Add Standalone Login Page Renderer

Add a hash-bound, no-store login document with focused C and Node host
tests. Keep rendering inert until the 8D.3 authentication cutover.

docs/phase8d_plan.md

@@ -1,6 +1,6 @@
 # Phase 8D — Incremental web administration plan
 
-Status: **8D.0 through 8D.2 validated by user sign-off on 2026-09-05. 8D.2 implemented, host-tested and build-verified. Reserve budgets remain pending. 8D.3 has an inert request-parser preparatory split; its live cutover and 8D.4–8D.22 remain planned.** See the [8D.0 baseline and M1 contract](phase8d_baseline.md); no browser authentication cutover is claimed.
+Status: **8D.0 through 8D.2 validated by user sign-off on 2026-09-05. 8D.2 implemented, host-tested and build-verified. Reserve budgets remain pending. 8D.3 has inert request-parser and login-renderer preparatory splits; its live cutover and 8D.4–8D.22 remain planned.** See the [8D.0 baseline and M1 contract](phase8d_baseline.md); no browser authentication cutover is claimed.
 
 This is the execution plan for [roadmap Phase 8D](roadmap.md#phase-8--role-based-users-and-administrative-access). The roadmap retains the feature/security requirements; this document defines small work units, dependencies, and release gates. The [administration test matrix](user_administration_tests.md#planned-phase-8d-integrated-web-administration) remains the final acceptance checklist.
 
@@ -92,6 +92,8 @@ If 8D.3 exceeds the work-unit limit, first split out inert login-page rendering
 
 **Preparatory split (2026-09-05):** Scope review selected private request parsing first; the complete challenge/throttle/route/browser/test change exceeds the authored-line work-unit target. Added allocation-free `src/web_auth_parse.{c,h}` with no live HTTP callers: bounded canonical same-origin comparison, unique cookie extraction and strict UTF-8 login JSON decoding. `python3 tests/web_auth_parse/run.py` passes **268 cases** against production C; both existing session-store host modes pass. Final `pio run` passes in **7.50 seconds** and reports **95,260 B RAM / 1,601,925 B flash**, unchanged from 8D.2 because helpers are not live linked paths. No route/task/socket/stack-size/asset changes. No target/browser validation, runtime reserve approval or M1 completion is implied. Continue within **8D.3**, with the full atomic cutover still pending; see `docs/agent/current-state.md` for exact integration obligations.
 
+**Login-renderer preparatory split (2026-09-05):** Added `src/web_login_ui.{c,h}` with no live caller/route, leaving Basic and existing serial UI unchanged. Standalone 7,387-byte HTML plus terminator has no protected asset dependencies, five security headers including no-store and exact script-hash CSP. Explicit-only challenge/login flow, bounded request/response handling, safe errors/manual backoff, disabled pending inputs, best-effort password/reference cleanup and generation-safe page-exit cancellation. Review fixes abort every attempt on exit (including unread error bodies) and clear re-entered passwords. `python3 tests/web_login_ui/run.py` passes production C rendering/failure checks, exact CSP hash and eight Node VM groups; parser and both session test modes also pass. Final `pio run` passes in **8.25 seconds**, unchanged **95,260 B RAM / 1,601,925 B flash**: unused renderer costs are not live-linked/runtime costs yet. No new task/socket/route/stack-size/module heap or generated-asset change. No real-browser/HTTPD/hardware validation or M1 completion. **Next is the atomic live 8D.3 cutover using both prepared pieces**, followed by the mandatory M1 target gate; no additional login-rendering split is needed.
+
 ## M2 — Reuse the admin shell, then expose it
 
 ### 8D.4 — Small transport-neutral console boundary
@@ -161,11 +163,11 @@ Update the roadmap and user/command documentation to distinguish completed featu
 
 ## Progress and next-request template
 
-Progress: **8D.0 through 8D.2 validated by user sign-off; 8D.2 implemented / host-tested / build-verified. Reserve gates pending. 8D.3 inert parser preparation implemented; live cutover and 8D.4–8D.22 planned.** Record incremental results in `docs/agent/current-state.md`, retaining the [baseline](phase8d_baseline.md) and cumulative resource measurements as work proceeds. The baseline records user-provided evidence and sign-off; this does not imply completion of later browser-authentication acceptance checks.
+Progress: **8D.0 through 8D.2 validated by user sign-off; 8D.2 implemented / host-tested / build-verified. Reserve gates pending. 8D.3 inert parser and login-renderer preparation implemented; live cutover and 8D.4–8D.22 planned.** Record incremental results in `docs/agent/current-state.md`, retaining the [baseline](phase8d_baseline.md) and cumulative resource measurements as work proceeds. The baseline records user-provided evidence and sign-off; this does not imply completion of later browser-authentication acceptance checks.
 
 Suggested next request:
 
-> Continue Phase 8D.3 after its inert request-parser split. Complete login/logout authentication atomically (or split inert login rendering first if needed), preserve 8D.2 sign-off and open numeric reserve gates, and stop for M1 target/browser validation before 8D.4.
+> Continue Phase 8D.3 with the atomic live login/logout cutover; request parsing and standalone login rendering are prepared and host-tested. Preserve 8D.2 sign-off and open numeric reserve gates, and stop for M1 target/browser validation before 8D.4.
 
 For later chunks: