docs: add drift monitoring plan

Author: Riverbraid

docs/DRIFT_MONITORING_PLAN.md

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+# Drift Monitoring Plan
+
+**Status**: DRAFT / PLAN ONLY  
+**Scope**: how Riverbraid may detect and report drift  
+**Implementation status**: NOT_IMPLEMENTED
+
+## Purpose
+
+Drift monitoring is the process of detecting when a repository, verifier, registry entry, claim, or evidence surface moves away from its declared state.
+
+The goal is not to prevent all change. The goal is to make unaccounted-for change visible.
+
+## Drift categories
+
+| Drift type | Description | Example |
+|---|---|---|
+| Claim drift | Documentation claims more than evidence supports. | A README implies production readiness. |
+| Registry drift | Registry pin no longer reflects intended proof surface. | Refusal-Gold has a later fail-closed patch not reflected in the pinned registry. |
+| Verifier-depth drift | A verifier's actual depth differs from declared depth. | Petal says deterministic-vector check but only checks file presence. |
+| Workflow drift | CI path changes without evidence update. | Verification command changed but evidence ledger not updated. |
+| Dependency drift | Dependencies change without boundary update. | Lockfile regenerated without recorded evidence. |
+| Artifact drift | Generated files, logs, or evidence packets diverge from expected state. | Evidence packet schema changes without version bump. |
+| Governance drift | Authority or decision process changes without recording. | Registry pin updated outside succession rules. |
+
+## Detection sources
+
+Potential sources:
+
+- GitHub compare results
+- GitHub Actions metadata
+- Evidence packets
+- claim ledger
+- evidence ledger
+- readiness matrix
+- registry scope gap
+- package lockfiles
+- workflow files
+- petal manifests
+
+## Drift record format
+
+```yaml
+drift_id:
+detected_at:
+repository:
+drift_type:
+observed_change:
+expected_state:
+evidence_source:
+severity:
+status:
+assigned_issue:
+resolution:
+non_claims:
+```
+
+Allowed statuses:
+
+```text
+OPEN
+UNDER_REVIEW
+ACCEPTED
+FALSE_POSITIVE
+RESOLVED
+DEFERRED
+```
+
+## Severity guide
+
+| Severity | Meaning |
+|---|---|
+| Low | Documentation or metadata drift that does not affect proof claims. |
+| Medium | Drift that may affect claim clarity or reviewability. |
+| High | Drift that affects verification behavior or registry truth. |
+| Critical | Drift that may create a false public trust signal. |
+
+## First implementation target
+
+The first drift monitor should be static and report-only:
+
+1. Compare tracked documentation claims against known non-claims.
+2. Compare active repo list against registry list.
+3. Compare declared verifier depth against known classification.
+4. Report differences.
+5. Open no automatic PRs.
+
+## Fail-closed rule
+
+If drift affects a proof claim, the affected claim should be downgraded to `UNKNOWN_PENDING_EVIDENCE` until reviewed.
+
+## Non-claim
+
+This plan does not implement drift monitoring and does not claim real-time monitoring exists.