Add Phase 9C security hardening

Generate exact-hash SDK source overrides without modifying dependencies.
Harden
SSH allocation and algorithm policy, tighten web authentication cleanup,
and add
focused host contract tests and documentation.

docs/roadmap.md

@@ -39,7 +39,7 @@ These constraints apply across all phases:
 | 6 | Authenticated SSH serial transport | **Complete** |
 | 7 | Local display and button interface | **Complete** |
 | 8 | Role-based users and administrative access | **Complete (8D.22 accepted 2026-09-13)** |
-| 9 | Security and production hardening | **In progress (9A/9B implemented; combined phase validation deferred)** |
+| 9 | Security and production hardening | **In progress (9A–9C implemented; combined phase validation deferred)** |
 | 10 | Authenticated, rollback-capable OTA | **Planned** |
 | 11 | BLE serial transport and provisioning evaluation | **Planned** |
 | 12 | Advanced network integration | **Under evaluation** |
@@ -209,14 +209,14 @@ Phase 8 is complete for its accepted scope. Phase 9 has started at the user's re
 
 ### Phase 9 — Security and production hardening
 
-**In progress.** Harden network authentication, secret lifetimes, crash/debug exposure and operational maintenance. Secure boot and encrypted NVS are explicitly excluded by user preference. No eFuse, partition, at-rest encryption or dependency-upgrade changes are part of 9A/9B; no future flash/PSRAM encryption commitment is implied. Physical extraction and firmware replacement remain outside the threat model after Phase 9, and software debug restrictions do not imply physical JTAG fuse restrictions.
+**In progress.** Harden network authentication, secret lifetimes, crash/debug exposure and operational maintenance. Secure boot and encrypted NVS are explicitly excluded by user preference. No eFuse, partition, at-rest encryption or dependency-version upgrades are part of 9A–9C; 9C adds source-pinned build-tree dependency corrections; no future flash/PSRAM encryption commitment is implied. Physical extraction and firmware replacement remain outside the threat model after Phase 9, and software debug restrictions do not imply physical JTAG fuse restrictions.
 
 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. **Next — Complete secret-lifetime and protocol review.** Audit remaining application/library allocations, private-key and packet-buffer destruction; review TLS/SSH algorithms, certificates, browser headers, password/KDF policy and remaining web-admission exposure. 9B's focused fixes are not full zeroization or protocol certification.
-4. **Later — Maintenance and lifecycle.** Review dependency advisories and licenses without assuming pinned versions are permanently safe; document provisioning, rotation, factory reset, backup, recovery and decommissioning. OTA signing trust needs an independent policy without secure boot (Phase 10).
+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).
 
 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.