docs: add CHANGELOG (baseline 0.2.0)

CHANGELOG.md

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+# Changelog
+
+All notable changes to Agentmetry are recorded here. The format follows
+[Keep a Changelog](https://keepachangelog.com/en/1.1.0/), and the project aims to
+follow [Semantic Versioning](https://semver.org/spec/v2.0.0.html) once out of
+alpha. While in **public alpha**, minor versions may carry breaking changes to
+APIs and integration surfaces. The canonical event schema is versioned
+separately (currently `1.1.0`) and changes additively.
+
+## [Unreleased]
+
+### Fixed
+- Inferred approvals now bind to the action that was actually approved. The
+  matcher compared tool names only, so an approval for `Bash(rm -rf /tmp/x)`
+  could be consumed by a later `Bash(ls)`. It now compares `input_hash` when both
+  sides carry one. A mismatch leaves the approval pending and resolves as denied
+  at session end, exposing the proposed-versus-executed gap in the trail.
+- API key comparison is constant-time (`secrets.compare_digest`), so the key can
+  no longer be recovered a byte at a time through response timing.
+
+### Changed
+- `core/config.py` is reorganized so the SIEM recorder settings come first and
+  the optional governed-runtime settings are grouped and signposted separately.
+  No settings changed: field names, defaults, and environment aliases are
+  identical.
+
+## [0.2.0] - 2026-07-19
+
+First tagged public-alpha release. A local-first flight recorder and mini-SIEM
+for AI coding agents: capture tool calls at the IDE and MCP boundary, tag them
+with MITRE ATT&CK, correlate sequences into detections, and keep a
+tamper-evident JSONL trail you own.
+
+### Added
+- **Capture.** IDE lifecycle hooks for Cursor, Claude Code, Codex and
+  Antigravity, plus an MCP stdio audit proxy. Hooks self-install at orchestrator
+  boot (`bootstrap_tier_b_hooks`), with no per-repo setup.
+- **Canonical schema v1.1.0.** Typed, SIEM-ready JSON with `actor`, `initiator`,
+  `model`, and a `tool` block carrying `input_hash`, `parameters_redacted`, and a
+  MITRE `{tactic_id, tactic, technique_id, technique}` object.
+- **Correlated detection.** Nine sequence rules (`credential-exfil`,
+  `approval-denied-then-executed`, `encoded-command-download`,
+  `pr-merged-without-review`, `untrusted-input-then-risky-action`,
+  `destructive-delete-burst`, `autonomous-unapproved-write`,
+  `discovery-then-collect`, opt-in `off-hours-activity`), including the two
+  published Agent Data Injection chains ([arXiv:2607.05120](https://arxiv.org/abs/2607.05120)).
+  Ordering is enforced by position, not co-occurrence. Detections stream to every
+  sink as first-class events.
+- **Durable live detection state.** SQLite checkpoint of emitted rules and
+  session event windows, which survives an orchestrator restart without
+  re-firing.
+- **Local DLP.** A regex engine scanning tool arguments at the hook boundary,
+  `log` (default) or `block` mode, recording the rule id and never the matched
+  value. Covers cloud keys, GitHub PATs, Slack tokens, bearer headers, private
+  keys, US SSN, invisible-Unicode instruction smuggling, and known supply-chain
+  exfil artifacts.
+- **Tool allow/deny policy.** A YAML manifest enforced at the hook boundary
+  before DLP; `command_pattern` rules match across all four IDE payload shapes.
+- **Pre-execution enforcement.** `block` decisions are emitted only on genuinely
+  pre-execution hooks. After-hooks record the match but never deny, since the
+  tool has already run.
+- **JSONL hash chain.** The file sink writes tamper-evident chained envelopes;
+  `agentmetry verify --trail` validates the chain, reports legacy unchained
+  prefix lines separately, and prints the chain head for out-of-band recording.
+- **SIEM forwarding.** File, generic webhook, Elastic ECS, Splunk HEC, Loki via
+  Grafana Alloy, a Sigma pack, and an alert webhook on denied or error outcomes.
+- **Dashboard (Phase 1).** A Next.js hunt layout with an Event stream, a
+  Detections triage view, and Analytics (MITRE breakdown, session process tree),
+  light and dark, with CSV/JSONL export.
+- **Evidence.** Export packs with a SHA-256 integrity manifest; `agentmetry
+  verify` recomputes it.
+- **Ops CLI.** `agentmetry doctor`, `stats`, `export`, `verify`, `verify
+  --trail`, and `start`/`stop`/`status`.
+- **Compliance kit.** An ISO 42001 mapping and an EU AI Act deployer checklist.
+- **Install.** Windows one-flow `scripts/install.ps1`. The orchestrator, tests,
+  and hook bootstrap also run on Linux (CI runs on Ubuntu).
+
+### Known limitations
+- Approval *responses* are inferred, not observed, since no IDE reports the
+  human's click. Inferred events are marked `inferred:*` and never presented as
+  native.
+- The MCP proxy is stdio-only; remote Streamable-HTTP servers are not yet seen.
+- DLP is regex, not entropy- or ML-based.
+- Tamper-evidence covers lines written after chaining was enabled, so a
+  long-running trail can carry a large legacy unchained prefix. The chain
+  protects the JSONL, not the SQLite index the dashboard reads.
+- Agentmetry records the agents you wire in. It is not a CASB and does not see
+  unmanaged ChatGPT or an IDE with hooks disabled.
+
+[Unreleased]: https://github.com/blitzcrieg1/agentmetry/compare/v0.2.0...HEAD
+[0.2.0]: https://github.com/blitzcrieg1/agentmetry/releases/tag/v0.2.0