feat: implement Phase 3 state reconstruction and structural slice

[DSCmatter]

User description

• core/reducer.py: pure event fold, reconstruct() with snapshot shortcut and SHA-256 state hashing
• core/snapshots.py: interval snapshots (32 events/agent) + integrity verification
• core/slicing.py: structural_slice (SQL-first, BFS fallback) and why() decision evidence
• storage/postgres.py: event range fetch + snapshot persistence
• cli/main.py: agents/slice/why/reconstruct vs fixture or Postgres
• tests: four mandated property tests, fixture contract, integration
• tooling: scripts/test_phase3.ps1; README + TEST.md updated

pytest/ruff/ty green, integration verified against real Postgres.

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CodeAnt-AI Description

Add state reconstruction and causal decision debugging for event logs

What Changed

• Rebuilds an agent’s state at any point in its event history, including memory, tool activity, context, outputs, and status.
• Adds verified checkpoints that shorten later reconstruction and detect corrupted state.
• Adds structural event slicing that follows declared causal parents, with deterministic results and PostgreSQL support.
• Adds why evidence for decisions, including declared cross-agent inputs and mismatches between recorded values and event payloads.
• Adds fixture and PostgreSQL CLI workflows for listing agents, slicing events, inspecting decision evidence, and reconstructing state.
• Adds unit, property, CLI, and integration coverage plus Phase 3 validation and usage documentation.

Impact

✅ Reconstructable agent state at any event sequence
✅ Faster replay after snapshot checkpoints
✅ Clearer causal evidence for failed decisions

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🤖 CodeAnt AI — Review Status

Status	Commit	Started (UTC)	Finished (UTC)
✅ Reviewed your PR	fd0ccd3	Aug 24, 2026 · 07:00	07:06

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