feat(v2): complete v2 reimplementation

docs/release/m10-evidence.md

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+# M10 SSH source evidence
+
+The released source capability is `ssh`: private-key-only, pinned-host-key,
+forced-SFTP chroot access. No password, shell, command channel, agent, default
+key discovery, or arbitrary remote root is supported.
+
+## Fixture
+
+`tests/compose.ssh.yaml` builds a test-only OpenSSH server. Each run generates
+host and client Ed25519 keys under pytest `tmp_path`, mounts no committed keys,
+and configures a dedicated `backup` account with `ChrootDirectory /home/backup`
+and `ForceCommand internal-sftp`. The ordinary operator Compose stack is not
+modified. Run `make test-ssh-integration` to build, run, and tear down the
+fixture.
+
+## Verification
+
+- Fake transport tests cover pin mismatch before authentication/SFTP, bounded
+  reads, unsafe entries, and accepted/rejected private-key algorithms.
+- The opt-in live test covers a private-key probe, backup, signed verification,
+  and restore through the forced-SFTP fixture.
+- `make test-ssh-integration` passed after fixture isolation and SFTP-channel
+  concurrency fixes.
+- Final `make check` passed: 107 unit/contract, 73 integration (one skipped),
+  15 fault, and 33 security tests; Ruff, mypy, TypeScript, and the frontend
+  build passed.
+
+See `docs/runbooks/ssh-sources.md` for deployment prerequisites, rotation, and
+containment limitations.