new batch mode docs, add doc/ to -build branch

dist/doc/batch_nrpe.md

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+# NRPE Output Format
+
+`--batch nrpe` produces output that conforms to the
+[Nagios Plugin Development Guidelines](https://nagios-plugins.org/doc/guidelines.html),
+making it directly consumable by Nagios, Icinga, Zabbix (via NRPE), and
+compatible monitoring stacks.
+
+```sh
+sudo ./spectre-meltdown-checker.sh --batch nrpe
+```
+
+## Output structure
+
+The plugin emits one mandatory status line followed by optional long output:
+
+```
+STATUS: summary | checked=N vulnerable=N unknown=N
+NOTE: ...          ← context notes (when applicable)
+[CRITICAL] CVE-XXXX-YYYY (NAME): description
+[UNKNOWN]  CVE-XXXX-YYYY (NAME): description
+```
+
+### Line 1 (status line)
+
+Always present.  Parsed by every Nagios-compatible monitoring system.
+
+```
+STATUS: summary | perfdata
+```
+
+| Field | Values | Meaning |
+|---|---|---|
+| `STATUS` | `OK` / `CRITICAL` / `UNKNOWN` | Overall check outcome (see below) |
+| `summary` | human-readable string | Count and CVE IDs of affected checks |
+| `perfdata` | `checked=N vulnerable=N unknown=N` | Machine-readable counters for graphing |
+
+#### Status values
+
+| Status | Exit code | Condition |
+|---|---|---|
+| `OK` | `0` | All CVE checks passed |
+| `CRITICAL` | `2` | At least one CVE is vulnerable |
+| `UNKNOWN` | `3` | No VULN found, but at least one check is inconclusive **or** the script was not run as root and found apparent vulnerabilities (see below) |
+
+#### Summary format
+
+| Condition | Summary |
+|---|---|
+| All OK | `All N CVE checks passed` |
+| VULN only | `N/T CVE(s) vulnerable: CVE-A CVE-B ...` |
+| VULN + UNK | `N/T CVE(s) vulnerable: CVE-A CVE-B ..., M inconclusive` |
+| UNK only | `N/T CVE checks inconclusive` |
+| Non-root + VULN | `N/T CVE(s) appear vulnerable (unconfirmed, not root): CVE-A ...` |
+
+### Lines 2+ (long output)
+
+Shown in the detail/extended info view of most monitoring frontends.
+Never parsed by the monitoring core; safe to add or reorder.
+
+#### Context notes
+
+Printed before per-CVE details when applicable:
+
+| Note | Condition |
+|---|---|
+| `NOTE: paranoid mode active, stricter mitigation requirements applied` | `--paranoid` was used |
+| `NOTE: hypervisor host detected (reason); L1TF/MDS severity is elevated` | System is a VM host (KVM, Xen, VMware…) |
+| `NOTE: not a hypervisor host` | System is confirmed not a VM host |
+| `NOTE: not running as root; MSR reads skipped, results may be incomplete` | Script ran without root privileges |
+
+#### Per-CVE detail lines
+
+One line per non-OK CVE.  VULN entries (`[CRITICAL]`) appear before UNK
+entries (`[UNKNOWN]`); within each group the order follows the CVE registry.
+
+```
+[CRITICAL] CVE-XXXX-YYYY (SHORT NAME): mitigation status description
+[UNKNOWN]  CVE-XXXX-YYYY (SHORT NAME): reason check was inconclusive
+```
+
+## Exit codes
+
+| Code | Nagios meaning | Condition |
+|---|---|---|
+| `0` | OK | All checked CVEs are mitigated or hardware-unaffected |
+| `2` | CRITICAL | At least one CVE is vulnerable (script ran as root) |
+| `3` | UNKNOWN | At least one check inconclusive, or apparent VULN found without root |
+| `255` | - | Script error (bad arguments, unsupported platform) |
+
+Exit code `1` (WARNING) is not used; there is no "degraded but acceptable"
+state for CPU vulnerability mitigations.
+
+## Non-root behaviour
+
+Running without root privileges skips MSR reads and limits access to some
+kernel interfaces.  When the script finds apparent vulnerabilities without root:
+
+- The status word becomes `UNKNOWN` instead of `CRITICAL`
+- The exit code is `3` instead of `2`
+- The summary says `appear vulnerable (unconfirmed, not root)`
+- A `NOTE: not running as root` line is added to the long output
+
+**Recommendation:** always run with `sudo` for authoritative results.  A
+`CRITICAL` from a root-run scan is a confirmed vulnerability; an `UNKNOWN`
+from a non-root scan is a signal to investigate further.
+
+## Hypervisor hosts
+
+When `NOTE: hypervisor host detected` is present, L1TF (CVE-2018-3646) and
+MDS (CVE-2018-12126/12130/12127) carry significantly higher risk because
+they can be exploited across VM boundaries by a malicious guest.  Prioritise
+remediation on these hosts.
+
+## Examples
+
+**All mitigated (root):**
+```
+OK: All 31 CVE checks passed | checked=31 vulnerable=0 unknown=0
+NOTE: not a hypervisor host
+```
+Exit: `0`
+
+**Two CVEs vulnerable (root):**
+```
+CRITICAL: 2/31 CVE(s) vulnerable: CVE-2018-3615 CVE-2019-11135 | checked=31 vulnerable=2 unknown=0
+NOTE: not a hypervisor host
+[CRITICAL] CVE-2018-3615 (L1TF SGX): your CPU supports SGX and the microcode is not up to date
+[CRITICAL] CVE-2019-11135 (TAA): Your kernel doesn't support TAA mitigation, update it
+```
+Exit: `2`
+
+**Apparent vulnerabilities, non-root scan:**
+```
+UNKNOWN: 2/31 CVE(s) appear vulnerable (unconfirmed, not root): CVE-2018-3615 CVE-2019-11135 | checked=31 vulnerable=2 unknown=0
+NOTE: not a hypervisor host
+NOTE: not running as root; MSR reads skipped, results may be incomplete
+[CRITICAL] CVE-2018-3615 (L1TF SGX): your CPU supports SGX and the microcode is not up to date
+[CRITICAL] CVE-2019-11135 (TAA): Your kernel doesn't support TAA mitigation, update it
+```
+Exit: `3`
+
+**Inconclusive checks, paranoid mode, VMM host:**
+```
+UNKNOWN: 3/31 CVE checks inconclusive | checked=31 vulnerable=0 unknown=3
+NOTE: paranoid mode active, stricter mitigation requirements applied
+NOTE: hypervisor host detected (kvm); L1TF/MDS severity is elevated
+[UNKNOWN]  CVE-2018-3646 (L1TF VMM): SMT is enabled on a hypervisor host, not mitigated under paranoid mode
+```
+Exit: `3`