Apply Phase 9D security mitigations

- Add fail-closed wolfSSL small-math policy and vectors
- Backport DHCP, EMS, and X.509 allocation fixes
- Extend source override validation and operational documentation

docs/roadmap.md

@@ -216,7 +216,7 @@ Staged work:
 1. **9A — Crash/debug build policy and operational profiles — In progress; hardware pending.** `src/security_build_policy.c` requires `CONFIG_ESP_COREDUMP_ENABLE_TO_NONE=y` and `CONFIG_ESP_SYSTEM_PANIC_SILENT_REBOOT=y`; rejects core-dump enable/flash/UART, panic print/halt/GDBstub, runtime GDBstub and ESP/FreeRTOS debugger-aware options. `sdkconfig.defaults` makes the baseline explicit. Development/test/production use the same build baseline, not separate PlatformIO environments. Host matrix (`python3 tests/security_build_policy/run.py`) compiles the actual guard: 17 cases plus the generated-header check passed on 2026-09-15. `pio run` passed (94,196 B linked RAM / 1,828,565 B flash); target panic/recovery tests have not run. Production readiness remains pending.
 2. **9B — SSH admission and credential handling — Implemented; combined target validation deferred.** Boot-lifetime, owner-only token buckets independently bound handshakes, password/signed-key requests and unsigned probes; reconnect/restart/counter clearing do not replenish them. Existing per-slot attempt limits/currentness remain. Explicit keyboard-interactive rejection, pending-signature result fencing, secret-free admission counters, consumed admin-buffer wipes and fail-closed hidden-prompt overflow/unsupported-byte handling are implemented. Four focused suites (including 35 pinned-vendor control-flow cases), 11 related regressions and `pio run` passed on 2026-09-15: 94,340 B linked RAM / 1,829,925 B flash. Global-budget starvation remains a documented tradeoff, not a solved availability problem.
 3. **9C — Library cleanup and protocol policy — Implemented; combined target validation deferred.** Exact-hash build-tree overrides correct HTTPS cleanup/leaks, HTTPD scratch failure/wiping/first-read handling, bounded SSH password parsing/wiping and server-local TLS policy without modifying installed dependencies. Secure wolfSSL allocation hooks and explicit SSH policy fail closed; early web quota probing avoids receiving already-throttled bodies. TLS1.2 ECDHE-ECDSA AES-GCM and SSH GCM/modern-KEX allowlists intentionally exclude legacy-only clients; no identity migration. Bounded password/certificate/header/destructor review is documented, not exhaustive zeroization. Final build PASS 94,340 B linked RAM / 1,831,309 B flash; focused and related host/source-contract tests passed. [Review and maintenance contract](security_library_review.md).
-4. **Next — 9D maintenance and lifecycle.** Review current dependency advisories and licenses without assuming pinned versions or local corrections are permanently safe; document provisioning, rotation, factory reset, backup, recovery and decommissioning. Upgrades require re-auditing the source overrides. OTA signing trust needs an independent policy without secure boot (Phase 10).
+4. **9D — Maintenance and lifecycle — In progress; unresolved security and distribution questions.** [Security operations](security_operations.md) documents provisioning, explicit saves, rotation, recovery, reconstruction (no implemented backup/export) and approved destructive reset/decommissioning. The [wolfSSL/wolfSSH implementation addendum](wolf_security_review.md) records the implemented Xtensa small X25519/Ed25519 mitigation (CVE-2025-12888), with consistent library/consumer flags and a resolved-settings guard; small X25519 is not combined with blinding. Server-recommended message-order work (CVE-2025-14942) and parser/ECC reviews remain pending. The [IDF implementation addendum](idf_security_review.md) records pinned DHCP (CVE-2026-45160), TLS 1.2 EMS (CVE-2026-50581) and X.509 allocation-failure (CVE-2026-34874) backports; historical research remains labeled and retained. Supplied parent build PASS: **94,340 B linked RAM / 1,767,217 B flash**, unchanged RAM / **−64,092 B flash** from 9C; SDK-override, wolf-crypto-policy, wolfSSH-auth-contract and SSH-protocol-policy suites all passed. Independent reviewer reports the first two suites passed with no blocking implementation defects; see [evidence and limits](security_hardening.md#mitigation-hostbuild-evidence--2026-09-15). The [bounded license inventory](dependency_licenses.md) marks modification/date notices resolved for all seven generated files (2026-09-15; upstream licenses retained), but radio-blob corresponding-source/exception, source/notice delivery and packaging/provenance questions remain open. Upgrades/backports require coherent source/header review, override rebasing and contract tests, not blind repinning. Broader dependency advisory coverage remains unfinished. No dependency upgrade was performed. **Phase 9 is not complete or production-ready; scoped mitigations do not establish full advisory closure, device validation or license/distribution clearance.** OTA signing trust remains separate Phase 10 work.
 
 At the user's request, hardware validation is deferred to **Phase 9 as a whole**, not required between implementation slices. [Security hardening](security_hardening.md) collects profiles, host evidence and the combined target checklist. Silent panic reboot removes useful crash diagnostics, not ordinary reset/boot/status information or every possible log disclosure. Raw flash/RAM/dumps remain secret-bearing, not routine diagnostic exports. Existing coredump bytes are not retroactively cleared; no secure erase is claimed. Isolated synthetic-secret debug builds require explicit reviewed source-policy changes, not a provided bypass flag.