docs: consolidate Coven security policy, threat boundary, and support claims

[CompleteDotTech]

Summary

• Replace the duplicated SECURITY.md (repository policy followed by a copied organization-wide OpenCoven Security Disclosure Addendum) with one Coven-specific operational security contract that keeps exactly one normative policy and visibly separates its five concerns: supported surfaces/status, enforced properties today, residual risk and safe configuration, private vulnerability reporting, and design goals vs guarantees.
• Retire the stale OpenTrust-scope addendum, the personal Discord DM (@BunsDev) as a normative reporting path, and the 48-hour acknowledgment / 14-day remediation promises that no accountable process currently backs. GitHub Security Advisories on this repository are the primary private intake; organization-wide reporting is pointed at the organization-level security policy.
• Tie every enforced property to its source-adjacent contract and verification family instead of restating implementation details: Rust authority revalidation and fail-closed handling (docs/SAFETY-MODEL.md, docs/AUTH.md), capability advertisement never grants permission and explicit replay-before-mutable ordering (docs/API-CONTRACT.md), owner-protected local transport and peer negotiation (same-user IPC, peer-fingerprint-bound client negotiation), redaction and sensitive-artifact defaults (specs/coven-trust-layer/PRODUCT.md, specs/coven-session-artifacts/TECH.md), and the secret/privacy guards (scripts/check-secrets.py, scripts/check-coven-privacy.py, CI Policy guard) with their documented new-changes baseline.
• Mark experimental surfaces explicitly: the AFS NFS mount backend is feature-gated and stays uncertified until the test: certify Coven end-to-end from packaged artifact through recovery and release evidence #779 certification gate closes the remaining loopback/SQLite gates in specs/coven-agent-fs/MOUNT-SPIKE.md; the OpenClaw plugin and remote/tunnel transports are opt-in/unsupported without a separate auth design (Design: authenticated remote listener for the daemon (companion clients) #463). State that same-user local trust is not sandboxing, and that no absolute containment ("cannot escape") claim is made for any surface.
• Move aspirational properties (session isolation, memory ownership, familiar identity integrity, execution boundaries) into a labeled design-goals section cross-referencing P0: enforce target input-guardrail parity across coven-agents handoffs #803/P1: refactor coven-agents onto invocation/delegation contracts without a second distributed runtime #804, rather than implying the current local Runner implements A2A isolation; note that release-gating security claims belong in the shipped-truth/certification evidence (test: certify Coven end-to-end from packaged artifact through recovery and release evidence #779, P0: enforce exact-commit release governance and shipped-truth attestation #805) and docs link/freshness validation under ci(docs): add canonical docs build, link, and browser journey #778.

Issue

Refs #808

Vehicle note: opened in the fork CompleteDotTech/coven as the CI vehicle — this token cannot write to OpenCoven/coven. Re-target upstream once write access is restored. Refs #808.

Implementation

• Approach: docs-only rewrite of SECURITY.md (~114 → ~215 lines), preserving the still-accurate operational content of the current policy (privacy-guard baseline, retention defaults, redaction coverage, synthetic placeholder rules) reorganized under the required structure. Internal links are relative repo links so they resolve in repository and deployed-doc contexts; external pointers (docs.opencoven.ai safety overview, org-level policy, releases, Security Advisories) are full URLs.
• User-visible behavior: the repository security policy rendered on GitHub and by docs tooling changes; no runtime, API, or build behavior changes.
• Compatibility notes: none (documentation only). The retired addendum's commitments are intentionally removed; researchers are directed to GitHub Security Advisories and the org-level policy for organization-wide scope.

Test plan

Local (docs-only change; Rust/npm suites unaffected and not executable in this environment — no cargo/python toolchain available, deferred to CI):

• Link validation: every relative link resolves against the tree; section anchors (#2-enforced-properties-today, #5-design-goals-vs-guarantees) verified against heading slugs; all five external URLs point at live, verified targets (org-level policy verified via REST).
• git diff --check (whitespace) — clean.
• Claim freshness pass against current source: retention defaults (7/30 days, coven logs prune), redaction implementation and unit tests (crates/coven-cli/src/privacy.rs), client peer-fingerprint negotiation tests (crates/coven-client/tests/health.rs), AFS conformance tests (crates/coven-afs/tests/spec_consistency.rs), mount feature gating (crates/coven-afs/Cargo.toml), release family (v0.4.x) — all verified at base SHA.
• Synthetic placeholders only; no real session ids, chat ids, phone numbers, absolute home paths, or credentials in examples.
• python scripts/check-secrets.py and python scripts/check-coven-privacy.py — deferred to CI Policy guard (no local Python).
• Maintainer/security-owner review of the operational commitments (advisory intake, no-SLA stance, scope split) — requested via review.

CI (docs-only classification expects changes, Policy guard, and PR gate):

• Policy guard (secret scan + privacy guard + workflow/script checks) green.
• PR gate green.

Risk and Rollback

• Risk level: low — documentation only; worst case is imprecise wording, mitigated by linking each claim to its owning contract/spec and keeping non-guarantees in a separate labeled section.
• Rollback plan: revert the single commit.

Agent Handoff

• Current state: single signed commit on agent/issue-808-p1-consolidate-coven-security-policy-threat; draft until CI is green.
• Follow-ups: link this policy from the canonical docs/support path in OpenCoven/coven-docs (that repository is outside this diff) and keep the AgentFS section synchronized with test: certify Coven end-to-end from packaged artifact through recovery and release evidence #779; fold in a maintainer/security-owner review of the reporting process.
• Known gaps: no accountable on-call rotation exists for advisory triage yet, so no acknowledgment/remediation SLA is published; fallback contact beyond GitHub Security Advisories is intentionally left unspecified rather than pointing at a personal channel.

CI note (fork vehicle)

• No CI exists on this fork vehicle. 11+ minutes after opening, the head commit has 0 check runs, 0 workflow runs, and 0 commit statuses (gh api repos/CompleteDotTech/coven/commits/<sha>/check-runs → total_count=0; actions/runs → 0) even though Actions are enabled on the fork. The upstream OpenCoven/coven CI (Classify changes → Policy guard → PR gate) has not run and cannot be triggered from here. The local verification checkboxes above are the only executed evidence; treat the Policy guard/PR gate boxes as pending until the PR is re-targeted upstream or CI runs on this vehicle.

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Recreated upstream from CompleteDotTech#1, preserving source head f670660 and branch agent/issue-808-p1-consolidate-coven-security-policy-threat.