wip(mesh): S7A generic mesh driver contract doc (no code yet)

docs/driver-mesh.md

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+# Mesh driver (`adapters/mesh/driver`) — WIP design contract
+
+Status: WIP (lane S7A, ANTIFL0CK-OSS-COMPLETION-02). No code yet; this file is the CONTRACT step.
+
+## Provider interface (no vendor dependency)
+`driver.Driver` is implemented once, generically, over a `MeshProvider`:
+`Status`, `Peers`, `Connect(InterfaceConfig)`, `Disconnect`, `RotateKey`, `RevokedPeers`.
+Implementations: `wireguard` (real; trusted `wg` + `ip` via injected runner, config on stdin <= 64 KiB),
+`tailscalestatus` (observe-only over `adapters/mesh/tailscale`; mutators return
+`AF-DRIVER-MESH-PROVIDER-OBSERVE-ONLY`), `fake` (in-memory; conformance, partition, roaming tests).
+No control plane is required; partition is reported as DEGRADED + `AF-DRIVER-MESH-PARTITION`, never
+as a successful verify.
+
+## Privilege boundary
+One trusted binary per provider (absolute, root-owned, non-writable path, copied from
+`agent/enforcement/nftables.go:278-330`); `wg setconf <iface> /dev/stdin`; `ip link/addr` helper
+declared in the boundary description. Private keys: generated with stdlib `crypto/ecdh` X25519, held
+in process memory only; never logged, never in snapshots, receipts, journal or safe messages — only
+sha256-truncated fingerprints.
+
+## Recovery statement
+The address used to reach the node must not be served by the mesh interface or a peer AllowedIP
+unless a recovery allowlist route covers it; Simulate flags `AF-DRIVER-MESH-RECOVERY-LOSS`.
+Revoked peers are removed on apply and never re-added by rollback or recovery.
+
+## Probe keys
+`mesh.connect.observe`, `mesh.connect.enforce`.
+
+## Environment finding (2026-08-23)
+WSL Ubuntu-22.04: `unshare -rn` works, `ip link add wg0 type wireguard` succeeds (kernel module
+present), but no `wg` userspace binary is installed and root-owned files appear as uid 65534 inside
+the rootless namespace, so the root-ownership trust check must be relaxed test-only for the netns
+proof.