feat(e2): make plan and state loading non-destructive

[agustif]

Summary

Implements Epic #208 and sub-issues #215 #216 #217 #218.

This PR removes destructive load-time fallback behavior for plan/state persistence and adds explicit safety controls.

What Changed

1) Explicit persistence safety errors

• Added PersistenceSafetyError for deterministic persistence failures.
• Added explicit error-code prefixes:
  • DLP_PERSISTENCE_PLAN_*
  • DLP_PERSISTENCE_STATE_*

2) Quarantine snapshot recovery path

• On unreadable/invalid payloads, loaders now write a *.quarantine.*.json snapshot with:
  • source path
  • reason
  • raw text
• Load now fails with actionable error instead of silently resetting to empty.

3) Future schema guard

• Loading future schema versions now fails by default.
• Added CLI/global recovery override:
  • --allow-unsafe-coerce
• Unsafe override path is explicitly marked and logged.

4) Non-destructive malformed-section handling

• Plan/state normalization now preserves malformed sections in _load_quarantine rather than silently dropping data.
• Added section-level quarantine for:
  • container type mismatches
  • invalid issue payloads (state)
  • invalid skipped entries (plan)

5) Save-path hardening

• save_plan / save_state now block writes when _unsafe_load_reasons exists.
• Override is possible only with --allow-unsafe-coerce (manual recovery workflow).
• Internal unsafe markers are stripped before persistence output.

6) Runtime + CLI wiring

• Added runtime context flag: allow_unsafe_coerce.
• Added parser flag: --allow-unsafe-coerce.
• CLI runtime scope now propagates this setting to persistence loaders/savers.

Test Coverage Added/Updated

• Added: desloppify/tests/plan/test_persistence_safety.py
• Updated: desloppify/tests/state/test_state.py

Test Evidence

Executed with local venv (.venv):

1. python -m pytest desloppify/tests/plan/test_persistence_safety.py desloppify/tests/state/test_state.py -q

• Result: 66 passed

2. python -m pytest desloppify/tests/plan/test_schema_migrations.py desloppify/tests/state/test_state_internal_direct.py desloppify/tests/core/test_runtime_state.py desloppify/tests/core/test_config.py -q

• Result: 54 passed

3. python -m pytest desloppify/tests/commands/test_cli.py -q

• Result: 97 passed

4. python -m compileall -q desloppify

• Result: success

Tracking

Parent program: #206