocks: [], blockedBy: [] (with type guards for hand-edited files) plus defensive timestamp defaults. This is the correct single fix point: the same unguarded accesses exist across the store's mutation paths and index.ts (including ...task.metadata spreads that ?. can't fix), not only the widget — normalizing once means every consumer receives a canonical Task.
2. Guard the widget render — renderWidget now wraps the build in try/catch and returns a safe fallback, so a render error can never again escape to the TUI timer and take down the host. Defense-in-depth against the whole class of "extension render throw crashes pi".

Tests

• test/task-store.test.ts — loading a legacy-shaped file (pending task, no blockedBy/blocks/metadata) yields a task with those fields defaulted, existing fields preserved.
• test/task-widget.test.ts — rendering a task missing legacy fields does not throw.
• Verified the exact issue scenario end-to-end (legacy file → load → widget renders the subject, no crash).

Credit

Normalization approach based on #30 by @arrokh (thanks!) — this supersedes it. Reported by @eSaadster.

Test plan

• npx tsc --noEmit — clean
• npx vitest run — 190 passing (incl. 2 new)
• npx biome check src/ test/ — clean